From: Chris Murphy <lists@colorremedies.com>
To: Zygo Blaxell <zblaxell@furryterror.org>
Cc: Btrfs BTRFS <linux-btrfs@vger.kernel.org>
Subject: Re: filesystem corruption
Date: Mon, 3 Nov 2014 10:11:18 -0700 [thread overview]
Message-ID: <935F962F-7DD6-4C18-88F3-65EF614B80E4@colorremedies.com> (raw)
In-Reply-To: <20141103034337.GM17395@hungrycats.org>
On Nov 2, 2014, at 8:43 PM, Zygo Blaxell <zblaxell@furryterror.org> wrote:
> On Sun, Nov 02, 2014 at 02:57:22PM -0700, Chris Murphy wrote:
>>
>> For example if I have a two device Btrfs raid1 for both data and
>> metadata, and one device is removed and I mount -o degraded,rw one
>> of them and make some small changes, unmount, then reconnect the
>> missing device and mount NOT degraded - what happens? I haven't tried
>> this.
>
> I have. It's a filesystem-destroying disaster. Never do it, never let
> it happen accidentally. Make sure that if a disk gets temporarily
> disconnected, you either never mount it degraded, or never let it come
> back (i.e. take the disk to another machine and wipefs it). Don't ever,
> ever put 'degraded' in /etc/fstab mount options. Nope. No.
Well I guess I now see why opensuse's plan for Btrfs by default proscribes multiple device Btrfs volumes. The described scenario is really common with users, I see it often on linux-raid@. And md doesn't have this problem. The worst case scenario is if devices don't have bitmaps, and then a whole device rebuild has to happen rather than just a quick "catchup".
>
> btrfs seems to assume the data is correct on both disks (the generation
> numbers and checksums are OK) but gets confused by equally plausible but
> different metadata on each disk. It doesn't take long before the
> filesystem becomes data soup or crashes the kernel.
This is a pretty significant problem to still be present, honestly. I can understand the "catchup" mechanism is probably not built yet, but clearly the two devices don't have the same generation. The lower generation device should probably be booted/ignored or declared missing in the meantime to prevent trashing the file system.
Chris Murphy
next prev parent reply other threads:[~2014-11-03 17:11 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-31 0:29 filesystem corruption Tobias Holst
2014-10-31 1:02 ` Tobias Holst
2014-10-31 2:41 ` Rich Freeman
2014-10-31 17:34 ` Tobias Holst
2014-11-02 4:49 ` Robert White
2014-11-02 21:57 ` Chris Murphy
2014-11-03 3:43 ` Zygo Blaxell
2014-11-03 17:11 ` Chris Murphy [this message]
2014-11-04 4:31 ` Zygo Blaxell
2014-11-04 8:25 ` Duncan
2014-11-04 18:28 ` Chris Murphy
2014-11-04 21:44 ` Duncan
2014-11-04 22:19 ` Robert White
2014-11-04 22:34 ` Zygo Blaxell
2014-11-03 2:55 ` Tobias Holst
2014-11-03 3:49 ` Robert White
2018-12-03 9:31 Filesystem Corruption Stefan Malte Schumacher
2018-12-03 11:34 ` Qu Wenruo
2018-12-03 16:29 ` remi
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