[Pacemaker] 3rd node just for quorum

[Klaus Darilion]

Klaus Darilion wrote:
> Hi!
> 
> Currently I have a 2 node cluster and I want to add a 3rd node to use
> quorum to avoid split brain.
> 
> The service (DRBD+DB) should only run either on node1 or node2. Node3
> can not provide the service - it should just help the other nodes to
> find out if their network is broken or the other node's network is broken.
> 
> Is my idea useful?
> 
> How do I add such a "simple" 3rd node - just by using location
> constraints for the service to be run only on node1 or node2?

Seems like this is called a asymmetric cluster:
http://www.clusterlabs.org/wiki/DRBD_HowTo_1.0#Specifying_the_nodes_where_the_DRBD_RA_can_be_run

But I do not understand the example in above howto:
First it states that the location constraint is only needed for 
asymmetric clusters. But then it states that the location constraint is 
only valid for symmetric clusters and the rule needs to be inverted. 
Thus, the howto contradict itself - what is correct?

Thanks
Klaus