Dear all I have a ceph cluster where so far all OSDs have been rotational hdd disks (actually there are some SSDs, used only for block.db and wal.db) I now want to add some SSD disks to be used as OSD. My use case is: 1) for the existing pools keep using only hdd disks 2) create some new pools using only sdd disks Let's start with 1 (I didn't have added yet the ssd disks in the cluster) I have some replicated pools and some ec pools. The replicated pools are using a replicated_ruleset rule [*]. I created a new "replicated_hdd" rule [**] using the command: ceph osd crush rule create-replicated replicated_hdd default host hdd I then changed the crush rule of a existing pool (that was using 'replicated_ruleset') using the command: ceph osd pool set <poolname> crush_rule replicated_hdd This triggered the remapping of some pgs and therefore some data movement. Is this normal/expected, since for the time being I have only hdd osds ? Thanks, Massimo [*] rule replicated_ruleset { id 0 type replicated min_size 1 max_size 10 step take default step chooseleaf firstn 0 type host step emit } [**] rule replicated_hdd { id 7 type replicated min_size 1 max_size 10 step take default class hdd step chooseleaf firstn 0 type host step emit }