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ceph/doc/rados/operations/pools.rst

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=======
Pools
=======
Pools are logical partitions for storing objects.
When you first deploy a cluster without creating a pool, Ceph uses the default
pools for storing data. A pool provides you with:
- **Resilience**: You can set how many OSD are allowed to fail without losing data.
For replicated pools, it is the desired number of copies/replicas of an object.
A typical configuration stores an object and two additional copies
(i.e., ``size = 3``), but you can configure the number of copies/replicas at
pool granularity.
For `erasure coded pools <../erasure-code>`_, it is the number of coding chunks
(i.e. ``m=2`` in the **erasure code profile**)
- **Placement Groups**: You can set the number of placement groups for the pool.
A typical configuration targets approximately 100 placement groups per OSD to
provide optimal balancing without using up too many computing resources. When
setting up multiple pools, be careful to set a reasonable number of
placement groups for each pool and for the cluster as a whole. Note that each PG
belongs to a specific pool, so when multiple pools use the same OSDs, you must
take care that the **sum** of PG replicas per OSD is in the desired PG per OSD
target range.
- **CRUSH Rules**: When you store data in a pool, placement of the object
and its replicas (or chunks for erasure coded pools) in your cluster is governed
by CRUSH rules. You can create a custom CRUSH rule for your pool if the default
rule is not appropriate for your use case.
- **Snapshots**: When you create snapshots with ``ceph osd pool mksnap``,
you effectively take a snapshot of a particular pool.
To organize data into pools, you can list, create, and remove pools.
You can also view the utilization statistics for each pool.
Pool Names
==========
Pool names beginning with ``.`` are reserved for use by Ceph's internal
operations. Please do not create or manipulate pools with these names.
List Pools
==========
To list your cluster's pools, execute::
ceph osd lspools
.. _createpool:
Create a Pool
=============
Before creating pools, refer to the `Pool, PG and CRUSH Config Reference`_.
Ideally, you should override the default value for the number of placement
groups in your Ceph configuration file, as the default is NOT ideal.
For details on placement group numbers refer to `setting the number of placement groups`_
.. note:: Starting with Luminous, all pools need to be associated to the
application using the pool. See `Associate Pool to Application`_ below for
more information.
For example::
osd_pool_default_pg_num = 128
osd_pool_default_pgp_num = 128
To create a pool, execute::
ceph osd pool create {pool-name} [{pg-num} [{pgp-num}]] [replicated] \
[crush-rule-name] [expected-num-objects]
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>]
Where:
.. describe:: {pool-name}
The name of the pool. It must be unique.
:Type: String
:Required: Yes.
.. describe:: {pg-num}
The total number of placement groups for the pool. See :ref:`placement groups`
for details on calculating a suitable number. The
default value ``8`` is NOT suitable for most systems.
:Type: Integer
:Required: Yes.
:Default: 8
.. describe:: {pgp-num}
The total number of placement groups for placement purposes. This
**should be equal to the total number of placement groups**, except
for placement group splitting scenarios.
:Type: Integer
:Required: Yes. Picks up default or Ceph configuration value if not specified.
:Default: 8
.. describe:: {replicated|erasure}
The pool type which may either be **replicated** to
recover from lost OSDs by keeping multiple copies of the
objects or **erasure** to get a kind of
`generalized RAID5 <../erasure-code>`_ capability.
The **replicated** pools require more
raw storage but implement all Ceph operations. The
**erasure** pools require less raw storage but only
implement a subset of the available operations.
:Type: String
:Required: No.
:Default: replicated
.. describe:: [crush-rule-name]
The name of a CRUSH rule to use for this pool. The specified
rule must exist.
:Type: String
:Required: No.
:Default: For **replicated** pools it is the rule specified by the
:confval:`osd_pool_default_crush_rule` config variable. This rule must exist.
For **erasure** pools it is ``erasure-code`` if the ``default``
`erasure code profile`_ is used or ``{pool-name}`` otherwise. This
rule will be created implicitly if it doesn't exist already.
.. describe:: [erasure-code-profile=profile]
For **erasure** pools only. Use the `erasure code profile`_. It
must be an existing profile as defined by
**osd erasure-code-profile set**.
:Type: String
:Required: No.
.. _erasure code profile: ../erasure-code-profile
.. describe:: --autoscale-mode=<on,off,warn>
If you set the autoscale mode to ``on`` or ``warn``, you can let the system
autotune or recommend changes to the number of placement groups in your pool
based on actual usage. If you leave it off, then you should refer to
:ref:`placement groups` for more information.
:Type: String
:Required: No.
:Default: The default behavior is controlled by the :confval:`osd_pool_default_pg_autoscale_mode` option.
.. describe:: [expected-num-objects]
The expected number of objects for this pool. By setting this value (
together with a negative **filestore merge threshold**), the PG folder
splitting would happen at the pool creation time, to avoid the latency
impact to do a runtime folder splitting.
:Type: Integer
:Required: No.
:Default: 0, no splitting at the pool creation time.
.. _associate-pool-to-application:
Associate Pool to Application
=============================
Pools need to be associated with an application before use. Pools that will be
used with CephFS or pools that are automatically created by RGW are
automatically associated. Pools that are intended for use with RBD should be
initialized using 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.::
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``.
Set Pool Quotas
===============
You can set pool quotas for the maximum number of bytes and/or the maximum
number of objects per pool. ::
ceph osd pool set-quota {pool-name} [max_objects {obj-count}] [max_bytes {bytes}]
For example::
ceph osd pool set-quota data max_objects 10000
To remove a quota, set its value to ``0``.
Delete a Pool
=============
To delete a pool, execute::
ceph osd pool delete {pool-name} [{pool-name} --yes-i-really-really-mean-it]
To remove a pool the mon_allow_pool_delete flag must be set to true in the Monitor's
configuration. Otherwise they will refuse to remove a pool.
See `Monitor Configuration`_ for more information.
.. _Monitor Configuration: ../../configuration/mon-config-ref
If you created your own rules for a pool you created, you should consider
removing them when you no longer need your pool::
ceph osd pool get {pool-name} crush_rule
If the rule was "123", for example, you can check the other pools like so::
ceph osd dump | grep "^pool" | grep "crush_rule 123"
If no other pools use that custom rule, then it's safe to delete that
rule from the cluster.
If you created users with permissions strictly for a pool that no longer
exists, you should consider deleting those users too::
ceph auth ls | grep -C 5 {pool-name}
ceph auth del {user}
Rename a Pool
=============
To rename a pool, execute::
ceph osd pool rename {current-pool-name} {new-pool-name}
If you rename a pool and you have per-pool capabilities for an authenticated
user, you must update the user's capabilities (i.e., caps) with the new pool
name.
Show Pool Statistics
====================
To show a pool's utilization statistics, execute::
rados df
Additionally, to obtain I/O information for a specific pool or all, execute::
ceph osd pool stats [{pool-name}]
Make a Snapshot of a Pool
=========================
To make a snapshot of a pool, execute::
ceph osd pool mksnap {pool-name} {snap-name}
Remove a Snapshot of a Pool
===========================
To remove a snapshot of a pool, execute::
ceph osd pool rmsnap {pool-name} {snap-name}
.. _setpoolvalues:
Set Pool Values
===============
To set a value to a pool, execute the following::
ceph osd pool set {pool-name} {key} {value}
You may set values for the following keys:
.. _compression_algorithm:
.. describe:: compression_algorithm
Sets inline compression algorithm to use for underlying BlueStore. This setting overrides the global setting
:confval:`bluestore_compression_algorithm`.
:Type: String
:Valid Settings: ``lz4``, ``snappy``, ``zlib``, ``zstd``
.. describe:: compression_mode
Sets the policy for the inline compression algorithm for underlying BlueStore. This setting overrides the
global setting :confval:`bluestore_compression_mode`.
:Type: String
:Valid Settings: ``none``, ``passive``, ``aggressive``, ``force``
.. describe:: compression_min_blob_size
Chunks smaller than this are never compressed. This setting overrides the global settings of
:confval:`bluestore_compression_min_blob_size`, :confval:`bluestore_compression_min_blob_size_hdd` and
:confval:`bluestore_compression_min_blob_size_ssd`
:Type: Unsigned Integer
.. describe:: compression_max_blob_size
Chunks larger than this are broken into smaller blobs sizing
``compression_max_blob_size`` before being compressed.
:Type: Unsigned Integer
.. _size:
.. describe:: size
Sets the number of replicas for objects in the pool.
See `Set the Number of Object Replicas`_ for further details.
Replicated pools only.
:Type: Integer
.. _min_size:
.. describe:: min_size
Sets the minimum number of replicas required for I/O.
See `Set the Number of Object Replicas`_ for further details.
In the case of Erasure Coded pools this should be set to a value
greater than 'k' since if we allow IO at the value 'k' 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
.. _pg_num:
.. describe:: pg_num
The effective number of placement groups to use when calculating
data placement.
:Type: Integer
:Valid Range: Superior to ``pg_num`` current value.
.. _pgp_num:
.. describe:: pgp_num
The effective number of placement groups for placement to use
when calculating data placement.
:Type: Integer
:Valid Range: Equal to or less than ``pg_num``.
.. _crush_rule:
.. describe:: crush_rule
The rule to use for mapping object placement in the cluster.
:Type: String
.. _allow_ec_overwrites:
.. describe:: allow_ec_overwrites
Whether writes to an erasure coded pool can update part
of an object, so cephfs and rbd can use it. See
`Erasure Coding with Overwrites`_ for more details.
:Type: Boolean
.. versionadded:: 12.2.0
.. _hashpspool:
.. describe:: hashpspool
Set/Unset HASHPSPOOL flag on a given pool.
:Type: Integer
:Valid Range: 1 sets flag, 0 unsets flag
.. _nodelete:
.. describe:: nodelete
Set/Unset NODELETE flag on a given pool.
:Type: Integer
:Valid Range: 1 sets flag, 0 unsets flag
:Version: Version ``FIXME``
.. _nopgchange:
.. describe:: nopgchange
:Description: Set/Unset NOPGCHANGE flag on a given pool.
:Type: Integer
:Valid Range: 1 sets flag, 0 unsets flag
:Version: Version ``FIXME``
.. _nosizechange:
.. describe:: nosizechange
Set/Unset NOSIZECHANGE flag on a given pool.
:Type: Integer
:Valid Range: 1 sets flag, 0 unsets flag
:Version: Version ``FIXME``
.. _bulk:
.. describe:: bulk
Set/Unset bulk flag on a given pool.
:Type: Boolean
:Valid Range: true/1 sets flag, false/0 unsets flag
.. _write_fadvise_dontneed:
.. describe:: write_fadvise_dontneed
Set/Unset WRITE_FADVISE_DONTNEED flag on a given pool.
:Type: Integer
:Valid Range: 1 sets flag, 0 unsets flag
.. _noscrub:
.. describe:: noscrub
Set/Unset NOSCRUB flag on a given pool.
:Type: Integer
:Valid Range: 1 sets flag, 0 unsets flag
.. _nodeep-scrub:
.. describe:: nodeep-scrub
Set/Unset NODEEP_SCRUB flag on a given pool.
:Type: Integer
:Valid Range: 1 sets flag, 0 unsets flag
.. _hit_set_type:
.. describe:: hit_set_type
Enables hit set tracking for cache pools.
See `Bloom Filter`_ for additional information.
:Type: String
:Valid Settings: ``bloom``, ``explicit_hash``, ``explicit_object``
:Default: ``bloom``. Other values are for testing.
.. _hit_set_count:
.. describe:: hit_set_count
The number of hit sets to store for cache pools. The higher
the number, the more RAM consumed by the ``ceph-osd`` daemon.
:Type: Integer
:Valid Range: ``1``. Agent doesn't handle > 1 yet.
.. _hit_set_period:
.. describe:: hit_set_period
The duration of a hit set period in seconds for cache pools.
The higher the number, the more RAM consumed by the
``ceph-osd`` daemon.
:Type: Integer
:Example: ``3600`` 1hr
.. _hit_set_fpp:
.. describe:: hit_set_fpp
The false positive probability for the ``bloom`` hit set type.
See `Bloom Filter`_ for additional information.
:Type: Double
:Valid Range: 0.0 - 1.0
:Default: ``0.05``
.. _cache_target_dirty_ratio:
.. describe:: cache_target_dirty_ratio
The percentage of the cache pool containing modified (dirty)
objects before the cache tiering agent will flush them to the
backing storage pool.
:Type: Double
:Default: ``.4``
.. _cache_target_dirty_high_ratio:
.. describe:: cache_target_dirty_high_ratio
The percentage of the cache pool containing modified (dirty)
objects before the cache tiering agent will flush them to the
backing storage pool with a higher speed.
:Type: Double
:Default: ``.6``
.. _cache_target_full_ratio:
.. describe:: cache_target_full_ratio
The percentage of the cache pool containing unmodified (clean)
objects before the cache tiering agent will evict them from the
cache pool.
:Type: Double
:Default: ``.8``
.. _target_max_bytes:
.. describe:: target_max_bytes
Ceph will begin flushing or evicting objects when the
``max_bytes`` threshold is triggered.
:Type: Integer
:Example: ``1000000000000`` #1-TB
.. _target_max_objects:
.. describe:: target_max_objects
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
Temperature decay rate between two successive hit_sets
:Type: Integer
:Valid Range: 0 - 100
:Default: ``20``
.. describe:: hit_set_search_last_n
Count at most N appearance in hit_sets for temperature calculation
:Type: Integer
:Valid Range: 0 - hit_set_count
:Default: ``1``
.. _cache_min_flush_age:
.. describe:: cache_min_flush_age
The time (in seconds) before the cache tiering agent will flush
an object from the cache pool to the storage pool.
:Type: Integer
:Example: ``600`` 10min
.. _cache_min_evict_age:
.. describe:: cache_min_evict_age
The time (in seconds) before the cache tiering agent will evict
an object from the cache pool.
:Type: Integer
:Example: ``1800`` 30min
.. _fast_read:
.. describe:: fast_read
On Erasure Coding pool, if this flag is turned on, the read request
would issue sub reads to all shards, and waits until it receives enough
shards to decode to serve the client. In the case of jerasure and isa
erasure plugins, once the first K replies return, client's request is
served immediately using the data decoded from these replies. This
helps to tradeoff some resources for better performance. Currently this
flag is only supported for Erasure Coding pool.
:Type: Boolean
:Defaults: ``0``
.. _scrub_min_interval:
.. describe:: scrub_min_interval
The minimum interval in seconds for pool scrubbing when
load is low. If it is 0, the value osd_scrub_min_interval
from config is used.
:Type: Double
:Default: ``0``
.. _scrub_max_interval:
.. describe:: scrub_max_interval
The maximum interval in seconds for pool scrubbing
irrespective of cluster load. If it is 0, the value
osd_scrub_max_interval from config is used.
:Type: Double
:Default: ``0``
.. _deep_scrub_interval:
.. describe:: deep_scrub_interval
The interval in seconds for pool “deep” scrubbing. If it
is 0, the value osd_deep_scrub_interval from config is used.
:Type: Double
:Default: ``0``
.. _recovery_priority:
.. describe:: recovery_priority
When a value is set it will increase or decrease the computed
reservation priority. This value must be in the range -10 to
10. Use a negative priority for less important pools so they
have lower priority than any new pools.
:Type: Integer
:Default: ``0``
.. _recovery_op_priority:
.. describe:: recovery_op_priority
Specify the recovery operation priority for this pool instead of :confval:`osd_recovery_op_priority`.
:Type: Integer
:Default: ``0``
Get Pool Values
===============
To get a value from a pool, execute the following::
ceph osd pool get {pool-name} {key}
You may get values for 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
Set the Number of Object Replicas
=================================
To set the number of object replicas on a replicated pool, execute the following::
ceph osd pool set {poolname} size {num-replicas}
.. important:: The ``{num-replicas}`` includes the object itself.
If you want the object and two copies of the object for a total of
three instances of the object, specify ``3``.
For example::
ceph osd pool set data size 3
You may execute this 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 required replicas for I/O, you should use the ``min_size`` setting.
For example::
ceph osd pool set data min_size 2
This ensures that no object in the data pool will receive I/O with fewer than
``min_size`` replicas.
Get the Number of Object Replicas
=================================
To get the number of object replicas, execute the following::
ceph osd dump | grep 'replicated size'
Ceph will list the pools, with the ``replicated size`` attribute highlighted.
By default, ceph creates two replicas of an object (a total of three copies, or
a size of 3).
.. _Pool, PG and CRUSH Config Reference: ../../configuration/pool-pg-config-ref
.. _Bloom Filter: https://en.wikipedia.org/wiki/Bloom_filter
.. _setting the number of placement groups: ../placement-groups#set-the-number-of-placement-groups
.. _Erasure Coding with Overwrites: ../erasure-code#erasure-coding-with-overwrites
.. _Block Device Commands: ../../../rbd/rados-rbd-cmds/#create-a-block-device-pool
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