[fedora-virt] I/O errors in guest when cache=none, qcow2 on Btrfs

Chris Murphy lists at colorremedies.com
Fri Mar 27 18:05:16 UTC 2015

On Fri, Mar 27, 2015 at 2:59 AM, Kevin Wolf <kwolf at redhat.com> wrote:
> Could you try using new qemu with old libvirt and vice versa?

Later today or this weekend it should be possible.

> To be honest, it sounds much like a problem with the btrfs driver and
> O_DIRECT to me. But if changing libvirt and qemu versions is enough to
> trigger it, we need to have a look at them - even if it's just to
> support the btrfs investigation.

I just discovered that Fedora 21 Live Workstation as guest does not
reproduce the problem, whereas Fedora 22 Live Workstation Beta TC4
does reproduce it.

So it seems there's something about the guest OS first of all; and
then it depends on the host version of either libvirt or qemu (or

>> blk_update_request: I/O error, dev vda, sector XXXXXXXX when qcow2 is on Btrfs
>> https://bugzilla.redhat.com/show_bug.cgi?id=1204569
> It might be helpful to get a trace of all write requests made by qemu to
> the image file.

I've done that and updated the bug.

Chris Murphy

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