Database Software

I am leading a team that is attempting to document a standard for RAC deployments across all of my company's facilities. We're incorporating industry best practices and internal infrastructure standards. One of the recommondations we would like to make is that RACs should have a minimum of 3 nodes.

Our unsubstantiated theory is that there are differences between 2 node clusters and > 2 node clusters and that adding a node to a 2 node cluster for scalability would be more difficult than adding a node to a cluster that already had at least 3 nodes. In addition, if we're willing to accept the risk involved with assuming that only 1 node in a RAC will fail at a time, we won't need buy servers with 200% capacity.

First of all, do these ideas make sense? And secondly, is there any documentation or even expert opinion out there to back up our recommendation?

Thanks for your help.

Mandy