[linux-lvm] Does LVM have any plan/schedule to support btrfs in fsadm
Gionatan Danti
g.danti at assyoma.it
Mon Jun 28 07:29:19 UTC 2021
Il 2021-06-28 05:28 Stuart D Gathman ha scritto:
> Yes. I like the checksums in metadata feature for enhanced integrity
> checking.
Until recently btrfs has issue when a LVM snapshot was mounted. It is
now solved?
> It seems too complicated to have anytime soon - but when a filesystem
> detects corruption, and is on an LVM (or md) RAID1 layer, an ioctl to
> read alternate mirror branches to see which (if any) has the correct
> data would allow recovery. Btrfs does this if it is doing the
> mirroring, but then you lose all the other features from LVM or md
> raid10, including running other filesystems and efficient virtual
> disks for
> virtual machines.
For this to work, LVM should be able to identify the corrupted data.
Without checksum, how can you do that? The solution is to use
dm-integrity under the RAID layer. It works pretty well, letting apart
the big performance drop in the default (journaled) configuration
(bitmap is faster, but leave a small window for corruption to happen
undetected).
That said, for rewrite-heavy workload (virtual machines, databases, etc)
btrfs is very slow (and disabling CoW is not a solution for me, as it
also disables checksum, compression, etc).
> We eventually got DISCARD operations to pass to lower layers.
> Dealing with mirror branches should really be a thing too.
As said above, the issue is not to read from the mirror leg separately;
rather, to detect *which* mirror leg contains valid data.
Regards.
--
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti at assyoma.it - info at assyoma.it
GPG public key ID: FF5F32A8
More information about the linux-lvm
mailing list