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Chapter 7. Setting placement group auto-scaling modes

Each pool in the Red Hat Ceph Storage cluster has a pg_autoscale_mode property for PGs that you can set to off, on, or warn.

  • off: Disables auto-scaling for the pool. It is up to the administrator to choose an appropriate PG number for each pool. Refer to the Placement group count section for more information.
  • on: Enables automated adjustments of the PG count for the given pool.
  • warn: Raises health alerts when the PG count needs adjustment.
Note

In Red Hat Ceph Storage 5 and later releases, pg_autoscale_mode is on by default. Upgraded storage clusters retain the existing pg_autoscale_mode setting. The pg_auto_scale mode is on for the newly created pools. PG count is automatically adjusted, and ceph status might display a recovering state during PG count adjustment.

The autoscaler uses the bulk flag to determine which pool should start with a full complement of PGs and only scales down when the usage ratio across the pool is not even. However, if the pool does not have the bulk flag, the pool starts with minimal PGs and only when there is more usage in the pool.

Note

The autoscaler identifies any overlapping roots and prevents the pools with such roots from scaling because overlapping roots can cause problems with the scaling process.

Procedure

  • Enable auto-scaling on an existing pool:

    Syntax

    ceph osd pool set POOL_NAME pg_autoscale_mode on
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    Example

    [ceph: root@host01 /]# ceph osd pool set testpool pg_autoscale_mode on
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  • Enable auto-scaling on a newly created pool:

    Syntax

    ceph config set global osd_pool_default_pg_autoscale_mode MODE
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    Example

    [ceph: root@host01 /]# ceph config set global osd_pool_default_pg_autoscale_mode on
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  • Create a pool with the bulk flag:

    Syntax

    ceph osd pool create POOL_NAME --bulk
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    Example

    [ceph: root@host01 /]#  ceph osd pool create testpool --bulk
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  • Set or unset the bulk flag for an existing pool:

    Important

    The values must be written as true, false, 1, or 0. 1 is equivalent to true and 0 is equivalent to false. If written with different capitalization, or with other content, an error is emitted.

    The following is an example of the command written with the wrong syntax: 

    [ceph: root@host01 /]# ceph osd pool set ec_pool_overwrite bulk True
Error EINVAL: expecting value 'true', 'false', '0', or '1'
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    Syntax

    ceph osd pool set POOL_NAME bulk true/false/1/0
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    Example

    [ceph: root@host01 /]#  ceph osd pool set testpool bulk true
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  • Get the bulk flag of an existing pool:

    Syntax

    ceph osd pool get POOL_NAME bulk
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    Example

    [ceph: root@host01 /]# ceph osd pool get testpool bulk
bulk: true
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