Creating pools

Learn how to create a pool. Pools can be replicated, erasure-coded, or as bulk.

Before you begin

See Pools, placement groups, and CRUSH configuration.

Note: The system administrators must expressly enable a pool to receive I/O operations from Ceph clients. See Enabling a client application for details. Failure to enable a pool results in a HEALTH_WARN status.

Based on the requirement, you can create a replicated pool, an erasure-coded pool, or a bulk pool.

About this task

When you create a pool, set the number of placement groups to a reasonable value (for example to 100). Consider the total number of placement groups per OSD too. Placement groups are computationally expensive, so performance degrades when you have many pools with many placement groups, for example, 50 pools with 100 placement groups each. The point of diminishing returns depends upon the power of the OSD host.

Creating a replicated pool
Creating an erasure-coded pool
Creating a bulk pool

In the examples, replace the variable names as follows:

POOL_NAME

Description: The name of the pool. It must be unique.
Type: String
Required: Yes. If not specified, it is set to the default value or manually set with the ceph config set command.
Default: ceph

PG_NUM

Description: The total number of placement groups for the pool. For more information about calculating a suitable number, see Placement groups and Ceph Placement Groups (PGs) per Pool Calculator on the Red Hat Customer Portal. 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 value must be equal to the total number of placement groups, except for placement group splitting scenarios.
Type: Integer
Required: Yes. If not specified it is set to the value listed or to the default value.
Default: 8

replicated or erasure

Description: The pool type can be either replicated to recover from lost OSDs by keeping multiple copies of the objects or erasure to get a generalized RAID5 capability. The replicated pools require more raw storage but implement all Ceph operations. The erasure-coded pools require less raw storage but implement only a subset of the available operations.
Type: String
Required: No
Default: replicated

crush-rule-name

Description: The name of the crush rule for the pool. The rule must exist. For replicated pools, the name is the rule that is specified by the osd_pool_default_crush_rule configuration setting. For erasure-coded pools the name is erasure-code if you specify the default erasure code profile or POOL_NAME otherwise. Ceph creates this rule with the specified name implicitly if the rule doesn’t exist.
Type: String
Required: No
Default: Uses erasure-code for an erasure-coded pool. For replicated pools, it uses the value of the osd_pool_default_crush_rule variable from the Ceph configuration.

expected-num-objects

Description: The expected number of objects for the pool. Ceph splits the placement groups at pool creation time to avoid the latency impact to perform runtime directory splitting.
Type: Integer
Required: No
Default: 0, no splitting at the pool creation time.

erasure-code-profile

Description: For erasure-coded pools only. Use the erasure code profile. It must be an existing profile as defined by the osd erasure-code-profile set variable in the Ceph configuration file. For more information, see Erasure code profiles.
Type: String
Required: No

Creating a replicated pool

ceph osd pool create POOL_NAME PG_NUM PGP_NUM [replicated] [CRUSH_RULE_NAME] [EXPECTED_NUMBER_OBJECTS]

Creating an erasure-coded pool

ceph osd pool create POOL_NAME PG_NUM PGP_NUM [erasure] ERASURE_CODE_PROFILE
         [CRUSH_RULE_NAME] [EXPECTED_NUMBER_OBJECTS]

Creating a bulk pool

```
ceph osd pool create POOL_NAME [--bulk]
```