https://docs.ceph.com/docs/master/rados/operations/bluestore-migration/
https://blog.widodh.nl/2018/01/placement-groups-with-ceph-luminous-stay-in-activating-state/
http://www.youtube.com/watch?v=kzTgIcp4FfY&t=16m0s
Todo.. Needs precise steps/commands - for various envs.