[ceph-users] Questions about the CRUSH details

Hello, I'm new to ceph and sorry in advance for the naive questions. 1. As far as I know, CRUSH utilizes the cluster map consisting of the PG map and others. I don't understand why CRUSH computation is required on client-side, even though PG-to-OSDs mapping can be acquired from the PG map. 2. how does the client get a valid(old) OSD set when the PG is being remapped to a new ODS set which CRUSH returns? thanks.