Re: [Qemu-discuss] Live VM backup

[Vincenzo Romano]

2017-08-30 11:40 GMT+02:00 Fam Zheng <address@hidden>:
> 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

Thanks again, Fam.

So I should issue both QMP commands, in theory, with the VM in a
frozen state. Right?

-- 
Vincenzo Romano - NotOrAnd.IT
Information Technologies
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