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Date:	Mon, 8 Aug 2011 22:07:58 +0200
From:	Christian Brunner <chb@....de>
To:	Yehuda Sadeh Weinraub <yehuda.sadeh@...amhost.com>
Cc:	Sage Weil <sage@...dream.net>, Theodore Tso <tytso@....edu>,
	Fyodor Ustinov <ufm@....su>, ceph-devel@...r.kernel.org,
	linux-ext4@...r.kernel.org
Subject: Re: Kernel 3.0.0 + ext4 + ceph == ...

I tried 3.0.1 today, which contains the commit Theodore suggested and
was no longer able to reproduce the problem.

So I think the corruption we have seen is indeed related to:

commit 7132de744ba76930d13033061018ddd7e3e8cd91
Author: Maxim Patlasov <maxim.patlasov@...il.com>
Date:   Sun Jul 10 19:37:48 2011 -0400

   ext4: fix i_blocks/quota accounting when extent insertion fails


I will now try to apply this patch to the RHEL6.1 kernel and see what
happens...

Thanks for your help.

Christian


2011/8/3 Yehuda Sadeh Weinraub <yehuda.sadeh@...amhost.com>:
> On Wed, Aug 3, 2011 at 7:16 AM, Christian Brunner <chb@....de> wrote:
> ...
>> I tried to reproduce this without ceph, but wasn't able to...
>>
>> In the meantime it seams, that I can also see the side effects on the
>> librbd side: I get an "librbd: data error!" when I do an "rbd copy".
>>
>> When I look at the librbd code this is related to a sparse_read not
>> returning the right size of the object.
>>
>> I don't know if it helps, but I think that the problem is also related
>> to sparse file usage.
>>
>
> There were a few sparse-read issues that we fixed not too long ago,
> but should have been fixed for at least the previous ceph version. I'm
> not sure what version you're using.
> There was a ext4 fiemap issue that I was hitting on specific
> environments but couldn't determine whether it was fixed in later
> kernel versions (I was using 2.6.32). Now is a good time to try and
> get to the bottom of it. Here's a script I was using to reproduce it:
>
> #!/bin/sh
> dd if=/dev/urandom of=bla bs=1 seek=$((0x6f000)) count=$((0x1000)); sync
> dd if=/dev/urandom of=bla bs=1 seek=$((0x70000)) count=$((0x1000)); sync
> dd if=/dev/urandom of=bla bs=1 seek=$((0x71000)) count=$((0x1000)); sync
> dd if=/dev/urandom of=bla bs=1 seek=$((0x72000)) count=$((0x1000)); sync
> dd if=/dev/urandom of=bla bs=1 seek=$((0x73000)) count=$((0x1000)); sync
> dd if=/dev/urandom of=bla bs=1 seek=$((0x74000)) count=$((0x2000)); sync
> dd if=/dev/urandom of=bla bs=1 seek=$((0x2ae000)) count=$((0x2000)); sync
>
> You can compile and run the following utility to dump all the extents:
> http://pastebin.com/h2Cnpk2Q
>
> Thanks,
> Yehuda
>
> Oh, btw, You can effectively disable the use of fiemap by setting the
> 'filestore fiemap threshold' config option with large enough value
> (e.g., anything bigger than 4 MB should be enough for rbd).
> --
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