Pools are logical partitions that are used to store objects.
Pools provide:
Resilience: It is possible to set the number of OSDs that are allowed to fail without any data being lost. If your cluster uses replicated pools, the number of OSDs that can fail without data loss is equal to the number of replicas.
For example: a typical configuration stores an object and two replicas (copies) of each RADOS object (that is:
size = 3), but you can configure the number of replicas on a per-pool basis. For erasure-coded pools, resilience is defined as the number of coding chunks (for example,m = 2in the default erasure code profile).Placement Groups: The :ref:`autoscaler <pg-autoscaler>` sets the number of placement groups (PGs) for the pool. In a typical configuration, the target number of PGs is approximately one-hundred and fifty PGs per OSD. This provides reasonable balancing without consuming excessive computing resources. When setting up multiple pools, set an appropriate number of PGs for each pool and for the cluster as a whole. Each PG belongs to a specific pool: when multiple pools use the same OSDs, make sure that the sum of PG replicas per OSD is in the desired PG-per-OSD target range. See :ref:`Setting the Number of Placement Groups <setting the number of placement groups>` for instructions on how to manually set the number of placement groups per pool (this procedure works only when the autoscaler is not used).
CRUSH Rules: When data is stored in a pool, the placement of the object and its replicas (or chunks, in the case of erasure-coded pools) in your cluster is governed by CRUSH rules. Custom CRUSH rules can be created for a pool if the default rule does not fit your use case.
Snapshots: The command
ceph osd pool mksnapcreates a snapshot of a pool.
Pool names beginning with . are reserved for use by Ceph's internal
operations. Do not create or manipulate pools with these names.
To list your cluster's pools, run the following command:
.. prompt:: bash $ ceph osd lspools
Before creating a pool, consult Pool, PG and CRUSH Config Reference. The
Ceph central configuration database in the monitor cluster contains a setting
(namely, pg_num) that determines the number of PGs per pool when a pool has
been created and no per-pool value has been specified. It is possible to change
this value from its default. For more on the subject of setting the number of
PGs per pool, see setting the number of placement groups.
Note
In Luminous and later releases, each pool must be associated with the application that will be using the pool. For more information, see Associating a Pool with an Application below.
To create a pool, run one of the following commands:
.. prompt:: bash $
ceph osd pool create {pool-name} [{pg-num} [{pgp-num}]] [replicated] \
[crush-rule-name] [expected-num-objects]
or:
.. prompt:: bash $
ceph osd pool create {pool-name} [{pg-num} [{pgp-num}]] erasure \
[erasure-code-profile] [crush-rule-name] [expected_num_objects] [--autoscale-mode=<on,off,warn>]
For a brief description of the elements of the above commands, consult the following:
.. describe:: {pool-name}
The name of the pool. It must be unique.
:Type: String
:Required: Yes.
.. describe:: {pg-num}
The total number of PGs in the pool. For details on calculating an
appropriate number, see :ref:`placement groups`. The default value ``8`` is
NOT suitable for most systems.
:Type: Integer
:Required: Yes.
:Default: 8
.. describe:: {pgp-num}
The total number of PGs for placement purposes. This **should be equal to
the total number of PGs**, except briefly while ``pg_num`` is being
increased or decreased.
:Type: Integer
:Required: Yes. If no value has been specified in the command, then the default value is used (unless a different value has been set in Ceph configuration).
:Default: 8
.. describe:: {replicated|erasure}
The pool type. This can be either **replicated** (to recover from lost OSDs
by keeping multiple copies of the objects) or **erasure** (to achieve a kind
of `generalized parity RAID <../erasure-code>`_ capability). The
**replicated** pools require more raw storage but can implement all Ceph
operations. The **erasure** pools require less raw storage but can perform
only some Ceph tasks and may provide decreased performance.
:Type: String
:Required: No.
:Default: replicated
.. describe:: [crush-rule-name]
The name of the CRUSH rule to use for this pool. The specified rule must
exist; otherwise the command will fail.
:Type: String
:Required: No.
:Default: For **replicated** pools, it is the rule specified by the :confval:`osd_pool_default_crush_rule` configuration variable. This rule must exist. For **erasure** pools, it is the ``erasure-code`` rule if the ``default`` `erasure code profile`_ is used or the ``{pool-name}`` rule if not. This rule will be created implicitly if it doesn't already exist.
.. describe:: [erasure-code-profile=profile] For **erasure** pools only. Instructs Ceph to use the specified `erasure code profile`_. This profile must be an existing profile as defined by **osd erasure-code-profile set**. :Type: String :Required: No.
.. describe:: --autoscale-mode=<on,off,warn> - ``on``: the Ceph cluster will autotune or recommend changes to the number of PGs in your pool based on actual usage. - ``warn``: the Ceph cluster will autotune or recommend changes to the number of PGs in your pool based on actual usage. - ``off``: refer to :ref:`placement groups` for more information. :Type: String :Required: No. :Default: The default behavior is determined by the :confval:`osd_pool_default_pg_autoscale_mode` option.
.. describe:: [expected-num-objects] The expected number of RADOS objects for this pool. By setting this value and assigning a negative value to **filestore merge threshold**, you arrange for the PG folder splitting to occur at the time of pool creation and avoid the latency impact that accompanies runtime folder splitting. :Type: Integer :Required: No. :Default: 0, no splitting at the time of pool creation.
Pools need to be associated with an application before they can be used. Pools
that are intended for use with CephFS and pools that are created automatically
by RGW are associated automatically. Pools that are intended for use with RBD
should be initialized with the rbd tool (see Block Device Commands for
more information).
For other cases, you can manually associate a free-form application name to a pool by running the following command.:
.. prompt:: bash $
ceph osd pool application enable {pool-name} {application-name}
Note
CephFS uses the application name cephfs, RBD uses the
application name rbd, and RGW uses the application name rgw.
To set pool quotas for the maximum number of bytes and/or the maximum number of RADOS objects per pool, run the following command:
.. prompt:: bash $
ceph osd pool set-quota {pool-name} [max_objects {obj-count}] [max_bytes {bytes}]
For example:
.. prompt:: bash $ ceph osd pool set-quota data max_objects 10000
To remove a quota, set its value to 0.
To delete a pool, run a command of the following form:
.. prompt:: bash $
ceph osd pool delete {pool-name} [{pool-name} --yes-i-really-really-mean-it]
To remove a pool, you must set the mon_allow_pool_delete flag to true
in the monitor's configuration. Otherwise, monitors will refuse to remove
pools.
For more information, see Monitor Configuration.
If there are custom rules for a pool that is no longer needed, consider deleting those rules.
.. prompt:: bash $
ceph osd pool get {pool-name} crush_rule
For example, if the custom rule is "123", check all pools to see whether they use the rule by running the following command:
.. prompt:: bash $
ceph osd dump | grep "^pool" | grep "crush_rule 123"
If no pools use this custom rule, then it is safe to delete the rule from the cluster.
Similarly, if there are users with permissions restricted to a pool that no longer exists, consider deleting those users by running commands of the following forms:
.. prompt:: bash $
ceph auth ls | grep -C 5 {pool-name}
ceph auth del {user}
To rename a pool, run a command of the following form:
.. prompt:: bash $
ceph osd pool rename {current-pool-name} {new-pool-name}
If you rename a pool for which an authenticated user has per-pool capabilities, you must update the user's capabilities ("caps") to refer to the new pool name.
To show a pool's utilization statistics, run the following command:
.. prompt:: bash $ rados df
To obtain I/O information for a specific pool or for all pools, run a command of the following form:
.. prompt:: bash $
ceph osd pool stats [{pool-name}]
To make a snapshot of a pool, run a command of the following form:
.. prompt:: bash $
ceph osd pool mksnap {pool-name} {snap-name}
To remove a snapshot of a pool, run a command of the following form:
.. prompt:: bash $
ceph osd pool rmsnap {pool-name} {snap-name}
To assign values to a pool's configuration keys, run a command of the following form:
.. prompt:: bash $
ceph osd pool set {pool-name} {key} {value}
You may set values for the following keys:
.. describe:: compression_algorithm :Description: Sets the inline compression algorithm used in storing data on the underlying BlueStore back end. This key's setting overrides the global setting :confval:`bluestore_compression_algorithm`. :Type: String :Valid Settings: ``lz4``, ``snappy``, ``zlib``, ``zstd``
.. describe:: compression_mode :Description: Sets the policy for the inline compression algorithm used in storing data on the underlying BlueStore back end. This key's setting overrides the global setting :confval:`bluestore_compression_mode`. :Type: String :Valid Settings: ``none``, ``passive``, ``aggressive``, ``force``
.. describe:: compression_min_blob_size :Description: Sets the minimum size for the compression of chunks: that is, chunks smaller than this are not compressed. This key's setting overrides the following global settings: * :confval:`bluestore_compression_min_blob_size` * :confval:`bluestore_compression_min_blob_size_hdd` * :confval:`bluestore_compression_min_blob_size_ssd` :Type: Unsigned Integer
.. describe:: compression_max_blob_size :Description: Sets the maximum size for chunks: that is, chunks larger than this are broken into smaller blobs of this size before compression is performed. :Type: Unsigned Integer
.. describe:: size :Description: Sets the number of replicas for objects in the pool. For further details, see `Setting the Number of RADOS Object Replicas`_. Replicated pools only. :Type: Integer
.. describe:: min_size :Description: Sets the minimum number of replicas required for I/O. For further details, see `Setting the Number of RADOS Object Replicas`_. For erasure-coded pools, this should be set to a value greater than 'k'. If I/O is allowed at the value 'k', then there is no redundancy and data will be lost in the event of a permanent OSD failure. For more information, see `Erasure Code <../erasure-code>`_ :Type: Integer :Version: ``0.54`` and above
.. describe:: pg_num :Description: Sets the effective number of PGs to use when calculating data placement. :Type: Integer :Valid Range: ``0`` to ``mon_max_pool_pg_num``. If set to ``0``, the value of ``osd_pool_default_pg_num`` will be used.
.. describe:: pgp_num :Description: Sets the effective number of PGs to use when calculating data placement. :Type: Integer :Valid Range: Between ``1`` and the current value of ``pg_num``.
.. describe:: crush_rule :Description: Sets the CRUSH rule that Ceph uses to map object placement within the pool. :Type: String
.. describe:: allow_ec_overwrites :Description: Determines whether writes to an erasure-coded pool are allowed to update only part of a RADOS object. This allows CephFS and RBD to use an EC (erasure-coded) pool for user data (but not for metadata). For more details, see `Erasure Coding with Overwrites`_. :Type: Boolean .. versionadded:: 12.2.0
.. describe:: hashpspool :Description: Sets and unsets the HASHPSPOOL flag on a given pool. :Type: Integer :Valid Range: 1 sets flag, 0 unsets flag
.. describe:: nodelete :Description: Sets and unsets the NODELETE flag on a given pool. :Type: Integer :Valid Range: 1 sets flag, 0 unsets flag :Version: Version ``FIXME``
.. describe:: nopgchange :Description: Sets and unsets the NOPGCHANGE flag on a given pool. :Type: Integer :Valid Range: 1 sets flag, 0 unsets flag :Version: Version ``FIXME``
.. describe:: nosizechange :Description: Sets and unsets the NOSIZECHANGE flag on a given pool. :Type: Integer :Valid Range: 1 sets flag, 0 unsets flag :Version: Version ``FIXME``
.. describe:: bulk :Description: Sets and unsets the bulk flag on a given pool. :Type: Boolean :Valid Range: ``true``/``1`` sets flag, ``false``/``0`` unsets flag
.. describe:: write_fadvise_dontneed :Description: Sets and unsets the WRITE_FADVISE_DONTNEED flag on a given pool. :Type: Integer :Valid Range: ``1`` sets flag, ``0`` unsets flag
.. describe:: noscrub :Description: Sets and unsets the NOSCRUB flag on a given pool. :Type: Integer :Valid Range: ``1`` sets flag, ``0`` unsets flag
.. describe:: nodeep-scrub :Description: Sets and unsets the NODEEP_SCRUB flag on a given pool. :Type: Integer :Valid Range: ``1`` sets flag, ``0`` unsets flag
.. describe:: hit_set_type
:Description: Enables HitSet tracking for cache pools.
For additional information, see `Bloom Filter`_.
:Type: String
:Valid Settings: ``bloom``, ``explicit_hash``, ``explicit_object``
:Default: ``bloom``. Other values are for testing.
.. describe:: hit_set_count
:Description: Determines the number of HitSets to store for cache pools. The
higher the value, the more RAM is consumed by the ``ceph-osd``
daemon.
:Type: Integer
:Valid Range: ``1``. Agent doesn't handle > ``1`` yet.
.. describe:: hit_set_period
:Description: Determines the duration of a HitSet period (in seconds) for
cache pools. The higher the value, the more RAM is consumed
by the ``ceph-osd`` daemon.
:Type: Integer
:Example: ``3600`` (3600 seconds: one hour)
.. describe:: hit_set_fpp
:Description: Determines the probability of false positives for the
``bloom`` HitSet type. For additional information, see `Bloom
Filter`_.
:Type: Double
:Valid Range: ``0.0`` - ``1.0``
:Default: ``0.05``
.. describe:: cache_target_dirty_ratio
:Description: Sets a flush threshold for the percentage of the cache pool
containing modified (dirty) objects. When this threshold is
reached, the cache-tiering agent will flush these objects to
the backing storage pool.
:Type: Double
:Default: ``.4``
.. describe:: cache_target_dirty_high_ratio
:Description: Sets a flush threshold for the percentage of the cache pool
containing modified (dirty) objects. When this threshold is
reached, the cache-tiering agent will flush these objects to
the backing storage pool with a higher speed (as compared with
``cache_target_dirty_ratio``).
:Type: Double
:Default: ``.6``
.. describe:: cache_target_full_ratio
:Description: Sets an eviction threshold for the percentage of the cache
pool containing unmodified (clean) objects. When this
threshold is reached, the cache-tiering agent will evict
these objects from the cache pool.
:Type: Double
:Default: ``.8``
.. describe:: target_max_bytes
:Description: Ceph will begin flushing or evicting objects when the
``max_bytes`` threshold is triggered.
:Type: Integer
:Example: ``1000000000000`` #1-TB
.. describe:: target_max_objects
:Description: Ceph will begin flushing or evicting objects when the
``max_objects`` threshold is triggered.
:Type: Integer
:Example: ``1000000`` #1M objects
.. describe:: hit_set_grade_decay_rate
:Description: Sets the temperature decay rate between two successive
HitSets.
:Type: Integer
:Valid Range: 0 - 100
:Default: ``20``
.. describe:: hit_set_search_last_n
:Description: Count at most N appearances in HitSets. Used for temperature
calculation.
:Type: Integer
:Valid Range: 0 - hit_set_count
:Default: ``1``
.. describe:: cache_min_flush_age
:Description: Sets the time (in seconds) before the cache-tiering agent
flushes an object from the cache pool to the storage pool.
:Type: Integer
:Example: ``600`` (600 seconds: ten minutes)
.. describe:: cache_min_evict_age
:Description: Sets the time (in seconds) before the cache-tiering agent
evicts an object from the cache pool.
:Type: Integer
:Example: ``1800`` (1800 seconds: thirty minutes)
.. describe:: fast_read
:Description: For erasure-coded pools, if this flag is turned ``on``, the
read request issues "sub reads" to all shards, and then waits
until it receives enough shards to decode before it serves
the client. If *jerasure* or *isa* erasure plugins are in
use, then after the first *K* replies have returned, the
client's request is served immediately using the data decoded
from these replies. This approach sacrifices resources in
exchange for better performance. This flag is supported only
for erasure-coded pools.
:Type: Boolean
:Defaults: ``0``
.. describe:: scrub_min_interval :Description: Sets the minimum interval (in seconds) for successive scrubs of the pool's PGs when the load is low. If the default value of ``0`` is in effect, then the value of ``osd_scrub_min_interval`` from central config is used. :Type: Double :Default: ``0``
.. describe:: scrub_max_interval :Description: Sets the maximum interval (in seconds) for scrubs of the pool's PGs regardless of cluster load. If the value of ``scrub_max_interval`` is ``0``, then the value ``osd_scrub_max_interval`` from central config is used. :Type: Double :Default: ``0``
.. describe:: deep_scrub_interval :Description: Sets the interval (in seconds) for pool “deep” scrubs of the pool's PGs. If the value of ``deep_scrub_interval`` is ``0``, the value ``osd_deep_scrub_interval`` from central config is used. :Type: Double :Default: ``0``
.. describe:: recovery_priority :Description: Setting this value adjusts a pool's computed reservation priority. This value must be in the range ``-10`` to ``10``. Any pool assigned a negative value will be given a lower priority than any new pools, so users are directed to assign negative values to low-priority pools. :Type: Integer :Default: ``0``
.. describe:: recovery_op_priority :Description: Sets the recovery operation priority for a specific pool's PGs. This overrides the general priority determined by :confval:`osd_recovery_op_priority`. :Type: Integer :Default: ``0``
To get a value from a pool's key, run a command of the following form:
.. prompt:: bash $
ceph osd pool get {pool-name} {key}
You may get values from the following keys:
size
| Description: | See size. |
|---|---|
| Type: | Integer |
min_size
| Description: | See min_size. |
|---|---|
| Type: | Integer |
| Version: | 0.54 and above |
pg_num
| Description: | See pg_num. |
|---|---|
| Type: | Integer |
pgp_num
| Description: | See pgp_num. |
|---|---|
| Type: | Integer |
| Valid Range: | Equal to or less than pg_num. |
crush_rule
| Description: | See crush_rule. |
|---|
hit_set_type
| Description: | See hit_set_type. |
|---|---|
| Type: | String |
| Valid Settings: | bloom, explicit_hash, explicit_object |
hit_set_count
| Description: | See hit_set_count. |
|---|---|
| Type: | Integer |
hit_set_period
| Description: | See hit_set_period. |
|---|---|
| Type: | Integer |
hit_set_fpp
| Description: | See hit_set_fpp. |
|---|---|
| Type: | Double |
cache_target_dirty_ratio
| Description: | See cache_target_dirty_ratio. |
|---|---|
| Type: | Double |
cache_target_dirty_high_ratio
| Description: | See cache_target_dirty_high_ratio. |
|---|---|
| Type: | Double |
cache_target_full_ratio
| Description: | See cache_target_full_ratio. |
|---|---|
| Type: | Double |
target_max_bytes
| Description: | See target_max_bytes. |
|---|---|
| Type: | Integer |
target_max_objects
| Description: | See target_max_objects. |
|---|---|
| Type: | Integer |
cache_min_flush_age
| Description: | See cache_min_flush_age. |
|---|---|
| Type: | Integer |
cache_min_evict_age
| Description: | See cache_min_evict_age. |
|---|---|
| Type: | Integer |
fast_read
| Description: | See fast_read. |
|---|---|
| Type: | Boolean |
scrub_min_interval
| Description: | See scrub_min_interval. |
|---|---|
| Type: | Double |
scrub_max_interval
| Description: | See scrub_max_interval. |
|---|---|
| Type: | Double |
deep_scrub_interval
| Description: | See deep_scrub_interval. |
|---|---|
| Type: | Double |
allow_ec_overwrites
| Description: | See allow_ec_overwrites. |
|---|---|
| Type: | Boolean |
recovery_priority
| Description: | See recovery_priority. |
|---|---|
| Type: | Integer |
recovery_op_priority
| Description: | See recovery_op_priority. |
|---|---|
| Type: | Integer |
To set the number of data replicas on a replicated pool, run a command of the following form:
.. prompt:: bash $
ceph osd pool set {poolname} size {num-replicas}
Important
The {num-replicas} argument includes the primary object
itself. For example, if you want there to be two replicas of the object in
addition to the original object (for a total of three instances of the
object) specify 3 by running the following command:
.. prompt:: bash $ ceph osd pool set data size 3
You may run the above command for each pool.
Note
An object might accept I/Os in degraded mode with fewer than pool
size replicas. To set a minimum number of replicas required for I/O, you
should use the min_size setting. For example, you might run the
following command:
.. prompt:: bash $ ceph osd pool set data min_size 2
This command ensures that no object in the data pool will receive I/O if it has
fewer than min_size (in this case, two) replicas.
To get the number of object replicas, run the following command:
.. prompt:: bash $ ceph osd dump | grep 'replicated size'
Ceph will list pools and highlight the replicated size attribute. By
default, Ceph creates two replicas of an object (a total of three copies, for a
size of 3).