Ceph Glossary

Ceph is growing rapidly. As firms deploy Ceph, the technical terms such as “RADOS”, “RBD,” “RGW” and so forth require corresponding marketing terms that explain what each component does. The terms in this glossary are intended to complement the existing technical terminology.

Sometimes more than one term applies to a definition. Generally, the first term reflects a term consistent with Ceph’s marketing, and secondary terms reflect either technical terms or legacy ways of referring to Ceph systems.

Ceph Project
The aggregate term for the people, software, mission and infrastructure of Ceph.
cephx
The Ceph authentication protocol. Cephx operates like Kerberos, but it has no single point of failure.
Ceph
Ceph Platform
All Ceph software, which includes any piece of code hosted at https://github.com/ceph.
Ceph System
Ceph Stack
A collection of two or more components of Ceph.
Ceph Node
Node
Host
Any single machine or server in a Ceph System.
Ceph Storage Cluster
Ceph Object Store
RADOS
RADOS Cluster
Reliable Autonomic Distributed Object Store
The core set of storage software which stores the user’s data (MON+OSD).
Ceph Cluster Map
cluster map
The set of maps comprising the monitor map, OSD map, PG map, MDS map and CRUSH map. See Cluster Map for details.
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 Gateway
RADOS Gateway
RGW
The S3/Swift gateway component of Ceph.
Ceph Block Device
RBD
The block storage component of Ceph.
Ceph Block Storage
The block storage “product,” service or capabilities when used in conjunction with librbd, a hypervisor such as QEMU or Xen, and a hypervisor abstraction layer such as libvirt.
Ceph Filesystem
CephFS
Ceph FS
The POSIX filesystem components of Ceph.
Cloud Platforms
Cloud Stacks
Third party cloud provisioning platforms such as OpenStack, CloudStack, OpenNebula, ProxMox, etc.
Object Storage Device
OSD
A physical or logical storage unit (e.g., LUN). Sometimes, Ceph users use the term “OSD” to refer to Ceph OSD Daemon, though the proper term is “Ceph OSD”.
Ceph OSD Daemon
Ceph OSD Daemons
Ceph OSD
The Ceph OSD software, which interacts with a logical disk (OSD). Sometimes, Ceph users use the term “OSD” to refer to “Ceph OSD Daemon”, though the proper term is “Ceph OSD”.
OSD id
The integer that defines an OSD. It is generated by the monitors as part of the creation of a new OSD.
OSD fsid
This is a unique identifier used to further improve the uniqueness of an OSD and it is found in the OSD path in a file called osd_fsid. This fsid term is used interchangeably with uuid
OSD uuid
Just like the OSD fsid, this is the OSD unique identifer and is used interchangeably with fsid
bluestore
OSD BlueStore is a new back end for OSD daemons (kraken and newer versions). Unlike filestore it stores objects directly on the Ceph block devices without any file system interface.
filestore
A back end for OSD daemons, where a Journal is needed and files are written to the filesystem.
Ceph Monitor
MON
The Ceph monitor software.
Ceph Manager
MGR
The Ceph manager software, which collects all the state from the whole cluster in one place.
Ceph Metadata Server
MDS
The Ceph metadata software.
Ceph Clients
Ceph Client
The collection of Ceph components which can access a Ceph Storage Cluster. These include the Ceph Object Gateway, the Ceph Block Device, the Ceph Filesystem, and their corresponding libraries, kernel modules, and FUSEs.
Ceph Kernel Modules
The collection of kernel modules which can be used to interact with the Ceph System (e.g., ceph.ko, rbd.ko).
Ceph Client Libraries
The collection of libraries that can be used to interact with components of the Ceph System.
Ceph Release
Any distinct numbered version of Ceph.
Ceph Point Release
Any ad-hoc release that includes only bug or security fixes.
Ceph Interim Release
Versions of Ceph that have not yet been put through quality assurance testing, but may contain new features.
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.
Ceph Test Framework
Teuthology
The collection of software that performs scripted tests on Ceph.
CRUSH
Controlled Replication Under Scalable Hashing. It is the algorithm Ceph uses to compute object storage locations.
ruleset
A set of CRUSH data placement rules that applies to a particular pool(s).
Pool
Pools
Pools are logical partitions for storing objects.
systemd oneshot
A systemd type where a command is defined in ExecStart which will exit upon completion (it is not intended to daemonize)
LVM tags
Extensible metadata for LVM volumes and groups. It is used to store Ceph-specific information about devices and its relationship with OSDs.