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

[Paolo Bonzini <pbonzini@redhat.com>]

Il 19/03/2014 18:46, Dr. David Alan Gilbert ha scritto:
> * 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.

No, this is not supported upstream.  Upstream only supports forward 
migration.

>>> 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...

This is correct.

Paolo