Sometimes it is necessary to copy Ceph pool objects from one Ceph pool to another - such as when changing CRUSH/erasure rule sets on an expanding cluster. There is a built-in command in RADOS for doing this. However the command in question, rados cppool , has some limitations. It only seems to work with replicated target pools. Thus it cannot copy Ceph pool objects from a erasure pool to a replicated pool, or between erasure pools.