libvirt users - Mar 2018 - Re: qemu-img snapshot on running virtual machine

Hi all,
I have a question about internal qcow2 snapshots of a live/running 
virtual machine taken via "qemu-img snapshot command".

My question is: is it safe to execute the command above against a 
running machine? Or it will cause corruption? Naively I think it should 
*not* be safe, however, I would like a direct confirmation.

Thanks.

-- 
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8

On Wed, Mar 14, 2018 at 09:36:52AM +0100, Gionatan Danti
wrote:
>Hi all,
>I have a question about internal qcow2 snapshots of a live/running
>virtual machine taken via "qemu-img snapshot command".
>
>My question is: is it safe to execute the command above against a
>running machine? Or it will cause corruption? Naively I think it should
>*not* be safe, however, I would like a direct confirmation.
>
It is not safe.

For a running domain, you need to go through libvirt and also save the
memory of the VM - doing just the disk snapshot for a running machine
would be an equivalent of copying a physical hard drive after pulling
out the power cord.

Jan

Il 15-03-2018 09:13 Ján Tomko ha scritto:
> It is not safe.
> 
> For a running domain, you need to go through libvirt and also save the
> memory of the VM - doing just the disk snapshot for a running machine
> would be an equivalent of copying a physical hard drive after pulling
> out the power cord.
> 
> Jan
Hi Jan, I 100% agree that taking a snapshot without dumping the memory 
content would be akin to "pulling the plug" on the guest.

However, I was speaking about disk image file consistency. In other 
words: does taking a snapshot of an in-use virtual disk have a chance to 
corrupt the *original* disk Qcow2 image file?

Thanks.

-- 
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8