A very interesting question and I would add the follow up question:

Is there an easy way to add an external DB/WAL devices to an existing

I suspect that it might be something on the lines of:

- stop osd
- create a link in ...ceph/osd/ceph-XX/block.db to the target device
- (maybe run some kind of osd mkfs ?)
- start osd

Has anyone done this so far or recommendations on how to do it?

Which also makes me wonder: what is actually the format of WAL and
BlockDB in bluestore? Is there any documentation available about it?



Caspar Smit <caspars...@supernas.eu> writes:

> Hi All,
> What would be the proper way to preventively replace a DB/WAL SSD (when it
> is nearing it's DWPD/TBW limit and not failed yet).
> It hosts DB partitions for 5 OSD's
> Maybe something like:
> 1) ceph osd reweight 0 the 5 OSD's
> 2) let backfilling complete
> 3) destroy/remove the 5 OSD's
> 4) replace SSD
> 5) create 5 new OSD's with seperate DB partition on new SSD
> When these 5 OSD's are big HDD's (8TB) a LOT of data has to be moved so i
> thought maybe the following would work:
> 1) ceph osd set noout
> 2) stop the 5 OSD's (systemctl stop)
> 3) 'dd' the old SSD to a new SSD of same or bigger size
> 4) remove the old SSD
> 5) start the 5 OSD's (systemctl start)
> 6) let backfilling/recovery complete (only delta data between OSD stop and
> now)
> 6) ceph osd unset noout
> Would this be a viable method to replace a DB SSD? Any udev/serial nr/uuid
> stuff preventing this to work?
> Or is there another 'less hacky' way to replace a DB SSD without moving too
> much data?
> Kind regards,
> Caspar
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