As of the release date for VMware ESX 3.5 Update 1, Microsoft Clustering Service (MSCS) is supported with VMware ESX 3.5 and VMware ESXi 3.5. The Hardware Compatibility List (HCL) has been updated to state: MSCS is supported with VMware ESX 3.5 with both 32-bit and 64-bit VMs running Windows 2003. Please check the Hardware Compatibility List for updates weekly for Storage Arrays certified for MSCS.