You can configure Messaging Server and Calendar Server to be highly available by using clustering software. Messaging Server supports both Sun Cluster and Veritas Cluster Server software. Calendar Server supports Sun Cluster software.
In a tiered Communications Suite architecture, where front-end and back-end components are distributed onto separate machines, you would want to make the back-end components highly available through cluster technology as the back ends are the “stores” maintaining persistent data. Cluster technology is not typically warranted on the Messaging Server or Calendar Server front ends as they do not hold persistent data. Typically, you would want to make the Messaging Server MTA and MMP, Webmail Server, and Calendar Server front ends highly available through redundancy, that is, by deploying multiple front-end hosts. You could also add high availability to the MTA by protecting its disk subsystems through RAID technology.
See Chapter 2, Key Concepts for Hardware Service Providers, in Sun Cluster Concepts Guide for Solaris OS for more information on Sun Cluster topologies.
See Chapter 3, Configuring High Availability, in Sun Java System Messaging Server 6.3 Administration Guide for more information on configuring Messaging Server for high availability.
See Chapter 6, Configuring Calendar Server 6.3 Software for High Availability (Failover Service), in Sun Java System Calendar Server 6.3 Administration Guide for more information on configuring Calendar Server for high availability.