Hi,
On 22.06.21 11:55, Thomas Roth wrote:
Hi all,
newbie question:
The documentation seems to suggest that with ceph-volume, one OSD is
created for each HDD (cf. 4-HDD-example in
https://docs.ceph.com/en/latest/rados/configuration/bluestore-config-ref/)
This seems odd: what if a server has a finite number of disks? I was
going to try cephfs on ~10 servers with 70 HDD each. That would make
each system having to deal with 70 OSDs, on 70 LVs?
Really no aggregation of the disks?
The recommendation is one OSD per HDD. And most deployment tools
(ceph-ansible / cephadm) follow this guide. The main reason is keeping
the single failure unit small. Using raid with several HDDs might result
in 10-20 TB of data to be recovered if a single disk fails. The same
goes for large storage boxes; just imagine a complete unrecoverable
failure of a box with 70x 10TB disks. More data to recover results in
longer recovery time, which increases the probability for a second or
(usually fatal) third failure.
If you plan to use other setups you either need to adopt the deployment
tools (should be possible with ceph-ansible, difficult in case of
cephadm), or deploy the OSDs manually.
We use manual deployment and linux software raid with raid level 0 and
two/three disks in larger storage boxes, also due to the memory /CPU
core requirements.
Regards,
Burkhard
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