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.
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.
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 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 |
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).