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ceph/doc/glossary.rst
Zac Dover 7c70a66414 doc/glossary: capitalize "DAS" correctly 
Correctly capitalize "Direct-Attached Storage" in the glossary. (And
test the "Quincy" branch, which seems lately not to have picked up any
docs backports.)

Signed-off-by: Zac Dover <zac.dover@gmail.com>
2022-12-31 14:22:26 +10:00

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===============
Ceph Glossary
===============
.. glossary::
:ref:`BlueStore<rados_config_storage_devices_bluestore>`
OSD BlueStore is a storage back end used by OSD daemons, and
was designed specifically for use with Ceph. BlueStore was
introduced in the Ceph Kraken release. In the Ceph Luminous
release, BlueStore became Ceph's default storage back end,
supplanting FileStore. Unlike :term:`filestore`, BlueStore
stores objects directly on Ceph block devices without any file
system interface. Since Luminous (12.2), BlueStore has been
Ceph's default and recommended storage back end.
Ceph
Ceph is a distributed network storage and file system with
distributed metadata management and POSIX semantics.
Ceph Block Device
Also called "RADOS Block Device" and :term:`RBD`. A software
instrument that orchestrates the storage of block-based data in
Ceph. Ceph Block Device splits block-based application data
into "chunks". RADOS stores these chunks as objects. Ceph Block
Device orchestrates the storage of those objects across the
storage cluster.
Ceph Block Storage
One of the three kinds of storage supported by Ceph (the other
two are object storage and file storage). Ceph Block Storage is
the block storage "product", which refers to block-storage
related services and capabilities when used in conjunction with
the collection of (1) ``librbd`` (a python module that provides
file-like access to :term:`RBD` images), (2) a hypervisor such
as QEMU or Xen, and (3) a hypervisor abstraction layer such as
``libvirt``.
Ceph Client
Any of the Ceph components that can access a Ceph Storage
Cluster. This includes the Ceph Object Gateway, the Ceph Block
Device, the Ceph File System, and their corresponding
libraries. It also includes kernel modules, and FUSEs
(Filesystems in USERspace).
Ceph Client Libraries
The collection of libraries that can be used to interact with
components of the Ceph Cluster.
Ceph Cluster Map
See :term:`Cluster Map`
Ceph Dashboard
:ref:`The Ceph Dashboard<mgr-dashboard>` is a built-in
web-based Ceph management and monitoring application through
which you can inspect and administer various resources within
the cluster. It is implemented as a :ref:`ceph-manager-daemon`
module.
Ceph File System
See :term:`CephFS`
:ref:`CephFS<ceph-file-system>`
The **Ceph F**\ile **S**\ystem, or CephFS, is a
POSIX-compliant file system built on top of Ceph’s distributed
object store, RADOS. See :ref:`CephFS Architecture
<arch-cephfs>` for more details.
Ceph Interim Release
See :term:`Releases`.
Ceph Kernel Modules
The collection of kernel modules that can be used to interact
with the Ceph Cluster (for example: ``ceph.ko``, ``rbd.ko``).
:ref:`Ceph Manager<ceph-manager-daemon>`
The Ceph manager daemon (ceph-mgr) is a daemon that runs
alongside monitor daemons to provide monitoring and interfacing
to external monitoring and management systems. Since the
Luminous release (12.x), no Ceph cluster functions properly
unless it contains a running ceph-mgr daemon.
Ceph Manager Dashboard
See :term:`Ceph Dashboard`.
Ceph Metadata Server
See :term:`MDS`.
Ceph Monitor
A daemon that maintains a map of the state of the cluster. This
"cluster state" includes the monitor map, the manager map, the
OSD map, and the CRUSH map. A Ceph cluster must contain a
minimum of three running monitors in order to be both redundant
and highly-available. Ceph monitors and the nodes on which they
run are often referred to as "mon"s. See :ref:`Monitor Config
Reference <monitor-config-reference>`.
Ceph Node
A Ceph node is a unit of the Ceph Cluster that communicates with
other nodes in the Ceph Cluster in order to replicate and
redistribute data. All of the nodes together are called the
:term:`Ceph Storage Cluster`. Ceph nodes include :term:`OSD`\s,
:term:`Ceph Monitor`\s, :term:`Ceph Manager`\s, and
:term:`MDS`\es. The term "node" is usually equivalent to "host"
in the Ceph documentation. If you have a running Ceph Cluster,
you can list all of the nodes in it by running the command
``ceph node ls all``.
:ref:`Ceph Object Gateway<object-gateway>`
An object storage interface built on top of librados. Ceph
Object Gateway provides a RESTful gateway between applications
and Ceph storage clusters.
Ceph Object Storage
The object storage "product", service or capabilities, which
consists essentially of a Ceph Storage Cluster and a Ceph Object
Gateway.
Ceph Object Store
A Ceph Object Store consists of a :term:`Ceph Storage Cluster`
and a :term:`Ceph Object Gateway` (RGW).
:ref:`Ceph OSD<rados_configuration_storage-devices_ceph_osd>`
Ceph **O**\bject **S**\torage **D**\aemon. The Ceph OSD
software, which interacts with logical disks (:term:`OSD`).
Around 2013, there was an attempt by "research and industry"
(Sage's own words) to insist on using the term "OSD" to mean
only "Object Storage Device", but the Ceph community has always
persisted in using the term to mean "Object Storage Daemon" and
no less an authority than Sage Weil himself confirms in
November of 2022 that "Daemon is more accurate for how Ceph is
built" (private correspondence between Zac Dover and Sage Weil,
07 Nov 2022).
Ceph OSD Daemon
See :term:`Ceph OSD`.
Ceph OSD Daemons
See :term:`Ceph OSD`.
Ceph Platform
All Ceph software, which includes any piece of code hosted at
`https://github.com/ceph`_.
Ceph Point Release
See :term:`Releases`.
Ceph Project
The aggregate term for the people, software, mission and
infrastructure of Ceph.
Ceph Release
See :term:`Releases`.
Ceph Release Candidate
See :term:`Releases`.
Ceph Stable Release
See :term:`Releases`.
Ceph Stack
A collection of two or more components of Ceph.
:ref:`Ceph Storage Cluster<arch-ceph-storage-cluster>`
The collection of :term:`Ceph Monitor`\s, :term:`Ceph
Manager`\s, :term:`Ceph Metadata Server`\s, and :term:`OSD`\s
that work together to store and replicate data for use by
applications, Ceph Users, and :term:`Ceph Client`\s. Ceph
Storage Clusters receive data from :term:`Ceph Client`\s.
CephX
The Ceph authentication protocol. CephX operates like Kerberos,
but it has no single point of failure. See the :ref:`CephX
Configuration Reference<rados-cephx-config-ref>`.
Cloud Platforms
Cloud Stacks
Third party cloud provisioning platforms such as OpenStack,
CloudStack, OpenNebula, and Proxmox VE.
Cluster Map
The set of maps consisting of the monitor map, OSD map, PG map,
MDS map, and CRUSH map, which together report the state of the
Ceph cluster. See :ref:`the "Cluster Map" section of the
Architecture document<architecture_cluster_map>` for details.
CRUSH
**C**\ontrolled **R**\eplication **U**\nder **S**\calable
**H**\ashing. The algorithm that Ceph uses to compute object
storage locations.
CRUSH rule
The CRUSH data placement rule that applies to a particular
pool or pools.
DAS
**D**\irect-\ **A**\ttached **S**\torage. Storage that is
attached directly to the computer accessing it, without passing
through a network. Contrast with NAS and SAN.
:ref:`Dashboard<mgr-dashboard>`
A built-in web-based Ceph management and monitoring application
to administer various aspects and objects of the cluster. The
dashboard is implemented as a Ceph Manager module. See
:ref:`mgr-dashboard` for more details.
Dashboard Module
Another name for :term:`Dashboard`.
Dashboard Plugin
filestore
A back end for OSD daemons, where a Journal is needed and files
are written to the filesystem.
FQDN
**F**\ully **Q**\ualified **D**\omain **N**\ame. A domain name
that is applied to a node in a network and that specifies the
node's exact location in the tree hierarchy of the DNS.
In the context of Ceph cluster administration, FQDNs are often
applied to hosts. In this documentation, the term "FQDN" is
used mostly to distinguish between FQDNs and relatively simpler
hostnames, which do not specify the exact location of the host
in the tree hierarchy of the DNS but merely name the host.
Host
Any single machine or server in a Ceph Cluster. See :term:`Ceph
Node`.
LVM tags
**L**\ogical **V**\olume **M**\anager tags. Extensible metadata
for LVM volumes and groups. They are used to store
Ceph-specific information about devices and its relationship
with OSDs.
:ref:`MDS<cephfs_add_remote_mds>`
The Ceph **M**\eta\ **D**\ata **S**\erver daemon. Also referred
to as "ceph-mds". The Ceph metadata server daemon must be
running in any Ceph cluster that runs the CephFS file system.
The MDS stores all filesystem metadata.
MGR
The Ceph manager software, which collects all the state from
the whole cluster in one place.
MON
The Ceph monitor software.
Node
See :term:`Ceph Node`.
Object Storage Device
See :term:`OSD`.
OSD
Probably :term:`Ceph Object Storage Daemon<Ceph OSD>`, but not
necessarily. Sometimes (especially in older correspondence, and
especially in documentation that is not specifically written
for Ceph), "OSD" means "**O**\bject **S**\torage **D**\evice",
which refers to a physical or logical storage unit (for
example: LUN). The Ceph community has always used the term
"OSD" to refer to :term:`Ceph OSD Daemon` despite an industry
push in the mid-2010s to insist that "OSD" should refer to
"Object Storage Device", so it is important to know which
meaning is intended.
OSD fsid
This is a unique identifier used to identify an OSD. It is
found in the OSD path in a file called ``osd_fsid``. The
term ``fsid`` is used interchangeably with ``uuid``
OSD id
The integer that defines an OSD. It is generated by the
monitors during the creation of each OSD.
OSD uuid
This is the unique identifier of an OSD. This term is used
interchangeably with ``fsid``
:ref:`Pool<rados_pools>`
A pool is a logical partition used to store objects.
Pools
See :term:`pool`.
RADOS
**R**\eliable **A**\utonomic **D**\istributed **O**\bject
**S**\tore. RADOS is the object store that provides a scalable
service for variably-sized objects. The RADOS object store is
the core component of a Ceph cluster. `This blog post from
2009
<https://ceph.io/en/news/blog/2009/the-rados-distributed-object-store/>`_
provides a beginner's introduction to RADOS. Readers interested
in a deeper understanding of RADOS are directed to `RADOS: A
Scalable, Reliable Storage Service for Petabyte-scale Storage
Clusters <https://ceph.io/assets/pdfs/weil-rados-pdsw07.pdf>`_.
RADOS Cluster
A proper subset of the Ceph Cluster consisting of
:term:`OSD`\s, :term:`Ceph Monitor`\s, and :term:`Ceph
Manager`\s.
RADOS Gateway
See :term:`RGW`.
RBD
**R**\ADOS **B**\lock **D**\evice. See :term:`Ceph Block
Device`.
Releases
Ceph Interim Release
A version of Ceph that has not yet been put through
quality assurance testing. May contain new features.
Ceph Point Release
Any ad hoc release that includes only bug fixes and
security fixes.
Ceph Release
Any distinct numbered version of Ceph.
Ceph Release Candidate
A major version of Ceph that has undergone initial
quality assurance testing and is ready for beta
testers.
Ceph Stable Release
A major version of Ceph where all features from the
preceding interim releases have been put through
quality assurance testing successfully.
Reliable Autonomic Distributed Object Store
The core set of storage software which stores the user's data
(MON+OSD). See also :term:`RADOS`.
:ref:`RGW<object-gateway>`
**R**\ADOS **G**\ate\ **w**\ay.
Also called "Ceph Object Gateway". The component of Ceph that
provides a gateway to both the Amazon S3 RESTful API and the
OpenStack Swift API.
secrets
Secrets are credentials used to perform digital authentication
whenever privileged users must access systems that require
authentication. Secrets can be passwords, API keys, tokens, SSH
keys, private certificates, or encryption keys.
SDS
**S**\oftware-**d**\efined **S**\torage.
systemd oneshot
A systemd ``type`` where a command is defined in ``ExecStart``
which will exit upon completion (it is not intended to
daemonize)
Teuthology
The collection of software that performs scripted tests on Ceph.
.. _https://github.com/ceph: https://github.com/ceph
.. _Cluster Map: ../architecture#cluster-map
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