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Date: Thu, 16 Jun 2011 09:21:03 +0300
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Subject: Re: [ANNOUNCE] Native Linux KVM tool v2
From: Pekka Enberg <penberg@kernel.org>
To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Alexander Graf <agraf@suse.de>, Prasad Joshi <prasadjoshi124@gmail.com>,
        Avi Kivity <avi@redhat.com>, linux-kernel@vger.kernel.org,
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        Linus Torvalds <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@elte.hu>, Sasha Levin <levinsasha928@gmail.com>,
        Cyrill Gorcunov <gorcunov@gmail.com>, Asias He <asias.hejun@gmail.com>,
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On Thu, Jun 16, 2011 at 1:44 AM, Anthony Liguori <anthony@codemonkey.ws> wrote:
>>> That's probably why it's fast, it doesn't preserve data integrity :(
>>
>> Actually, I misread the code.  It does unstable writes but it does do
>> fsync() on FLUSH.

On Thu, Jun 16, 2011 at 8:41 AM, Pekka Enberg <penberg@kernel.org> wrote:
> Yes. That's fine, right? Or did we misread how virtio block devices
> are supposed to work?

And btw, we use sync_file_range() to make sure the metadata part of a
QCOW2 image is never corrupted. The rational here is that if the guest
doesn't do VIRTIO_BLK_T_FLUSH, you can corrupt your _guest filesystem_
but the _image_ will still work just fine and you can do fsck on it.

Also, Prasad ran xfstests and did over-night stress tests to iron out
corruption issues. Now we obviously can't promise that we'll never eat
your data but I can assure you that we've done as much as we've been
able to with the resources we have at the moment.

                                Pekka