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Date: Sat, 18 May 2002 13:47:50 +0100
From: "Stephen C. Tweedie" <sct@redhat.com>
To: "Stephen C. Tweedie" <sct@redhat.com>, Neil Brown <neilb@cse.unsw.edu.au>,
        linux-kernel@vger.kernel.org
Subject: Re: Thoughts on using fs/jbd from drivers/md
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Hi,

On Fri, May 17, 2002 at 06:35:37PM -0700, Mike Fedyk wrote:
> On Fri, May 17, 2002 at 07:34:10PM +0100, Stephen C. Tweedie wrote:
> > 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?

Nope, partity updates still occur.  It's more expensive than in
non-degraded mode, but parity still gets updated.  If it wasn't, you
would not be able to write to a degraded array at all, as updating
parity is the only way that you can write to a block which maps to a
failed disk.  By using parity, we only ever fail requests if there are
two or more failed disks in the array.

Cheers,
 Stephen