Which Ceph release?
> On Aug 7, 2025, at 10:18 AM, Robert Sander <[email protected]>
> wrote:
>
> Hi,
>
> we have OSD nodes currently consisting of two 605GB SSDs and six 18TB
> HDDs. The hosts have room for twelve HDDs.
>
> We created a drivegroup spec that looks like this:
>
> spec:
> block_db_size: 100GB
> data_devices:
> rotational: true
> size: '18TB:'
> db_devices:
> rotational: false
> size: '550GB:650GB'
> db_slots: 6
block_db_size and db_slots are meant to be mutually exclusive. The former
specifies the size of a slice; the latter says to divide up the device into N
even slices.
That said, it's not entirely clear that db_slots always works as expected. I
would leave it out.
What manner of SSD is 605GB?
>
> Initially this creates 6 OSDs with their RocksDB+WAL on the SSDs,
> 3 each which is nice for load balancing.
>
> But when we add another HDD it gets a 17.9TB data volume and a 100GB DB
Is it the same HDD SKU as existing OSDs? You could be suffering from this new
HDD being ever so slightly smaller than the existing HDDs, and from base 2
units (TiB) vs base 10 (TB). Which is likely the same reason you have a size
range for the DB device spec.
I suggest:
set the OSD service to unmanaged
thoroughly zap the new HDD until it shows completely empty
take out db_slots
change the osdspec to
size: '15TB:'
Then see if you get the results you expect.
> volume, both on the HDD:
>
> sdm
> 8:192 0 18T 0 disk
> ├─ceph--846e1a59--aff6--4ef8--9b71--de7241531677-osd--block--026e8cef--123d--47d9--9b30--211f94edf96c
> 252:16 0 17.9T 0 lvm
> └─ceph--846e1a59--aff6--4ef8--9b71--de7241531677-osd--db--88c47d0b--f5c6--4cec--8909--c5f8036ca459
> 252:17 0 100G 0 lvm
>
>
> I would have assumed that the remaining 305GB on the SSDs would be used.
>
> How do we achieve this?
>
> Regards
> --
> Robert Sander
> Heinlein Consulting GmbH
> Schwedter Str. 8/9b, 10119 Berlin
>
> http://www.heinlein-support.de
>
> Tel: 030 / 405051-43
> Fax: 030 / 405051-19
>
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