From: Gionatan Danti <g.danti@assyoma.it>
To: LVM general discussion and development <linux-lvm@redhat.com>
Cc: Stuart, Zhong Lidong <lidong.zhong@suse.com>,
David Teigland <teigland@redhat.com>,
Zdenek Kabelac <zkabelac@redhat.com>
Subject: Re: [linux-lvm] Does LVM have any plan/schedule to support btrfs in fsadm
Date: Mon, 28 Jun 2021 09:29:19 +0200 [thread overview]
Message-ID: <35d4978f0aa1c0a78c8c618557ba15e5@assyoma.it> (raw)
In-Reply-To: <b0c22aef-8a9-73e6-db74-c24633c3496@gathman.org>
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@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8
_______________________________________________
linux-lvm mailing list
linux-lvm@redhat.com
https://listman.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
next prev parent reply other threads:[~2021-06-28 7:32 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-25 5:28 [linux-lvm] Does LVM have any plan/schedule to support btrfs in fsadm heming.zhao
2021-06-25 10:57 ` Zdenek Kabelac
2021-06-27 17:40 ` heming.zhao
2021-06-28 3:28 ` Stuart D Gathman
2021-06-28 7:29 ` Gionatan Danti [this message]
2021-06-28 23:00 ` Chris Murphy
2021-06-29 22:32 ` Gionatan Danti
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=35d4978f0aa1c0a78c8c618557ba15e5@assyoma.it \
--to=g.danti@assyoma.it \
--cc=lidong.zhong@suse.com \
--cc=linux-lvm@redhat.com \
--cc=teigland@redhat.com \
--cc=zkabelac@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).