Chapter 8. Viewing placement group scaling recommendations

You can view the pool, it’s relative utilization and any suggested changes to the PG count in the storage cluster.

SIZE is the amount of data stored in the pool.

TARGET SIZE, if present, is the amount of data the administrator has specified they expect to eventually be stored in this pool. The system uses the larger of the two values for its calculation.

RATE is the multiplier for the pool that determines how much raw storage capacity the pool uses. For example, a 3 replica pool has a ratio of 3.0, while a k=4,m=2 erasure coded pool has a ratio of 1.5.

RAW CAPACITY is the total amount of raw storage capacity on the OSDs that are responsible for storing the pool’s data.

RATIO is the ratio of the total capacity that the pool is consuming, that is, ratio = size * rate / raw capacity.

TARGET RATIO, if present, is the ratio of storage the administrator has specified that they expect the pool to consume relative to other pools with target ratios set. If both target size bytes and ratio are specified, the ratio takes precedence. The default value of TARGET RATIO is 0 unless it was specified while creating the pool. The more the --target_ratio you give in a pool, the larger the PGs you are expecting the pool to have.

EFFECTIVE RATIO, is the target ratio after adjusting in two ways: 1. subtracting any capacity expected to be used by pools with target size set. 2. normalizing the target ratios among pools with target ratio set so they collectively target the rest of the space. For example, 4 pools with target ratio 1.0 would have an effective ratio of 0.25. The system uses the larger of the actual ratio and the effective ratio for its calculation.

BIAS, is used as a multiplier to manually adjust a pool’s PG based on prior information about how much PGs a specific pool is expected to have. By default, the value if 1.0 unless it was specified when creating a pool. The more --bias you give in a pool, the larger the PGs you are expecting the pool to have.

PG_NUM is the current number of PGs for the pool, or the current number of PGs that the pool is working towards, if a pg_num change is in progress. NEW PG_NUM, if present, is the suggested number of PGs (pg_num). It is always a power of 2, and is only present if the suggested value varies from the current value by more than a factor of 3.

AUTOSCALE, is the pool pg_autoscale_mode, and is either on, off, or warn.

BULK, is used to determine which pool should start out with a full complement of PGs. BULK only scales down when the usage ratio cross the pool is not even. If the pool does not have this flag the pool starts out with a minimal amount of PGs and only used when there is more usage in the pool.

The BULK values are true, false, 1, or 0, where 1 is equivalent to true and 0 is equivalent to false. The default value is false.

Set the BULK value either during or after pool creation.

For more information about using the bulk flag, see Creating a pool and Setting placement group auto-scaling modes.