Local Pool Module

The localpool module can automatically create RADOS pools that are localized to a subset of the overall cluster. For example, by default, it will create a pool for each distinct rack in the cluster. This can be useful for deployments where it is desirable to distribute some data locally and other data globally across the cluster. One use-case is measuring performance and testing behavior of specific drive, NIC, or chassis models in isolation.


The localpool module is enabled with:

ceph mgr module enable localpool


The localpool module understands the following options:

  • subtree (default: rack): which CRUSH subtree type the module should create a pool for.

  • failure_domain (default: host): what failure domain we should separate data replicas across.

  • pg_num (default: 128): number of PGs to create for each pool

  • num_rep (default: 3): number of replicas for each pool. (Currently, pools are always replicated.)

  • min_size (default: none): value to set min_size to (unchanged from Ceph’s default if this option is not set)

  • prefix (default: by-$subtreetype-): prefix for the pool name.

These options are set via the config-key interface. For example, to change the replication level to 2x with only 64 PGs,

ceph config set mgr mgr/localpool/num_rep 2
ceph config set mgr mgr/localpool/pg_num 64