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Re: [PATCH 1/5] repair: handle repair of image files on large sector siz

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH 1/5] repair: handle repair of image files on large sector size filesystems
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Mon, 10 Oct 2011 11:17:08 +1100
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20111009235240.GD13527@xxxxxxxxxxxxx>
References: <1318201910-11144-1-git-send-email-david@xxxxxxxxxxxxx> <1318201910-11144-2-git-send-email-david@xxxxxxxxxxxxx> <20111009235240.GD13527@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Sun, Oct 09, 2011 at 07:52:40PM -0400, Christoph Hellwig wrote:
> On Mon, Oct 10, 2011 at 10:11:46AM +1100, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@xxxxxxxxxx>
> > 
> > Because repair uses direct IO, it cannot do IO smaller than a sector
> > on the underlying device. When repairing a filesystem image, the
> > filesystem hosting the image may have a sector size larger than the
> > sector size of the image, and so single image sector reads and
> > writes will fail.
> Does it?  Given that the loop driver uses buffered I/O that would be
> unexpected behaviour.  I'll try to reproduce it as soon as my 4k
> disk is available again.

My 3TB, RAID6 based image storage filesystem has a 4k sector size,
and I can't run xfs_repair on an image file that has smaller sector
sizes than 4k without this mod. In that case, xfs_repair is doing
direct IO on a file, not a device, and the file is on the 4k sector
sized filesytem. I've been carrying this patch for a while.

So it's definitely a real problem.


Dave Chinner

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