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diff --git a/doc/glossary.rst b/doc/glossary.rst new file mode 100644 index 000000000..4d7037684 --- /dev/null +++ b/doc/glossary.rst @@ -0,0 +1,460 @@ +=============== + Ceph Glossary +=============== + +.. glossary:: + + Application + More properly called a :term:`client`, an application is any program + external to Ceph that uses a Ceph Cluster to store and + replicate data. + + :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. The Luminous release of + Ceph promoted BlueStore to the default OSD back end, + supplanting FileStore. As of the Reef release, FileStore is no + longer available as a storage back end. + + BlueStore stores objects directly on raw block devices or + partitions, and does not interact with mounted file systems. + BlueStore uses RocksDB's key/value database to map object names + to block locations on disk. + + Bucket + In the context of :term:`RGW`, a bucket is a group of objects. + In a filesystem-based analogy in which objects are the + counterpart of files, buckets are the counterpart of + directories. :ref:`Multisite sync + policies<radosgw-multisite-sync-policy>` can be set on buckets, + to provide fine-grained control of data movement from one zone + to another zone. + + The concept of the bucket has been taken from AWS S3. See also + `the AWS S3 page on creating buckets <https://docs.aws.amazon.com/AmazonS3/latest/userguide/creating-buckets-s3.html>`_ + and `the AWS S3 'Buckets Overview' page <https://docs.aws.amazon.com/AmazonS3/latest/userguide/UsingBucket.html>`_. + + OpenStack Swift uses the term "containers" for what RGW and AWS call "buckets". + See `the OpenStack Storage API overview page <https://docs.openstack.org/swift/latest/api/object_api_v1_overview.html>`_. + + 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 + See :term:`Ceph Object Store`. + + 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 authenticates users and + daemons. CephX operates like Kerberos, but it has no single + point of failure. See the :ref:`High-availability + Authentication section<arch_high_availability_authentication>` + of the Architecture document and the :ref:`CephX Configuration + Reference<rados-cephx-config-ref>`. + + Client + A client is any program external to Ceph that uses a Ceph + Cluster to store and replicate data. + + 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 + 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`. + + Hybrid OSD + Refers to an OSD that has both HDD and SSD drives. + + 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. + + :ref:`MON<arch_monitor>` + The Ceph monitor software. + + Node + See :term:`Ceph Node`. + + Object Storage Device + See :term:`OSD`. + + OSD + Probably :term:`Ceph OSD`, but not necessarily. Sometimes + (especially in older correspondence, and especially in + documentation that is not written specifically 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`` + + Period + In the context of :term:`RGW`, a period is the configuration + state of the :term:`Realm`. The period stores the configuration + state of a multi-site configuration. When the period is updated, + the "epoch" is said thereby to have been changed. + + Placement Groups (PGs) + Placement groups (PGs) are subsets of each logical Ceph pool. + Placement groups perform the function of placing objects (as a + group) into OSDs. Ceph manages data internally at + placement-group granularity: this scales better than would + managing individual (and therefore more numerous) RADOS + objects. A cluster that has a larger number of placement groups + (for example, 100 per OSD) is better balanced than an otherwise + identical cluster with a smaller number of placement groups. + + Ceph's internal RADOS objects are each mapped to a specific + placement group, and each placement group belongs to exactly + one Ceph pool. + + :ref:`Pool<rados_pools>` + A pool is a logical partition used to store objects. + + Pools + See :term:`pool`. + + :ref:`Primary Affinity <rados_ops_primary_affinity>` + The characteristic of an OSD that governs the likelihood that + a given OSD will be selected as the primary OSD (or "lead + OSD") in an acting set. Primary affinity was introduced in + Firefly (v. 0.80). See :ref:`Primary Affinity + <rados_ops_primary_affinity>`. + + Quorum + Quorum is the state that exists when a majority of the + :ref:`Monitors<arch_monitor>` in the cluster are ``up``. A + minimum of three :ref:`Monitors<arch_monitor>` must exist in + the cluster in order for Quorum to be possible. + + 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`. + + :ref:`Realm<rgw-realms>` + In the context of RADOS Gateway (RGW), a realm is a globally + unique namespace that consists of one or more zonegroups. + + 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. + + scrubs + + The processes by which Ceph ensures data integrity. During the + process of scrubbing, Ceph generates a catalog of all objects + in a placement group, then ensures that none of the objects are + missing or mismatched by comparing each primary object against + its replicas, which are stored across other OSDs. Any PG + is determined to have a copy of an object that is different + than the other copies or is missing entirely is marked + "inconsistent" (that is, the PG is marked "inconsistent"). + + There are two kinds of scrubbing: light scrubbing and deep + scrubbing (also called "normal scrubbing" and "deep scrubbing", + respectively). Light scrubbing is performed daily and does + nothing more than confirm that a given object exists and that + its metadata is correct. Deep scrubbing is performed weekly and + reads the data and uses checksums to ensure data integrity. + + See :ref:`Scrubbing <rados_config_scrubbing>` in the RADOS OSD + Configuration Reference Guide and page 141 of *Mastering Ceph, + second edition* (Fisk, Nick. 2019). + + 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. + + User + An individual or a system actor (for example, an application) + that uses Ceph clients to interact with the :term:`Ceph Storage + Cluster`. See :ref:`User<rados-ops-user>` and :ref:`User + Management<user-management>`. + + Zone + In the context of :term:`RGW`, a zone is a logical group that + consists of one or more :term:`RGW` instances. A zone's + configuration state is stored in the :term:`period`. See + :ref:`Zones<radosgw-zones>`. + +.. _https://github.com/ceph: https://github.com/ceph +.. _Cluster Map: ../architecture#cluster-map |