doc: Move outdated documentation to legacy

Change-Id: I0ceba9a993e8b1cdef4ff6a784bfd69c08107d88
BUG: 811311
Signed-off-by: Vijay Bellur <vijay@gluster.com>
Reviewed-on: http://review.gluster.com/3116
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Reviewed-by: Anand Avati <avati@redhat.com>

1 files changed, 2697 insertions, 0 deletions

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+This is ../../../doc/user-guide/user-guide.info, produced by makeinfo version 4.13 from ../../../doc/user-guide/user-guide.texi.
+
+START-INFO-DIR-ENTRY
+* GlusterFS: (user-guide). GlusterFS distributed filesystem user guide
+END-INFO-DIR-ENTRY
+
+   This is the user manual for GlusterFS 2.0.
+
+   Copyright (c) 2007-2011 Gluster, Inc. Permission is granted to
+copy, distribute and/or modify this document under the terms of the GNU
+Free Documentation License, Version 1.2 or any later version published
+by the Free Software Foundation; with no Invariant Sections, no
+Front-Cover Texts, and no Back-Cover Texts. A copy of the license is
+included in the chapter entitled "GNU Free Documentation License".
+
+
+File: user-guide.info,  Node: Top,  Next: Acknowledgements,  Up: (dir)
+
+GlusterFS 2.0 User Guide
+************************
+
+This is the user manual for GlusterFS 2.0.
+
+   Copyright (c) 2007-2011 Gluster, Inc. Permission is granted to
+copy, distribute and/or modify this document under the terms of the GNU
+Free Documentation License, Version 1.2 or any later version published
+by the Free Software Foundation; with no Invariant Sections, no
+Front-Cover Texts, and no Back-Cover Texts. A copy of the license is
+included in the chapter entitled "GNU Free Documentation License".
+
+* Menu:
+
+* Acknowledgements::
+* Introduction::
+* Installation and Invocation::
+* Concepts::
+* Translators::
+* Usage Scenarios::
+* Troubleshooting::
+* GNU Free Documentation Licence::
+* Index::
+
+ --- The Detailed Node Listing ---
+
+Installation and Invocation
+
+* Pre requisites::
+* Getting GlusterFS::
+* Building::
+* Running GlusterFS::
+* A Tutorial Introduction::
+
+Running GlusterFS
+
+* Server::
+* Client::
+
+Concepts
+
+* Filesystems in Userspace::
+* Translator::
+* Volume specification file::
+
+Translators
+
+* Storage Translators::
+* Client and Server Translators::
+* Clustering Translators::
+* Performance Translators::
+* Features Translators::
+
+Storage Translators
+
+* POSIX::
+
+Client and Server Translators
+
+* Transport modules::
+* Client protocol::
+* Server protocol::
+
+Clustering Translators
+
+* Unify::
+* Replicate::
+* Stripe::
+
+Performance Translators
+
+* Read Ahead::
+* Write Behind::
+* IO Threads::
+* IO Cache::
+
+Features Translators
+
+* POSIX Locks::
+* Fixed ID::
+
+Miscellaneous Translators
+
+* ROT-13::
+* Trace::
+
+
+File: user-guide.info,  Node: Acknowledgements,  Next: Introduction,  Prev: Top,  Up: Top
+
+Acknowledgements
+****************
+
+GlusterFS continues to be a wonderful and enriching experience for all
+of us involved.
+
+   GlusterFS development would not have been possible at this pace if
+not for our enthusiastic users. People from around the world have
+helped us with bug reports, performance numbers, and feature
+suggestions.  A huge thanks to them all.
+
+   Matthew Paine - for RPMs & general enthu
+
+   Leonardo Rodrigues de Mello - for DEBs
+
+   Julian Perez & Adam D'Auria - for multi-server tutorial
+
+   Paul England - for HA spec
+
+   Brent Nelson - for many bug reports
+
+   Jacques Mattheij - for Europe mirror.
+
+   Patrick Negri - for TCP non-blocking connect.
+        http://gluster.org/core-team.php (<list-hacking@gluster.com>)
+                                                          Gluster
+
+
+File: user-guide.info,  Node: Introduction,  Next: Installation and Invocation,  Prev: Acknowledgements,  Up: Top
+
+1 Introduction
+**************
+
+GlusterFS is a distributed filesystem. It works at the file level, not
+block level.
+
+   A network filesystem is one which allows us to access remote files. A
+distributed filesystem is one that stores data on multiple machines and
+makes them all appear to be a part of the same filesystem.
+
+   Need for distributed filesystems
+
+   * Scalability: A distributed filesystem allows us to store more data
+     than what can be stored on a single machine.
+
+   * Redundancy: We might want to replicate crucial data on to several
+     machines.
+
+   * Uniform access: One can mount a remote volume (for example your
+     home directory) from any machine and access the same data.
+
+1.1 Contacting us
+=================
+
+You can reach us through the mailing list *gluster-devel*
+(<gluster-devel@nongnu.org>).
+
+   You can also find many of the developers on IRC, on the `#gluster'
+channel on Freenode (<irc.freenode.net>).
+
+   The GlusterFS documentation wiki is also useful:
+<http://gluster.org/docs/index.php/GlusterFS>
+
+   For commercial support, you can contact Gluster at:
+
+     3194 Winding Vista Common
+     Fremont, CA 94539
+     USA.
+
+     Phone: +1 (510) 354 6801
+     Toll free: +1 (888) 813 6309
+     Fax: +1 (510) 372 0604
+
+   You can also email us at <support@gluster.com>.
+
+
+File: user-guide.info,  Node: Installation and Invocation,  Next: Concepts,  Prev: Introduction,  Up: Top
+
+2 Installation and Invocation
+*****************************
+
+* Menu:
+
+* Pre requisites::
+* Getting GlusterFS::
+* Building::
+* Running GlusterFS::
+* A Tutorial Introduction::
+
+
+File: user-guide.info,  Node: Pre requisites,  Next: Getting GlusterFS,  Up: Installation and Invocation
+
+2.1 Pre requisites
+==================
+
+Before installing GlusterFS make sure you have the following components
+installed.
+
+2.1.1 FUSE
+----------
+
+You'll need FUSE version 2.6.0 or higher to use GlusterFS. You can omit
+installing FUSE if you want to build _only_ the server. Note that you
+won't be able to mount a GlusterFS filesystem on a machine that does
+not have FUSE installed.
+
+   FUSE can be downloaded from: <http://fuse.sourceforge.net/>
+
+   To get the best performance from GlusterFS, however, it is
+recommended that you use our patched version of FUSE. See Patched FUSE
+for details.
+
+2.1.2 Patched FUSE
+------------------
+
+The GlusterFS project maintains a patched version of FUSE meant to be
+used with GlusterFS. The patches increase GlusterFS performance. It is
+recommended that all users use the patched FUSE.
+
+   The patched FUSE tarball can be downloaded from:
+
+   <ftp://ftp.gluster.com/pub/gluster/glusterfs/fuse/>
+
+   The specific changes made to FUSE are:
+
+   * The communication channel size between FUSE kernel module and
+     GlusterFS has been increased to 1MB, permitting large reads and
+     writes to be sent in bigger chunks.
+
+   * The kernel's read-ahead boundry has been extended upto 1MB.
+
+   * Block size returned in the `stat()'/`fstat()' calls tuned to 1MB,
+     to make cp and similar commands perform I/O using that block size.
+
+   * `flock()' locking support has been added (although some rework in
+     GlusterFS is needed for perfect compliance).
+
+2.1.3 libibverbs (optional)
+---------------------------
+
+This is only needed if you want GlusterFS to use InfiniBand as the
+interconnect mechanism between server and client. You can get it from:
+
+   <http://www.openfabrics.org/downloads.htm>.
+
+2.1.4 Bison and Flex
+--------------------
+
+These should be already installed on most Linux systems. If not, use
+your distribution's normal software installation procedures to install
+them. Make sure you install the relevant developer packages also.
+
+
+File: user-guide.info,  Node: Getting GlusterFS,  Next: Building,  Prev: Pre requisites,  Up: Installation and Invocation
+
+2.2 Getting GlusterFS
+=====================
+
+There are many ways to get hold of GlusterFS. For a production
+deployment, the recommended method is to download the latest release
+tarball.  Release tarballs are available at:
+<http://gluster.org/download.php>.
+
+   If you want the bleeding edge development source, you can get them
+from the GNU Arch(1) repository. First you must install GNU Arch
+itself. Then register the GlusterFS archive by doing:
+
+     $ tla register-archive http://arch.sv.gnu.org/archives/gluster
+
+   Now you can check out the source itself:
+
+     $ tla get -A gluster@sv.gnu.org glusterfs--mainline--3.0
+
+   ---------- Footnotes ----------
+
+   (1) <http://www.gnu.org/software/gnu-arch/>
+
+
+File: user-guide.info,  Node: Building,  Next: Running GlusterFS,  Prev: Getting GlusterFS,  Up: Installation and Invocation
+
+2.3 Building
+============
+
+You can skip this section if you're installing from RPMs or DEBs.
+
+   GlusterFS uses the Autotools mechanism to build. As such, the
+procedure is straight-forward. First, change into the GlusterFS source
+directory.
+
+     $ cd glusterfs-<version>
+
+   If you checked out the source from the Arch repository, you'll need
+to run `./autogen.sh' first. Note that you'll need to have Autoconf and
+Automake installed for this.
+
+   Run `configure'.
+
+     $ ./configure
+
+   The configure script accepts the following options:
+
+`--disable-ibverbs'
+     Disable the InfiniBand transport mechanism.
+
+`--disable-fuse-client'
+     Disable the FUSE client.
+
+`--disable-server'
+     Disable building of the GlusterFS server.
+
+`--disable-bdb'
+     Disable building of Berkeley DB based storage translator.
+
+`--disable-mod_glusterfs'
+     Disable building of Apache/lighttpd glusterfs plugins.
+
+`--disable-epoll'
+     Use poll instead of epoll.
+
+`--disable-libglusterfsclient'
+     Disable building of libglusterfsclient
+
+
+   Build and install GlusterFS.
+
+     # make install
+
+   The binaries (`glusterfsd' and `glusterfs') will be by default
+installed in `/usr/local/sbin/'. Translator, scheduler, and transport
+shared libraries will be installed in
+`/usr/local/lib/glusterfs/<version>/'. Sample volume specification
+files will be in `/usr/local/etc/glusterfs/'.  This document itself can
+be found in `/usr/local/share/doc/glusterfs/'. If you passed the
+`--prefix' argument to the configure script, then replace `/usr/local'
+in the preceding paths with the prefix.
+
+
+File: user-guide.info,  Node: Running GlusterFS,  Next: A Tutorial Introduction,  Prev: Building,  Up: Installation and Invocation
+
+2.4 Running GlusterFS
+=====================
+
+* Menu:
+
+* Server::
+* Client::
+
+
+File: user-guide.info,  Node: Server,  Next: Client,  Up: Running GlusterFS
+
+2.4.1 Server
+------------
+
+The GlusterFS server is necessary to export storage volumes to remote
+clients (See *note Server protocol:: for more info). This section
+documents the invocation of the GlusterFS server program and all the
+command-line options accepted by it.
+
+     Basic Options
+
+`-f, --volfile=<path>'
+     Use the volume file as the volume specification.
+
+`-s, --volfile-server=<hostname>'
+     Server to get volume file from. This option overrides -volfile
+     option.
+
+`-l, --log-file=<path>'
+     Specify the path for the log file.
+
+`-L, --log-level=<level>'
+     Set the log level for the server. Log level should be one of DEBUG,
+     WARNING, ERROR, CRITICAL, or NONE.
+
+     Advanced Options
+
+`--debug'
+     Run in debug mode. This option sets -no-daemon, -log-level to
+     DEBUG and       -log-file to console.
+
+`-N, --no-daemon'
+     Run glusterfsd as a foreground process.
+
+`-p, --pid-file=<path>'
+     Path for the PID file.
+
+`--volfile-id=<key>'
+     'key' of the volfile to be fetched from server.
+
+`--volfile-server-port=<port-number>'
+     Listening port number of volfile server.
+
+`--volfile-server-transport=[socket|ib-verbs]'
+     Transport type to get volfile from server. [default: `socket']
+
+`--xlator-options=<volume-name.option=value>'
+     Add/override a translator option for a volume with specified value.
+
+     Miscellaneous Options
+
+`-?, --help'
+     Show this help text.
+
+`--usage'
+     Display a short usage message.
+
+`-V, --version'
+     Show version information.
+
+
+File: user-guide.info,  Node: Client,  Prev: Server,  Up: Running GlusterFS
+
+2.4.2 Client
+------------
+
+The GlusterFS client process is necessary to access remote storage
+volumes and mount them locally using FUSE. This section documents the
+invocation of the client process and all its command-line arguments.
+
+       # glusterfs [options] <mountpoint>
+
+   The `mountpoint' is the directory where you want the GlusterFS
+filesystem to appear. Example:
+
+       # glusterfs -f /usr/local/etc/glusterfs-client.vol /mnt
+
+   The command-line options are detailed below.
+
+     Basic Options
+
+`-f, --volfile=<path>'
+     Use the volume file as the volume specification.
+
+`-s, --volfile-server=<hostname>'
+     Server to get volume file from. This option overrides -volfile
+     option.
+
+`-l, --log-file=<path>'
+     Specify the path for the log file.
+
+`-L, --log-level=<level>'
+     Set the log level for the server. Log level should be one of DEBUG,
+     WARNING, ERROR, CRITICAL, or NONE.
+
+     Advanced Options
+
+`--debug'
+     Run in debug mode. This option sets -no-daemon, -log-level to
+     DEBUG and       -log-file to console.
+
+`-N, --no-daemon'
+     Run `glusterfs' as a foreground process.
+
+`-p, --pid-file=<path>'
+     Path for the PID file.
+
+`--volfile-id=<key>'
+     'key' of the volfile to be fetched from server.
+
+`--volfile-server-port=<port-number>'
+     Listening port number of volfile server.
+
+`--volfile-server-transport=[socket|ib-verbs]'
+     Transport type to get volfile from server. [default: `socket']
+
+`--xlator-options=<volume-name.option=value>'
+     Add/override a translator option for a volume with specified value.
+
+`--volume-name=<volume name>'
+     Volume name in client spec to use. Defaults to the root volume.
+
+     FUSE Options
+
+`--attribute-timeout=<n>'
+     Attribute timeout for inodes in the kernel, in seconds. Defaults
+     to 1 second.
+
+`--disable-direct-io-mode'
+     Disable direct I/O mode in FUSE kernel module.
+
+`-e, --entry-timeout=<n>'
+     Entry timeout for directory entries in the kernel, in seconds.
+        Defaults to 1 second.
+
+     Missellaneous Options
+
+`-?, --help'
+     Show this help information.
+
+`-V, --version'
+     Show version information.
+
+
+File: user-guide.info,  Node: A Tutorial Introduction,  Prev: Running GlusterFS,  Up: Installation and Invocation
+
+2.5 A Tutorial Introduction
+===========================
+
+This section will show you how to quickly get GlusterFS up and running.
+We'll configure GlusterFS as a simple network filesystem, with one
+server and one client.  In this mode of usage, GlusterFS can serve as a
+replacement for NFS.
+
+   We'll make use of two machines; call them _server_ and _client_ (If
+you don't want to setup two machines, just run everything that follows
+on the same machine).  In the examples that follow, the shell prompts
+will use these names to clarify the machine on which the command is
+being run. For example, a command that should be run on the server will
+be shown with the prompt:
+
+     [root@server]#
+
+   Our goal is to make a directory on the _server_ (say, `/export')
+accessible to the _client_.
+
+   First of all, get GlusterFS installed on both the machines, as
+described in the previous sections. Make sure you have the FUSE kernel
+module loaded. You can ensure this by running:
+
+     [root@server]# modprobe fuse
+
+   Before we can run the GlusterFS client or server programs, we need
+to write two files called _volume specifications_ (equivalently refered
+to as _volfiles_).  The volfile describes the _translator tree_ on a
+node. The next chapter will explain the concepts of `translator' and
+`volume specification' in detail. For now, just assume that the volfile
+is like an NFS `/etc/export' file.
+
+   On the server, create a text file somewhere (we'll assume the path
+`/tmp/glusterfsd.vol') with the following contents.
+
+     volume colon-o
+       type storage/posix
+       option directory /export
+     end-volume
+
+     volume server
+       type protocol/server
+       subvolumes colon-o
+       option transport-type tcp
+       option auth.addr.colon-o.allow *
+     end-volume
+
+   A brief explanation of the file's contents. The first section
+defines a storage volume, named "colon-o" (the volume names are
+arbitrary), which exports the `/export' directory. The second section
+defines options for the translator which will make the storage volume
+accessible remotely. It specifies `colon-o' as a subvolume. This
+defines the _translator tree_, about which more will be said in the
+next chapter. The two options specify that the TCP protocol is to be
+used (as opposed to InfiniBand, for example), and that access to the
+storage volume is to be provided to clients with any IP address at all.
+If you wanted to restrict access to this server to only your subnet for
+example, you'd specify something like `192.168.1.*' in the second
+option line.
+
+   On the client machine, create the following text file (again, we'll
+assume the path to be `/tmp/glusterfs-client.vol'). Replace
+_server-ip-address_ with the IP address of your server machine. If you
+are doing all this on a single machine, use `127.0.0.1'.
+
+     volume client
+       type protocol/client
+       option transport-type tcp
+       option remote-host _server-ip-address_
+       option remote-subvolume colon-o
+     end-volume
+
+   Now we need to start both the server and client programs. To start
+the server:
+
+     [root@server]# glusterfsd -f /tmp/glusterfs-server.vol
+
+   To start the client:
+
+     [root@client]# glusterfs -f /tmp/glusterfs-client.vol /mnt/glusterfs
+
+   You should now be able to see the files under the server's `/export'
+directory in the `/mnt/glusterfs' directory on the client. That's it;
+GlusterFS is now working as a network file system.
+
+
+File: user-guide.info,  Node: Concepts,  Next: Translators,  Prev: Installation and Invocation,  Up: Top
+
+3 Concepts
+**********
+
+* Menu:
+
+* Filesystems in Userspace::
+* Translator::
+* Volume specification file::
+
+
+File: user-guide.info,  Node: Filesystems in Userspace,  Next: Translator,  Up: Concepts
+
+3.1 Filesystems in Userspace
+============================
+
+A filesystem is usually implemented in kernel space. Kernel space
+development is much harder than userspace development. FUSE is a kernel
+module/library that allows us to write a filesystem completely in
+userspace.
+
+   FUSE consists of a kernel module which interacts with the userspace
+implementation using a device file `/dev/fuse'. When a process makes a
+syscall on a FUSE filesystem, VFS hands the request to the FUSE module,
+which writes the request to `/dev/fuse'. The userspace implementation
+polls `/dev/fuse', and when a request arrives, processes it and writes
+the result back to `/dev/fuse'. The kernel then reads from the device
+file and returns the result to the user process.
+
+   In case of GlusterFS, the userspace program is the GlusterFS client.
+The control flow is shown in the diagram below. The GlusterFS client
+services the request by sending it to the server, which in turn hands
+it to the local POSIX filesystem.
+
+
+                   Fig 1. Control flow in GlusterFS
+
+
+File: user-guide.info,  Node: Translator,  Next: Volume specification file,  Prev: Filesystems in Userspace,  Up: Concepts
+
+3.2 Translator
+==============
+
+The _translator_ is the most important concept in GlusterFS. In fact,
+GlusterFS is nothing but a collection of translators working together,
+forming a translator _tree_.
+
+   The idea of a translator is perhaps best understood using an
+analogy. Consider the VFS in the Linux kernel. The VFS abstracts the
+various filesystem implementations (such as EXT3, ReiserFS, XFS, etc.)
+supported by the kernel. When an application calls the kernel to
+perform an operation on a file, the kernel passes the request on to the
+appropriate filesystem implementation.
+
+   For example, let's say there are two partitions on a Linux machine:
+`/', which is an EXT3 partition, and `/usr', which is a ReiserFS
+partition. Now if an application wants to open a file called, say,
+`/etc/fstab', then the kernel will internally pass the request to the
+EXT3 implementation.  If on the other hand, an application wants to
+read a file called `/usr/src/linux/CREDITS', then the kernel will call
+upon the ReiserFS implementation to do the job.
+
+   The "filesystem implementation" objects are analogous to GlusterFS
+translators. A GlusterFS translator implements all the filesystem
+operations.  Whereas in VFS there is a two-level tree (with the kernel
+at the root and all the filesystem implementation as its children), in
+GlusterFS there exists a more elaborate tree structure.
+
+   We can now define translators more precisely. A GlusterFS translator
+is a shared object (`.so') that implements every filesystem call.
+GlusterFS translators can be arranged in an arbitrary tree structure
+(subject to constraints imposed by the translators). When GlusterFS
+receives a filesystem call, it passes it on to the translator at the
+root of the translator tree. The root translator may in turn pass it on
+to any or all of its children, and so on, until the leaf nodes are
+reached. The result of a filesystem call is communicated in the reverse
+fashion, from the leaf nodes up to the root node, and then on to the
+application.
+
+   So what might a translator tree look like?
+
+
+                    Fig 2. A sample translator tree
+
+   The diagram depicts three servers and one GlusterFS client. It is
+important to note that conceptually, the translator tree spans machine
+boundaries.  Thus, the client machine in the diagram, `10.0.0.1', can
+access the aggregated storage of the filesystems on the server machines
+`10.0.0.2', `10.0.0.3', and `10.0.0.4'. The translator diagram will
+make more sense once you've read the next chapter and understood the
+functions of the various translators.
+
+
+File: user-guide.info,  Node: Volume specification file,  Prev: Translator,  Up: Concepts
+
+3.3 Volume specification file
+=============================
+
+The volume specification file describes the translator tree for both the
+server and client programs.
+
+   A volume specification file is a sequence of volume definitions.
+The syntax of a volume definition is explained below:
+
+     *volume* _volume-name_
+       *type* _translator-name_
+       *option* _option-name_ _option-value_
+       ...
+       *subvolumes* _subvolume1_ _subvolume2_ ...
+     *end-volume*
+
+   ...
+
+_volume-name_
+     An identifier for the volume. This is just a human-readable name,
+     and can contain any alphanumeric character. For instance,
+     "storage-1", "colon-o", or "forty-two".
+
+_translator-name_
+     Name of one of the available translators. Example:
+     `protocol/client', `cluster/unify'.
+
+_option-name_
+     Name of a valid option for the translator.
+
+_option-value_
+     Value for the option. Everything following the "option" keyword to
+     the end of the line is considered the value; it is up to the
+     translator to parse it.
+
+_subvolume1_, _subvolume2_, ...
+     Volume names of sub-volumes. The sub-volumes must already have
+     been defined earlier in the file.
+
+   There are a few rules you must follow when writing a volume
+specification file:
+
+   * Everything following a ``#'' is considered a comment and is
+     ignored. Blank lines are also ignored.
+
+   * All names and keywords are case-sensitive.
+
+   * The order of options inside a volume definition does not matter.
+
+   * An option value may not span multiple lines.
+
+   * If an option is not specified, it will assume its default value.
+
+   * A sub-volume must have already been defined before it can be
+     referenced. This means you have to write the specification file
+     "bottom-up", starting from the leaf nodes of the translator tree
+     and moving up to the root.
+
+   A simple example volume specification file is shown below:
+
+     # This is a comment line
+     volume client
+      type protocol/client
+      option transport-type tcp
+      option remote-host localhost      # Also a comment
+      option remote-subvolume brick
+     # The subvolumes line may be absent
+     end-volume
+
+     volume iot
+      type performance/io-threads
+      option thread-count 4
+      subvolumes client
+     end-volume
+
+     volume wb
+      type performance/write-behind
+      subvolumes iot
+     end-volume
+
+
+File: user-guide.info,  Node: Translators,  Next: Usage Scenarios,  Prev: Concepts,  Up: Top
+
+4 Translators
+*************
+
+* Menu:
+
+* Storage Translators::
+* Client and Server Translators::
+* Clustering Translators::
+* Performance Translators::
+* Features Translators::
+* Miscellaneous Translators::
+
+   This chapter documents all the available GlusterFS translators in
+detail.  Each translator section will show its name (for example,
+`cluster/unify'), briefly describe its purpose and workings, and list
+every option accepted by that translator and their meaning.
+
+
+File: user-guide.info,  Node: Storage Translators,  Next: Client and Server Translators,  Up: Translators
+
+4.1 Storage Translators
+=======================
+
+The storage translators form the "backend" for GlusterFS. Currently,
+the only available storage translator is the POSIX translator, which
+stores files on a normal POSIX filesystem. A pleasant consequence of
+this is that your data will still be accessible if GlusterFS crashes or
+cannot be started.
+
+   Other storage backends are planned for the future. One of the
+possibilities is an Amazon S3 translator. Amazon S3 is an unlimited
+online storage service accessible through a web services API. The S3
+translator will allow you to access the storage as a normal POSIX
+filesystem.  (1)
+
+* Menu:
+
+* POSIX::
+* BDB::
+
+   ---------- Footnotes ----------
+
+   (1) Some more discussion about this can be found at:
+
+http://developer.amazonwebservices.com/connect/message.jspa?messageID=52873
+
+
+File: user-guide.info,  Node: POSIX,  Next: BDB,  Up: Storage Translators
+
+4.1.1 POSIX
+-----------
+
+     type storage/posix
+
+   The `posix' translator uses a normal POSIX filesystem as its
+"backend" to actually store files and directories. This can be any
+filesystem that supports extended attributes (EXT3, ReiserFS, XFS,
+...). Extended attributes are used by some translators to store
+metadata, for example, by the replicate and stripe translators. See
+*note Replicate:: and *note Stripe::, respectively for details.
+
+`directory <path>'
+     The directory on the local filesystem which is to be used for
+     storage.
+
+
+File: user-guide.info,  Node: BDB,  Prev: POSIX,  Up: Storage Translators
+
+4.1.2 BDB
+---------
+
+     type storage/bdb
+
+   The `BDB' translator uses a Berkeley DB database as its "backend" to
+actually store files as key-value pair in the database and directories
+as regular POSIX directories. Note that BDB does not provide extended
+attribute support for regular files. Do not use BDB as storage
+translator while using any translator that demands extended attributes
+on "backend".
+
+`directory <path>'
+     The directory on the local filesystem which is to be used for
+     storage.
+
+`mode [cache|persistent] (cache)'
+     When BDB is run in `cache' mode, recovery of back-end is not
+     completely guaranteed. `persistent' guarantees that BDB can
+     recover back-end from Berkeley DB even if GlusterFS crashes.
+
+`errfile <path>'
+     The path of the file to be used as `errfile' for Berkeley DB to
+     report detailed error messages, if any. Note that all the contents
+     of this file will be written by Berkeley DB, not GlusterFS.
+
+`logdir <path>'
+
+
+File: user-guide.info,  Node: Client and Server Translators,  Next: Clustering Translators,  Prev: Storage Translators,  Up: Translators
+
+4.2 Client and Server Translators
+=================================
+
+The client and server translator enable GlusterFS to export a
+translator tree over the network or access a remote GlusterFS server.
+These two translators implement GlusterFS's network protocol.
+
+* Menu:
+
+* Transport modules::
+* Client protocol::
+* Server protocol::
+
+
+File: user-guide.info,  Node: Transport modules,  Next: Client protocol,  Up: Client and Server Translators
+
+4.2.1 Transport modules
+-----------------------
+
+The client and server translators are capable of using any of the
+pluggable transport modules. Currently available transport modules are
+`tcp', which uses a TCP connection between client and server to
+communicate; `ib-sdp', which uses a TCP connection over InfiniBand, and
+`ibverbs', which uses high-speed InfiniBand connections.
+
+   Each transport module comes in two different versions, one to be
+used on the server side and the other on the client side.
+
+4.2.1.1 TCP
+...........
+
+The TCP transport module uses a TCP/IP connection between the server
+and the client.
+
+       option transport-type tcp
+
+   The TCP client module accepts the following options:
+
+`non-blocking-connect [no|off|on|yes] (on)'
+     Whether to make the connection attempt asynchronous.
+
+`remote-port <n> (24007)'
+     Server port to connect to.
+
+`remote-host <hostname> *'
+     Hostname or IP address of the server. If the host name resolves to
+     multiple IP addresses, all of them will be tried in a round-robin
+     fashion. This feature can be used to implement fail-over.
+
+   The TCP server module accepts the following options:
+
+`bind-address <address> (0.0.0.0)'
+     The local interface on which the server should listen to requests.
+     Default is to listen on all interfaces.
+
+`listen-port <n> (24007)'
+     The local port to listen on.
+
+4.2.1.2 IB-SDP
+..............
+
+       option transport-type ib-sdp
+
+   kernel implements socket interface for ib hardware. SDP is over
+ib-verbs.  This module accepts the same options as `tcp'
+
+4.2.1.3 ibverbs
+...............
+
+       option transport-type tcp
+
+   InfiniBand is a scalable switched fabric interconnect mechanism
+primarily used in high-performance computing. InfiniBand can deliver
+data throughput of the order of 10 Gbit/s, with latencies of 4-5 ms.
+
+   The `ib-verbs' transport accesses the InfiniBand hardware through
+the "verbs" API, which is the lowest level of software access possible
+and which gives the highest performance. On InfiniBand hardware, it is
+always best to use `ib-verbs'. Use `ib-sdp' only if you cannot get
+`ib-verbs' working for some reason.
+
+   The `ib-verbs' client module accepts the following options:
+
+`non-blocking-connect [no|off|on|yes] (on)'
+     Whether to make the connection attempt asynchronous.
+
+`remote-port <n> (24007)'
+     Server port to connect to.
+
+`remote-host <hostname> *'
+     Hostname or IP address of the server. If the host name resolves to
+     multiple IP addresses, all of them will be tried in a round-robin
+     fashion. This feature can be used to implement fail-over.
+
+   The `ib-verbs' server module accepts the following options:
+
+`bind-address <address> (0.0.0.0)'
+     The local interface on which the server should listen to requests.
+     Default is to listen on all interfaces.
+
+`listen-port <n> (24007)'
+     The local port to listen on.
+
+   The following options are common to both the client and server
+modules:
+
+   If you are familiar with InfiniBand jargon, the mode is used by
+GlusterFS is "reliable connection-oriented channel transfer".
+
+`ib-verbs-work-request-send-count <n> (64)'
+     Length of the send queue in datagrams. [Reason to
+     increase/decrease?]
+
+`ib-verbs-work-request-recv-count <n> (64)'
+     Length of the receive queue in datagrams. [Reason to
+     increase/decrease?]
+
+`ib-verbs-work-request-send-size <size> (128KB)'
+     Size of each datagram that is sent. [Reason to increase/decrease?]
+
+`ib-verbs-work-request-recv-size <size> (128KB)'
+     Size of each datagram that is received. [Reason to
+     increase/decrease?]
+
+`ib-verbs-port <n> (1)'
+     Port number for ib-verbs.
+
+`ib-verbs-mtu [256|512|1024|2048|4096] (2048)'
+     The Maximum Transmission Unit [Reason to increase/decrease?]
+
+`ib-verbs-device-name <device-name> (first device in the list)'
+     InfiniBand device to be used.
+
+   For maximum performance, you should ensure that the send/receive
+counts on both the client and server are the same.
+
+   ib-verbs is preferred over ib-sdp.
+
+
+File: user-guide.info,  Node: Client protocol,  Next: Server protocol,  Prev: Transport modules,  Up: Client and Server Translators
+
+4.2.2 Client
+------------
+
+     type procotol/client
+
+   The client translator enables the GlusterFS client to access a
+remote server's translator tree.
+
+`transport-type [tcp,ib-sdp,ib-verbs] (tcp)'
+     The transport type to use. You should use the client versions of
+     all the transport modules (`tcp', `ib-sdp', `ib-verbs').
+
+`remote-subvolume <volume_name> *'
+     The name of the volume on the remote host to attach to. Note that
+     this is _not_ the name of the `protocol/server' volume on the
+     server. It should be any volume under the server.
+
+`transport-timeout <n> (120- seconds)'
+     Inactivity timeout. If a reply is expected and no activity takes
+     place on the connection within this time, the transport connection
+     will be broken, and a new connection will be attempted.
+
+
+File: user-guide.info,  Node: Server protocol,  Prev: Client protocol,  Up: Client and Server Translators
+
+4.2.3 Server
+------------
+
+     type protocol/server
+
+   The server translator exports a translator tree and makes it
+accessible to remote GlusterFS clients.
+
+`client-volume-filename <path> (<CONFDIR>/glusterfs-client.vol)'
+     The volume specification file to use for the client. This is the
+     file the client will receive when it is invoked with the
+     `--server' option (*note Client::).
+
+`transport-type [tcp,ib-verbs,ib-sdp] (tcp)'
+     The transport to use. You should use the server versions of all
+     the transport modules (`tcp', `ib-sdp', `ib-verbs').
+
+`auth.addr.<volume name>.allow <IP address wildcard pattern>'
+     IP addresses of the clients that are allowed to attach to the
+     specified volume.  This can be a wildcard. For example, a wildcard
+     of the form `192.168.*.*' allows any host in the `192.168.x.x'
+     subnet to connect to the server.
+
+
+
+File: user-guide.info,  Node: Clustering Translators,  Next: Performance Translators,  Prev: Client and Server Translators,  Up: Translators
+
+4.3 Clustering Translators
+==========================
+
+The clustering translators are the most important GlusterFS
+translators, since it is these that make GlusterFS a cluster
+filesystem. These translators together enable GlusterFS to access an
+arbitrarily large amount of storage, and provide RAID-like redundancy
+and distribution over the entire cluster.
+
+   There are three clustering translators: *unify*, *replicate*, and
+*stripe*.  The unify translator aggregates storage from many server
+nodes. The replicate translator provides file replication. The stripe
+translator allows a file to be spread across many server nodes. The
+following sections look at each of these translators in detail.
+
+* Menu:
+
+* Unify::
+* Replicate::
+* Stripe::
+
+
+File: user-guide.info,  Node: Unify,  Next: Replicate,  Up: Clustering Translators
+
+4.3.1 Unify
+-----------
+
+     type cluster/unify
+
+   The unify translator presents a `unified' view of all its
+sub-volumes. That is, it makes the union of all its sub-volumes appear
+as a single volume. It is the unify translator that gives GlusterFS the
+ability to access an arbitrarily large amount of storage.
+
+   For unify to work correctly, certain invariants need to be
+maintained across the entire network. These are:
+
+   * The directory structure of all the sub-volumes must be identical.
+
+   * A particular file can exist on only one of the sub-volumes.
+     Phrasing it in another way, a pathname such as
+     `/home/calvin/homework.txt') is unique across the entire cluster.
+
+
+
+Looking at the second requirement, you might wonder how one can
+accomplish storing redundant copies of a file, if no file can exist
+multiple times.  To answer, we must remember that these invariants are
+from _unify's perspective_.  A translator such as replicate at a lower
+level in the translator tree than unify may subvert this picture.
+
+   The first invariant might seem quite tedious to ensure. We shall see
+later that this is not so, since unify's _self-heal_ mechanism takes
+care of maintaining it.
+
+   The second invariant implies that unify needs some way to decide
+which file goes where.  Unify makes use of _scheduler_ modules for this
+purpose.
+
+   When a file needs to be created, unify's scheduler decides upon the
+sub-volume to be used to store the file. There are many schedulers
+available, each using a different algorithm and suitable for different
+purposes.
+
+   The various schedulers are described in detail in the sections that
+follow.
+
+4.3.1.1 ALU
+...........
+
+       option scheduler alu
+
+   ALU stands for "Adaptive Least Usage". It is the most advanced
+scheduler available in GlusterFS. It balances the load across volumes
+taking several factors in account. It adapts itself to changing I/O
+patterns according to its configuration. When properly configured, it
+can eliminate the need for regular tuning of the filesystem to keep
+volume load nicely balanced.
+
+   The ALU scheduler is composed of multiple least-usage
+sub-schedulers. Each sub-scheduler keeps track of a certain type of
+load, for each of the sub-volumes, getting statistics from the
+sub-volumes themselves. The sub-schedulers are these:
+
+   * disk-usage: The used and free disk space on the volume.
+
+   * read-usage: The amount of reading done from this volume.
+
+   * write-usage: The amount of writing done to this volume.
+
+   * open-files-usage: The number of files currently open from this
+     volume.
+
+   * disk-speed-usage: The speed at which the disks are spinning. This
+     is a constant value and therefore not very useful.
+
+   The ALU scheduler needs to know which of these sub-schedulers to use,
+and in which order to evaluate them. This is done through the `option
+alu.order' configuration directive.
+
+   Each sub-scheduler needs to know two things: when to kick in (the
+entry-threshold), and how long to stay in control (the exit-threshold).
+For example: when unifying three disks of 100GB, keeping an exact
+balance of disk-usage is not necesary. Instead, there could be a 1GB
+margin, which can be used to nicely balance other factors, such as
+read-usage. The disk-usage scheduler can be told to kick in only when a
+certain threshold of discrepancy is passed, such as 1GB. When it
+assumes control under this condition, it will write all subsequent data
+to the least-used volume. If it is doing so, it is unwise to stop right
+after the values are below the entry-threshold again, since that would
+make it very likely that the situation will occur again very soon. Such
+a situation would cause the ALU to spend most of its time disk-usage
+scheduling, which is unfair to the other sub-schedulers. The
+exit-threshold therefore defines the amount of data that needs to be
+written to the least-used disk, before control is relinquished again.
+
+   In addition to the sub-schedulers, the ALU scheduler also has
+"limits" options. These can stop the creation of new files on a volume
+once values drop below a certain threshold. For example, setting
+`option alu.limits.min-free-disk 5GB' will stop the scheduling of files
+to volumes that have less than 5GB of free disk space, leaving the
+files on that disk some room to grow.
+
+   The actual values you assign to the thresholds for sub-schedulers and
+limits depend on your situation. If you have fast-growing files, you'll
+want to stop file-creation on a disk much earlier than when hardly any
+of your files are growing. If you care less about disk-usage balance
+than about read-usage balance, you'll want a bigger disk-usage
+scheduler entry-threshold and a smaller read-usage scheduler
+entry-threshold.
+
+   For thresholds defining a size, values specifying "KB", "MB" and "GB"
+are allowed. For example: `option alu.limits.min-free-disk 5GB'.
+
+`alu.order <order> * ("disk-usage:write-usage:read-usage:open-files-usage:disk-speed")'
+
+`alu.disk-usage.entry-threshold <size> (1GB)'
+
+`alu.disk-usage.exit-threshold <size> (512MB)'
+
+`alu.write-usage.entry-threshold <%> (25)'
+
+`alu.write-usage.exit-threshold <%> (5)'
+
+`alu.read-usage.entry-threshold <%> (25)'
+
+`alu.read-usage.exit-threshold <%> (5)'
+
+`alu.open-files-usage.entry-threshold <n> (1000)'
+
+`alu.open-files-usage.exit-threshold <n> (100)'
+
+`alu.limits.min-free-disk <%>'
+
+`alu.limits.max-open-files <n>'
+
+4.3.1.2 Round Robin (RR)
+........................
+
+       option scheduler rr
+
+   Round-Robin (RR) scheduler creates files in a round-robin fashion.
+Each client will have its own round-robin loop. When your files are
+mostly similar in size and I/O access pattern, this scheduler is a good
+choice. RR scheduler checks for free disk space on the server before
+scheduling, so you can know when to add another server node. The
+default value of min-free-disk is 5% and is checked on file creation
+calls, with atleast 10 seconds (by default) elapsing between two checks.
+
+   Options:
+`rr.limits.min-free-disk <%> (5)'
+     Minimum free disk space a node must have for RR to schedule a file
+     to it.
+
+`rr.refresh-interval <t> (10 seconds)'
+     Time between two successive free disk space checks.
+
+4.3.1.3 Random
+..............
+
+       option scheduler random
+
+   The random scheduler schedules file creation randomly among its
+child nodes.  Like the round-robin scheduler, it also checks for a
+minimum amount of free disk space before scheduling a file to a node.
+
+`random.limits.min-free-disk <%> (5)'
+     Minimum free disk space a node must have for random to schedule a
+     file to it.
+
+`random.refresh-interval <t> (10 seconds)'
+     Time between two successive free disk space checks.
+
+4.3.1.4 NUFA
+............
+
+       option scheduler nufa
+
+   It is common in many GlusterFS computing environments for all
+deployed machines to act as both servers and clients. For example, a
+research lab may have 40 workstations each with its own storage. All of
+these workstations might act as servers exporting a volume as well as
+clients accessing the entire cluster's storage.  In such a situation,
+it makes sense to store locally created files on the local workstation
+itself (assuming files are accessed most by the workstation that
+created them). The Non-Uniform File Allocation (NUFA) scheduler
+accomplishes that.
+
+   NUFA gives the local system first priority for file creation over
+other nodes. If the local volume does not have more free disk space
+than a specified amount (5% by default) then NUFA schedules files among
+the other child volumes in a round-robin fashion.
+
+   NUFA is named after the similar strategy used for memory access,
+NUMA(1).
+
+`nufa.limits.min-free-disk <%> (5)'
+     Minimum disk space that must be free (local or remote) for NUFA to
+     schedule a file to it.
+
+`nufa.refresh-interval <t> (10 seconds)'
+     Time between two successive free disk space checks.
+
+`nufa.local-volume-name <volume>'
+     The name of the volume corresponding to the local system. This
+     volume must be one of the children of the unify volume. This
+     option is mandatory.
+
+4.3.1.5 Namespace
+.................
+
+Namespace volume needed because:  - persistent inode numbers.   - file
+exists even when node is down.
+
+   namespace files are simply touched. on every lookup it is checked.
+
+`namespace <volume> *'
+     Name of the namespace volume (which should be one of the unify
+     volume's children).
+
+`self-heal [on|off] (on)'
+     Enable/disable self-heal. Unless you know what you are doing, do
+     not disable self-heal.
+
+4.3.1.6 Self Heal
+.................
+
+* When a 'lookup()/stat()' call is made on directory for the first
+time, a self-heal call is made, which checks for the consistancy of its
+child nodes. If an entry is present in storage node, but not in
+namespace, that entry is created in namespace, and vica-versa. There is
+an writedir() API introduced which is used for the same. It also checks
+for permissions, and uid/gid consistencies.
+
+   * This check is also done when an server goes down and comes up.
+
+   * If one starts with an empty namespace export, but has data in
+storage nodes, a 'find .>/dev/null' or 'ls -lR >/dev/null' should help
+to build namespace in one shot. Even otherwise, namespace is built on
+demand when a file is looked up for the first time.
+
+   NOTE: There are some issues (Kernel 'Oops' msgs) seen with
+fuse-2.6.3, when someone deletes namespace in backend, when glusterfs is
+running. But with fuse-2.6.5, this issue is not there.
+
+   ---------- Footnotes ----------
+
+   (1) Non-Uniform Memory Access:
+<http://en.wikipedia.org/wiki/Non-Uniform_Memory_Access>
+
+
+File: user-guide.info,  Node: Replicate,  Next: Stripe,  Prev: Unify,  Up: Clustering Translators
+
+4.3.2 Replicate (formerly AFR)
+------------------------------
+
+     type cluster/replicate
+
+   Replicate provides RAID-1 like functionality for GlusterFS.
+Replicate replicates files and directories across the subvolumes. Hence
+if Replicate has four subvolumes, there will be four copies of all
+files and directories. Replicate provides high-availability, i.e., in
+case one of the subvolumes go down (e. g. server crash, network
+disconnection) Replicate will still service the requests using the
+redundant copies.
+
+   Replicate also provides self-heal functionality, i.e., in case the
+crashed servers come up, the outdated files and directories will be
+updated with the latest versions. Replicate uses extended attributes of
+the backend file system to track the versioning of files and
+directories and provide the self-heal feature.
+
+     volume replicate-example
+      type cluster/replicate
+      subvolumes brick1 brick2 brick3
+     end-volume
+
+   This sample configuration will replicate all directories and files on
+brick1, brick2 and brick3.
+
+   All the read operations happen from the first alive child. If all the
+three sub-volumes are up, reads will be done from brick1; if brick1 is
+down read will be done from brick2. In case read() was being done on
+brick1 and it goes down, replicate transparently falls back to brick2.
+
+   The next release of GlusterFS will add the following features:
+   * Ability to specify the sub-volume from which read operations are
+     to be done (this will help users who have one of the sub-volumes
+     as a local storage volume).
+
+   * Allow scheduling of read operations amongst the sub-volumes in a
+     round-robin fashion.
+
+   The order of the subvolumes list should be same across all the
+'replicate's as they will be used for locking purposes.
+
+4.3.2.1 Self Heal
+.................
+
+Replicate has self-heal feature, which updates the outdated file and
+directory copies by the most recent versions. For example consider the
+following config:
+
+     volume replicate-example
+      type cluster/replicate
+      subvolumes brick1 brick2
+     end-volume
+
+4.3.2.2 File self-heal
+......................
+
+Now if we create a file foo.txt on replicate-example, the file will be
+created on brick1 and brick2. The file will have two extended
+attributes associated with it in the backend filesystem. One is
+trusted.afr.createtime and the other is trusted.afr.version. The
+trusted.afr.createtime xattr has the create time (in terms of seconds
+since epoch) and trusted.afr.version is a number that is incremented
+each time a file is modified. This increment happens during close
+(incase any write was done before close).
+
+   If brick1 goes down, we edit foo.txt the version gets incremented.
+Now the brick1 comes back up, when we open() on foo.txt replicate will
+check if their versions are same. If they are not same, the outdated
+copy is replaced by the latest copy and its version is updated. After
+the sync the open() proceeds in the usual manner and the application
+calling open() can continue on its access to the file.
+
+   If brick1 goes down, we delete foo.txt and create a file with the
+same name again i.e foo.txt. Now brick1 comes back up, clearly there is
+a chance that the version on brick1 being more than the version on
+brick2, this is where createtime extended attribute helps in deciding
+which the outdated copy is. Hence we need to consider both createtime
+and version to decide on the latest copy.
+
+   The version attribute is incremented during the close() call. Version
+will not be incremented in case there was no write() done. In case the
+fd that the close() gets was got by create() call, we also create the
+createtime extended attribute.
+
+4.3.2.3 Directory self-heal
+...........................
+
+Suppose brick1 goes down, we delete foo.txt, brick1 comes back up, now
+we should not create foo.txt on brick2 but we should delete foo.txt on
+brick1. We handle this situation by having the createtime and version
+attribute on the directory similar to the file. when lookup() is done
+on the directory, we compare the createtime/version attributes of the
+copies and see which files needs to be deleted and delete those files
+and update the extended attributes of the outdated directory copy.
+Each time a directory is modified (a file or a subdirectory is created
+or deleted inside the directory) and one of the subvols is down, we
+increment the directory's version.
+
+   lookup() is a call initiated by the kernel on a file or directory
+just before any access to that file or directory. In glusterfs, by
+default, lookup() will not be called in case it was called in the past
+one second on that particular file or directory.
+
+   The extended attributes can be seen in the backend filesystem using
+the `getfattr' command. (`getfattr -n trusted.afr.version <file>')
+
+`debug [on|off]  (off)'
+
+`self-heal [on|off] (on)'
+
+`replicate <pattern> (*:1)'
+
+`lock-node <child_volume> (first child is used by default)'
+
+
+File: user-guide.info,  Node: Stripe,  Prev: Replicate,  Up: Clustering Translators
+
+4.3.3 Stripe
+------------
+
+     type cluster/stripe
+
+   The stripe translator distributes the contents of a file over its
+sub-volumes.  It does this by creating a file equal in size to the
+total size of the file on each of its sub-volumes. It then writes only
+a part of the file to each sub-volume, leaving the rest of it empty.
+These empty regions are called `holes' in Unix terminology. The holes
+do not consume any disk space.
+
+   The diagram below makes this clear.
+
+
+
+You can configure stripe so that only filenames matching a pattern are
+striped. You can also configure the size of the data to be stored on
+each sub-volume.
+
+`block-size <pattern>:<size>  (*:0 no striping)'
+     Distribute files matching `<pattern>' over the sub-volumes,
+     storing at least `<size>' on each sub-volume. For example,
+
+            option block-size *.mpg:1M
+
+     distributes all files ending in `.mpg', storing at least 1 MB on
+     each sub-volume.
+
+     Any number of `block-size' option lines may be present, specifying
+     different sizes for different file name patterns.
+
+
+File: user-guide.info,  Node: Performance Translators,  Next: Features Translators,  Prev: Clustering Translators,  Up: Translators
+
+4.4 Performance Translators
+===========================
+
+* Menu:
+
+* Read Ahead::
+* Write Behind::
+* IO Threads::
+* IO Cache::
+* Booster::
+
+
+File: user-guide.info,  Node: Read Ahead,  Next: Write Behind,  Up: Performance Translators
+
+4.4.1 Read Ahead
+----------------
+
+     type performance/read-ahead
+
+   The read-ahead translator pre-fetches data in advance on every read.
+This benefits applications that mostly process files in sequential
+order, since the next block of data will already be available by the
+time the application is done with the current one.
+
+   Additionally, the read-ahead translator also behaves as a
+read-aggregator.  Many small read operations are combined and issued as
+fewer, larger read requests to the server.
+
+   Read-ahead deals in "pages" as the unit of data fetched. The page
+size is configurable, as is the "page count", which is the number of
+pages that are pre-fetched.
+
+   Read-ahead is best used with InfiniBand (using the ib-verbs
+transport).  On FastEthernet and Gigabit Ethernet networks, GlusterFS
+can achieve the link-maximum throughput even without read-ahead, making
+it quite superflous.
+
+   Note that read-ahead only happens if the reads are perfectly
+sequential. If your application accesses data in a random fashion,
+using read-ahead might actually lead to a performance loss, since
+read-ahead will pointlessly fetch pages which won't be used by the
+application.
+
+   Options:
+`page-size <n> (256KB)'
+     The unit of data that is pre-fetched.
+
+`page-count <n> (2)'
+     The number of pages that are pre-fetched.
+
+`force-atime-update [on|off|yes|no] (off|no)'
+     Whether to force an access time (atime) update on the file on
+     every read. Without this, the atime will be slightly imprecise, as
+     it will reflect the time when the read-ahead translator read the
+     data, not when the application actually read it.
+
+
+File: user-guide.info,  Node: Write Behind,  Next: IO Threads,  Prev: Read Ahead,  Up: Performance Translators
+
+4.4.2 Write Behind
+------------------
+
+     type performance/write-behind
+
+   The write-behind translator improves the latency of a write
+operation.  It does this by relegating the write operation to the
+background and returning to the application even as the write is in
+progress. Using the write-behind translator, successive write requests
+can be pipelined.  This mode of write-behind operation is best used on
+the client side, to enable decreased write latency for the application.
+
+   The write-behind translator can also aggregate write requests. If the
+`aggregate-size' option is specified, then successive writes upto that
+size are accumulated and written in a single operation. This mode of
+operation is best used on the server side, as this will decrease the
+disk's head movement when multiple files are being written to in
+parallel.
+
+   The `aggregate-size' option has a default value of 128KB. Although
+this works well for most users, you should always experiment with
+different values to determine the one that will deliver maximum
+performance. This is because the performance of write-behind depends on
+your interconnect, size of RAM, and the work load.
+
+`aggregate-size <n> (128KB)'
+     Amount of data to accumulate before doing a write
+
+`flush-behind [on|yes|off|no] (off|no)'
+
+
+File: user-guide.info,  Node: IO Threads,  Next: IO Cache,  Prev: Write Behind,  Up: Performance Translators
+
+4.4.3 IO Threads
+----------------
+
+     type performance/io-threads
+
+   The IO threads translator is intended to increase the responsiveness
+of the server to metadata operations by doing file I/O (read, write) in
+a background thread.  Since the GlusterFS server is single-threaded,
+using the IO threads translator can significantly improve performance.
+This translator is best used on the server side, loaded just below the
+server protocol translator.
+
+   IO threads operates by handing out read and write requests to a
+separate thread.  The total number of threads in existence at a time is
+constant, and configurable.
+
+`thread-count <n> (1)'
+     Number of threads to use.
+
+
+File: user-guide.info,  Node: IO Cache,  Next: Booster,  Prev: IO Threads,  Up: Performance Translators
+
+4.4.4 IO Cache
+--------------
+
+     type performance/io-cache
+
+   The IO cache translator caches data that has been read. This is
+useful if many applications read the same data multiple times, and if
+reads are much more frequent than writes (for example, IO caching may be
+useful in a web hosting environment, where most clients will simply
+read some files and only a few will write to them).
+
+   The IO cache translator reads data from its child in `page-size'
+chunks.  It caches data upto `cache-size' bytes. The cache is
+maintained as a prioritized least-recently-used (LRU) list, with
+priorities determined by user-specified patterns to match filenames.
+
+   When the IO cache translator detects a write operation, the cache
+for that file is flushed.
+
+   The IO cache translator periodically verifies the consistency of
+cached data, using the modification times on the files. The
+verification timeout is configurable.
+
+`page-size <n> (128KB)'
+     Size of a page.
+
+`cache-size (n) (32MB)'
+     Total amount of data to be cached.
+
+`force-revalidate-timeout <n> (1)'
+     Timeout to force a cache consistency verification, in seconds.
+
+`priority <pattern> (*:0)'
+     Filename patterns listed in order of priority.
+
+
+File: user-guide.info,  Node: Booster,  Prev: IO Cache,  Up: Performance Translators
+
+4.4.5 Booster
+-------------
+
+       type performance/booster
+
+   The booster translator gives applications a faster path to
+communicate read and write requests to GlusterFS. Normally, all
+requests to GlusterFS from applications go through FUSE, as indicated
+in *note Filesystems in Userspace::.  Using the booster translator in
+conjunction with the GlusterFS booster shared library, an application
+can bypass the FUSE path and send read/write requests directly to the
+GlusterFS client process.
+
+   The booster mechanism consists of two parts: the booster translator,
+and the booster shared library. The booster translator is meant to be
+loaded on the client side, usually at the root of the translator tree.
+The booster shared library should be `LD_PRELOAD'ed with the
+application.
+
+   The booster translator when loaded opens a Unix domain socket and
+listens for read/write requests on it. The booster shared library
+intercepts read and write system calls and sends the requests to the
+GlusterFS process directly using the Unix domain socket, bypassing FUSE.
+This leads to superior performance.
+
+   Once you've loaded the booster translator in your volume
+specification file, you can start your application as:
+
+       $ LD_PRELOAD=/usr/local/bin/glusterfs-booster.so your_app
+
+   The booster translator accepts no options.
+
+
+File: user-guide.info,  Node: Features Translators,  Next: Miscellaneous Translators,  Prev: Performance Translators,  Up: Translators
+
+4.5 Features Translators
+========================
+
+* Menu:
+
+* POSIX Locks::
+* Fixed ID::
+
+
+File: user-guide.info,  Node: POSIX Locks,  Next: Fixed ID,  Up: Features Translators
+
+4.5.1 POSIX Locks
+-----------------
+
+     type features/posix-locks
+
+   This translator provides storage independent POSIX record locking
+support (`fcntl' locking). Typically you'll want to load this on the
+server side, just above the POSIX storage translator. Using this
+translator you can get both advisory locking and mandatory locking
+support.  It also handles `flock()' locks properly.
+
+   Caveat: Consider a file that does not have its mandatory locking bits
+(+setgid, -group execution) turned on. Assume that this file is now
+opened by a process on a client that has the write-behind xlator
+loaded. The write-behind xlator does not cache anything for files which
+have mandatory locking enabled, to avoid incoherence. Let's say that
+mandatory locking is now enabled on this file through another client.
+The former client will not know about this change, and write-behind may
+erroneously report a write as being successful when in fact it would
+fail due to the region it is writing to being locked.
+
+   There seems to be no easy way to fix this. To work around this
+problem, it is recommended that you never enable the mandatory bits on
+a file while it is open.
+
+`mandatory [on|off] (on)'
+     Turns mandatory locking on.
+
+
+File: user-guide.info,  Node: Fixed ID,  Prev: POSIX Locks,  Up: Features Translators
+
+4.5.2 Fixed ID
+--------------
+
+     type features/fixed-id
+
+   The fixed ID translator makes all filesystem requests from the client
+to appear to be coming from a fixed, specified UID/GID, regardless of
+which user actually initiated the request.
+
+`fixed-uid <n> [if not set, not used]'
+     The UID to send to the server
+
+`fixed-gid <n> [if not set, not used]'
+     The GID to send to the server
+
+
+File: user-guide.info,  Node: Miscellaneous Translators,  Prev: Features Translators,  Up: Translators
+
+4.6 Miscellaneous Translators
+=============================
+
+* Menu:
+
+* ROT-13::
+* Trace::
+
+
+File: user-guide.info,  Node: ROT-13,  Next: Trace,  Up: Miscellaneous Translators
+
+4.6.1 ROT-13
+------------
+
+     type encryption/rot-13
+
+   ROT-13 is a toy translator that can "encrypt" and "decrypt" file
+contents using the ROT-13 algorithm. ROT-13 is a trivial algorithm that
+rotates each alphabet by thirteen places. Thus, 'A' becomes 'N', 'B'
+becomes 'O', and 'Z' becomes 'M'.
+
+   It goes without saying that you shouldn't use this translator if you
+need _real_ encryption (a future release of GlusterFS will have real
+encryption translators).
+
+`encrypt-write [on|off] (on)'
+     Whether to encrypt on write
+
+`decrypt-read [on|off] (on)'
+     Whether to decrypt on read
+
+
+File: user-guide.info,  Node: Trace,  Prev: ROT-13,  Up: Miscellaneous Translators
+
+4.6.2 Trace
+-----------
+
+     type debug/trace
+
+   The trace translator is intended for debugging purposes. When
+loaded, it logs all the system calls received by the server or client
+(wherever trace is loaded), their arguments, and the results. You must
+use a GlusterFS log level of DEBUG (See *note Running GlusterFS::) for
+trace to work.
+
+   Sample trace output (lines have been wrapped for readability):
+     2007-10-30 00:08:58 D [trace.c:1579:trace_opendir] trace: callid: 68
+     (*this=0x8059e40, loc=0x8091984 {path=/iozone3_283, inode=0x8091f00},
+      fd=0x8091d50)
+
+     2007-10-30 00:08:58 D [trace.c:630:trace_opendir_cbk] trace:
+     (*this=0x8059e40, op_ret=4, op_errno=1, fd=0x8091d50)
+
+     2007-10-30 00:08:58 D [trace.c:1602:trace_readdir] trace: callid: 69
+     (*this=0x8059e40, size=4096, offset=0 fd=0x8091d50)
+
+     2007-10-30 00:08:58 D [trace.c:215:trace_readdir_cbk] trace:
+     (*this=0x8059e40, op_ret=0, op_errno=0, count=4)
+
+     2007-10-30 00:08:58 D [trace.c:1624:trace_closedir] trace: callid: 71
+     (*this=0x8059e40, *fd=0x8091d50)
+
+     2007-10-30 00:08:58 D [trace.c:809:trace_closedir_cbk] trace:
+     (*this=0x8059e40, op_ret=0, op_errno=1)
+
+
+File: user-guide.info,  Node: Usage Scenarios,  Next: Troubleshooting,  Prev: Translators,  Up: Top
+
+5 Usage Scenarios
+*****************
+
+5.1 Advanced Striping
+=====================
+
+This section is based on the Advanced Striping tutorial written by
+Anand Avati on the GlusterFS wiki (1).
+
+5.1.1 Mixed Storage Requirements
+--------------------------------
+
+There are two ways of scheduling the I/O. One at file level (using
+unify translator) and other at block level (using stripe translator).
+Striped I/O is good for files that are potentially large and require
+high parallel throughput (for example, a single file of 400GB being
+accessed by 100s and 1000s of systems simultaneously and randomly). For
+most of the cases, file level scheduling works best.
+
+   In the real world, it is desirable to mix file level and block level
+scheduling on a single storage volume. Alternatively users can choose
+to have two separate volumes and hence two mount points, but the
+applications may demand a single storage system to host both.
+
+   This document explains how to mix file level scheduling with stripe.
+
+5.1.2 Configuration Brief
+-------------------------
+
+This setup demonstrates how users can configure unify translator with
+appropriate I/O scheduler for file level scheduling and strip for only
+matching patterns. This way, GlusterFS chooses appropriate I/O profile
+and knows how to efficiently handle both the types of data.
+
+   A simple technique to achieve this effect is to create a stripe set
+of unify and stripe blocks, where unify is the first sub-volume. Files
+that do not match the stripe policy passed on to first unify sub-volume
+and inturn scheduled arcoss the cluster using its file level I/O
+scheduler.
+
+ 5.1.3 Preparing GlusterFS Envoronment
+-------------------------------------
+
+Create the directories /export/namespace, /export/unify and
+/export/stripe on all the storage bricks.
+
+   Place the following server and client volume spec file under
+/etc/glusterfs (or appropriate installed path) and replace the IP
+addresses / access control fields to match your environment.
+
+       ## file: /etc/glusterfs/glusterfsd.vol
+        volume posix-unify
+                type storage/posix
+                option directory /export/for-unify
+        end-volume
+
+        volume posix-stripe
+                type storage/posix
+                option directory /export/for-stripe
+        end-volume
+
+        volume posix-namespace
+                type storage/posix
+                option directory /export/for-namespace
+        end-volume
+
+        volume server
+                type protocol/server
+                option transport-type tcp
+                option auth.addr.posix-unify.allow 192.168.1.*
+                option auth.addr.posix-stripe.allow 192.168.1.*
+                option auth.addr.posix-namespace.allow 192.168.1.*
+                subvolumes posix-unify posix-stripe posix-namespace
+        end-volume
+
+      ## file: /etc/glusterfs/glusterfs.vol
+        volume client-namespace
+          type protocol/client
+          option transport-type tcp
+          option remote-host 192.168.1.1
+          option remote-subvolume posix-namespace
+        end-volume
+
+        volume client-unify-1
+          type protocol/client
+          option transport-type tcp
+          option remote-host 192.168.1.1
+          option remote-subvolume posix-unify
+        end-volume
+
+        volume client-unify-2
+          type protocol/client
+          option transport-type tcp
+          option remote-host 192.168.1.2
+          option remote-subvolume posix-unify
+        end-volume
+
+        volume client-unify-3
+          type protocol/client
+          option transport-type tcp
+          option remote-host 192.168.1.3
+          option remote-subvolume posix-unify
+        end-volume
+
+        volume client-unify-4
+          type protocol/client
+          option transport-type tcp
+          option remote-host 192.168.1.4
+          option remote-subvolume posix-unify
+        end-volume
+
+        volume client-stripe-1
+          type protocol/client
+          option transport-type tcp
+          option remote-host 192.168.1.1
+          option remote-subvolume posix-stripe
+        end-volume
+
+        volume client-stripe-2
+          type protocol/client
+          option transport-type tcp
+          option remote-host 192.168.1.2
+          option remote-subvolume posix-stripe
+        end-volume
+
+        volume client-stripe-3
+          type protocol/client
+          option transport-type tcp
+          option remote-host 192.168.1.3
+          option remote-subvolume posix-stripe
+        end-volume
+
+        volume client-stripe-4
+          type protocol/client
+          option transport-type tcp
+          option remote-host 192.168.1.4
+          option remote-subvolume posix-stripe
+        end-volume
+
+        volume unify
+          type cluster/unify
+          option scheduler rr
+          subvolumes cluster-unify-1 cluster-unify-2 cluster-unify-3 cluster-unify-4
+        end-volume
+
+        volume stripe
+          type cluster/stripe
+          option block-size *.img:2MB # All files ending with .img are striped with 2MB stripe block size.
+          subvolumes unify cluster-stripe-1 cluster-stripe-2 cluster-stripe-3 cluster-stripe-4
+        end-volume
+
+   Bring up the Storage
+
+   Starting GlusterFS Server: If you have installed through binary
+package, you can start the service through init.d startup script. If
+not:
+
+     [root@server]# glusterfsd
+
+   Mounting GlusterFS Volumes:
+
+     [root@client]# glusterfs -s [BRICK-IP-ADDRESS] /mnt/cluster
+
+   Improving upon this Setup
+
+   Infiniband Verbs RDMA transport is much faster than TCP/IP GigE
+transport.
+
+   Use of performance translators such as read-ahead, write-behind,
+io-cache, io-threads, booster is recommended.
+
+   Replace round-robin (rr) scheduler with ALU to handle more dynamic
+storage environments.
+
+   ---------- Footnotes ----------
+
+   (1)
+http://gluster.org/docs/index.php/Mixing_Striped_and_Regular_Files
+
+
+File: user-guide.info,  Node: Troubleshooting,  Next: GNU Free Documentation Licence,  Prev: Usage Scenarios,  Up: Top
+
+6 Troubleshooting
+*****************
+
+This chapter is a general troubleshooting guide to GlusterFS. It lists
+common GlusterFS server and client error messages, debugging hints, and
+concludes with the suggested procedure to report bugs in GlusterFS.
+
+6.1 GlusterFS error messages
+============================
+
+6.1.1 Server errors
+-------------------
+
+     glusterfsd: FATAL: could not open specfile:
+     '/etc/glusterfs/glusterfsd.vol'
+
+   The GlusterFS server expects the volume specification file to be at
+`/etc/glusterfs/glusterfsd.vol'. The example specification file will be
+installed as `/etc/glusterfs/glusterfsd.vol.sample'. You need to edit
+it and rename it, or provide a different specification file using the
+`--spec-file' command line option (See *note Server::).
+
+     gf_log_init: failed to open logfile "/usr/var/log/glusterfs/glusterfsd.log"
+                  (Permission denied)
+
+   You don't have permission to create files in the
+`/usr/var/log/glusterfs' directory. Make sure you are running GlusterFS
+as root. Alternatively, specify a different path for the log file using
+the `--log-file' option (See *note Server::).
+
+6.1.2 Client errors
+-------------------
+
+     fusermount: failed to access mountpoint /mnt:
+                 Transport endpoint is not connected
+
+   A previous failed (or hung) mount of GlusterFS is preventing it from
+being mounted again in the same location. The fix is to do:
+
+     # umount /mnt
+
+   and try mounting again.
+
+   *"Transport endpoint is not connected".*
+
+   If you get this error when you try a command such as `ls' or `cat',
+it means the GlusterFS mount did not succeed. Try running GlusterFS in
+`DEBUG' logging level and study the log messages to discover the cause.
+
+   *"Connect to server failed", "SERVER-ADDRESS: Connection refused".*
+
+   GluserFS Server is not running or dead. Check your network
+connections and firewall settings. To check if the server is reachable,
+try:
+
+     telnet IP-ADDRESS 24007
+
+   If the server is accessible, your `telnet' command should connect and
+block. If not you will see an error message such as `telnet: Unable to
+connect to remote host: Connection refused'. 24007 is the default
+GlusterFS port. If you have changed it, then use the corresponding port
+instead.
+
+     gf_log_init: failed to open logfile "/usr/var/log/glusterfs/glusterfs.log"
+                  (Permission denied)
+
+   You don't have permission to create files in the
+`/usr/var/log/glusterfs' directory. Make sure you are running GlusterFS
+as root. Alternatively, specify a different path for the log file using
+the `--log-file' option (See *note Client::).
+
+6.2 FUSE error messages
+=======================
+
+`modprobe fuse' fails with: "Unknown symbol in module, or unknown
+parameter".
+
+   If you are using fuse-2.6.x on Redhat Enterprise Linux Work Station 4
+and Advanced Server 4 with 2.6.9-42.ELlargesmp, 2.6.9-42.ELsmp,
+2.6.9-42.EL kernels and get this error while loading FUSE kernel
+module, you need to apply the following patch.
+
+   For fuse-2.6.2:
+
+<http://ftp.gluster.com/pub/gluster/glusterfs/fuse/fuse-2.6.2-rhel-build.patch>
+
+   For fuse-2.6.3:
+
+<http://ftp.gluster.com/pub/gluster/glusterfs/fuse/fuse-2.6.3-rhel-build.patch>
+
+6.3 AppArmour and GlusterFS
+===========================
+
+Under OpenSuSE GNU/Linux, the AppArmour security feature does not allow
+GlusterFS to create temporary files or network socket connections even
+while running as root. You will see error messages like `Unable to open
+log file: Operation not permitted' or `Connection refused'. Disabling
+AppArmour using YaST or properly configuring AppArmour to recognize
+`glusterfsd' or `glusterfs'/`fusermount' should solve the problem.
+
+6.4 Reporting a bug
+===================
+
+If you encounter a bug in GlusterFS, please follow the below guidelines
+when you report it to the mailing list. Be sure to report it! User
+feedback is crucial to the health of the project and we value it highly.
+
+6.4.1 General instructions
+--------------------------
+
+When running GlusterFS in a non-production environment, be sure to
+build it with the following command:
+
+      $ make CFLAGS='-g -O0 -DDEBUG'
+
+   This includes debugging information which will be helpful in getting
+backtraces (see below) and also disable optimization. Enabling
+optimization can result in incorrect line numbers being reported to gdb.
+
+6.4.2 Volume specification files
+--------------------------------
+
+Attach all relevant server and client spec files you were using when
+you encountered the bug. Also tell us details of your setup, i.e., how
+many clients and how many servers.
+
+6.4.3 Log files
+---------------
+
+Set the loglevel of your client and server programs to DEBUG (by
+passing the -L DEBUG option) and attach the log files with your bug
+report. Obviously, if only the client is failing (for example), you
+only need to send us the client log file.
+
+6.4.4 Backtrace
+---------------
+
+If GlusterFS has encountered a segmentation fault or has crashed for
+some other reason, include the backtrace with the bug report. You can
+get the backtrace using the following procedure.
+
+   Run the GlusterFS client or server inside gdb.
+
+      $ gdb ./glusterfs
+      (gdb) set args -f client.spec -N -l/path/to/log/file -LDEBUG /mnt/point
+      (gdb) run
+
+   Now when the process segfaults, you can get the backtrace by typing:
+
+      (gdb) bt
+
+   If the GlusterFS process has crashed and dumped a core file (you can
+find this in / if running as a daemon and in the current directory
+otherwise), you can do:
+
+      $ gdb /path/to/glusterfs /path/to/core.<pid>
+
+   and then get the backtrace.
+
+   If the GlusterFS server or client seems to be hung, then you can get
+the backtrace by attaching gdb to the process. First get the `PID' of
+the process (using ps), and then do:
+
+      $ gdb ./glusterfs <pid>
+
+   Press Ctrl-C to interrupt the process and then generate the
+backtrace.
+
+6.4.5 Reproducing the bug
+-------------------------
+
+If the bug is reproducible, please include the steps necessary to do
+so. If the bug is not reproducible, send us the bug report anyway.
+
+6.4.6 Other information
+-----------------------
+
+If you think it is relevant, send us also the version of FUSE you're
+using, the kernel version, platform.
+
+
+File: user-guide.info,  Node: GNU Free Documentation Licence,  Next: Index,  Prev: Troubleshooting,  Up: Top
+
+Appendix A GNU Free Documentation Licence
+*****************************************
+
+                      Version 1.2, November 2002
+
+     Copyright (C) 2000,2001,2002 Free Software Foundation, Inc.
+     59 Temple Place, Suite 330, Boston, MA  02111-1307, USA
+
+     Everyone is permitted to copy and distribute verbatim copies
+     of this license document, but changing it is not allowed.
+
+  0. PREAMBLE
+
+     The purpose of this License is to make a manual, textbook, or other
+     functional and useful document "free" in the sense of freedom: to
+     assure everyone the effective freedom to copy and redistribute it,
+     with or without modifying it, either commercially or
+     noncommercially.  Secondarily, this License preserves for the
+     author and publisher a way to get credit for their work, while not
+     being considered responsible for modifications made by others.
+
+     This License is a kind of "copyleft", which means that derivative
+     works of the document must themselves be free in the same sense.
+     It complements the GNU General Public License, which is a copyleft
+     license designed for free software.
+
+     We have designed this License in order to use it for manuals for
+     free software, because free software needs free documentation: a
+     free program should come with manuals providing the same freedoms
+     that the software does.  But this License is not limited to
+     software manuals; it can be used for any textual work, regardless
+     of subject matter or whether it is published as a printed book.
+     We recommend this License principally for works whose purpose is
+     instruction or reference.
+
+  1. APPLICABILITY AND DEFINITIONS
+
+     This License applies to any manual or other work, in any medium,
+     that contains a notice placed by the copyright holder saying it
+     can be distributed under the terms of this License.  Such a notice
+     grants a world-wide, royalty-free license, unlimited in duration,
+     to use that work under the conditions stated herein.  The
+     "Document", below, refers to any such manual or work.  Any member
+     of the public is a licensee, and is addressed as "you".  You
+     accept the license if you copy, modify or distribute the work in a
+     way requiring permission under copyright law.
+
+     A "Modified Version" of the Document means any work containing the
+     Document or a portion of it, either copied verbatim, or with
+     modifications and/or translated into another language.
+
+     A "Secondary Section" is a named appendix or a front-matter section
+     of the Document that deals exclusively with the relationship of the
+     publishers or authors of the Document to the Document's overall
+     subject (or to related matters) and contains nothing that could
+     fall directly within that overall subject.  (Thus, if the Document
+     is in part a textbook of mathematics, a Secondary Section may not
+     explain any mathematics.)  The relationship could be a matter of
+     historical connection with the subject or with related matters, or
+     of legal, commercial, philosophical, ethical or political position
+     regarding them.
+
+     The "Invariant Sections" are certain Secondary Sections whose
+     titles are designated, as being those of Invariant Sections, in
+     the notice that says that the Document is released under this
+     License.  If a section does not fit the above definition of
+     Secondary then it is not allowed to be designated as Invariant.
+     The Document may contain zero Invariant Sections.  If the Document
+     does not identify any Invariant Sections then there are none.
+
+     The "Cover Texts" are certain short passages of text that are
+     listed, as Front-Cover Texts or Back-Cover Texts, in the notice
+     that says that the Document is released under this License.  A
+     Front-Cover Text may be at most 5 words, and a Back-Cover Text may
+     be at most 25 words.
+
+     A "Transparent" copy of the Document means a machine-readable copy,
+     represented in a format whose specification is available to the
+     general public, that is suitable for revising the document
+     straightforwardly with generic text editors or (for images
+     composed of pixels) generic paint programs or (for drawings) some
+     widely available drawing editor, and that is suitable for input to
+     text formatters or for automatic translation to a variety of
+     formats suitable for input to text formatters.  A copy made in an
+     otherwise Transparent file format whose markup, or absence of
+     markup, has been arranged to thwart or discourage subsequent
+     modification by readers is not Transparent.  An image format is
+     not Transparent if used for any substantial amount of text.  A
+     copy that is not "Transparent" is called "Opaque".
+
+     Examples of suitable formats for Transparent copies include plain
+     ASCII without markup, Texinfo input format, LaTeX input format,
+     SGML or XML using a publicly available DTD, and
+     standard-conforming simple HTML, PostScript or PDF designed for
+     human modification.  Examples of transparent image formats include
+     PNG, XCF and JPG.  Opaque formats include proprietary formats that
+     can be read and edited only by proprietary word processors, SGML or
+     XML for which the DTD and/or processing tools are not generally
+     available, and the machine-generated HTML, PostScript or PDF
+     produced by some word processors for output purposes only.
+
+     The "Title Page" means, for a printed book, the title page itself,
+     plus such following pages as are needed to hold, legibly, the
+     material this License requires to appear in the title page.  For
+     works in formats which do not have any title page as such, "Title
+     Page" means the text near the most prominent appearance of the
+     work's title, preceding the beginning of the body of the text.
+
+     A section "Entitled XYZ" means a named subunit of the Document
+     whose title either is precisely XYZ or contains XYZ in parentheses
+     following text that translates XYZ in another language.  (Here XYZ
+     stands for a specific section name mentioned below, such as
+     "Acknowledgements", "Dedications", "Endorsements", or "History".)
+     To "Preserve the Title" of such a section when you modify the
+     Document means that it remains a section "Entitled XYZ" according
+     to this definition.
+
+     The Document may include Warranty Disclaimers next to the notice
+     which states that this License applies to the Document.  These
+     Warranty Disclaimers are considered to be included by reference in
+     this License, but only as regards disclaiming warranties: any other
+     implication that these Warranty Disclaimers may have is void and
+     has no effect on the meaning of this License.
+
+  2. VERBATIM COPYING
+
+     You may copy and distribute the Document in any medium, either
+     commercially or noncommercially, provided that this License, the
+     copyright notices, and the license notice saying this License
+     applies to the Document are reproduced in all copies, and that you
+     add no other conditions whatsoever to those of this License.  You
+     may not use technical measures to obstruct or control the reading
+     or further copying of the copies you make or distribute.  However,
+     you may accept compensation in exchange for copies.  If you
+     distribute a large enough number of copies you must also follow
+     the conditions in section 3.
+
+     You may also lend copies, under the same conditions stated above,
+     and you may publicly display copies.
+
+  3. COPYING IN QUANTITY
+
+     If you publish printed copies (or copies in media that commonly
+     have printed covers) of the Document, numbering more than 100, and
+     the Document's license notice requires Cover Texts, you must
+     enclose the copies in covers that carry, clearly and legibly, all
+     these Cover Texts: Front-Cover Texts on the front cover, and
+     Back-Cover Texts on the back cover.  Both covers must also clearly
+     and legibly identify you as the publisher of these copies.  The
+     front cover must present the full title with all words of the
+     title equally prominent and visible.  You may add other material
+     on the covers in addition.  Copying with changes limited to the
+     covers, as long as they preserve the title of the Document and
+     satisfy these conditions, can be treated as verbatim copying in
+     other respects.
+
+     If the required texts for either cover are too voluminous to fit
+     legibly, you should put the first ones listed (as many as fit
+     reasonably) on the actual cover, and continue the rest onto
+     adjacent pages.
+
+     If you publish or distribute Opaque copies of the Document
+     numbering more than 100, you must either include a
+     machine-readable Transparent copy along with each Opaque copy, or
+     state in or with each Opaque copy a computer-network location from
+     which the general network-using public has access to download
+     using public-standard network protocols a complete Transparent
+     copy of the Document, free of added material.  If you use the
+     latter option, you must take reasonably prudent steps, when you
+     begin distribution of Opaque copies in quantity, to ensure that
+     this Transparent copy will remain thus accessible at the stated
+     location until at least one year after the last time you
+     distribute an Opaque copy (directly or through your agents or
+     retailers) of that edition to the public.
+
+     It is requested, but not required, that you contact the authors of
+     the Document well before redistributing any large number of
+     copies, to give them a chance to provide you with an updated
+     version of the Document.
+
+  4. MODIFICATIONS
+
+     You may copy and distribute a Modified Version of the Document
+     under the conditions of sections 2 and 3 above, provided that you
+     release the Modified Version under precisely this License, with
+     the Modified Version filling the role of the Document, thus
+     licensing distribution and modification of the Modified Version to
+     whoever possesses a copy of it.  In addition, you must do these
+     things in the Modified Version:
+
+       A. Use in the Title Page (and on the covers, if any) a title
+          distinct from that of the Document, and from those of
+          previous versions (which should, if there were any, be listed
+          in the History section of the Document).  You may use the
+          same title as a previous version if the original publisher of
+          that version gives permission.
+
+       B. List on the Title Page, as authors, one or more persons or
+          entities responsible for authorship of the modifications in
+          the Modified Version, together with at least five of the
+          principal authors of the Document (all of its principal
+          authors, if it has fewer than five), unless they release you
+          from this requirement.
+
+       C. State on the Title page the name of the publisher of the
+          Modified Version, as the publisher.
+
+       D. Preserve all the copyright notices of the Document.
+
+       E. Add an appropriate copyright notice for your modifications
+          adjacent to the other copyright notices.
+
+       F. Include, immediately after the copyright notices, a license
+          notice giving the public permission to use the Modified
+          Version under the terms of this License, in the form shown in
+          the Addendum below.
+
+       G. Preserve in that license notice the full lists of Invariant
+          Sections and required Cover Texts given in the Document's
+          license notice.
+
+       H. Include an unaltered copy of this License.
+
+       I. Preserve the section Entitled "History", Preserve its Title,
+          and add to it an item stating at least the title, year, new
+          authors, and publisher of the Modified Version as given on
+          the Title Page.  If there is no section Entitled "History" in
+          the Document, create one stating the title, year, authors,
+          and publisher of the Document as given on its Title Page,
+          then add an item describing the Modified Version as stated in
+          the previous sentence.
+
+       J. Preserve the network location, if any, given in the Document
+          for public access to a Transparent copy of the Document, and
+          likewise the network locations given in the Document for
+          previous versions it was based on.  These may be placed in
+          the "History" section.  You may omit a network location for a
+          work that was published at least four years before the
+          Document itself, or if the original publisher of the version
+          it refers to gives permission.
+
+       K. For any section Entitled "Acknowledgements" or "Dedications",
+          Preserve the Title of the section, and preserve in the
+          section all the substance and tone of each of the contributor
+          acknowledgements and/or dedications given therein.
+
+       L. Preserve all the Invariant Sections of the Document,
+          unaltered in their text and in their titles.  Section numbers
+          or the equivalent are not considered part of the section
+          titles.
+
+       M. Delete any section Entitled "Endorsements".  Such a section
+          may not be included in the Modified Version.
+
+       N. Do not retitle any existing section to be Entitled
+          "Endorsements" or to conflict in title with any Invariant
+          Section.
+
+       O. Preserve any Warranty Disclaimers.
+
+     If the Modified Version includes new front-matter sections or
+     appendices that qualify as Secondary Sections and contain no
+     material copied from the Document, you may at your option
+     designate some or all of these sections as invariant.  To do this,
+     add their titles to the list of Invariant Sections in the Modified
+     Version's license notice.  These titles must be distinct from any
+     other section titles.
+
+     You may add a section Entitled "Endorsements", provided it contains
+     nothing but endorsements of your Modified Version by various
+     parties--for example, statements of peer review or that the text
+     has been approved by an organization as the authoritative
+     definition of a standard.
+
+     You may add a passage of up to five words as a Front-Cover Text,
+     and a passage of up to 25 words as a Back-Cover Text, to the end
+     of the list of Cover Texts in the Modified Version.  Only one
+     passage of Front-Cover Text and one of Back-Cover Text may be
+     added by (or through arrangements made by) any one entity.  If the
+     Document already includes a cover text for the same cover,
+     previously added by you or by arrangement made by the same entity
+     you are acting on behalf of, you may not add another; but you may
+     replace the old one, on explicit permission from the previous
+     publisher that added the old one.
+
+     The author(s) and publisher(s) of the Document do not by this
+     License give permission to use their names for publicity for or to
+     assert or imply endorsement of any Modified Version.
+
+  5. COMBINING DOCUMENTS
+
+     You may combine the Document with other documents released under
+     this License, under the terms defined in section 4 above for
+     modified versions, provided that you include in the combination
+     all of the Invariant Sections of all of the original documents,
+     unmodified, and list them all as Invariant Sections of your
+     combined work in its license notice, and that you preserve all
+     their Warranty Disclaimers.
+
+     The combined work need only contain one copy of this License, and
+     multiple identical Invariant Sections may be replaced with a single
+     copy.  If there are multiple Invariant Sections with the same name
+     but different contents, make the title of each such section unique
+     by adding at the end of it, in parentheses, the name of the
+     original author or publisher of that section if known, or else a
+     unique number.  Make the same adjustment to the section titles in
+     the list of Invariant Sections in the license notice of the
+     combined work.
+
+     In the combination, you must combine any sections Entitled
+     "History" in the various original documents, forming one section
+     Entitled "History"; likewise combine any sections Entitled
+     "Acknowledgements", and any sections Entitled "Dedications".  You
+     must delete all sections Entitled "Endorsements."
+
+  6. COLLECTIONS OF DOCUMENTS
+
+     You may make a collection consisting of the Document and other
+     documents released under this License, and replace the individual
+     copies of this License in the various documents with a single copy
+     that is included in the collection, provided that you follow the
+     rules of this License for verbatim copying of each of the
+     documents in all other respects.
+
+     You may extract a single document from such a collection, and
+     distribute it individually under this License, provided you insert
+     a copy of this License into the extracted document, and follow
+     this License in all other respects regarding verbatim copying of
+     that document.
+
+  7. AGGREGATION WITH INDEPENDENT WORKS
+
+     A compilation of the Document or its derivatives with other
+     separate and independent documents or works, in or on a volume of
+     a storage or distribution medium, is called an "aggregate" if the
+     copyright resulting from the compilation is not used to limit the
+     legal rights of the compilation's users beyond what the individual
+     works permit.  When the Document is included in an aggregate, this
+     License does not apply to the other works in the aggregate which
+     are not themselves derivative works of the Document.
+
+     If the Cover Text requirement of section 3 is applicable to these
+     copies of the Document, then if the Document is less than one half
+     of the entire aggregate, the Document's Cover Texts may be placed
+     on covers that bracket the Document within the aggregate, or the
+     electronic equivalent of covers if the Document is in electronic
+     form.  Otherwise they must appear on printed covers that bracket
+     the whole aggregate.
+
+  8. TRANSLATION
+
+     Translation is considered a kind of modification, so you may
+     distribute translations of the Document under the terms of section
+     4.  Replacing Invariant Sections with translations requires special
+     permission from their copyright holders, but you may include
+     translations of some or all Invariant Sections in addition to the
+     original versions of these Invariant Sections.  You may include a
+     translation of this License, and all the license notices in the
+     Document, and any Warranty Disclaimers, provided that you also
+     include the original English version of this License and the
+     original versions of those notices and disclaimers.  In case of a
+     disagreement between the translation and the original version of
+     this License or a notice or disclaimer, the original version will
+     prevail.
+
+     If a section in the Document is Entitled "Acknowledgements",
+     "Dedications", or "History", the requirement (section 4) to
+     Preserve its Title (section 1) will typically require changing the
+     actual title.
+
+  9. TERMINATION
+
+     You may not copy, modify, sublicense, or distribute the Document
+     except as expressly provided for under this License.  Any other
+     attempt to copy, modify, sublicense or distribute the Document is
+     void, and will automatically terminate your rights under this
+     License.  However, parties who have received copies, or rights,
+     from you under this License will not have their licenses
+     terminated so long as such parties remain in full compliance.
+
+ 10. FUTURE REVISIONS OF THIS LICENSE
+
+     The Free Software Foundation may publish new, revised versions of
+     the GNU Free Documentation License from time to time.  Such new
+     versions will be similar in spirit to the present version, but may
+     differ in detail to address new problems or concerns.  See
+     `http://www.gnu.org/copyleft/'.
+
+     Each version of the License is given a distinguishing version
+     number.  If the Document specifies that a particular numbered
+     version of this License "or any later version" applies to it, you
+     have the option of following the terms and conditions either of
+     that specified version or of any later version that has been
+     published (not as a draft) by the Free Software Foundation.  If
+     the Document does not specify a version number of this License,
+     you may choose any version ever published (not as a draft) by the
+     Free Software Foundation.
+
+A.0.1 ADDENDUM: How to use this License for your documents
+----------------------------------------------------------
+
+To use this License in a document you have written, include a copy of
+the License in the document and put the following copyright and license
+notices just after the title page:
+
+       Copyright (C)  YEAR  YOUR NAME.
+       Permission is granted to copy, distribute and/or modify this document
+       under the terms of the GNU Free Documentation License, Version 1.2
+       or any later version published by the Free Software Foundation;
+       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
+       Texts.  A copy of the license is included in the section entitled ``GNU
+       Free Documentation License''.
+
+   If you have Invariant Sections, Front-Cover Texts and Back-Cover
+Texts, replace the "with...Texts." line with this:
+
+         with the Invariant Sections being LIST THEIR TITLES, with
+         the Front-Cover Texts being LIST, and with the Back-Cover Texts
+         being LIST.
+
+   If you have Invariant Sections without Cover Texts, or some other
+combination of the three, merge those two alternatives to suit the
+situation.
+
+   If your document contains nontrivial examples of program code, we
+recommend releasing these examples in parallel under your choice of
+free software license, such as the GNU General Public License, to
+permit their use in free software.
+
+
+File: user-guide.info,  Node: Index,  Prev: GNU Free Documentation Licence,  Up: Top
+
+Index
+*****
+
+
+* Menu:
+
+* alu (scheduler):                       Unify.               (line  49)
+* AppArmour:                             Troubleshooting.     (line  96)
+* arch:                                  Getting GlusterFS.   (line   6)
+* booster:                               Booster.             (line   6)
+* commercial support:                    Introduction.        (line  36)
+* DNS round robin:                       Transport modules.   (line  29)
+* fcntl:                                 POSIX Locks.         (line   6)
+* FDL, GNU Free Documentation License:   GNU Free Documentation Licence.
+                                                              (line   6)
+* fixed-id (translator):                 Fixed ID.            (line   6)
+* GlusterFS client:                      Client.              (line   6)
+* GlusterFS mailing list:                Introduction.        (line  28)
+* GlusterFS server:                      Server.              (line   6)
+* infiniband transport:                  Transport modules.   (line  58)
+* InfiniBand, installation:              Pre requisites.      (line  51)
+* io-cache (translator):                 IO Cache.            (line   6)
+* io-threads (translator):               IO Threads.          (line   6)
+* IRC channel, #gluster:                 Introduction.        (line  31)
+* libibverbs:                            Pre requisites.      (line  51)
+* namespace:                             Unify.               (line 207)
+* nufa (scheduler):                      Unify.               (line 175)
+* OpenSuSE:                              Troubleshooting.     (line  96)
+* posix-locks (translator):              POSIX Locks.         (line   6)
+* random (scheduler):                    Unify.               (line 159)
+* read-ahead (translator):               Read Ahead.          (line   6)
+* record locking:                        POSIX Locks.         (line   6)
+* Redhat Enterprise Linux:               Troubleshooting.     (line  78)
+* Replicate:                             Replicate.           (line   6)
+* rot-13 (translator):                   ROT-13.              (line   6)
+* rr (scheduler):                        Unify.               (line 138)
+* scheduler (unify):                     Unify.               (line   6)
+* self heal (replicate):                 Replicate.           (line  46)
+* self heal (unify):                     Unify.               (line 223)
+* stripe (translator):                   Stripe.              (line   6)
+* trace (translator):                    Trace.               (line   6)
+* unify (translator):                    Unify.               (line   6)
+* unify invariants:                      Unify.               (line  16)
+* write-behind (translator):             Write Behind.        (line   6)
+* Gluster, Inc.:                      Introduction.        (line  36)
+
+
+
+Tag Table:
+Node: Top704
+Node: Acknowledgements2304
+Node: Introduction3214
+Node: Installation and Invocation4649
+Node: Pre requisites4933
+Node: Getting GlusterFS7023
+Ref: Getting GlusterFS-Footnote-17809
+Node: Building7857
+Node: Running GlusterFS9559
+Node: Server9770
+Node: Client11358
+Node: A Tutorial Introduction13564
+Node: Concepts17101
+Node: Filesystems in Userspace17316
+Node: Translator18457
+Node: Volume specification file21160
+Node: Translators23632
+Node: Storage Translators24201
+Ref: Storage Translators-Footnote-125008
+Node: POSIX25142
+Node: BDB25765
+Node: Client and Server Translators26822
+Node: Transport modules27298
+Node: Client protocol31445
+Node: Server protocol32384
+Node: Clustering Translators33373
+Node: Unify34260
+Ref: Unify-Footnote-143859
+Node: Replicate43951
+Node: Stripe49006
+Node: Performance Translators50164
+Node: Read Ahead50438
+Node: Write Behind52170
+Node: IO Threads53579
+Node: IO Cache54367
+Node: Booster55691
+Node: Features Translators57105
+Node: POSIX Locks57333
+Node: Fixed ID58650
+Node: Miscellaneous Translators59136
+Node: ROT-1359334
+Node: Trace60013
+Node: Usage Scenarios61282
+Ref: Usage Scenarios-Footnote-167215
+Node: Troubleshooting67290
+Node: GNU Free Documentation Licence73638
+Node: Index96087
+
+End Tag Table