I have been getting several Sun Cluster inquiries from people recently. So, here is a quick intro with links to lots of resources:
Sun Cluster is Sun’s clustering technology that can bring high availability to your applications or you can extend it to fit your high availability needs.. Since it’s free to download, you can install it on a single physical machine with multiple cluster nodes in different zones in Solaris 10 for testing purpose. You can also install it on at least 16-nodes to make your application both fault tolerant and scaling. Before you ask further questions, make sure you have read the documentation.