"Spreading a workload across multiple processors, coupled with various software recovery techniques, provides a highly available environment and enhances overall RAS (Reliability, Availability, and Serviceability) of the environment. Benefits include faster recovery from unplanned outages, as well as minimal effects of planned outages on the end user."
"This article illustrates the robust Apache Web server stack with 6 Apache server nodes (though 3 nodes is sufficient for following the steps outlined here) as well as 3 Linux Virtual Server (LVS) directors. We used 6 Apache server nodes to drive higher workload throughputs during testing and thereby simulate larger deployments. The architecture presented here should scale to many more directors and backend Apache servers as your resources permit, but we haven't tried anything larger ourselves. Figure 1 shows our implementation using the Linux Virtual Server and the linux-ha.org components."
http://www.ibm.com/developerworks/linux/library/l-linux-ha/index.html