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diff --git a/doc/admin-guide/en-US/markdown/glossary.md b/doc/admin-guide/en-US/markdown/glossary.md deleted file mode 100644 index 496d0a428d4..00000000000 --- a/doc/admin-guide/en-US/markdown/glossary.md +++ /dev/null @@ -1,300 +0,0 @@ -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 expressed by combining a server with an export directory in the following format: - - `SERVER:EXPORT` - For example: - `myhostname:/exports/myexportdir/` - -**Volume** -: A volume is a logical collection of bricks. Most of the gluster - management operations happen on the volume. - - -**Subvolume** -: A brick after being processed by at least one translator or in other words - set of one or more xlator stacked together is called a sub-volume. - - -**Volfile** -: Volume (vol) files are configuration files that determine the behavior of the - GlusterFs trusted storage pool. Volume file is a textual representation of a - collection of modules (also known as translators) that together implement the - various functions required. The collection of modules are arranged in a graph-like - fashion. E.g, A replicated volume's volfile, among other things, would have a - section describing the replication translator and its tunables. - This section describes how the volume would replicate data written to it. - Further, a client process that serves a mount point, would interpret its volfile - and load the translators described in it. While serving I/O, it would pass the - request to the collection of modules in the order specified in the volfile. - - At a high level, GlusterFs has three entities,that is, Server, Client and Management daemon. - Each of these entities have their own volume files. - Volume files for servers and clients are generated by the management daemon - after the volume is created. - - Server and Client Vol files are located in /var/lib/glusterd/vols/VOLNAME directory. - The management daemon vol file is named as glusterd.vol and is located in /etc/glusterfs/ - directory. - -**glusterd** -: The daemon/service that manages volumes and cluster membership. It is required to - run on all the servers in the trusted storage pool. - -**Cluster** -: A trusted pool of linked computers working together, resembling a single computing resource. - In GlusterFs, a cluster is also referred to as a trusted storage pool. - -**Client** -: Any machine that mounts a GlusterFS volume. Any applications that use libgfapi access - mechanism can also be treated as clients in GlusterFS context. - - -**Server** -: The machine (virtual or bare metal) that hosts the bricks in which data is stored. - - -**Block Storage** -: Block special files, or block devices, correspond to devices through which the system moves - data in the form of blocks. These device nodes often represent addressable devices such as - hard disks, CD-ROM drives, or memory regions. GlusterFS requires a filesystem (like XFS) that - supports extended attributes. - - - -**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][] - -**Distributed File System** -: A file system that allows multiple clients to concurrently access data which is spread across - servers/bricks in a trusted storage pool. Data sharing among multiple locations is fundamental - to all distributed file systems. - -**Virtual File System (VFS) - VFS is a kernel software layer which handles all system calls related to the standard Linux file system. - It provides a common interface to several kinds of file systems. - -**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. - -**Extended Attributes** -: Extended file attributes (abbreviated xattr) is a filesystem feature - that enables users/programs to associate files/dirs with metadata. - - -**FUSE** -: Filesystem in Userspace (FUSE) is a loadable kernel module for - Unix-like computer operating systems that lets non-privileged users - create their own filesystems without editing kernel code. This is - achieved by running filesystem code in user space while the FUSE - module provides only a "bridge" to the actual kernel interfaces. - - Source: [Wikipedia][1] - - -**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. - - -**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] - - - -**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** -: Quota allows 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. - -**Scale-Up Storage** -: Increases the capacity of the storage device in a single dimension. - For example, adding additional disk capacity to an existing trusted storage pool. - -**Scale-Out Storage** - Scale out systems are designed to scale on both capacity and performance. - It increases the capability of a storage device in single dimension. - For example, adding more systems of the same size, or adding servers to a trusted storage pool - that increases CPU, disk capacity, and throughput for the trusted storage pool. - -**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. - - -**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. - -**N-way Replication** -: Local synchronous data replication which is typically deployed across campus - or Amazon Web Services Availability Zones. - -**Distributed Hash Table Terminology** -**Hashed subvolume** -: A Distributed Hash Table Translator subvolume to which the file or directory name is hashed to. - -**Cached subvolume** -: A Distributed Hash Table Translator subvolume where the file content is actually present. - For directories, the concept of cached-subvolume is not relevant. It is loosely used to mean - subvolumes which are not hashed-subvolume. - -**Linkto-file** - -: For a newly created file, the hashed and cached subvolumes are the same. - When directory entry operations like rename (which can change the name and hence hashed - subvolume of the file) are performed on the file, instead of moving the entire data in the file - to a new hashed subvolume, a file is created with the same name on the newly hashed subvolume. - The purpose of this file is only to act as a pointer to the node where the data is present. - In the extended attributes of this file, the name of the cached subvolume is stored. - This file on the newly hashed-subvolume is called a linkto-file. - The linkto file is relevant only for non-directory entities. - -**Directory Layout** -: The directory layout specifies the hash-ranges of the subdirectories of a directory to which - subvolumes they correspond to. - -**Properties of directory layouts:** -: The layouts are created at the time of directory creation and are persisted as extended attributes - of the directory. - A subvolume is not included in the layout if it remained offline at the time of directory creation - and no directory entries ( such as files and directories) of that directory are created on - that subvolume. The subvolume is not part of the layout until the fix-layout is complete - as part of running the rebalance command. If a subvolume is down during access (after directory creation), - access to any files that hash to that subvolume fails. - -**Fix Layout** -: A command that is executed during the rebalance process. - The rebalance process itself comprises of two stages: - Fixes the layouts of directories to accommodate any subvolumes that are added or removed. - It also heals the directories, checks whether the layout is non-contiguous, and persists the - layout in extended attributes, if needed. It also ensures that the directories have the same - attributes across all the subvolumes. - - Migrates the data from the cached-subvolume to the hashed-subvolume. - - [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 |