Pools

When you first deploy a cluster without creating a pool, Ceph uses the defaultpools 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 one additional copy(i.e., size = 2), but you can determine the number of copies/replicas.For erasure coded pools, 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 uses approximately 100 placement groups per OSD toprovide optimal balancing without using up too many computing resources. Whensetting up multiple pools, be careful to ensure you set a reasonable number ofplacement groups for both the pool and the cluster as a whole.

• CRUSH Rules: When you store data in a pool, placement of the objectand its replicas (or chunks for erasure coded pools) in your cluster is governedby CRUSH rules. You can create a custom CRUSH rule for your pool if the defaultrule 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.

List Pools

To list your cluster’s pools, execute:

ceph osd lspools

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 placementgroups 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 theapplication using the pool. See Associate Pool to Application below formore information.

For example:

osd pool default pg num = 100
osd pool default pgp num = 100

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]

Where:

{pool-name}

• Description

• The name of the pool. It must be unique.

• Type

• String

• Required

• Yes.

{pg-num}

• Description

• The total number of placement groups for the pool. See PlacementGroups for details on calculating a suitable number. Thedefault value 8 is NOT suitable for most systems.

• Type

• Integer

• Required

• Yes.

• Default

• 8

{pgp-num}

• Description

• The total number of placement groups for placement purposes. Thisshould be equal to the total number of placement groups, exceptfor placement group splitting scenarios.

• Type

• Integer

• Required

• Yes. Picks up default or Ceph configuration value if not specified.

• Default

• 8

{replicated|erasure}

• Description

• The pool type which may either be replicated torecover from lost OSDs by keeping multiple copies of theobjects or erasure to get a kind ofgeneralized RAID5 capability.The replicated pools require moreraw storage but implement all Ceph operations. Theerasure pools require less raw storage but onlyimplement a subset of the available operations.

• Type

• String

• Required

• No.

• Default

• replicated

[crush-rule-name]

• Description

• The name of a CRUSH rule to use for this pool. The specifiedrule must exist.

• Type

• String

• Required

• No.

• Default

• For replicated pools it is the rule specified by the osdpool default crush rule config variable. This rule must exist.For erasure pools it is erasure-code if the defaulterasure code profile is used or {pool-name} otherwise. Thisrule will be created implicitly if it doesn’t exist already.

[erasure-code-profile=profile]

• Description

• For erasure pools only. Use the erasure code profile. Itmust be an existing profile as defined byosd erasure-code-profile set.

• Type

• String

• Required

• No.

When you create a pool, set the number of placement groups to a reasonable value(e.g., 100). Consider the total number of placement groups per OSD too.Placement groups are computationally expensive, so performance will degrade whenyou have many pools with many placement groups (e.g., 50 pools with 100placement groups each). The point of diminishing returns depends upon the powerof the OSD host.

See Placement Groups for details on calculating an appropriate number ofplacement groups for your pool.

[expected-num-objects]

• Description

• The expected number of objects for this pool. By setting this value (together with a negative filestore merge threshold), the PG foldersplitting would happen at the pool creation time, to avoid the latencyimpact to do a runtime folder splitting.

• Type

• Integer

• Required

• No.

• Default

• 0, no splitting at the pool creation time.

Associate Pool to Application

Pools need to be associated with an application before use. Pools that will beused with CephFS or pools that are automatically created by RGW areautomatically associated. Pools that are intended for use with RBD should beinitialized using the rbd tool (see Block Device Commands for moreinformation).

For other cases, you can manually associate a free-form application name toa pool.:

ceph osd pool application enable {pool-name} {application-name}

Note

CephFS uses the application name cephfs, RBD uses theapplication 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 maximumnumber 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’sconfiguration. Otherwise they will refuse to remove a pool.

See Monitor Configuration for more information.

If you created your own rules for a pool you created, you should considerremoving 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 thatrule from the cluster.

If you created users with permissions strictly for a pool that no longerexists, 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 authenticateduser, you must update the user’s capabilities (i.e., caps) with the new poolname.

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}

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

• Description

• Sets inline compression algorithm to use for underlying BlueStore. This setting overrides the global setting of bluestore compression algorithm.

• Type

• String

• Valid Settings

• lz4, snappy, zlib, zstd

compression_mode

• Description

• Sets the policy for the inline compression algorithm for underlying BlueStore. This setting overrides the global setting of bluestore compression mode.

• Type

• String

• Valid Settings

• none, passive, aggressive, force

compression_min_blob_size

• Description

• Chunks smaller than this are never compressed. This setting overrides the global setting of bluestore compression min blob *.

• Type

• Unsigned Integer

compression_max_blob_size

• Description

• Chunks larger than this are broken into smaller blobs sizingcompression_max_blob_size before being compressed.

• Type

• Unsigned Integer

size

• Description

• 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

• Description

• Sets the minimum number of replicas required for I/O.See Set the Number of Object Replicas for further details.Replicated pools only.

• Type

• Integer

• Version

• 0.54 and above

pg_num

• Description

• The effective number of placement groups to use when calculatingdata placement.

• Type

• Integer

• Valid Range

• Superior to pg_num current value.

pgp_num

• Description

• The effective number of placement groups for placement to usewhen calculating data placement.

• Type

• Integer

• Valid Range

• Equal to or less than pg_num.

crush_rule

• Description

• The rule to use for mapping object placement in the cluster.

• Type

• String

allow_ec_overwrites

• Description

• Whether writes to an erasure coded pool can update partof an object, so cephfs and rbd can use it. SeeErasure Coding with Overwrites for more details.

• Type

• Boolean

• Version

• 12.2.0 and above

hashpspool

• Description

• Set/Unset HASHPSPOOL flag on a given pool.

• Type

• Integer

• Valid Range

• 1 sets flag, 0 unsets flag

nodelete

• Description

• Set/Unset NODELETE flag on a given pool.

• Type

• Integer

• Valid Range

• 1 sets flag, 0 unsets flag

• Version

• Version FIXME

nopgchange

• Description

• Set/Unset NOPGCHANGE flag on a given pool.

• Type

• Integer

• Valid Range

• 1 sets flag, 0 unsets flag

• Version

• Version FIXME

nosizechange

• Description

• Set/Unset NOSIZECHANGE flag on a given pool.

• Type

• Integer

• Valid Range

• 1 sets flag, 0 unsets flag

• Version

• Version FIXME

write_fadvise_dontneed

• Description

• Set/Unset WRITE_FADVISE_DONTNEED flag on a given pool.

• Type

• Integer

• Valid Range

• 1 sets flag, 0 unsets flag

noscrub

• Description

• Set/Unset NOSCRUB flag on a given pool.

• Type

• Integer

• Valid Range

• 1 sets flag, 0 unsets flag

nodeep-scrub

• Description

• Set/Unset NODEEP_SCRUB flag on a given pool.

• Type

• Integer

• Valid Range

• 1 sets flag, 0 unsets flag

hit_set_type

• Description

• 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

• Description

• The number of hit sets to store for cache pools. The higherthe number, the more RAM consumed by the ceph-osd daemon.

• Type

• Integer

• Valid Range

• 1. Agent doesn’t handle > 1 yet.

hit_set_period

• Description

• The duration of a hit set period in seconds for cache pools.The higher the number, the more RAM consumed by theceph-osd daemon.

• Type

• Integer

• Example

• 3600 1hr

hit_set_fpp

• Description

• 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

• Description

• The percentage of the cache pool containing modified (dirty)objects before the cache tiering agent will flush them to thebacking storage pool.

• Type

• Double

• Default

• .4

cache_target_dirty_high_ratio

• Description

• The percentage of the cache pool containing modified (dirty)objects before the cache tiering agent will flush them to thebacking storage pool with a higher speed.

• Type

• Double

• Default

• .6

cache_target_full_ratio

• Description

• The percentage of the cache pool containing unmodified (clean)objects before the cache tiering agent will evict them from thecache pool.

• Type

• Double

• Default

• .8

target_max_bytes

• Description

• Ceph will begin flushing or evicting objects when themax_bytes threshold is triggered.

• Type

• Integer

• Example

• 1000000000000 #1-TB

target_max_objects

• Description

• Ceph will begin flushing or evicting objects when themax_objects threshold is triggered.

• Type

• Integer

• Example

• 1000000 #1M objects

hit_set_grade_decay_rate

• Description

• Temperature decay rate between two successive hit_sets

• Type

• Integer

• Valid Range

• 0 - 100

• Default

• 20

hit_set_search_last_n

• Description

• 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

• Description

• The time (in seconds) before the cache tiering agent will flushan object from the cache pool to the storage pool.

• Type

• Integer

• Example

• 600 10min

cache_min_evict_age

• Description

• The time (in seconds) before the cache tiering agent will evictan object from the cache pool.

• Type

• Integer

• Example

• 1800 30min

fast_read

• Description

• On Erasure Coding pool, if this flag is turned on, the read requestwould issue sub reads to all shards, and waits until it receives enoughshards to decode to serve the client. In the case of jerasure and isaerasure plugins, once the first K replies return, client’s request isserved immediately using the data decoded from these replies. Thishelps to tradeoff some resources for better performance. Currently thisflag is only supported for Erasure Coding pool.

• Type

• Boolean

• Defaults

• 0

scrub_min_interval

• Description

• The minimum interval in seconds for pool scrubbing whenload is low. If it is 0, the value osd_scrub_min_intervalfrom config is used.

• Type

• Double

• Default

• 0

scrub_max_interval

• Description

• The maximum interval in seconds for pool scrubbingirrespective of cluster load. If it is 0, the valueosd_scrub_max_interval from config is used.

• Type

• Double

• Default

• 0

deep_scrub_interval

• Description

• The interval in seconds for pool “deep” scrubbing. If itis 0, the value osd_deep_scrub_interval from config is used.

• Type

• Double

• Default

• 0

recovery_priority

• Description

• When a value is set it will increase or decrease the computedreservation priority. This value must be in the range -10 to10. Use a negative priority for less important pools so theyhave lower priority than any new pools.

• Type

• Integer

• Default

• 0

recovery_op_priority

• Description

• Specify the recovery operation priority for this pool instead of 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 ofthree 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 acceptI/Os in degraded mode with fewer than pool size replicas. To set a minimumnumber 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 thanmin_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, ora size of 3).