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Glossary
========
**Brick**
: A Brick is the basic unit of storage in GlusterFS, represented by an
export directory on a server in the trusted storage pool. A Brick is
represented by combining a server name with an export directory in the
following format:
`SERVER:EXPORT`
For example:
`myhostname:/exports/myexportdir/`
**Client**
: Any machine that mounts a GlusterFS volume.
**Cluster**
: A cluster is a group of linked computers, working together closely
thus in many respects forming a single computer.
**Distributed File System**
: A file system that allows multiple clients to concurrently access
data over a computer network.
**Extended Attributes**
: Extended file attributes (abbreviated xattr) is a file system feature
that enables users/programs to associate files/dirs with metadata.
**Filesystem**
: A method of storing and organizing computer files and their data.
Essentially, it organizes these files into a database for the
storage, organization, manipulation, and retrieval by the computer's
operating system.
Source: [Wikipedia][]
**FUSE**
: Filesystem in Userspace (FUSE) is a loadable kernel module for
Unix-like computer operating systems that lets non-privileged users
create their own file systems without editing kernel code. This is
achieved by running file system code in user space while the FUSE
module provides only a "bridge" to the actual kernel interfaces.
Source: [Wikipedia][1]
**Geo-Replication**
: Geo-replication provides a continuous, asynchronous, and incremental
replication service from site to another over Local Area Networks
(LAN), Wide Area Network (WAN), and across the Internet.
**GFID**
: Each file/directory on a GlusterFS volume has a unique 128-bit number
associated with it called the GFID. This is analogous to inode in a
regular filesystem.
**glusterd**
: The Gluster management daemon that needs to run on all servers in
the trusted storage pool.
**Infiniband**
InfiniBand is a switched fabric computer network communications link
used in high-performance computing and enterprise data centers.
**Metadata**
: Metadata is data providing information about one or more other
pieces of data.
**Namespace**
: Namespace is an abstract container or environment created to hold a
logical grouping of unique identifiers or symbols. Each Gluster
volume exposes a single namespace as a POSIX mount point that
contains every file in the cluster.
**Node**
: A server or computer that hosts one or more bricks.
**Open Source**
: Open source describes practices in production and development that
promote access to the end product's source materials. Some consider
open source a philosophy, others consider it a pragmatic
methodology.
Before the term open source became widely adopted, developers and
producers used a variety of phrases to describe the concept; open
source gained hold with the rise of the Internet, and the attendant
need for massive retooling of the computing source code.
Opening the source code enabled a self-enhancing diversity of
production models, communication paths, and interactive communities.
Subsequently, a new, three-word phrase "open source software" was
born to describe the environment that the new copyright, licensing,
domain, and consumer issues created.
Source: [Wikipedia][2]
**Petabyte**
: A petabyte (derived from the SI prefix peta- ) is a unit of
information equal to one quadrillion (short scale) bytes, or 1000
terabytes. The unit symbol for the petabyte is PB. The prefix peta-
(P) indicates a power of 1000:
1 PB = 1,000,000,000,000,000 B = 10005 B = 1015 B.
The term "pebibyte" (PiB), using a binary prefix, is used for the
corresponding power of 1024.
Source: [Wikipedia][3]
**POSIX**
: Portable Operating System Interface (for Unix) is the name of a
family of related standards specified by the IEEE to define the
application programming interface (API), along with shell and
utilities interfaces for software compatible with variants of the
Unix operating system. Gluster exports a fully POSIX compliant file
system.
**Quorum**
: The configuration of quorum in a trusted storage pool determines the
number of server failures that the trusted storage pool can sustain.
If an additional failure occurs, the trusted storage pool becomes
unavailable.
**Quota**
: Quotas allow you to set limits on usage of disk space by directories or
by volumes.
**RAID**
: Redundant Array of Inexpensive Disks (RAID) is a technology that
provides increased storage reliability through redundancy, combining
multiple low-cost, less-reliable disk drives components into a
logical unit where all drives in the array are interdependent.
**RDMA**
: Remote direct memory access (RDMA) is a direct memory access from the
memory of one computer into that of another without involving either
one's operating system. This permits high-throughput, low-latency
networking, which is especially useful in massively parallel computer
clusters.
**Rebalance**
: A process of fixing layout and resdistributing data in a volume when a
brick is added or removed.
**RRDNS**
: Round Robin Domain Name Service (RRDNS) is a method to distribute
load across application servers. RRDNS is implemented by creating
multiple A records with the same name and different IP addresses in
the zone file of a DNS server.
**Samba**
: Samba allows file and print sharing between computers running Windows and
computers running Linux. It is an implementation of several services and
protocols including SMB and CIFS.
**Self-Heal**
: The self-heal daemon that runs in the background, identifies
inconsistencies in files/dirs in a replicated volume and then resolves
or heals them. This healing process is usually required when one or more
bricks of a volume goes down and then comes up later.
**Split-brain**
: This is a situation where data on two or more bricks in a replicated
volume start to diverge in terms of content or metadata. In this state,
one cannot determine programitically which set of data is "right" and
which is "wrong".
**Translator**
: Translators (also called xlators) are stackable modules where each
module has a very specific purpose. Translators are stacked in a
hierarchical structure called as graph. A translator receives data
from its parent translator, performs necessary operations and then
passes the data down to its child translator in hierarchy.
**Trusted Storage Pool**
: A storage pool is a trusted network of storage servers. When you
start the first server, the storage pool consists of that server
alone.
**Userspace**
: Applications running in user space don’t directly interact with
hardware, instead using the kernel to moderate access. Userspace
applications are generally more portable than applications in kernel
space. Gluster is a user space application.
**Volfile**
: Volfile is a configuration file used by glusterfs process. Volfile
will be usually located at `/var/lib/glusterd/vols/VOLNAME`.
**Volume**
: A volume is a logical collection of bricks. Most of the gluster
management operations happen on the volume.
[Wikipedia]: http://en.wikipedia.org/wiki/Filesystem
[1]: http://en.wikipedia.org/wiki/Filesystem_in_Userspace
[2]: http://en.wikipedia.org/wiki/Open_source
[3]: http://en.wikipedia.org/wiki/Petabyte
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