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diff --git a/doc/user-guide/user-guide.texi b/doc/user-guide/user-guide.texi new file mode 100644 index 00000000000..8365419a611 --- /dev/null +++ b/doc/user-guide/user-guide.texi @@ -0,0 +1,2226 @@ +\input texinfo +@setfilename user-guide.info +@settitle GlusterFS 2.0 User Guide +@afourpaper + +@direntry +* GlusterFS: (user-guide). GlusterFS distributed filesystem user guide +@end direntry + +@copying +This is the user manual for GlusterFS 2.0. + +Copyright @copyright{} 2008,2007 @email{@b{Z}} Research, Inc. Permission is granted to +copy, distribute and/or modify this document under the terms of the +@acronym{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 ``@acronym{GNU} Free +Documentation License''. +@end copying + +@titlepage +@title GlusterFS 2.0 User Guide [DRAFT] +@subtitle January 15, 2008 +@author http://gluster.org/core-team.php +@author @email{@b{Z}} @b{Research} + +@page +@vskip 0pt plus 1filll +@insertcopying +@end titlepage + +@c Info stuff +@ifnottex +@node Top +@top GlusterFS 2.0 User Guide + +@insertcopying +@menu +* Acknowledgements:: +* Introduction:: +* Installation and Invocation:: +* Concepts:: +* Translators:: +* Usage Scenarios:: +* Troubleshooting:: +* GNU Free Documentation Licence:: +* Index:: + +@detailmenu + --- 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:: + +@end detailmenu +@end menu + +@end ifnottex +@c Info stuff end + +@contents + +@node Acknowledgements +@unnumbered 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. +@flushright +http://gluster.org/core-team.php (@email{list-hacking@@zresearch.com}) +@email{@b{Z}} Research +@end flushright + +@node Introduction +@chapter 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 + +@itemize @bullet +@item Scalability: A distributed filesystem allows us to store more data than what can be stored on a single machine. + +@item Redundancy: We might want to replicate crucial data on to several machines. + +@item Uniform access: One can mount a remote volume (for example your home directory) from any machine and access the same data. +@end itemize + +@section Contacting us +You can reach us through the mailing list @strong{gluster-devel} +(@email{gluster-devel@@nongnu.org}). +@cindex GlusterFS mailing list + +You can also find many of the developers on @acronym{IRC}, on the @code{#gluster} +channel on Freenode (@indicateurl{irc.freenode.net}). +@cindex IRC channel, #gluster + +The GlusterFS documentation wiki is also useful: @* +@indicateurl{http://gluster.org/docs/index.php/GlusterFS} + +For commercial support, you can contact @email{@b{Z}} Research at: +@cindex commercial support +@cindex Z Research, Inc. + +@display +3194 Winding Vista Common +Fremont, CA 94539 +USA. + +Phone: +1 (510) 354 6801 +Toll free: +1 (888) 813 6309 +Fax: +1 (510) 372 0604 +@end display + +You can also email us at @email{support@@zresearch.com}. + +@node Installation and Invocation +@chapter Installation and Invocation + +@menu +* Pre requisites:: +* Getting GlusterFS:: +* Building:: +* Running GlusterFS:: +* A Tutorial Introduction:: +@end menu + +@node Pre requisites +@section Pre requisites + +Before installing GlusterFS make sure you have the +following components installed. + +@subsection @acronym{FUSE} +You'll need @acronym{FUSE} version 2.6.0 or higher to +use GlusterFS. You can omit installing @acronym{FUSE} if you want to +build @emph{only} the server. Note that you won't be able to mount +a GlusterFS filesystem on a machine that does not have @acronym{FUSE} +installed. + +@acronym{FUSE} can be downloaded from: @indicateurl{http://fuse.sourceforge.net/} + +To get the best performance from GlusterFS, however, it is recommended that you use +our patched version of @acronym{FUSE}. See Patched FUSE for details. + +@subsection Patched FUSE + +The GlusterFS project maintains a patched version of @acronym{FUSE} meant to be used +with GlusterFS. The patches increase GlusterFS performance. It is recommended that +all users use the patched @acronym{FUSE}. + +The patched @acronym{FUSE} tarball can be downloaded from: + +@indicateurl{ftp://ftp.zresearch.com/pub/gluster/glusterfs/fuse/} + +The specific changes made to @acronym{FUSE} are: + +@itemize +@item The communication channel size between @acronym{FUSE} kernel module and GlusterFS has been increased to 1MB, permitting large reads and writes to be sent in bigger chunks. + +@item The kernel's read-ahead boundry has been extended upto 1MB. + +@item Block size returned in the @command{stat()}/@command{fstat()} calls tuned to 1MB, to make cp and similar commands perform I/O using that block size. + +@item @command{flock()} locking support has been added (although some rework in GlusterFS is needed for perfect compliance). +@end itemize + +@subsection libibverbs (optional) +@cindex InfiniBand, installation +@cindex libibverbs +This is only needed if you want GlusterFS to use InfiniBand as the +interconnect mechanism between server and client. You can get it from: + +@indicateurl{http://www.openfabrics.org/downloads.htm}. + +@subsection 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. + +@node Getting GlusterFS +@section Getting GlusterFS +@cindex arch +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: @indicateurl{http://gluster.org/download.php}. + +If you want the bleeding edge development source, you can get them +from the @acronym{GNU} +Arch@footnote{@indicateurl{http://www.gnu.org/software/gnu-arch/}} +repository. First you must install @acronym{GNU} Arch itself. Then +register the GlusterFS archive by doing: + +@example +$ tla register-archive http://arch.sv.gnu.org/archives/gluster +@end example + +Now you can check out the source itself: + +@example +$ tla get -A gluster@@sv.gnu.org glusterfs--mainline--3.0 +@end example + +@node Building +@section Building +You can skip this section if you're installing from @acronym{RPM}s +or @acronym{DEB}s. + +GlusterFS uses the Autotools mechanism to build. As such, the procedure +is straight-forward. First, change into the GlusterFS source directory. + +@example +$ cd glusterfs-<version> +@end example + +If you checked out the source from the Arch repository, you'll need +to run @command{./autogen.sh} first. Note that you'll need to have +Autoconf and Automake installed for this. + +Run @command{configure}. + +@example +$ ./configure +@end example + +The configure script accepts the following options: + +@cartouche +@table @code + +@item --disable-ibverbs +Disable the InfiniBand transport mechanism. + +@item --disable-fuse-client +Disable the @acronym{FUSE} client. + +@item --disable-server +Disable building of the GlusterFS server. + +@item --disable-bdb +Disable building of Berkeley DB based storage translator. + +@item --disable-mod_glusterfs +Disable building of Apache/lighttpd glusterfs plugins. + +@item --disable-epoll +Use poll instead of epoll. + +@item --disable-libglusterfsclient +Disable building of libglusterfsclient + +@end table +@end cartouche + +Build and install GlusterFS. + +@example +# make install +@end example + +The binaries (@command{glusterfsd} and @command{glusterfs}) will be by +default installed in @command{/usr/local/sbin/}. Translator, +scheduler, and transport shared libraries will be installed in +@command{/usr/local/lib/glusterfs/<version>/}. Sample volume +specification files will be in @command{/usr/local/etc/glusterfs/}. +This document itself can be found in +@command{/usr/local/share/doc/glusterfs/}. If you passed the @command{--prefix} +argument to the configure script, then replace @command{/usr/local} in the preceding +paths with the prefix. + +@node Running GlusterFS +@section Running GlusterFS + +@menu +* Server:: +* Client:: +@end menu + +@node Server +@subsection Server +@cindex GlusterFS server + +The GlusterFS server is necessary to export storage volumes to remote clients +(See @ref{Server protocol} for more info). This section documents the invocation +of the GlusterFS server program and all the command-line options accepted by it. + +@cartouche +@table @code +Basic Options +@item -f, --volfile=<path> + Use the volume file as the volume specification. + +@item -s, --volfile-server=<hostname> + Server to get volume file from. This option overrides --volfile option. + +@item -l, --log-file=<path> + Specify the path for the log file. + +@item -L, --log-level=<level> + Set the log level for the server. Log level should be one of @acronym{DEBUG}, +@acronym{WARNING}, @acronym{ERROR}, @acronym{CRITICAL}, or @acronym{NONE}. + +Advanced Options +@item --debug + Run in debug mode. This option sets --no-daemon, --log-level to DEBUG and + --log-file to console. + +@item -N, --no-daemon + Run glusterfsd as a foreground process. + +@item -p, --pid-file=<path> + Path for the @acronym{PID} file. + +@item --volfile-id=<key> + 'key' of the volfile to be fetched from server. + +@item --volfile-server-port=<port-number> + Listening port number of volfile server. + +@item --volfile-server-transport=[socket|ib-verbs] + Transport type to get volfile from server. [default: @command{socket}] + +@item --xlator-options=<volume-name.option=value> + Add/override a translator option for a volume with specified value. + +Miscellaneous Options +@item -?, --help + Show this help text. + +@item --usage + Display a short usage message. + +@item -V, --version + Show version information. +@end table +@end cartouche + +@node Client +@subsection Client +@cindex GlusterFS client + +The GlusterFS client process is necessary to access remote storage volumes and +mount them locally using @acronym{FUSE}. This section documents the invocation of the +client process and all its command-line arguments. + +@example + # glusterfs [options] <mountpoint> +@end example + +The @command{mountpoint} is the directory where you want the GlusterFS +filesystem to appear. Example: + +@example + # glusterfs -f /usr/local/etc/glusterfs-client.vol /mnt +@end example + +The command-line options are detailed below. + +@tex +\vfill +@end tex +@page + +@cartouche +@table @code + +Basic Options +@item -f, --volfile=<path> + Use the volume file as the volume specification. + +@item -s, --volfile-server=<hostname> + Server to get volume file from. This option overrides --volfile option. + +@item -l, --log-file=<path> + Specify the path for the log file. + +@item -L, --log-level=<level> + Set the log level for the server. Log level should be one of @acronym{DEBUG}, +@acronym{WARNING}, @acronym{ERROR}, @acronym{CRITICAL}, or @acronym{NONE}. + +Advanced Options +@item --debug + Run in debug mode. This option sets --no-daemon, --log-level to DEBUG and + --log-file to console. + +@item -N, --no-daemon + Run @command{glusterfs} as a foreground process. + +@item -p, --pid-file=<path> + Path for the @acronym{PID} file. + +@item --volfile-id=<key> + 'key' of the volfile to be fetched from server. + +@item --volfile-server-port=<port-number> + Listening port number of volfile server. + +@item --volfile-server-transport=[socket|ib-verbs] + Transport type to get volfile from server. [default: @command{socket}] + +@item --xlator-options=<volume-name.option=value> + Add/override a translator option for a volume with specified value. + +@item --volume-name=<volume name> + Volume name in client spec to use. Defaults to the root volume. + +@acronym{FUSE} Options +@item --attribute-timeout=<n> + Attribute timeout for inodes in the kernel, in seconds. Defaults to 1 second. + +@item --disable-direct-io-mode + Disable direct @acronym{I/O} mode in @acronym{FUSE} kernel module. + +@item -e, --entry-timeout=<n> + Entry timeout for directory entries in the kernel, in seconds. + Defaults to 1 second. + +Missellaneous Options +@item -?, --help + Show this help information. + +@item -V, --version + Show version information. +@end table +@end cartouche + +@node A Tutorial Introduction +@section 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 @emph{server} and +@emph{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: + +@example +[root@@server]# +@end example + +Our goal is to make a directory on the @emph{server} (say, @command{/export}) +accessible to the @emph{client}. + +First of all, get GlusterFS installed on both the machines, as described in the +previous sections. Make sure you have the @acronym{FUSE} kernel module loaded. You +can ensure this by running: + +@example +[root@@server]# modprobe fuse +@end example + +Before we can run the GlusterFS client or server programs, we need to write +two files called @emph{volume specifications} (equivalently refered to as @emph{volfiles}). +The volfile describes the @emph{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 @command{/etc/export} file. + +On the server, create a text file somewhere (we'll assume the path +@command{/tmp/glusterfsd.vol}) with the following contents. + +@cartouche +@example +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 +@end example +@end cartouche + +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 +@command{/export} directory. The second section defines options for the translator +which will make the storage volume accessible remotely. It specifies @command{colon-o} as +a subvolume. This defines the @emph{translator tree}, about which more will be said +in the next chapter. The two options specify that the @acronym{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 @acronym{IP} address at all. If you wanted to +restrict access to this server to only your subnet for example, you'd specify +something like @command{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 @command{/tmp/glusterfs-client.vol}). Replace +@emph{server-ip-address} with the @acronym{IP} address of your server machine. If you +are doing all this on a single machine, use @command{127.0.0.1}. + +@cartouche +@example +volume client + type protocol/client + option transport-type tcp + option remote-host @emph{server-ip-address} + option remote-subvolume colon-o +end-volume +@end example +@end cartouche + +Now we need to start both the server and client programs. To start the server: + +@example +[root@@server]# glusterfsd -f /tmp/glusterfs-server.vol +@end example + +To start the client: + +@example +[root@@client]# glusterfs -f /tmp/glusterfs-client.vol /mnt/glusterfs +@end example + +You should now be able to see the files under the server's @command{/export} directory +in the @command{/mnt/glusterfs} directory on the client. That's it; GlusterFS is now +working as a network file system. + +@node Concepts +@chapter Concepts + +@menu +* Filesystems in Userspace:: +* Translator:: +* Volume specification file:: +@end menu + +@node Filesystems in Userspace +@section Filesystems in Userspace + +A filesystem is usually implemented in kernel space. Kernel space +development is much harder than userspace development. @acronym{FUSE} +is a kernel module/library that allows us to write a filesystem +completely in userspace. + +@acronym{FUSE} consists of a kernel module which interacts with the userspace +implementation using a device file @code{/dev/fuse}. When a process +makes a syscall on a @acronym{FUSE} filesystem, @acronym{VFS} hands the request to the +@acronym{FUSE} module, which writes the request to @code{/dev/fuse}. The +userspace implementation polls @code{/dev/fuse}, and when a request arrives, +processes it and writes the result back to @code{/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 @acronym{POSIX} filesystem. + +@center @image{fuse,44pc,,,.pdf} +@center Fig 1. Control flow in GlusterFS + +@node Translator +@section Translator + +The @emph{translator} is the most important concept in GlusterFS. In +fact, GlusterFS is nothing but a collection of translators working +together, forming a translator @emph{tree}. + +The idea of a translator is perhaps best understood using an +analogy. Consider the @acronym{VFS} in the Linux kernel. The +@acronym{VFS} abstracts the various filesystem implementations (such +as @acronym{EXT3}, ReiserFS, @acronym{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: +@command{/}, which is an @acronym{EXT3} partition, and @command{/usr}, +which is a ReiserFS partition. Now if an application wants to open a +file called, say, @command{/etc/fstab}, then the kernel will +internally pass the request to the @acronym{EXT3} implementation. If +on the other hand, an application wants to read a file called +@command{/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 @acronym{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 (@command{.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? + +@tex +\vfill +@end tex +@page + +@center @image{xlator,44pc,,,.pdf} +@center 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, @command{10.0.0.1}, can access +the aggregated storage of the filesystems on the server machines @command{10.0.0.2}, +@command{10.0.0.3}, and @command{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. + +@node Volume specification file +@section 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: + +@cartouche +@example +@strong{volume} @emph{volume-name} + @strong{type} @emph{translator-name} + @strong{option} @emph{option-name} @emph{option-value} + @dots{} + @strong{subvolumes} @emph{subvolume1} @emph{subvolume2} @dots{} +@strong{end-volume} +@end example + +@dots{} +@end cartouche + +@table @asis +@item @emph{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''. + +@item @emph{translator-name} + Name of one of the available translators. Example: @command{protocol/client}, +@command{cluster/unify}. + +@item @emph{option-name} + Name of a valid option for the translator. + +@item @emph{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. + +@item @emph{subvolume1}, @emph{subvolume2}, @dots{} + Volume names of sub-volumes. The sub-volumes must already have been defined earlier +in the file. +@end table + +There are a few rules you must follow when writing a volume specification file: + +@itemize +@item Everything following a `@command{#}' is considered a comment and is ignored. Blank lines are also ignored. +@item All names and keywords are case-sensitive. +@item The order of options inside a volume definition does not matter. +@item An option value may not span multiple lines. +@item If an option is not specified, it will assume its default value. +@item 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. +@end itemize + +A simple example volume specification file is shown below: + +@cartouche +@example +# 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 +@end example +@end cartouche + +@node Translators +@chapter Translators + +@menu +* Storage Translators:: +* Client and Server Translators:: +* Clustering Translators:: +* Performance Translators:: +* Features Translators:: +* Miscellaneous Translators:: +@end menu + +This chapter documents all the available GlusterFS translators in detail. +Each translator section will show its name (for example, @command{cluster/unify}), +briefly describe its purpose and workings, and list every option accepted by +that translator and their meaning. + +@node Storage Translators +@section Storage Translators + +The storage translators form the ``backend'' for GlusterFS. Currently, +the only available storage translator is the @acronym{POSIX} +translator, which stores files on a normal @acronym{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 @acronym{API}. The S3 translator will allow you to access +the storage as a normal @acronym{POSIX} filesystem. +@footnote{Some more discussion about this can be found at: + +http://developer.amazonwebservices.com/connect/message.jspa?messageID=52873} + +@menu +* POSIX:: +* BDB:: +@end menu + +@node POSIX +@subsection POSIX +@example +type storage/posix +@end example + +The @command{posix} translator uses a normal @acronym{POSIX} +filesystem as its ``backend'' to actually store files and +directories. This can be any filesystem that supports extended +attributes (@acronym{EXT3}, ReiserFS, @acronym{XFS}, ...). Extended +attributes are used by some translators to store metadata, for +example, by the replicate and stripe translators. See +@ref{Replicate} and @ref{Stripe}, respectively for details. + +@cartouche +@table @code +@item directory <path> +The directory on the local filesystem which is to be used for storage. +@end table +@end cartouche + +@node BDB +@subsection BDB +@example +type storage/bdb +@end example + +The @command{BDB} translator uses a @acronym{Berkeley DB} database as its +``backend'' to actually store files as key-value pair in the database and +directories as regular @acronym{POSIX} directories. Note that @acronym{BDB} +does not provide extended attribute support for regular files. Do not use +@acronym{BDB} as storage translator while using any translator that demands +extended attributes on ``backend''. + +@cartouche +@table @code +@item directory <path> +The directory on the local filesystem which is to be used for storage. +@item mode [cache|persistent] (cache) +When @acronym{BDB} is run in @command{cache} mode, recovery of back-end is not completely +guaranteed. @command{persistent} guarantees that @acronym{BDB} can recover back-end from +@acronym{Berkeley DB} even if GlusterFS crashes. +@item errfile <path> +The path of the file to be used as @command{errfile} for @acronym{Berkeley DB} to report +detailed error messages, if any. Note that all the contents of this file will be written +by @acronym{Berkeley DB}, not GlusterFS. +@item logdir <path> + + +@end table +@end cartouche + +@node Client and Server Translators, Clustering Translators, Storage Translators, Translators +@section 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:: +@end menu + +@node Transport modules +@subsection Transport modules +The client and server translators are capable of using any of the +pluggable transport modules. Currently available transport modules are +@command{tcp}, which uses a @acronym{TCP} connection between client +and server to communicate; @command{ib-sdp}, which uses a +@acronym{TCP} connection over InfiniBand, and @command{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. + +@subsubsection TCP + +The @acronym{TCP} transport module uses a @acronym{TCP/IP} connection between +the server and the client. + +@example + option transport-type tcp +@end example + +The @acronym{TCP} client module accepts the following options: + +@cartouche +@table @code +@item non-blocking-connect [no|off|on|yes] (on) +Whether to make the connection attempt asynchronous. +@item remote-port <n> (6996) +Server port to connect to. +@cindex DNS round robin +@item remote-host <hostname> * +Hostname or @acronym{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. +@end table +@end cartouche + +The @acronym{TCP} server module accepts the following options: + +@cartouche +@table @code +@item 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. +@item listen-port <n> (6996) +The local port to listen on. +@end table +@end cartouche + +@subsubsection IB-SDP +@example + option transport-type ib-sdp +@end example + +kernel implements socket interface for ib hardware. SDP is over ib-verbs. +This module accepts the same options as @command{tcp} + +@subsubsection ibverbs + +@example + option transport-type tcp +@end example + +@cindex infiniband transport + +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 @command{ib-verbs} transport accesses the InfiniBand hardware through +the ``verbs'' @acronym{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 @command{ib-verbs}. Use @command{ib-sdp} only if you cannot get +@command{ib-verbs} working for some reason. + +The @command{ib-verbs} client module accepts the following options: + +@cartouche +@table @code +@item non-blocking-connect [no|off|on|yes] (on) +Whether to make the connection attempt asynchronous. +@item remote-port <n> (6996) +Server port to connect to. +@cindex DNS round robin +@item remote-host <hostname> * +Hostname or @acronym{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. +@end table +@end cartouche + +The @command{ib-verbs} server module accepts the following options: + +@cartouche +@table @code +@item 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. +@item listen-port <n> (6996) +The local port to listen on. +@end table +@end cartouche + +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''. + +@cartouche +@table @code +@item ib-verbs-work-request-send-count <n> (64) +Length of the send queue in datagrams. [Reason to increase/decrease?] + +@item ib-verbs-work-request-recv-count <n> (64) +Length of the receive queue in datagrams. [Reason to increase/decrease?] + +@item ib-verbs-work-request-send-size <size> (128KB) +Size of each datagram that is sent. [Reason to increase/decrease?] + +@item ib-verbs-work-request-recv-size <size> (128KB) +Size of each datagram that is received. [Reason to increase/decrease?] + +@item ib-verbs-port <n> (1) +Port number for ib-verbs. + +@item ib-verbs-mtu [256|512|1024|2048|4096] (2048) +The Maximum Transmission Unit [Reason to increase/decrease?] + +@item ib-verbs-device-name <device-name> (first device in the list) +InfiniBand device to be used. +@end table +@end cartouche + +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. + +@node Client protocol +@subsection Client +@example +type procotol/client +@end example + +The client translator enables the GlusterFS client to access a remote server's +translator tree. + +@cartouche +@table @code + +@item transport-type [tcp,ib-sdp,ib-verbs] (tcp) +The transport type to use. You should use the client versions of all the +transport modules (@command{tcp}, @command{ib-sdp}, +@command{ib-verbs}). +@item remote-subvolume <volume_name> * +The name of the volume on the remote host to attach to. Note that +this is @emph{not} the name of the @command{protocol/server} volume on the +server. It should be any volume under the server. +@item 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. +@end table +@end cartouche + +@node Server protocol +@subsection Server +@example +type protocol/server +@end example + +The server translator exports a translator tree and makes it accessible to +remote GlusterFS clients. + +@cartouche +@table @code +@item 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 @command{--server} option +(@ref{Client}). + +@item transport-type [tcp,ib-verbs,ib-sdp] (tcp) +The transport to use. You should use the server versions of all the transport +modules (@command{tcp}, @command{ib-sdp}, @command{ib-verbs}). + +@item 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 @command{192.168.*.*} +allows any host in the @command{192.168.x.x} subnet to connect to the server. + +@end table +@end cartouche + +@node Clustering Translators +@section 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 @acronym{RAID}-like +redundancy and distribution over the entire cluster. + +There are three clustering translators: @strong{unify}, @strong{replicate}, +and @strong{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:: +@end menu + +@node Unify +@subsection Unify +@cindex unify (translator) +@cindex scheduler (unify) +@example +type cluster/unify +@end example + +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: + +@cindex unify invariants +@itemize +@item The directory structure of all the sub-volumes must be identical. +@item A particular file can exist on only one of the sub-volumes. Phrasing it in another way, a pathname such as @command{/home/calvin/homework.txt}) is unique across the entire cluster. +@end itemize + +@tex +\vfill +@end tex +@page + +@center @image{unify,44pc,,,.pdf} + +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 @emph{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 @emph{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 @emph{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. + +@subsubsection ALU +@cindex alu (scheduler) + +@example + option scheduler alu +@end example + +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: + +@itemize +@item disk-usage: The used and free disk space on the volume. + +@item read-usage: The amount of reading done from this volume. + +@item write-usage: The amount of writing done to this volume. + +@item open-files-usage: The number of files currently open from this volume. + +@item disk-speed-usage: The speed at which the disks are spinning. This is a constant value and therefore not very useful. +@end itemize + +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 +@command{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 +@command{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: @command{option alu.limits.min-free-disk 5GB}. + +@cartouche +@table @code +@item alu.order <order> * ("disk-usage:write-usage:read-usage:open-files-usage:disk-speed") +@item alu.disk-usage.entry-threshold <size> (1GB) +@item alu.disk-usage.exit-threshold <size> (512MB) +@item alu.write-usage.entry-threshold <%> (25) +@item alu.write-usage.exit-threshold <%> (5) +@item alu.read-usage.entry-threshold <%> (25) +@item alu.read-usage.exit-threshold <%> (5) +@item alu.open-files-usage.entry-threshold <n> (1000) +@item alu.open-files-usage.exit-threshold <n> (100) +@item alu.limits.min-free-disk <%> +@item alu.limits.max-open-files <n> +@end table +@end cartouche + +@subsubsection Round Robin (RR) +@cindex rr (scheduler) + +@example + option scheduler rr +@end example + +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: +@cartouche +@table @code +@item rr.limits.min-free-disk <%> (5) +Minimum free disk space a node must have for RR to schedule a file to it. +@item rr.refresh-interval <t> (10 seconds) +Time between two successive free disk space checks. +@end table +@end cartouche + +@subsubsection Random +@cindex random (scheduler) + +@example + option scheduler random +@end example + +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. + +@cartouche +@table @code +@item random.limits.min-free-disk <%> (5) +Minimum free disk space a node must have for random to schedule a file to it. +@item random.refresh-interval <t> (10 seconds) +Time between two successive free disk space checks. +@end table +@end cartouche + +@subsubsection NUFA +@cindex nufa (scheduler) + +@example + option scheduler nufa +@end example + +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 (@acronym{NUFA}) +scheduler accomplishes that. + +@acronym{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 @acronym{NUFA} schedules files +among the other child volumes in a round-robin fashion. + +@acronym{NUFA} is named after the similar strategy used for memory access, +@acronym{NUMA}@footnote{Non-Uniform Memory Access: +@indicateurl{http://en.wikipedia.org/wiki/Non-Uniform_Memory_Access}}. + +@cartouche +@table @code +@item nufa.limits.min-free-disk <%> (5) +Minimum disk space that must be free (local or remote) for @acronym{NUFA} to schedule a +file to it. +@item nufa.refresh-interval <t> (10 seconds) +Time between two successive free disk space checks. +@item 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. +@end table +@end cartouche + +@cindex namespace +@subsubsection 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. + +@cartouche +@table @code +@item namespace <volume> * +Name of the namespace volume (which should be one of the unify volume's children). +@item self-heal [on|off] (on) +Enable/disable self-heal. Unless you know what you are doing, do not disable self-heal. +@end table +@end cartouche + +@cindex self heal (unify) +@subsubsection 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. + +@node Replicate +@subsection Replicate (formerly AFR) +@cindex Replicate +@example +type cluster/replicate +@end example + +Replicate provides @acronym{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. + +@example +volume replicate-example + type cluster/replicate + subvolumes brick1 brick2 brick3 +end-volume +@end example + +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: +@itemize +@item 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). +@item Allow scheduling of read operations amongst the sub-volumes in a round-robin fashion. +@end itemize + +The order of the subvolumes list should be same across all the 'replicate's as +they will be used for locking purposes. + +@cindex self heal (replicate) +@subsubsection 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: + +@example +volume replicate-example + type cluster/replicate + subvolumes brick1 brick2 +end-volume +@end example + +@subsubsection 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. + +@subsubsection 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 @command{getfattr} command. (@command{getfattr -n trusted.afr.version <file>}) + +@cartouche +@table @code +@item debug [on|off] (off) +@item self-heal [on|off] (on) +@item replicate <pattern> (*:1) +@item lock-node <child_volume> (first child is used by default) +@end table +@end cartouche + +@node Stripe +@subsection Stripe +@cindex stripe (translator) +@example +type cluster/stripe +@end example + +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. + +@center @image{stripe,44pc,,,.pdf} + +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. + +@cartouche +@table @code +@item block-size <pattern>:<size> (*:0 no striping) +Distribute files matching @command{<pattern>} over the sub-volumes, +storing at least @command{<size>} on each sub-volume. For example, + +@example + option block-size *.mpg:1M +@end example + +distributes all files ending in @command{.mpg}, storing at least 1 MB on +each sub-volume. + +Any number of @command{block-size} option lines may be present, specifying +different sizes for different file name patterns. +@end table +@end cartouche + +@node Performance Translators +@section Performance Translators + +@menu +* Read Ahead:: +* Write Behind:: +* IO Threads:: +* IO Cache:: +* Booster:: +@end menu + +@node Read Ahead +@subsection Read Ahead +@cindex read-ahead (translator) +@example +type performance/read-ahead +@end example + +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. + +@cartouche +Options: +@table @code +@item page-size <n> (256KB) +The unit of data that is pre-fetched. +@item page-count <n> (2) +The number of pages that are pre-fetched. +@item 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. +@end table +@end cartouche + +@node Write Behind +@subsection Write Behind +@cindex write-behind (translator) +@example +type performance/write-behind +@end example + +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 +@command{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 @command{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. + +@cartouche +@table @code +@item aggregate-size <n> (128KB) +Amount of data to accumulate before doing a write +@item flush-behind [on|yes|off|no] (off|no) + +@end table +@end cartouche + +@node IO Threads +@subsection IO Threads +@cindex io-threads (translator) +@example +type performance/io-threads +@end example + +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. + +@cartouche +@table @code +@item thread-count <n> (1) +Number of threads to use. +@end table +@end cartouche + +@node IO Cache +@subsection IO Cache +@cindex io-cache (translator) +@example +type performance/io-cache +@end example + +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 @command{page-size} chunks. +It caches data upto @command{cache-size} bytes. The cache is maintained as +a prioritized least-recently-used (@acronym{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. + +@cartouche +@table @code +@item page-size <n> (128KB) +Size of a page. +@item cache-size (n) (32MB) +Total amount of data to be cached. +@item force-revalidate-timeout <n> (1) +Timeout to force a cache consistency verification, in seconds. +@item priority <pattern> (*:0) +Filename patterns listed in order of priority. +@end table +@end cartouche + +@node Booster +@subsection Booster +@cindex booster +@example + type performance/booster +@end example + +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 @ref{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 @command{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: + +@example + $ LD_PRELOAD=/usr/local/bin/glusterfs-booster.so your_app +@end example + +The booster translator accepts no options. + +@node Features Translators +@section Features Translators + +@menu +* POSIX Locks:: +* Fixed ID:: +@end menu + +@node POSIX Locks +@subsection POSIX Locks +@cindex record locking +@cindex fcntl +@cindex posix-locks (translator) +@example +type features/posix-locks +@end example + +This translator provides storage independent POSIX record locking +support (@command{fcntl} locking). Typically you'll want to load this on the +server side, just above the @acronym{POSIX} storage translator. Using this +translator you can get both advisory locking and mandatory locking +support. It also handles @command{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. + +@cartouche +@table @code +@item mandatory [on|off] (on) +Turns mandatory locking on. +@end table +@end cartouche + +@node Fixed ID +@subsection Fixed ID +@cindex fixed-id (translator) +@example +type features/fixed-id +@end example + +The fixed ID translator makes all filesystem requests from the client +to appear to be coming from a fixed, specified +@acronym{UID}/@acronym{GID}, regardless of which user actually +initiated the request. + +@cartouche +@table @code +@item fixed-uid <n> [if not set, not used] +The @acronym{UID} to send to the server +@item fixed-gid <n> [if not set, not used] +The @acronym{GID} to send to the server +@end table +@end cartouche + +@node Miscellaneous Translators +@section Miscellaneous Translators + +@menu +* ROT-13:: +* Trace:: +@end menu + +@node ROT-13 +@subsection ROT-13 +@cindex rot-13 (translator) +@example +type encryption/rot-13 +@end example + +@acronym{ROT-13} is a toy translator that can ``encrypt'' and ``decrypt'' file +contents using the @acronym{ROT-13} algorithm. @acronym{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 +@emph{real} encryption (a future release of GlusterFS will have real encryption +translators). + +@cartouche +@table @code +@item encrypt-write [on|off] (on) +Whether to encrypt on write +@item decrypt-read [on|off] (on) +Whether to decrypt on read +@end table +@end cartouche + +@node Trace +@subsection Trace +@cindex trace (translator) +@example +type debug/trace +@end example + +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 @ref{Running GlusterFS}) for trace to work. + +Sample trace output (lines have been wrapped for readability): +@cartouche +@example +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) +@end example +@end cartouche + +@node Usage Scenarios +@chapter Usage Scenarios + +@section Advanced Striping + +This section is based on the Advanced Striping tutorial written by +Anand Avati on the GlusterFS wiki +@footnote{http://gluster.org/docs/index.php/Mixing_Striped_and_Regular_Files}. + +@subsection 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. + +@subsection 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. + +@image{advanced-stripe,44pc,,,.pdf} + +@subsection 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. + +@cartouche +@example + ## 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 +@end example +@end cartouche + +@cartouche +@example + ## 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 +@end example +@end cartouche + + +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: + +@example +[root@@server]# glusterfsd +@end example + +Mounting GlusterFS Volumes: + +@example +[root@@client]# glusterfs -s [BRICK-IP-ADDRESS] /mnt/cluster +@end example + +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. + +@node Troubleshooting +@chapter 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. + +@section GlusterFS error messages + +@subsection Server errors + +@example +glusterfsd: FATAL: could not open specfile: +'/etc/glusterfs/glusterfsd.vol' +@end example + +The GlusterFS server expects the volume specification file to be +at @command{/etc/glusterfs/glusterfsd.vol}. The example +specification file will be installed as +@command{/etc/glusterfs/glusterfsd.vol.sample}. You need to edit +it and rename it, or provide a different specification file using +the @command{--spec-file} command line option (See @ref{Server}). + +@vskip 4ex + +@example +gf_log_init: failed to open logfile "/usr/var/log/glusterfs/glusterfsd.log" + (Permission denied) +@end example + +You don't have permission to create files in the +@command{/usr/var/log/glusterfs} directory. Make sure you are running +GlusterFS as root. Alternatively, specify a different path for the log +file using the @command{--log-file} option (See @ref{Server}). + +@subsection Client errors + +@example +fusermount: failed to access mountpoint /mnt: + Transport endpoint is not connected +@end example + +A previous failed (or hung) mount of GlusterFS is preventing it from being +mounted again in the same location. The fix is to do: + +@example +# umount /mnt +@end example + +and try mounting again. + +@vskip 4ex + +@strong{``Transport endpoint is not connected''.} + +If you get this error when you try a command such as @command{ls} or @command{cat}, +it means the GlusterFS mount did not succeed. Try running GlusterFS in @command{DEBUG} +logging level and study the log messages to discover the cause. + +@vskip 4ex + +@strong{``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: + +@example +telnet IP-ADDRESS 6996 +@end example + +If the server is accessible, your `telnet' command should connect and +block. If not you will see an error message such as @command{telnet: Unable to +connect to remote host: Connection refused}. 6996 is the default +GlusterFS port. If you have changed it, then use the corresponding +port instead. + +@vskip 4ex + +@example +gf_log_init: failed to open logfile "/usr/var/log/glusterfs/glusterfs.log" + (Permission denied) +@end example + +You don't have permission to create files in the +@command{/usr/var/log/glusterfs} directory. Make sure you are running +GlusterFS as root. Alternatively, specify a different path for the log +file using the @command{--log-file} option (See @ref{Client}). + +@section FUSE error messages +@command{modprobe fuse} fails with: ``Unknown symbol in module, or unknown parameter''. +@cindex Redhat Enterprise Linux + +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 @acronym{FUSE} kernel +module, you need to apply the following patch. + +For fuse-2.6.2: + +@indicateurl{http://ftp.zresearch.com/pub/gluster/glusterfs/fuse/fuse-2.6.2-rhel-build.patch} + +For fuse-2.6.3: + +@indicateurl{http://ftp.zresearch.com/pub/gluster/glusterfs/fuse/fuse-2.6.3-rhel-build.patch} + +@section AppArmour and GlusterFS +@cindex AppArmour +@cindex OpenSuSE +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 @command{glusterfsd} or @command{glusterfs}/@command{fusermount} +should solve the problem. + +@section 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. + +@subsection General instructions + +When running GlusterFS in a non-production environment, be sure to +build it with the following command: + +@example + $ make CFLAGS='-g -O0 -DDEBUG' +@end example + +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. + +@subsection 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. + +@subsection Log files + +Set the loglevel of your client and server programs to @acronym{DEBUG} (by +passing the -L @acronym{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. + +@subsection 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. + +@example + $ gdb ./glusterfs + (gdb) set args -f client.spec -N -l/path/to/log/file -LDEBUG /mnt/point + (gdb) run +@end example + +Now when the process segfaults, you can get the backtrace by typing: + +@example + (gdb) bt +@end example + +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: + +@example + $ gdb /path/to/glusterfs /path/to/core.<pid> +@end example + +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 @command{PID} of +the process (using ps), and then do: + +@example + $ gdb ./glusterfs <pid> +@end example + +Press Ctrl-C to interrupt the process and then generate the backtrace. + +@subsection 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. + +@subsection Other information + +If you think it is relevant, send us also the version of @acronym{FUSE} you're +using, the kernel version, platform. + +@node GNU Free Documentation Licence +@appendix GNU Free Documentation Licence +@include fdl.texi + +@node Index +@unnumbered Index +@printindex cp + +@bye |