openstack team mailing list archive

["Daniel P. Berrange" <berrange@xxxxxxxxxx>]

On Tue, Aug 07, 2012 at 04:13:22PM -0400, Jay Pipes wrote:
> On 08/07/2012 08:57 AM, Blair Bethwaite wrote:
> >> I also feel a little concern about this statement:
> >>
> >>>  It don't work so well, it complicates migration code, and we are building
> >>> a replacement that works.
> >>
> >>
> >> I have to go further with my tests, maybe we could share some ideas, use
> >> case etc...
> > 
> > I think it may be worth asking about this on the KVM lists, unless
> > anyone here has further insights...?
> > 
> > I grabbed the KVM 1.0 source from Ubuntu Precise and vanilla KVM 1.1.1
> > from Sourceforge, block migration appears to remain in place despite
> > those (sparse) comments from the KVM meeting minutes (though I am
> > naive to the source layout and project structure, so could have easily
> > missed something). In any case, it seems unlikely Precise would see a
> > forced update to the 1.1.x series.
> 
> cc'd Daniel Berrange, who seems to be keyed in on upstream KVM/Qemu
> activity. Perhaps Daniel could shed some light.

Block migration is a part of the KVM that none of the upstream developers
really like, is not entirely reliable, and most distros typically do not
want to support it due to its poor design (eg not supported in RHEL).

It is quite likely that it will be removed in favour of an alternative
implementation. What that alternative impl will be, and when I will
arrive, I can't say right now. A lot of the work (possibly all) will
probably be pushed up into libvirt, or even the higher level mgmt apps
using libvirt. It could well involve the mgmt app having to setup an
NBD or iSCSI server on the source host, and then launching QEMU on the
destination host configured to stream the data across from the NBD/iSCSI
server in parallel with the migration stream. But this is all just talk
for now, no firm decisions have been made, beyond a general desire to
kill the current block migration code.

Regards,
Daniel
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