On Mon, Nov 30, 2015 at 04:34:14PM +0100, Lentes, Bernd wrote:
> Stefan wrote:
> > 
> > Hi Bernd,
> > qemu-img cannot be used on the disk image when the VM is running.
> > Please use virsh, it communicates with the running QEMU process and
> > ensures that the snapshot is crash-consistent.
> > 
> Hi Stefan,
> thanks for your answer.
> i read that virsh uses internally qemu-img
> (http://serverfault.com/questions/692435/qemu-img-snapshot-on-live-vm).
> Is that true ?

It's false in the general case.

While the VM is running libvirt will use the QEMU monitor to communicate
with the QEMU process instead of using qemu-img.

While the VM is shut down libvirt can use qemu-img safely.

The reason why qemu-img isn't safe is that the image file might be
written to by the running VM at the same time as qemu-img reads/writes
it.  This can corrupt image files.


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