For situations that require a high degree of availability (such as four or five nines), you might consider Sun Cluster software as part of your availability design. A cluster system is the coupling of redundant servers with storage and other network resources. The servers in a cluster continually communicate with each other. If one of the servers goes offline, the remainder of the devices in the cluster isolate the server and fail over any application or data from the failing node to another node. This failover process is achieved relatively quickly with little interruption of service to the users of the system.
Sun Cluster software requires additional dedicated hardware and specialized skills to configure, administer, and maintain.