Virtual Machine Cluster
From Livedoc - The Documentation Repository
Our virtual machine cluster consists of a set of servers, all running virtual machines, that share a common storage system. Any virtual machine can be moved to any server as needed.
The cluster consists of a number of components. iSCSI, ccs, cman, and clvm form the storage level, allowing all machines in the cluster to access the shared storage of the storage arrays concurrently. On each server, we run Xen, the virtualization software that powers our virtual machines.