Re: [Qemu-discuss] Live VM backup

[Fam Zheng]

On Wed, 08/30 11:16, Vincenzo Romano wrote:
> 2017-08-30 10:53 GMT+02:00 Fam Zheng <address@hidden>:
> > On Wed, 08/30 08:17, Vincenzo Romano wrote:
> >> Il 30 ago 2017 05:19, "Fam Zheng" <address@hidden> ha scritto:
> >>
> >> On Tue, 08/29 18:32, Vincenzo Romano wrote:
> >> > I'd like to move away from "another virtualization solution" to QEmu.
> >> > I've more or less all the needed bits in my hands in order to define,
> >> > run and manage QEmu VMs.
> >> > What I am missing is the knowledge of how to backup a live VM.
> >> > Of course, if I shutdown the VM, I can simply copy its files and the
> >> > startup script on another QEmu host.
> >> > But my main objective is to do the backup while the VM is running.
> >> > I think I could use the snapshot feature, but have no idea on how to
> >> proceed.
> >> > Any hint?
> >>
> >> In short, just do what libvirt would do: use QMP and send 'drive-backup'
> >> command.
> >>
> >> This is a very good howto:
> >>
> >> https://github.com/qemu/qemu/blob/master/docs/interop/live-b
> >> lock-operations.rst
> >>
> >> Fam
> >>
> >>
> >> Thanks.
> >> I presume there's a 'drive-restore', though I need to look better in the
> >> docs.
> >>
> >> Is there any side effect in case the CPU where the VM will be restored is
> >> not exactly the same as the one where the VM got backed up?
> >
> > No, there isn't a 'drive-restore'. 'drive-backup' only takes care of the 
> > disks,
> > so the CPU, ram and device states aren't saved.
> >
> > If you boot from the backup image, CPU and ram are restarted from powered 
> > off
> > state, so what happens is effectively like a power loss at the point of
> > 'drive-backup': anything not saved to disk are lost.
> >
> > Fam
> 
> I understand.
> 
> So, if I haven't miunderstood, at the moment QEmu-KVM doesn't
> implement  "VM snapshots".

It does. There are "savevm" and "migrate" (or "migrate -b") that can save the
CPU/ram etc:

https://www.linux-kvm.org/page/Migration#savevm.2Floadvm_to_an_external_state_file_.28using_pseudo-migration.29

Fam