Re: Moving devices to a different device class?

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Thanks Janne,

 It is good to know that moving the devices over to a new class is a safe

On Tue, Oct 24, 2023 at 2:16 PM Janne Johansson <> 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.
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