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(a)ungleich.ch>
Sent: 25 March 2021 13:29:10
To: Frank Schilder
Cc: Marc; Nico Schottelius; ceph-users(a)ceph.io
Subject: Re: [ceph-users] Re: LVM vs. direct disk acess
Frank Schilder <frans(a)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
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