What is VMware HA?
One of the most amazing capabilities of VMware ESX is VMHA. With 2 ESX Servers, a SAN for shared storage, Virtual Center, and a VMHA license, if a single ESX Server fails, the virtual guests on that server will move over to the other server and restart, within seconds. This feature works regardless of the operating system used or if the applications support it.
Figure 1: Image Source: VMware.com