On Wed, Aug 6, 2014 at 12:27 PM, Eric Blake <eblake@redhat.com> wrote:
On 08/06/2014 10:06 AM, Yuanzhen Gu wrote:
yes, I got your point, thanks very much Eric.
not entirely, because you still top-posted.
got it entirely this time, not top-posted.
If I want to take a distributed snapshot, which need pause all the VMs
and
then take snapshot, how can I control the pause for all the VMs?
You mean, you have multiple VMs, and want to take a snapshot of all their storage at the same point in time? Then it is up to you to manually pause all the guests before taking the snapshot in each of them. Taking an external disk snapshot works while a guest is paused.
I need take live snapshot for multiple VMs at the same time
Is there only way that I turn to freeze/thaw functions?
Guest freeze/thaw (virDomainFSFreeze) only works on a live guest. So what you will have to do is:
virDomainFSFreeze(vm1, ...) virDomainFSFreeze(vm2, ...) virDomainSuspend(vm1) virDomainSuspend(vm2) virDomainSnapshotCreateXML(vm1, ...) virDomainSnapshotCreateXML(vm2, ...) virDomainResume(vm1) virDomainResume(vm2) virDomainFSThaw(vm1, ...) virDOmainFSThaw(vm2, ...)
I see, thanks.
However, I honestly don't know why you think you need disk snapshots from the same point in time across multiple VMs, though.
you suggested that external disk-only snapshot, libvirt will freeze/thaw before/after taking snapshot
Compare it to bare metal - how would you take a snapshot of multiple hosts? Either they are independent storage (and it doesn't matter if they are not precisely at the same point in time), or they are using clustered storage visible by all hosts in the cluster (but in that case, use your cluster storage management tools to take the snapshot, rather than trying to take a point-in-time snapshot of the low-level storage on each host and coordinating all the hosts to do it at the same point in time).
good question. I'll think about it clear my mind first and then answer it, thanks!
and freeze/thaw only for file systems, not for the whole guest, am I
right?
freeze/thaw is for all freezeable file systems on the whole guest, but it requires guest cooperation.
-- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org