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Re: [Qemu-discuss] Freeze Windows Guests For Consistent Storage Snapshot

From: Eric Blake
Subject: Re: [Qemu-discuss] Freeze Windows Guests For Consistent Storage Snapshots
Date: Thu, 11 Dec 2014 08:29:29 -0700
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On 12/10/2014 11:40 PM, Payes Anand wrote:
> Hi,
> Is it possible to freeze windows guests for a consistent storage level
> snapshot.

Yes, if you install qemu-guest-agent in the guest, and wire up your
libvirt XML to have the guest-agent channel available.  Once you have
done that, use the --quiesce flag as part of creating your snapshots.

> I was able to freeze Centos guests by issuing the  command:
> virsh qemu-agent-command <guest_ID> '{"execute":"guest-fsfreeze-freeze"}'

That is an unsupported backdoor, because it relies on libvirt-qemu.so.
You should really prefer the libvirt commands from libvirt.so instead
(the --quiesce flag to 'virsh snapshot-create[-as]'), because it is less
likely to get libvirt out of sync by going behind libvirt's back.  Also,
libvirt 1.2.5 introduced 'virsh domfsfreeze' as the official way to do a
guest-agent 'guest'fsfreeze-freeze' command, although since you are
using older CentOS builds, your libvirt does not yet have that command

> For CentOS guests, I enabled access between compute nodes and guests
> through a socket by setting metadata parameter, hw_qemu_guest_agent=yes for
> the guest image.
> And then installing qemu-guest-agent inside the guest.
> What steps do i have to follow for windows ?

The same steps - qemu-guest-agent is available for both Linux and
Windows guests.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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