However the meta-data is saved in a different LV, isn't it? I.e. isn't practically the same as if you'd have used gpt partitions?
No, its not, it is saved in LVM tags. LVM takes care of storing these in a transparent way somewhere else than in a separate partition. Best regards, ================= Frank Schilder AIT Risø Campus Bygning 109, rum S14 ________________________________________ From: Nico Schottelius <nico.schottelius@ungleich.ch> Sent: 25 March 2021 13:29:10 To: Frank Schilder Cc: Marc; Nico Schottelius; ceph-users@ceph.io Subject: Re: [ceph-users] Re: LVM vs. direct disk acess Frank Schilder <frans@dtu.dk> writes:
I think there are a couple of reasons for LVM OSDs:
- bluestore cannot handle multi-path devices, you need LVM here - the OSD meta-data does not require a separate partition
However the meta-data is saved in a different LV, isn't it? I.e. isn't practically the same as if you'd have used gpt partitions?
- it is easy to provision 2 or more OSDs per disk - LVM's dm_cache is an alternative to separate block/db devices with the features that it can be dynamically re-sized at run-time and also allows to deviate from the 3/30/300 without wasting fast storage capacity; for example, we plan to have 1TB dm_cache per spinning disk on NVMe in the future; this would not only fit WAL/DB, it would also cache hot data; in addition one can configure it not to promote on first hit to prevent cache wiping by backup software
The last one is actually quite interesting and I've added it to our ceph todo list for the future.
I find it much easier to administrate LVM OSDs, I'm also using customized scripts and the ceph/volume lvm command suite simplifies things a lot.
Thanks a lot for the feedback, this is really helpful for us to see real use cases on LVM. Best regards from sunny Switzerland, Nico -- Sustainable and modern Infrastructures by ungleich.ch