[linux-lvm] LVM performance vs direct dm-thin
Gionatan Danti
g.danti at assyoma.it
Mon Jan 31 07:47:34 UTC 2022
Il 2022-01-30 22:39 Stuart D. Gathman ha scritto:
> I use LVM as flexible partitions (i.e. only classic LVs, no thin pool).
> Classic LVs perform like partitions, literally using the same driver
> (device mapper) with a small number of extents, and are if anything
> more recoverable than partition tables. We used to put LVM on bare
> drives (like AIX did) - who needs a partition table? But on Wintel,
> you need a partition table for EFI and so that alien operating systems
> know there is something already on a disk.
Classical (fat) LVs are rock solid, but how do you cope with fast (maybe
rolling) snapshotting? This is the main selling point of thinlvm.
> Since we use LVs like partitions - mixing with btrfs is not an issue.
> Just use the LVs like partitions. I haven't tried ZFS on linux - it
> may have LVM like features that could fight with LVM. ZFS would be my
> first choice on a BSD box.
I broadly use ZFS - and yes, it is a wonderful tools. Than said, it has
its own gotcha. For example:
- snapshot rollback is a destructive operation (ie: after rollback, you
permanently lose the current filesystem state);
- clones (writable snapshots) depend on the read-only base image (ie: on
the original snapshot), which you can not delete until you have its
clones around.
Moreover, snapshotting/cloning a ZFS dataset (or volume) does not appear
to be significantly faster then LVM - sometime it requires ~1s,
depending on the load.
> We do not use LVM raid - but either run mdraid underneath, or let btrfs
> do it's data duplication thing with LVs on different spindles.
I always found btrfs very underperforming when facing random rewrite
workloads as VMs and DBs. Can I ask your experience?
Regards.
--
Danti Gionatan
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Assyoma S.r.l. - www.assyoma.it
email: g.danti at assyoma.it - info at assyoma.it
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