ceph/doc/glossary.rst

   1 ===============
   2  Ceph Glossary
   3 ===============
   4
   5 .. glossary::
   6
   7         Application
   8                 More properly called a :term:`client`, an application is any program
   9                 external to Ceph that uses a Ceph Cluster to store and
  10                 replicate data.
  11
  12         :ref:`BlueStore<rados_config_storage_devices_bluestore>`
  13                 OSD BlueStore is a storage back end used by OSD daemons, and
  14                 was designed specifically for use with Ceph. BlueStore was
  15                 introduced in the Ceph Kraken release. The Luminous release of
  16                 Ceph promoted BlueStore to the default OSD back end,
  17                 supplanting FileStore. As of the Reef release, FileStore is no
  18                 longer available as a storage backend.
  19
  20                 BlueStore stores objects directly on Ceph block devices without
  21                 a mounted file system.
  22
  23         Bucket
  24                 In the context of :term:`RGW`, a bucket is a group of objects.
  25                 In a filesystem-based analogy in which objects are the
  26                 counterpart of files, buckets are the counterpart of
  27                 directories. :ref:`Multisite sync
  28                 policies<radosgw-multisite-sync-policy>` can be set on buckets,
  29                 to provide fine-grained control of data movement from one zone
  30                 to another zone.
  31
  32                 The concept of the bucket has been taken from AWS S3. See also
  33                 `the AWS S3 page on creating buckets <https://docs.aws.amazon.com/AmazonS3/latest/userguide/creating-buckets-s3.html>`_
  34                 and `the AWS S3 'Buckets Overview' page <https://docs.aws.amazon.com/AmazonS3/latest/userguide/UsingBucket.html>`_.
  35
  36                 OpenStack Swift uses the term "containers" for what RGW and AWS call "buckets".
  37                 See `the OpenStack Storage API overview page <https://docs.openstack.org/swift/latest/api/object_api_v1_overview.html>`_.
  38
  39         Ceph
  40                 Ceph is a distributed network storage and file system with
  41                 distributed metadata management and POSIX semantics.
  42
  43         Ceph Block Device
  44                 Also called "RADOS Block Device" and :term:`RBD`. A software
  45                 instrument that orchestrates the storage of block-based data in
  46                 Ceph. Ceph Block Device splits block-based application data
  47                 into "chunks". RADOS stores these chunks as objects. Ceph Block
  48                 Device orchestrates the storage of those objects across the
  49                 storage cluster.
  50
  51         Ceph Block Storage
  52                 One of the three kinds of storage supported by Ceph (the other
  53                 two are object storage and file storage). Ceph Block Storage is
  54                 the block storage "product", which refers to block-storage
  55                 related services and capabilities when used in conjunction with
  56                 the collection of (1) ``librbd`` (a python module that provides
  57                 file-like access to :term:`RBD` images), (2) a hypervisor such
  58                 as QEMU or Xen, and (3) a hypervisor abstraction layer such as
  59                 ``libvirt``.
  60
  61         Ceph Client
  62                 Any of the Ceph components that can access a Ceph Storage
  63                 Cluster. This includes the Ceph Object Gateway, the Ceph Block
  64                 Device, the Ceph File System, and their corresponding
  65                 libraries. It also includes kernel modules, and FUSEs
  66                 (Filesystems in USERspace).
  67
  68         Ceph Client Libraries
  69                 The collection of libraries that can be used to interact with
  70                 components of the Ceph Cluster.
  71
  72         Ceph Cluster Map
  73                 See :term:`Cluster Map`
  74
  75         Ceph Dashboard
  76                 :ref:`The Ceph Dashboard<mgr-dashboard>` is a built-in
  77                 web-based Ceph management and monitoring application through
  78                 which you can inspect and administer various resources within
  79                 the cluster. It is implemented as a :ref:`ceph-manager-daemon`
  80                 module.
  81
  82         Ceph File System
  83                 See :term:`CephFS`
  84
  85         :ref:`CephFS<ceph-file-system>`
  86                 The **Ceph F**\ile **S**\ystem, or CephFS, is a
  87                 POSIX-compliant file system built on top of Ceph’s distributed
  88                 object store, RADOS.  See :ref:`CephFS Architecture
  89                 <arch-cephfs>` for more details.
  90
  91         Ceph Interim Release
  92                 See :term:`Releases`.
  93
  94         Ceph Kernel Modules
  95                 The collection of kernel modules that can be used to interact
  96                 with the Ceph Cluster (for example: ``ceph.ko``, ``rbd.ko``).
  97
  98         :ref:`Ceph Manager<ceph-manager-daemon>`
  99                 The Ceph manager daemon (ceph-mgr) is a daemon that runs
 100                 alongside monitor daemons to provide monitoring and interfacing
 101                 to external monitoring and management systems. Since the
 102                 Luminous release (12.x), no Ceph cluster functions properly
 103                 unless it contains a running ceph-mgr daemon.
 104
 105         Ceph Manager Dashboard
 106                 See :term:`Ceph Dashboard`.
 107
 108         Ceph Metadata Server
 109                 See :term:`MDS`.
 110
 111         Ceph Monitor
 112                 A daemon that maintains a map of the state of the cluster. This
 113                 "cluster state" includes the monitor map, the manager map, the
 114                 OSD map, and the CRUSH map. A Ceph cluster must contain a
 115                 minimum of three running monitors in order to be both redundant
 116                 and highly-available. Ceph monitors and the nodes on which they
 117                 run are often referred to as "mon"s. See :ref:`Monitor Config
 118                 Reference <monitor-config-reference>`.
 119
 120         Ceph Node
 121                A Ceph node is a unit of the Ceph Cluster that communicates with
 122                other nodes in the Ceph Cluster in order to replicate and
 123                redistribute data. All of the nodes together are called the
 124                :term:`Ceph Storage Cluster`. Ceph nodes include :term:`OSD`\s,
 125                :term:`Ceph Monitor`\s, :term:`Ceph Manager`\s, and
 126                :term:`MDS`\es. The term "node" is usually equivalent to "host"
 127                in the Ceph documentation. If you have a running Ceph Cluster,
 128                you can list all of the nodes in it by running the command
 129                ``ceph node ls all``.
 130
 131         :ref:`Ceph Object Gateway<object-gateway>`
 132                 An object storage interface built on top of librados. Ceph
 133                 Object Gateway provides a RESTful gateway between applications
 134                 and Ceph storage clusters.
 135
 136         Ceph Object Storage
 137                 See :term:`Ceph Object Store`.
 138
 139         Ceph Object Store
 140                 A Ceph Object Store consists of a :term:`Ceph Storage Cluster`
 141                 and a :term:`Ceph Object Gateway` (RGW).
 142
 143         :ref:`Ceph OSD<rados_configuration_storage-devices_ceph_osd>`
 144                 Ceph **O**\bject **S**\torage **D**\aemon. The Ceph OSD
 145                 software, which interacts with logical disks (:term:`OSD`).
 146                 Around 2013, there was an attempt by "research and industry"
 147                 (Sage's own words) to insist on using the term "OSD" to mean
 148                 only "Object Storage Device", but the Ceph community has always
 149                 persisted in using the term to mean "Object Storage Daemon" and
 150                 no less an authority than Sage Weil himself confirms in
 151                 November of 2022 that "Daemon is more accurate for how Ceph is
 152                 built" (private correspondence between Zac Dover and Sage Weil,
 153                 07 Nov 2022).
 154
 155         Ceph OSD Daemon
 156                 See :term:`Ceph OSD`.
 157
 158         Ceph OSD Daemons
 159                 See :term:`Ceph OSD`.
 160
 161         Ceph Platform
 162                 All Ceph software, which includes any piece of code hosted at
 163                 `https://github.com/ceph`_.
 164
 165         Ceph Point Release
 166                 See :term:`Releases`.
 167
 168         Ceph Project
 169                 The aggregate term for the people, software, mission and
 170                 infrastructure of Ceph.
 171
 172         Ceph Release
 173                 See :term:`Releases`.
 174
 175         Ceph Release Candidate
 176                 See :term:`Releases`.
 177
 178         Ceph Stable Release
 179                 See :term:`Releases`.
 180
 181         Ceph Stack
 182                 A collection of two or more components of Ceph.
 183
 184         :ref:`Ceph Storage Cluster<arch-ceph-storage-cluster>`
 185                 The collection of :term:`Ceph Monitor`\s, :term:`Ceph
 186                 Manager`\s, :term:`Ceph Metadata Server`\s, and :term:`OSD`\s
 187                 that work together to store and replicate data for use by
 188                 applications, Ceph Users, and :term:`Ceph Client`\s. Ceph
 189                 Storage Clusters receive data from :term:`Ceph Client`\s.
 190
 191         CephX
 192                 The Ceph authentication protocol. CephX authenticates users and
 193                 daemons. CephX operates like Kerberos, but it has no single
 194                 point of failure. See the :ref:`High-availability
 195                 Authentication section<arch_high_availability_authentication>`
 196                 of the Architecture document and the :ref:`CephX Configuration
 197                 Reference<rados-cephx-config-ref>`.
 198
 199         Client
 200                 A client is any program external to Ceph that uses a Ceph
 201                 Cluster to store and replicate data.
 202
 203         Cloud Platforms
 204         Cloud Stacks
 205                 Third party cloud provisioning platforms such as OpenStack,
 206                 CloudStack, OpenNebula, and Proxmox VE.
 207
 208         Cluster Map
 209                 The set of maps consisting of the monitor map, OSD map, PG map,
 210                 MDS map, and CRUSH map, which together report the state of the
 211                 Ceph cluster. See :ref:`the "Cluster Map" section of the
 212                 Architecture document<architecture_cluster_map>` for details.
 213
 214         CRUSH
 215                 **C**\ontrolled **R**\eplication **U**\nder **S**\calable
 216                 **H**\ashing. The algorithm that Ceph uses to compute object
 217                 storage locations.
 218
 219         CRUSH rule
 220                 The CRUSH data placement rule that applies to a particular
 221                 pool or pools.
 222
 223         DAS
 224                 **D**\irect-\ **A**\ttached **S**\torage. Storage that is
 225                 attached directly to the computer accessing it, without passing
 226                 through a network.  Contrast with NAS and SAN.
 227
 228         :ref:`Dashboard<mgr-dashboard>`
 229                 A built-in web-based Ceph management and monitoring application
 230                 to administer various aspects and objects of the cluster. The
 231                 dashboard is implemented as a Ceph Manager module. See
 232                 :ref:`mgr-dashboard` for more details.
 233
 234         Dashboard Module
 235                 Another name for :term:`Dashboard`.
 236
 237         Dashboard Plugin
 238         FQDN
 239                 **F**\ully **Q**\ualified **D**\omain **N**\ame. A domain name
 240                 that is applied to a node in a network and that specifies the
 241                 node's exact location in the tree hierarchy of the DNS.
 242
 243                 In the context of Ceph cluster administration, FQDNs are often
 244                 applied to hosts. In this documentation, the term "FQDN" is
 245                 used mostly to distinguish between FQDNs and relatively simpler
 246                 hostnames, which do not specify the exact location of the host
 247                 in the tree hierarchy of the DNS but merely name the host.
 248
 249         Host
 250                 Any single machine or server in a Ceph Cluster. See :term:`Ceph
 251                 Node`.
 252
 253         Hybrid OSD
 254                 Refers to an OSD that has both HDD and SSD drives.
 255
 256         LVM tags
 257                 **L**\ogical **V**\olume **M**\anager tags. Extensible metadata
 258                 for LVM volumes and groups. They are used to store
 259                 Ceph-specific information about devices and its relationship
 260                 with OSDs.
 261
 262         :ref:`MDS<cephfs_add_remote_mds>`
 263                 The Ceph **M**\eta\ **D**\ata **S**\erver daemon. Also referred
 264                 to as "ceph-mds". The Ceph metadata server daemon must be
 265                 running in any Ceph cluster that runs the CephFS file system.
 266                 The MDS stores all filesystem metadata.
 267
 268         MGR
 269                 The Ceph manager software, which collects all the state from
 270                 the whole cluster in one place.
 271
 272         MON
 273                 The Ceph monitor software.
 274
 275         Node
 276                 See :term:`Ceph Node`.
 277
 278         Object Storage Device
 279                 See :term:`OSD`.
 280
 281         OSD
 282                 Probably :term:`Ceph OSD`, but not necessarily. Sometimes
 283                 (especially in older correspondence, and especially in
 284                 documentation that is not written specifically for Ceph), "OSD"
 285                 means "**O**\bject **S**\torage **D**\evice", which refers to a
 286                 physical or logical storage unit (for example: LUN). The Ceph
 287                 community has always used the term "OSD" to refer to
 288                 :term:`Ceph OSD Daemon` despite an industry push in the
 289                 mid-2010s to insist that "OSD" should refer to "Object Storage
 290                 Device", so it is important to know which meaning is intended.
 291
 292         OSD fsid
 293                 This is a unique identifier used to identify an OSD. It is
 294                 found in the OSD path in a file called ``osd_fsid``. The
 295                 term ``fsid`` is used interchangeably with ``uuid``
 296
 297         OSD id
 298                 The integer that defines an OSD. It is generated by the
 299                 monitors during the creation of each OSD.
 300
 301         OSD uuid
 302                 This is the unique identifier of an OSD. This term is used
 303                 interchangeably with ``fsid``
 304
 305         Period
 306                 In the context of :term:`RGW`, a period is the configuration
 307                 state of the :term:`Realm`. The period stores the configuration
 308                 state of a multi-site configuration. When the period is updated,
 309                 the "epoch" is said thereby to have been changed.
 310
 311         Placement Groups (PGs)
 312                 Placement groups (PGs) are subsets of each logical Ceph pool.
 313                 Placement groups perform the function of placing objects (as a
 314                 group) into OSDs. Ceph manages data internally at
 315                 placement-group granularity: this scales better than would
 316                 managing individual (and therefore more numerous) RADOS
 317                 objects. A cluster that has a larger number of placement groups
 318                 (for example, 100 per OSD) is better balanced than an otherwise
 319                 identical cluster with a smaller number of placement groups.
 320
 321                 Ceph's internal RADOS objects are each mapped to a specific
 322                 placement group, and each placement group belongs to exactly
 323                 one Ceph pool.
 324
 325         :ref:`Pool<rados_pools>`
 326                 A pool is a logical partition used to store objects.
 327
 328         Pools
 329                 See :term:`pool`.
 330
 331         RADOS
 332                 **R**\eliable **A**\utonomic **D**\istributed **O**\bject
 333                 **S**\tore. RADOS is the object store that provides a scalable
 334                 service for variably-sized objects. The RADOS object store is
 335                 the core component of a Ceph cluster.  `This blog post from
 336                 2009
 337                 <https://ceph.io/en/news/blog/2009/the-rados-distributed-object-store/>`_
 338                 provides a beginner's introduction to RADOS. Readers interested
 339                 in a deeper understanding of RADOS are directed to `RADOS: A
 340                 Scalable, Reliable Storage Service for Petabyte-scale Storage
 341                 Clusters <https://ceph.io/assets/pdfs/weil-rados-pdsw07.pdf>`_.
 342
 343         RADOS Cluster
 344                 A proper subset of the Ceph Cluster consisting of
 345                 :term:`OSD`\s, :term:`Ceph Monitor`\s, and :term:`Ceph
 346                 Manager`\s.
 347
 348         RADOS Gateway
 349                 See :term:`RGW`.
 350
 351         RBD
 352                 **R**\ADOS **B**\lock **D**\evice. See :term:`Ceph Block
 353                 Device`.
 354
 355         :ref:`Realm<rgw-realms>`
 356                 In the context of RADOS Gateway (RGW), a realm is a globally
 357                 unique namespace that consists of one or more zonegroups.
 358
 359         Releases
 360
 361                 Ceph Interim Release
 362                         A version of Ceph that has not yet been put through
 363                         quality assurance testing. May contain new features.
 364
 365                 Ceph Point Release
 366                         Any ad hoc release that includes only bug fixes and
 367                         security fixes.
 368
 369                 Ceph Release
 370                         Any distinct numbered version of Ceph.
 371
 372                 Ceph Release Candidate
 373                         A major version of Ceph that has undergone initial
 374                         quality assurance testing and is ready for beta
 375                         testers.
 376
 377                 Ceph Stable Release
 378                         A major version of Ceph where all features from the
 379                         preceding interim releases have been put through
 380                         quality assurance testing successfully.
 381
 382         Reliable Autonomic Distributed Object Store
 383                 The core set of storage software which stores the user's data
 384                 (MON+OSD). See also :term:`RADOS`.
 385
 386         :ref:`RGW<object-gateway>`
 387                 **R**\ADOS **G**\ate\ **w**\ay.
 388
 389                 Also called "Ceph Object Gateway". The component of Ceph that
 390                 provides a gateway to both the Amazon S3 RESTful API and the
 391                 OpenStack Swift API.
 392
 393         scrubs
 394
 395                 The processes by which Ceph ensures data integrity. During the
 396                 process of scrubbing, Ceph generates a catalog of all objects
 397                 in a placement group, then ensures that none of the objects are
 398                 missing or mismatched by comparing each primary object against
 399                 its replicas, which are stored across other OSDs. Any PG
 400                 is determined to have a copy of an object that is different
 401                 than the other copies or is missing entirely is marked
 402                 "inconsistent" (that is, the PG is marked "inconsistent").
 403
 404                 There are two kinds of scrubbing: light scrubbing and deep
 405                 scrubbing (also called "normal scrubbing" and "deep scrubbing",
 406                 respectively). Light scrubbing is performed daily and does
 407                 nothing more than confirm that a given object exists and that
 408                 its metadata is correct. Deep scrubbing is performed weekly and
 409                 reads the data and uses checksums to ensure data integrity.
 410
 411                 See :ref:`Scrubbing <rados_config_scrubbing>` in the RADOS OSD
 412                 Configuration Reference Guide and page 141 of *Mastering Ceph,
 413                 second edition* (Fisk, Nick. 2019).
 414
 415         secrets
 416                 Secrets are credentials used to perform digital authentication
 417                 whenever privileged users must access systems that require
 418                 authentication. Secrets can be passwords, API keys, tokens, SSH
 419                 keys, private certificates, or encryption keys.
 420
 421         SDS
 422                 **S**\oftware-**d**\efined **S**\torage.
 423
 424         systemd oneshot
 425                 A systemd ``type`` where a command is defined in ``ExecStart``
 426                 which will exit upon completion (it is not intended to
 427                 daemonize)
 428
 429         Teuthology
 430                 The collection of software that performs scripted tests on Ceph.
 431
 432         User
 433                 An individual or a system actor (for example, an application)
 434                 that uses Ceph clients to interact with the :term:`Ceph Storage
 435                 Cluster`. See :ref:`User<rados-ops-user>` and :ref:`User
 436                 Management<user-management>`.
 437
 438         Zone
 439                 In the context of :term:`RGW`, a zone is a logical group that
 440                 consists of one or more :term:`RGW` instances.  A zone's
 441                 configuration state is stored in the :term:`period`. See
 442                 :ref:`Zones<radosgw-zones>`.
 443
 444 .. _https://github.com/ceph: https://github.com/ceph
 445 .. _Cluster Map: ../architecture#cluster-map