[Pacemaker] stonith and avoiding split brain in two nodes cluster

[Jacek Konieczny]

On Mon, 25 Mar 2013 20:01:28 +0100
"Angel L. Mateo" <amateo at um.es> wrote:
> >quorum {
> >	provider: corosync_votequorum
> >	expected_votes: 2
> >	two_node: 1
> >}
> >
> >Corosync will then manage quorum for the two-node cluster and
> >Pacemaker
> 
>   I'm using corosync 1.1 which is the one  provided with my
> distribution (ubuntu 12.04). I could also use cman.

I don't think corosync 1.1 can do that, but I guess in this case cman
should be able provide this functionality.
 
> >can use that. You still need proper fencing to enforce the quorum
> >(both for pacemaker and the storage layer – dlm in case you use
> >clvmd), but no
> >extra quorum node is needed.
> >
>   I hace configured a dlm resource usted with clvm.
> 
>   One doubt... With this configuration, how split brain problem is
> handled?

The first node to notice that the other is unreachable will fence (kill)
the other, making sure it is the only one operating on the shared data.
Even though it is only half of the node, the cluster is considered
quorate as the other node is known not to be running any cluster
resources.

When the fenced node reboots its cluster stack starts, but with no
quorum until it comminicates with the surviving node again. So no
cluster services are started there until both nodes communicate
properly and the proper quorum is recovered.

Greets,
	Jacek