[ovirt-users] Restoring Hosted-Engine from a stale backup

[Martin Sivak]

>> A serious issue could instead happen with HA VMs:
>> if the engine finds earlier an HA VM as running on a different host it
>> will simply update its record, the issue is if it finds earlier the VM a not
>> on the original host since it will try to restart it causing a split brain
>> and probably a VM corruption.

>> https://bugzilla.redhat.com/show_bug.cgi?id=1419649

Uh? Why should this be the case? I think we need Arik to confirm this,
but the engine only does HA VM restarts during fencing. And fencing is
only activated 5 minutes after the engine start to make sure we
already have all host reports.

Martin


On Mon, Feb 6, 2017 at 5:45 PM, Doug Ingham <dougti at gmail.com> wrote:
> On 6 February 2017 at 13:30, Simone Tiraboschi <stirabos at redhat.com> wrote:
>>
>>
>>>>>> What problems can I expect to have with VMs added/modified since the
>>>>>> last backup?
>>>>
>>>> Modified VMs will be reverted to the previous configuration; additional
>>>> VMs should be seen as external VMs, then you could import.
>>>
>>>
>>> Given VDSM kept the VMs up whilst the HE's been down, how will the
>>> running VMs that were present before & after the backup be affected?
>>>
>>> Many of the VMs that were present during the last backup are now on
>>> different hosts, including the HE VM. Will that cause any issues?
>>
>>
>> For normal VMs I don't expect any issue: the engine will simply update the
>> correspondent record once it will find them on the managed hosts.
>> A serious issue could instead happen with HA VMs:
>> if the engine finds earlier an HA VM as running on a different host it
>> will simply update its record, the issue is if it finds earlier the VM a not
>> on the original host since it will try to restart it causing a split brain
>> and probably a VM corruption.
>> I opened a bug to track it:
>> https://bugzilla.redhat.com/show_bug.cgi?id=1419649
>
>
> Ouch. *All* of our VMs are HA by default.
>
> So the simplest current solution would be to shutdown the running VMs in
> VDSM, before restoring the backup & running engine-setup?
>
> Cheers,
> --
> Doug
>
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