vCenter Server 5.5 update 3.x supports Microsoft Cluster Service (MSCS) as an option for providing vCenter Server availability.
Multiple instances of vCenter Server are in an MSCS cluster, but only one instance is active at a time. Use this solution to perform maintenance, such as operating system patching or upgrades, excluding vCenter Server patching or upgrades, You perform maintenance on one node in the cluster without shutting down the vCenter Server database.
Another potential benefit of this approach is that MSCS uses a type of "shared-nothing" cluster architecture. The cluster does not involve concurrent disk accesses from multiple nodes. In other words, the cluster does not require a distributed lock manager. MSCS clusters typically include only two nodes and they use a shared SCSI connection between the nodes. Only one server needs the disks at any given time. No concurrent data access occurs. This sharing minimizes the impact if a node fails.
Unlike the vSphere HA cluster option, the MSCS option works only for Windows virtual machines. The MSCS option does not support vCenter Server Appliance.