How to remove OSD from Ceph cluster

It is not well described in the docs.

Look into OSD list (ceph osd tree). Select one you want to remove. Let’s say it is an ‘osd.11’.

1. Mark it ‘out’: ceph osd out osd.11
   If you see “osd.11 is already out” — it’s ok.
2. Mark it as ‘down’: ceph osd down osd.11
3. Remove it: ceph osd rm osd.11. If it says ‘Error EBUSY: osd.11 is still up; must be down before removal.’ that means OSD is not dead yet. Go to the host it resides on and kill it (systemctl stop ceph-osd@11), and repeat rm operation.
4. Now it would list in ceph osd tree with ‘DNE’ status (DNE = do not exists). To clean up this status, remove it from CRUSH map: ceph osd crush rm osd.11
5. Last step: remove it authorization (it should prevent problems with 'couldn’t add new osd with same number’): ceph auth del osd.11.

Please note: in the real life you should be really careful not to damage data on the OSD, so this instruction should be used only for dead OSDs without any hope for recover.