[virt-tools-list] Best way to backup my VMs

Chris Lalancette clalance at redhat.com
Tue Apr 12 15:34:33 UTC 2011

On 04/12/11 - 08:40:17AM, Eric Blake wrote:
> On 04/12/2011 08:18 AM, Richard W.M. Jones wrote:
> >> Is it possible to "pause" a machine with a simple command, rsync the
> >> machine's HD image in other computer and then safelly resume the machine? Is
> >> it necessary to shut down the virtual machine, in order to make this backup?
> > 
> > You are best to install some backup software into the virtual machine.
> > Treat the virtual machine like it was a physical machine and back it
> > up with some software which is aware of what's going on inside.
> That is indeed the safest advice.
> But in answer to the question, yes, it is possible to pause a guest,
> save the state of its memory and disks (saving just one or the other is
> insufficient - you need to save both, otherwise, in-flight data in
> memory that has not been flushed to disk will be corrupted).  That is,
> use the sequence:

Actually, this isn't right.  Think about the case where you lose power to
your computer; you don't get corrupted disks, you get "crash-consistent" disks
(this is what journaling filesystems are for).  So if you know what you are
doing, it is sufficient just to pause the guest (virsh suspend <guest>), take
the backup, and then resume the guest (virsh resume <guest>).  True, you
won't get all of the data that might have been in-flight in memory, but it
should be a valid state of the disk.

That all being said, installing backup software in the guest is the best
course of action.

Chris Lalancette

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