[Pacemaker] drbd-xen and fencing

Vadym Chepkov vchepkov at gmail.com
Thu Nov 11 08:19:18 EST 2010


I posted a less elaborate version of this question to drbd mail-list, but, unfortunately, didn't get a reply, 
maybe audience of this list has more experience.

I am trying to make xen live migration to work reliably, but wasn't successful so far.
Here is the problem.

In a cluster configuration I have two type of resources - file systems on drbd, with explicit drbd resources configuration and 
Xen resources with implicit, using drbd-xen block device helper. For the former everything works great, but the latter doesn't work quite well.
In order for helper script to work, drbd module has to be loaded and underlying resources up. So I have to start init.d/drbd script.
I can't make it an lsb cluster resource, because stop will be disastrous for file system resources. Enable it in startup sequence breaks
/usr/lib/drbd/crm-unfence-peer.sh, because cluster stack is not completely up by the time drbd script finishes, and there is no way to configure only specific resources that need to be initialized.
Also, I can't find a way fence Xen resource. I tried fence-peer "/usr/lib/drbd/crm-fence-peer.sh -i xen_vsvn",
where xen_svn is the name of Xen primitive, but it doesn't work, 
so there is a danger of starting Xen VM on an out-of-date node. Then there is no way of monitoring underlying drbd resources too. 
I thought of adding underlying drbd resource explicitly in the cluster, but I can't figure out what would be the configuration 
for "this resource can be master on both nodes, but if just on one, it's fine too".
allow-two-primaries has to be allowed for live migration and at the time of migration resources are primary on both nodes, but when migration finishes, 
it's again primary/slave. But if I configure drbd resource in the cluster with meta master-max="2" master-node-max="1", 
cluster insists on having them both primary all the time.

Hope I didn't bore you to death and there is an elegant solution for this conundrum :)

Thank you,

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