[openstack-dev] live-snapshot/cloning of virtual machines

Alessandro Pilotti apilotti at cloudbasesolutions.com
Tue Aug 27 14:06:54 UTC 2013

On Aug 27, 2013, at 16:48 , Russell Bryant <rbryant at redhat.com<mailto:rbryant at redhat.com>>

On 08/26/2013 08:15 PM, Tim Smith wrote:
Hi all,

On Mon, Aug 19, 2013 at 11:49 PM, Bob Ball <bob.ball at citrix.com<mailto:bob.ball at citrix.com>
<mailto:bob.ball at citrix.com>> wrote:

   I agree with the below from a XenServer perspective.  As with
   vmware, XenServer supports live snapshotting and creating multiple
   clones from that live snapshot.

   I understand that there is a XenAPI equivalent in the works and
   therefore would argue the API changes need to be accepted as a minimum.

Can nova technical leadership provide clarification on the current
standing of this blueprint? Two hypervisor vendors have expressed plans
for supporting this feature, and one has specifically requested that the
API changes be merged, but it appears that both the API changeset [1]
and novaclient support [2] have both been rejected pending libvirt
support (which has assumedly been ruled out for the Havana release).

[1] https://review.openstack.org/#/c/34036/
[2] https://review.openstack.org/#/c/43777/

   In order to minimize the feature divergence between hypervisors, I'd
   also argue that we should accept the libvirt implementation even if
   it uses unsupported APIs - perhaps disabled by default with a
   suitable warning that it isn't considered safe by libvirt/QEmu.

It's understandable that changes to the libvirt driver would be held
back until libvirt/qemu-upstream support for live snapshotting is
established (if ever), but given that other vendors whose release
cadences don't necessarily align with the nova release schedule have
expressed plans to support the interface it's unclear why lack of
libvirt driver support would block the entire blueprint.

Two other driver maintainers have expressed interest in it, but AFAIK,
there are not implementations of this feature ready for review and
merging for these drivers.  Given that's the case, it doesn't make any
sense to me to merge the API with no ability to use it.  I'm only saying
it should wait until it can be merged with something that makes it usable.

We are also planning to implement the live snapshot feature in the Hyper-V driver during the next release cycle.

I'm personally in favour of publishing the APIs in Havana, as this would provide a stable baseline at the beginning of the release cycle and also give the ability to users and third parties to backport the driver's feature to Havana (outside of the official repo of course).

Russell Bryant

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