Official News from Microsoft’s Information Platform
SQL Server support for Guest Failover Clustering in a virtualization environment is now available. Guest Failover Clustering is when you create a SQL Server failover cluster inside a virtual machine where the nodes are running as a virtual machine.
With this extension of support, SQL Server customers can achieve high availability of SQL Server products when they are running in a virtualized environment. What that means is, in the event of an unplanned downtime of a SQL Server instance running in a virtual machine, another SQL Server instance running in a different virtual machine can come online almost instantaneously and prevent any major business interruptions. Another benefit of guest failover clusters is the reduction in the planned downtime of the server, with the ability to do rolling patches/updates to the guest operating system.
Guest Failover Clustering is supported for SQL Server 2005 and SQL Server 2008 in a virtual machine for Windows Server 2008 with Hyper-V, Microsoft Hyper-V Server 2008, and SVVP certified configurations provided both of the following requirements are met:
For more information on support policy for SQL Server products that are running in a hardware virtualization environment please refer to http://support.microsoft.com/?id=956893.