Chapter 9. Setting placement group auto-scaling

Allowing the cluster to automatically scale PGs based on cluster usage is the simplest approach to scaling PGs. Red Hat Ceph Storage takes the total available storage and the target number of PGs for the whole system, compares how much data is stored in each pool, and apportions the PGs accordingly. The command only makes changes to a pool whose current number of PGs (pg_num) is more than three times off from the calculated or suggested PG number.

The target number of PGs per OSD is based on the mon_target_pg_per_osd configurable. The default value is set to 100.