linux-kernel - Re: csum errors

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Date:	Thu, 15 Jul 2010 22:00:24 +0200
From:	Johannes Hirte <johannes.hirte@....tu-ilmenau.de>
To:	Chris Mason <chris.mason@...cle.com>
Cc:	linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org
Subject: Re: csum errors

Am Donnerstag 15 Juli 2010, 21:35:51 schrieb Chris Mason:
> On Thu, Jul 15, 2010 at 09:32:12PM +0200, Johannes Hirte wrote:
> > Am Donnerstag 15 Juli 2010, 21:03:09 schrieb Chris Mason:
> > > On Thu, Jul 15, 2010 at 08:30:17PM +0200, Johannes Hirte wrote:
> > > > Am Dienstag 13 Juli 2010, 14:23:58 schrieb Johannes Hirte:
> > > > > ino 1959333 off 898342912 csum 4271223884 private 4271223883
> > > > 
> > > > I think, this is a different error. I've only seen them on
> > > > filesystems from my Opteron system. It seems that the recorded csums
> > > > are wrong and it looks to me like rounding errors. The data itself
> > > > should be correct, as I've tested one affected file via md5sum
> > > > against the original on another filesystem. Any ideas what is going
> > > > wrong here?
> > > 
> > > Are you doing data mirroring?
> > 
> > No, I don't.
> > 
> > > We can map that block and do a raw read off the device to see what the
> > > data blocks actually contain.
> > 
> > I've modified the btrfs-source a little to get the data. In inode.c I've
> 
> > changed the code to:
> Great.   The bad csums are all just one bit off, that can't be an
> accident. When were they written (which kernel?).  Did you boot a 32
> bit kernel on there at any time?

No, I don't have a bootable 32bit installation on this system. I've tested it 
now with a 32bit system by dumping the whole filesystem to an external drive 
and mounting this to a 32bit system. The result was the same.

The affected files were written by different kernels. I think at least 2.6.34, 
2.6.35-rc3 and 2.6.35-rc4 should be involved, perhaps 2.6.33 too. I'll try to 
figure it out more exactly.

regards,
  Johannes
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