Open Stack

On 4/24/2016 2:09 AM, Saverio Proto wrote:
>> We are in an even worst situation: we have flavors with 256GB of ram
>> but only 100GB on the local hard disk, which means that we cannot
>> snapshot VMs with this flavor.
>>
>> If there is any way to avoid saving the content of the ram to disk (or
>> maybe there is a way to snapshot the ram to, e.g., ceph), we would be
>> very happy.
>
> Hello Antonio,
>
> I received a new feedback in the Openstack patch review
> (https://review.openstack.org/#/c/295865/) pointing me to this:
>
> https://github.com/openstack/nova/blob/82a684fb1ae1dd1bd49e2a8792a2456b4d3ab037/nova/conf/workarounds.py#L72
>
> so it looks like live snapshots are disabled because of an old buggy
> libvirt. So actually this process of dumping all the RAM to disk is
> not a bad design, but it is a necessary workaround because of libvirt
> not being stable. It makes sense now.
>
> At the moment I am running libvirt version 1.2.12-0ubuntu14.4~cloud0.
> Maybe I can disable the workaround and try to do faster snapshots ?
>
> Any other operator has feedback about this ?
>
> Thank you
>
> Saverio
>
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>

To clarify, live snapshots aren't disabled by default because they don't 
work, it's because at least with libvirt 1.2.2 and QEMU 2.0 (which is 
what we test against in the gate), we'd hit a lot of failures (about 25% 
failure rate with the devstack/tempest jobs) when running live snapshot, 
so we suspect there are concurrency issues when running live snapshot on 
a compute along with other operations at the same time (the CI jobs run 
4 tests concurrently on a single-node devstack).

This might not be an issue on newer libvirt/QEMU, we'll see when we 
start testing with Ubuntu 16.04 nodes.

-- 

Thanks,

Matt Riedemann