+++ /dev/null
-=================
- Storage Devices
-=================
-
-There are two Ceph daemons that store data on disk:
-
-* **Ceph OSDs** (or Object Storage Daemons) are where most of the
- data is stored in Ceph. Generally speaking, each OSD is backed by
- a single storage device, like a traditional hard disk (HDD) or
- solid state disk (SSD). OSDs can also be backed by a combination
- of devices, like a HDD for most data and an SSD (or partition of an
- SSD) for some metadata. The number of OSDs in a cluster is
- generally a function of how much data will be stored, how big each
- storage device will be, and the level and type of redundancy
- (replication or erasure coding).
-* **Ceph Monitor** daemons manage critical cluster state like cluster
- membership and authentication information. For smaller clusters a
- few gigabytes is all that is needed, although for larger clusters
- the monitor database can reach tens or possibly hundreds of
- gigabytes.
-
-
-OSD Backends
-============
-
-There are two ways that OSDs can manage the data they store. Starting
-with the Luminous 12.2.z release, the new default (and recommended) backend is
-*BlueStore*. Prior to Luminous, the default (and only option) was
-*FileStore*.
-
-BlueStore
----------
-
-BlueStore is a special-purpose storage backend designed specifically
-for managing data on disk for Ceph OSD workloads. It is motivated by
-experience supporting and managing OSDs using FileStore over the
-last ten years. Key BlueStore features include:
-
-* Direct management of storage devices. BlueStore consumes raw block
- devices or partitions. This avoids any intervening layers of
- abstraction (such as local file systems like XFS) that may limit
- performance or add complexity.
-* Metadata management with RocksDB. We embed RocksDB's key/value database
- in order to manage internal metadata, such as the mapping from object
- names to block locations on disk.
-* Full data and metadata checksumming. By default all data and
- metadata written to BlueStore is protected by one or more
- checksums. No data or metadata will be read from disk or returned
- to the user without being verified.
-* Inline compression. Data written may be optionally compressed
- before being written to disk.
-* Multi-device metadata tiering. BlueStore allows its internal
- journal (write-ahead log) to be written to a separate, high-speed
- device (like an SSD, NVMe, or NVDIMM) to increased performance. If
- a significant amount of faster storage is available, internal
- metadata can also be stored on the faster device.
-* Efficient copy-on-write. RBD and CephFS snapshots rely on a
- copy-on-write *clone* mechanism that is implemented efficiently in
- BlueStore. This results in efficient IO both for regular snapshots
- and for erasure coded pools (which rely on cloning to implement
- efficient two-phase commits).
-
-For more information, see :doc:`bluestore-config-ref`.
-
-FileStore
----------
-
-FileStore is the legacy approach to storing objects in Ceph. It
-relies on a standard file system (normally XFS) in combination with a
-key/value database (traditionally LevelDB, now RocksDB) for some
-metadata.
-
-FileStore is well-tested and widely used in production but suffers
-from many performance deficiencies due to its overall design and
-reliance on a traditional file system for storing object data.
-
-Although FileStore is generally capable of functioning on most
-POSIX-compatible file systems (including btrfs and ext4), we only
-recommend that XFS be used. Both btrfs and ext4 have known bugs and
-deficiencies and their use may lead to data loss. By default all Ceph
-provisioning tools will use XFS.
-
-For more information, see :doc:`filestore-config-ref`.
Code Review / stor4nfv.git / blobdiff