Auto-scaling placement groups

Auto-scaling the number of PGs can make managing the cluster easier. The number of placement groups (PGs) in a pool plays a significant role in how a cluster peers, distributes data, and rebalances.

The auto-scaler analyzes pools and adjusts on a per-subtree basis.

Because each pool can map to a different CRUSH rule, and each rule can distribute data across different devices, Ceph considers utilization of each subtree of the hierarchy independently. For example, a pool that maps to OSDs of class ssd, and a pool that maps to OSDs of class hdd, will each have optimal PG counts that depend on the number of those respective device types.

The pg-autoscaling command provides recommendations for scaling PGs, or automatically scales PGs based on how the cluster is being used.

• To enable, or disable auto-scaling, see Setting placement group auto-scaling modes.
• To view placement group scaling recommendations, see Viewing placement group scaling recommendations.
• To set placement group auto-scaling, see Configuring placement group auto-scaling.
• To manually update autoscaler profile, see Manually updating autoscaler profile for a pool.
• To update the autoscaler globally, see Updating noautoscale flag.
• To set target pool size, see Specifying target pool size.