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Chapter 20. Create a Pool
Before creating pools, refer to the Pool, PG and CRUSH Config section of the Ceph Configuration Guide. Consider overriding the default value for the number of placement groups in you Ceph configuration file, as the default is NOT ideal. 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-ruleset-name]
ceph osd pool create <pool-name> <pg-num> <pgp-num> erasure \
[erasure-code-profile] [crush-ruleset-name]Where:
<pool-name>
- Description
- The name of the pool. It must be unique.
- Type
- String
- Required
- Yes. Picks up default or Ceph configuration value if not specified.
<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. Also, see Ceph Placement Groups per Pool Calculator. - 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 or 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-ruleset-name]
- Description
- The name of the crush ruleset for this pool. If specified ruleset doesn’t exist, the creation of replicated pool will fail with -ENOENT. But replicated pool will create a new erasure ruleset with specified name.
- Type
- String
- Required
- No.
- Default
- "erasure-code" for erasure pool. Pick up Ceph configuration variable osd_pool_default_crush_replicated_ruleset for replicated pool.
[erasure-code-profile=profile]
- Description
- For erasure pools only. Use the erasure code profiles. 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. Also see Ceph Placement Groups (PGs) per Pool Calculator.
