Thanks Janne, It is good to know that moving the devices over to a new class is a safe operation. On Tue, Oct 24, 2023 at 2:16 PM Janne Johansson <icepic.dz@gmail.com> wrote:
The documentation describes that I could set a device class for an OSD with a command like:
`ceph osd crush set-device-class CLASS OSD_ID [OSD_ID ..]`
Class names can be arbitrary strings like 'big_nvme". Before setting a new device class to an OSD that already has an assigned device class, should use `ceph osd crush rm-device-class ssd osd.XX`.
Yes, you can re-"name" them by removing old class and setting a new one.
Can I proceed to directly remove these OSDs from the current device class and assign to a new device class? Should they be moved one by one? What is the way to safely protect data from the existing pool that they are mapped to?
Yes, the PGs on them will be misplaced, so if their pool aims to only use "ssd" and you re-label them to big-nvme instead, the PGs will look for other "ssd"-named OSDs to land on, and move themselves if possible. It is a fairly safe operation where they continue to work, but will try to evacuate the PGs which should not be there.
Worst case, your planning is wrong, and the "ssd" OSDs can't accept them, and you can just undo the relabel and the PGs come back.
-- May the most significant bit of your life be positive.
-- Matt Larson, PhD Madison, WI 53705 U.S.A.