[virt-tools-list] The best strategies for backing up virtual machines

Eric Blake eblake at redhat.com
Wed Mar 26 03:14:45 UTC 2014

On 03/25/2014 09:08 PM, Peng Yu wrote:
> Hi,
> There are quite a number of webpages discussing backup and snapshots.
> But I'm not sure what the currently best practice is.
> For my application, I don't care memory images. I mainly care about
> the software installed on virtual machines and the OS configurations
> on the virtual machines. I know that I can not make a safe copy of the
> disk image of a virtual machine without shutting it down.

Not quite true.  It is possible to take an external snapshot while the
guest is still running; whether with the RAM state (to resume where you
left off if you roll back) or without the RAM state (faster, but acts
like power cord is pulled regarding disk state if you have to roll
back).  What more, if you don't save RAM state, you can also install
qemu-guest-agent in your Linux and Windows guests, then request that the
guest file systems quiesce prior to the snapshot, so that the file
systems are in a much stabler state for the revert than they would be on
a power cord pull.

> But this may
> not be always feasible, as in general my virtual machines should be
> on. Taking snapshots does not require virtual machine shutdown (if I
> understand it correctly), but it seems that it saves more than just
> disk images.

When taking external snapshots, you do not have to save RAM state.
However, there IS a drawback that libvirt does not yet have full support
for cleaning up after external snapshots; the libvirt-users has a number
of threads with more details on how to work around this.

> Could you anybody give me some suggestions on the best backup practice? Thanks.

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

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