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A short introduction to the first time user of an erasure coded pool. It includes a reminder of how it relates to cache tiering and links to define new profiles with an example. There was examples in the developer documentation but the operator expects to find such a guide in the rados operations chapter. http://tracker.ceph.com/issues/9970 Fixes: #9970 Signed-off-by: Loic Dachary <ldachary@redhat.com>
434 lines
12 KiB
ReStructuredText
434 lines
12 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 provides you with:
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- **Resilience**: You can set how many OSD are allowed to fail without losing data.
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For replicated pools, it is 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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For `erasure coded pools <../erasure-code>`_, it is the number of coding chunks
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(i.e. ``m=2`` in the **erasure code profile**)
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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 object
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and its replicas (or chunks for erasure coded pools) in your cluster.
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You can create a custom CRUSH rule for your 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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Before creating pools, refer to the `Pool, PG and CRUSH Config Reference`_.
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Ideally, you should override the default value for the number of placement
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groups in you Ceph configuration file, as the default is NOT ideal.
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For example::
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osd pool default pg num = 100
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osd pool default pgp num = 100
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To create a pool, execute::
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ceph osd pool create {pool-name} {pg-num} [{pgp-num}] [replicated] \
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[crush-ruleset-name]
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ceph osd pool create {pool-name} {pg-num} {pgp-num} erasure \
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[erasure-code-profile] [crush-ruleset-name]
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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. Picks up default or Ceph configuration value if not specified.
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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. Picks up default or Ceph configuration value if not specified.
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:Default: 8
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``{replicated|erasure}``
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:Description: The pool type which may either be **replicated** to
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recover from lost OSDs by keeping multiple copies of the
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objects or **erasure** to get a kind of
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`generalized RAID5 <../erasure-code>`_ capability.
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The **replicated** pools require more
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raw storage but implement all Ceph operations. The
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**erasure** pools require less raw storage but only
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implement a subset of the available operations.
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:Type: String
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:Required: No.
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:Default: replicated
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``[crush-ruleset-name]``
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:Description: The name of the crush ruleset for this pool. If specified ruleset
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doesn't exist, the creation of **replicated** pool will fail with
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-ENOENT. But **replicated** pool will create a new erasure
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ruleset with specified name.
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:Type: String
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:Required: No.
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:Default: "erasure-code" for **erasure pool**. Pick up Ceph configuraion variable
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**osd_pool_default_crush_replicated_ruleset** for **replicated** pool.
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``[erasure-code-profile=profile]``
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.. _erasure code profile: ../erasure-code-profile
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:Description: For **erasure** pools only. Use the `erasure code profile`_. It
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must be an existing profile as defined by
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**osd erasure-code-profile set**.
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:Type: String
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:Required: No.
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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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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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Set Pool Quotas
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===============
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You can set pool quotas for the maximum number of bytes and/or the maximum
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number of objects per pool. ::
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ceph osd pool set-quota {pool-name} [max_objects {obj-count}] [max_bytes {bytes}]
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For example::
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ceph osd pool set-quota data max_objects 10000
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To remove a quota, set its value to ``0``.
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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.
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See `Set the Number of Object Replicas`_ for further details.
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Replicated pools only.
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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 I/O.
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See `Set the Number of Object Replicas`_ for further details.
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Replicated pools only.
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:Type: Integer
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: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,
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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
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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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``hashpspool``
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:Description: Set/Unset HASHPSPOOL flag on a given pool.
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:Type: Integer
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:Valid Range: 1 sets flag, 0 unsets flag
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:Version: Version ``0.48`` Argonaut and above.
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``hit_set_type``
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:Description: Enables hit set tracking for cache pools.
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See `Bloom Filter`_ for additional information.
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:Type: String
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:Valid Settings: ``bloom``, ``explicit_hash``, ``explicit_object``
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:Default: ``bloom``. Other values are for testing.
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``hit_set_count``
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:Description: The number of hit sets to store for cache pools. The higher
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the number, the more RAM consumed by the ``ceph-osd`` daemon.
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:Type: Integer
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:Valid Range: ``1``. Agent doesn't handle > 1 yet.
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``hit_set_period``
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:Description: The duration of a hit set period in seconds for cache pools.
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The higher the number, the more RAM consumed by the
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``ceph-osd`` daemon.
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:Type: Integer
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:Example: ``3600`` 1hr
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``hit_set_fpp``
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:Description: The false positive probability for the ``bloom`` hit set type.
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See `Bloom Filter`_ for additional information.
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:Type: Double
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:Valid Range: 0.0 - 1.0
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:Default: ``0.05``
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``cache_target_dirty_ratio``
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:Description: The percentage of the cache pool containing modified (dirty)
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objects before the cache tiering agent will flush them to the
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backing storage pool.
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:Type: Double
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:Default: ``.4``
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``cache_target_full_ratio``
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:Description: The percentage of the cache pool containing unmodified (clean)
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objects before the cache tiering agent will evict them from the
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cache pool.
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:Type: Double
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:Default: ``.8``
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``target_max_bytes``
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:Description: Ceph will begin flushing or evicting objects when the
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``max_bytes`` threshold is triggered.
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:Type: Integer
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:Example: ``1000000000000`` #1-TB
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``target_max_objects``
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:Description: Ceph will begin flushing or evicting objects when the
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``max_objects`` threshold is triggered.
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:Type: Integer
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:Example: ``1000000`` #1M objects
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``cache_min_flush_age``
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:Description: The time (in seconds) before the cache tiering agent will flush
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an object from the cache pool to the storage pool.
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:Type: Integer
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:Example: ``600`` 10min
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``cache_min_evict_age``
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:Description: The time (in seconds) before the cache tiering agent will evict
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an object from the cache pool.
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:Type: Integer
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:Example: ``1800`` 30min
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Get Pool Values
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===============
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To get a value from 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 on a replicated pool, 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. **Note:** An object might accept
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I/Os in degraded mode with fewer than ``pool size`` replicas. To set a minimum
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number of required replicas for I/O, you should use the ``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 I/O 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 'replicated size'
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Ceph will list the pools, with the ``replicated size`` attribute highlighted.
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By default, ceph Creates two replicas of an object (a total of three copies, or
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a size of 3).
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.. _Pool, PG and CRUSH Config Reference: ../../configuration/pool-pg-config-ref
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.. _Bloom Filter: http://en.wikipedia.org/wiki/Bloom_filter
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