Pools

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 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 to provide optimal balancing without using up too many computing resources. When setting up multiple pools, be careful to ensure you set a reasonable number of placement groups for both the pool and the cluster as a whole.
• 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.

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 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 = 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 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

{pgp-num}

Description: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

{replicated|erasure}

Description: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 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

[crush-rule-name]

Description: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 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.

[erasure-code-profile=profile]

Description: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.

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 when you have many pools with many placement groups (e.g., 50 pools with 100 placement groups each). The point of diminishing returns depends upon the power of the OSD host.

See Placement Groups for details on calculating an appropriate number of placement 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 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

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.

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.

Note

Version 0.48 Argonaut and above.

Show Pool Statistics

To show a pool’s utilization statistics, execute:

rados df

Make a Snapshot of a Pool

To make a snapshot of a pool, execute:

ceph osd pool mksnap {pool-name} {snap-name}

Note

Version 0.48 Argonaut and above.

Remove a Snapshot of a Pool

To remove a snapshot of a pool, execute:

ceph osd pool rmsnap {pool-name} {snap-name}

Note

Version 0.48 Argonaut and above.

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 sizing compression_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 calculating data placement. Type:Integer Valid Range:Superior to pg_num current value.

pgp_num

Description: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

Description:The rule to use for mapping object placement in the cluster. Type:Integer

allow_ec_overwrites

Description: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 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 Version:Version 0.48 Argonaut and above.

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 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

Description: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

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 the backing 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 the backing 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 the cache pool. Type:Double Default:.8

target_max_bytes

Description:Ceph will begin flushing or evicting objects when the max_bytes threshold is triggered. Type:Integer Example:1000000000000 #1-TB

target_max_objects

Description:Ceph will begin flushing or evicting objects when the max_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 flush an 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 evict an 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 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

Description: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

Description: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

Description: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

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

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).