Re: [Qemu-devel] Live migration results in non-working virtio-net device (sometimes)

[Andreas Färber]

Am 30.01.2014 19:23, schrieb Neil Skrypuch:
> First, let me briefly outline the way we use live migration, as it is 
> probably 
> not typical. We use live migration (with block migration) to make backups of 
> VMs with zero downtime. The basic process goes like this:
> 
> 1) migrate src VM -> dest VM
> 2) migration completes
> 3) cont src VM
> 4) gracefully shut down dest VM
> 5) dest VM's disk image is now a valid backup
> 
> In general, this works very well.
> 
> Up until now we have been using qemu-kvm 1.1.2 and have not had any issues 
> with the above process. I am now attempting to upgrade us to a newer version 
> of qemu, but all newer versions I've tried occasionally result in the virtio-
> net device ceasing to function on the src VM after step 3.

While I don't know this particular symptom, I can definitely tell you
that migrating from qemu-kvm to qemu is bound to fail unless you enable
at least a version_id change in piix4.c, possibly also in kvmvapic.c.
Such errors would lead to migration not successfully completing though,
with cryptic error on the dest side.

Regards,
Andreas

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