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263 lines
7.0 KiB
ReStructuredText
=======
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Pools
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=======
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When you first deploy a cluster without creating a pool, Ceph uses the default
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pools for storing data. A pool differs from CRUSH's location-based buckets in
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that a pool doesn't have a single physical location, and a pool provides you
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with some additional functionality, including:
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- **Replicas**: You can set the desired number of copies/replicas of an object.
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A typical configuration stores an object and one additional copy
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(i.e., ``size = 2``), but you can determine the number of copies/replicas.
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- **Placement Groups**: You can set the number of placement groups for the pool.
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A typical configuration uses approximately 100 placement groups per OSD to
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provide optimal balancing without using up too many computing resources. When
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setting up multiple pools, be careful to ensure you set a reasonable number of
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placement groups for both the pool and the cluster as a whole.
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- **CRUSH Rules**: When you store data in a pool, a CRUSH ruleset mapped to the
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pool enables CRUSH to identify a rule for the placement of the primary object
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and object replicas in your cluster. You can create a custom CRUSH rule for your
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pool.
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- **Snapshots**: When you create snapshots with ``ceph osd pool mksnap``,
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you effectively take a snapshot of a particular pool.
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- **Set Ownership**: You can set a user ID as the owner of a pool.
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To organize data into pools, you can list, create, and remove pools.
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You can also view the utilization statistics for each pool.
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List Pools
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==========
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To list your cluster's pools, execute::
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ceph osd lspools
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The default pools include:
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- ``data``
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- ``metadata``
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- ``rbd``
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.. _createpool:
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Create a Pool
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=============
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To create a pool, execute::
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ceph osd pool create {pool-name} {pg-num} [{pgp-num}]
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Where:
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``{pool-name}``
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:Description: The name of the pool. It must be unique.
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:Type: String
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:Required: Yes
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``{pg-num}``
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:Description: The total number of placement groups for the pool. See `Placement
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Groups`_ for details on calculating a suitable number. The
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default value ``8`` is NOT suitable for most systems.
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:Type: Integer
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:Required: Yes
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:Default: 8
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``{pgp-num}``
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:Description: The total number of placement groups for placement purposes. This
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**should be equal to the total number of placement groups**, except
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for placement group splitting scenarios.
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:Type: Integer
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:Required: Yes
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:Default: 8
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When you create a pool, set the number of placement groups to a reasonable value
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(e.g., ``100``). Consider the total number of placement groups per OSD too.
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Placement groups are computationally expensive, so performance will degrade when
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you have many pools with many placement groups (e.g., 50 pools with 100
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placement groups each). The point of diminishing returns depends upon the power
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of the OSD host.
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.. important:: Increasing the number of placement groups in a pool after you
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create the pool is still an experimental feature in Bobtail (v 0.56). We
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recommend defining a reasonable number of placement groups and maintaining
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that number until Ceph's placement group splitting and merging
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functionality matures.
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See `Placement Groups`_ for details on calculating an appropriate number of
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placement groups for your pool.
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.. _Placement Groups: ../placement-groups
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Delete a Pool
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=============
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To delete a pool, execute::
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ceph osd pool delete {pool-name} [{pool-name} --yes-i-really-really-mean-it]
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If you created your own rulesets and rules for a pool you created, you should
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consider removing them when you no longer need your pool. If you created users
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with permissions strictly for a pool that no longer exists, you should consider
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deleting those users too.
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Rename a Pool
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=============
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To rename a pool, execute::
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ceph osd pool rename {current-pool-name} {new-pool-name}
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If you rename a pool and you have per-pool capabilities for an authenticated
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user, you must update the user's capabilities (i.e., caps) with the new pool
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name.
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.. note: Version ``0.48`` Argonaut and above.
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Show Pool Statistics
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====================
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To show a pool's utilization statistics, execute::
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rados df
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Make a Snapshot of a Pool
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=========================
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To make a snapshot of a pool, execute::
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ceph osd pool mksnap {pool-name} {snap-name}
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.. note: Version ``0.48`` Argonaut and above.
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Remove a Snapshot of a Pool
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===========================
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To remove a snapshot of a pool, execute::
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ceph osd pool rmsnap {pool-name} {snap-name}
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.. note: Version ``0.48`` Argonaut and above.
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.. _setpoolvalues:
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Set Pool Values
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===============
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To set a value to a pool, execute the following::
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ceph osd pool set {pool-name} {key} {value}
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You may set values for the following keys:
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``size``
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:Description: Sets the number of replicas for objects in the pool. See `Set the Number of Object Replicas`_ for further details.
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:Type: Integer
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``min_size``
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:Description: Sets the minimum number of replicas required for io. See `Set the Number of Object Replicas`_ for further details
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:Type: Integer
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.. note: Version ``0.54`` and above
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``crash_replay_interval``
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:Description: The number of seconds to allow clients to replay acknowledged, but uncommitted requests.
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:Type: Integer
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``pgp_num``
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:Description: The effective number of placement groups to use when calculating data placement.
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:Type: Integer
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:Valid Range: Equal to or less than ``pg_num``.
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``crush_ruleset``
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:Description: The ruleset to use for mapping object placement in the cluster.
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:Type: Integer
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.. note: Version ``0.48`` Argonaut and above.
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Get Pool Values
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===============
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To set a value to a pool, execute the following::
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ceph osd pool get {pool-name} {key}
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``pg_num``
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:Description: The number of placement groups for the pool.
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:Type: Integer
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``pgp_num``
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:Description: The effective number of placement groups to use when calculating data placement.
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:Type: Integer
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:Valid Range: Equal to or less than ``pg_num``.
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Set the Number of Object Replicas
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=================================
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To set the number of object replicas, execute the following::
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ceph osd pool set {poolname} size {num-replicas}
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.. important: The ``{num-replicas}`` includes the object itself.
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If you want the object and two copies of the object for a total of
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three instances of the object, specify ``3``.
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For example::
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ceph osd pool set data size 3
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You may execute this command for each pool.
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Note, however, that pool size is more of a best-effort setting: an object
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might accept ios in degraded mode with fewer than size replicas. To
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set a minimum number of required replicas for io, you should use the
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min_size setting.
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For example::
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ceph osd pool set data min_size 2
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This ensures that no object in the data pool will receive io with fewer than
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min_size replicas.
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Get the Number of Object Replicas
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=================================
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To get the number of object replicas, execute the following::
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ceph osd dump | grep 'rep size'
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Ceph will list the pools, with the ``rep size`` attribute highlighted.
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By default, Ceph creates two replicas of an object (two copies).
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