CRUSH on single host
The CRUSH algorithm intends to distribute objects across different hosts, so if
you set up all OSDs on the same host, CRUSH will complians. For instance,
a Ceph cluster with 3 OSDs on single host will likely get a 65 active, 54
active+degraded, 73 active+remapped state when fresh-deployed, which was
supposed to be 192 active+clean.