[Pacemaker] dealing with non uptodate dual primary drbd resources and possible constraints

[Andreas Kurz]

hello,

On 10/27/2011 09:34 PM, Bart Coninckx wrote:
> Hi,
> 
> 
> I found this a rather tough one.
> 
> I have a dual primary DRBD setup for Xen live migration.
> The DRBD part is taken care of by a master drbd resource (linbit). It
> has a monitoring operation that puts it primary (master) if it's
> secondary (salve) for some reason.
> I was surprised to see that in case of a drbd node with an invalidated
> resource, the resource was happily put into primary (master) state
> during the sync (so while not being uptodate).

You also noticed the different promotion scores?

> Obviously this poses a problem, as the cluster might decide to start a
> Xen DomU on the non-uptodate drbd node.

Not really as long as the resources are connected. It is completely
valid to use a Primary that is SyncTarget, blocks that are not uptodate
when requested are prefetched from the SyncSource.

> 
> Is there any way I can avoid that with a constraint? Or should I go
> about things differently so it is not able to set the resource into
> master before the acutal sync is done?

There would be different ways .... changing master-max to 1, add an
anticolocation constraint for the Master role and the SyncTarget, or
simply don't start Pacemaker on the SyncTarget if you expect a very long
resync time ... start DRBD manually and wait for the sync to finish.

Regards,
Andreas

-- 
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> 
> 
> Thx !!!
> 
> B.
> 
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