From: Mike Fedyk <mfedyk@matchmail.com>
To: "Stephen C. Tweedie" <sct@redhat.com>
Cc: Neil Brown <neilb@cse.unsw.edu.au>, linux-kernel@vger.kernel.org
Subject: Re: Thoughts on using fs/jbd from drivers/md
Date: Fri, 17 May 2002 18:35:37 -0700 [thread overview]
Message-ID: <20020518013537.GH627@matchmail.com> (raw)
In-Reply-To: <15587.18828.934431.941516@notabene.cse.unsw.edu.au> <20020516161749.D2410@redhat.com> <20020517182942.GF627@matchmail.com> <20020517193410.W2693@redhat.com>
On Fri, May 17, 2002 at 07:34:10PM +0100, Stephen C. Tweedie wrote:
> Hi,
>
> On Fri, May 17, 2002 at 11:29:42AM -0700, Mike Fedyk wrote:
> > On Thu, May 16, 2002 at 04:17:49PM +0100, Stephen C. Tweedie wrote:
>
> > > Right. The ability of soft raid5 to lose data in degraded mode over a
> > > reboot (including data that was not being modified at the time of the
> > > crash) is something that is not nearly as widely understood as it
> > > should be, and I'd love for us to do something about it.
> >
> > Are there workarounds to avoid this problem?
>
> No.
>
> > What does it take to trigger the corruption?
>
> It just takes degraded mode, an unexpected power cycle, and concurrent
> write activity.
>
> Degraded mode relies on the parity disk being in sync at all times ---
Doesn't degraded mode imply that there are not any parity
disk(raid4)/stripe(raid5) updates?
> you can't recover data from the missing spindle unless that is true.
> However, writes to a stripe are not atomic, and you can get a reboot
> when, say, a write to one of the surviving data chunks has succeeded,
> but the corresponding write to the parity disk has not. If this
> happens, the parity is no longer in sync, and the data belonging to
> the missing spindle in that stripe will be lost forever.
>
> > I ask this because I have used a degraded raid5 because the source drive
> > would become a member, but I needed to copy the data first. While doing so,
> > I had to reboot a couple times to reconfigure the boot loader. All seems to
> > be working fine on the system today though.
>
> If it was a clean shutdown and reboot, you're fine.
>
OK, that's good.
next prev parent reply other threads:[~2002-05-18 1:35 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-05-16 5:54 Thoughts on using fs/jbd from drivers/md Neil Brown
2002-05-16 15:17 ` Stephen C. Tweedie
2002-05-17 18:29 ` Mike Fedyk
2002-05-17 18:34 ` Stephen C. Tweedie
2002-05-18 1:35 ` Mike Fedyk [this message]
2002-05-18 12:47 ` Stephen C. Tweedie
2002-05-21 9:03 ` Helge Hafting
2002-05-26 8:41 ` Daniel Phillips
2002-05-27 11:34 ` Stephen C. Tweedie
2002-05-27 11:50 Neil Brown
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