Before jumping into the High availability it would be a really good if all of readers can sit on the same seat about the clustering technology as well. Recently enough I went through the history of the clustering to get and idea about it, interestingly enough there are lot more than meets the eye on clustering :) Some history info about clustering can be found over here What is clustering - In its most elementary definition, a server cluster is at least two independent computers that are logically and sometimes physically joined and presented to a network as a single host. That is to say, although each computer (called a node) in a cluster has its own resources, such as CPUs, RAM, hard drives, network cards, etc., the cluster as such is advertised to the network as a single host name with a single Internet Protocol (IP) address. As far as network users are concerned, the cluster is a single server, not a rack of two, four, eight or however many nodes comprise the cluster resource