Re: [libvirt] [Qemu-devel] qemu and qemu.git -> Migration + disk stress introduces qcow2 corruptions

On Mon, Nov 14, 2011 at 10:16:10AM +0000, Daniel P. Berrange wrote: > On Sat, Nov 12, 2011 at 12:25:34PM +0200, Avi Kivity wrote: > > On 11/11/2011 12:15 PM, Kevin Wolf wrote: > > > Am 10.11.2011 22:30, schrieb Anthony Liguori: > > > > Live migration with qcow2 or any other image format is just not going to work > > > > right now even with proper clustered storage. I think doing a block level flush > > > > cache interface and letting block devices decide how to do it is the best approach. > > > > > > I would really prefer reusing the existing open/close code. It means > > > less (duplicated) code, is existing code that is well tested and doesn't > > > make migration much of a special case. > > > > > > If you want to avoid reopening the file on the OS level, we can reopen > > > only the topmost layer (i.e. the format, but not the protocol) for now > > > and in 1.1 we can use bdrv_reopen(). > > > > > > > Intuitively I dislike _reopen style interfaces. If the second open > > yields different results from the first, does it invalidate any > > computations in between? > > > > What's wrong with just delaying the open? > > If you delay the 'open' until the mgmt app issues 'cont', then you loose > the ability to rollback to the source host upon open failure for most > deployed versions of libvirt. We only fairly recently switched to a five > stage migration handshake to cope with rollback when 'cont' fails. > > Daniel I guess reopen can fail as well, so this seems to me to be an important fix but not a blocker.