Re: [libvirt-users] Backup a VM (using live external snapshot and blockcommit)
On 09/11/2015 10:18 AM, Jérôme wrote:
> Yep, that about covers it. Note that the --quiesce step in
snapshot
> creation requires qemu-guest-agent running in the guest, and that you
> trust interaction with your guest.
Yes, I think I get this. I don't really figure out what these cases
could be. We're using Debian Jessie and I installed qemu-guest-agent.
Other VM could use other systems, but most likely Linux based.
qga with support for quiesce has also been ported to Windows guests.
Do you mean that, in cases where you shouldn't trust the guest, using
'--quiesce' might end up being worse than nothing? Or just useless?
If the agent is not running, using --quiesce will fail the entire
command; you'd learn pretty quickly to retry without --quiesce for
guests that don't know how to handle it. . But if the guest is
malicious, it can pretend to be a guest agent, but intentionally refuse
to reply to the --quiesce request, and leave libvirt hung waiting for a
reply. So it boils down to whether you trust your guests to be
reasonable with their guest agent connection (fine if it is your own
guests, not so much if you are hosting a cloud for other people's guests).
>> -> Anything wrong about my snapshot-create-as and blockcommit command
>> lines? May I remove the snapshot with only a rm command?
>
> Looks correct to me, and matches my recent KVM Forum slides:
> http://events.linuxfoundation.org/sites/events/files/slides/2015-qcow2-ex...
I'll have a look at these, thanks.
The libvirt commands were towards the end, in part 3; but the first two
parts might give a better understanding of the overall operations of
what is happening.
> virsh snapshot-delete --metadata $dom $badname
>
> to remove $badname snapshot that no longer exists because you changed
> things behind the scenes.
Before removing the .xml file, I tried the command indicated in the wiki
[1] with no success.
"NOTE-2: Optionally, you can also supply '--no-metadata' option to tell
libvirt to not track the snapshot metadata -- this is useful currently
as at a later point when you merge snapshot files, then you have to
explicitly clean the libvirt metadata (by invoking: virsh
snapshot-delete vm1 --delete --current -- repeat this as needed.)"
Shouldn't the
virsh snapshot-delete vm1 --delete --current
be rephrased as
virsh snapshot-delete vm1 --metadata --current
Yep, sounds like a bug in the wiki, so I fixed it.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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