Re: [Qemu-devel] migrating instances from qemu-kvm to qemu

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Serge E. Hallyn (serge@hallyn.com) wrote:
> Quoting Dr. David Alan Gilbert (dgilbert@redhat.com):
> > * Serge E. Hallyn (serge@hallyn.com) wrote:
> > 
> > > Although, some people are using newer qemu with '-M pc-1.0'.  So we'd be
> > > stopping thing from migrating to support the people coming from qemu-kvm.
> > > Hmm.
> > 
> > What sometimes happens is that you create a VM (lets say with virt-manager)
> > on an old installation, and it has the XML file for that VM which I think
> > includes the machine type.   You upgrade your host or copy your VMs over
> > and so you still use the old machine definition, and hence still have the
> > -M pc-1.0
> 
> Right, but so long as it is a shutdown vm image, it shouldn't matter to
> this case whether qemu 1.7 uses the old qemu-kvm cirrus vga ram size, or
> the qemu ram size, right?

Right - but they might have kept it as -M pc-1.0 on purpose, so that they
can migrate it back to another machine with an older qemu.

> > Some people have snapshots rather than just disk images taken with particular
> > versions and they expect those to be reloadable into newer versions.
> 
> Disk snapshots should be fine right?  Live snapshots no, but then
> I didn't they were actually very well supported anyway.  In any case,
> they point would remain that if x% of people have snapshots from qemu-kvm,
> and the rest have snapshots created using qemu but older machine types,
> then whether or not we change the values, either way the other x% or
> 100-x % will not be able to restore...
> 
> So still it seems the only sure way to handle this would be for qemu
> to say "old vram size != new vram size;  so let me resize the vram".

I'd say if the machine type and other config matches they must stay the same,
if the machine type or appropriate config is different you can change stuff.

Dave
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK