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=2in 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
On a freshly installed cluster, only the rbd pool exists.
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
8is 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 ruleconfig variable. This rule must exist. For erasure pools it iserasure-codeif thedefaulterasure 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_sizebefore 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:
0.54and above
pg_num
- Description:
The effective number of placement groups to use when calculating data placement.
- Type:
Integer
- Valid Range:
Superior to
pg_numcurrent 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:
String
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:
12.2.0and above
hashpspool
- Description:
Set/Unset HASHPSPOOL flag on a given pool.
- Type:
Integer
- Valid Range:
1 sets flag, 0 unsets flag
- Version:
Version
0.48Argonaut 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-osddaemon.- 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-osddaemon.- Type:
Integer
- Example:
36001hr
hit_set_fpp
- Description:
The false positive probability for the
bloomhit 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_bytesthreshold is triggered.- Type:
Integer
- Example:
1000000000000#1-TB
target_max_objects
- Description:
Ceph will begin flushing or evicting objects when the
max_objectsthreshold 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:
60010min
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:
180030min
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
recovery_priority
- Description:
When a value is set it will boost the computed reservation priority by this amount. This value should be less than 30.
- 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:
0.54and 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:
- Type:
Double
cache_target_dirty_high_ratio
- Description:
- Type:
Double
cache_target_full_ratio
- Description:
- Type:
Double
target_max_bytes
- Description:
see target_max_bytes
- Type:
Integer
target_max_objects
- Description:
- Type:
Integer
cache_min_flush_age
- Description:
- Type:
Integer
cache_min_evict_age
- Description:
- Type:
Integer
fast_read
- Description:
see fast_read
- Type:
Boolean
scrub_min_interval
- Description:
- Type:
Double
scrub_max_interval
- Description:
- Type:
Double
deep_scrub_interval
- Description:
- Type:
Double
allow_ec_overwrites
- Description:
- Type:
Boolean
recovery_priority
- Description:
- Type:
Integer
recovery_op_priority
- Description:
- 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).
Table Of Contents
- Intro to Ceph
- Installation (ceph-deploy)
- Installation (Manual)
- Ceph Storage Cluster
- Configuration
- Deployment
- Operations
- Operating a Cluster
- Health checks
- Monitoring a Cluster
- Monitoring OSDs and PGs
- User Management
- Data Placement Overview
- Pools
- Erasure code
- Cache Tiering
- Placement Groups
- Using the pg-upmap
- CRUSH Maps
- Manually editing a CRUSH Map
- Adding/Removing OSDs
- Adding/Removing Monitors
- BlueStore Migration
- Command Reference
- The Ceph Community
- Troubleshooting Monitors
- Troubleshooting OSDs
- Troubleshooting PGs
- Logging and Debugging
- CPU Profiling
- Memory Profiling
- Man Pages
- Troubleshooting
- APIs
- Ceph Filesystem
- Ceph Block Device
- Ceph Object Gateway
- Ceph Manager Daemon
- API Documentation
- Architecture
- Development
- ceph-volume
- Release Notes
- Ceph Releases
- Glossary