Baeke.info writes a really good comparison on his Website, comparing Virtual Server's Host Clustering ability to VMware ESX 3.0 HA and VMotion features.
He writes:
If you, as a potential customer, are not aware of some of the details, you might end up thinking that Microsoft’s offering is equal to VMware’s. This article will show it is not. Of course, you have to match what is offered to your needs. Depending on those needs, Virtual Server 2005 R2 might be a good fit.
To be fair, VMware provides high availability out of the box only with ESX 3.0 and its HA feature. At the time of this writing (June 22nd 2006), ESX 3.0 is only just available. ESX 2.x did not provide such a feature although some third party offerings were available.
The components you need to create a basic cluster for Virtual Server 2005 R2 are:
- Two servers running Windows Server 2003 Enterprise or higher to create a cluster (MSCS).
- SAN or iSCSI LUNs to provide some form of shared storage.
- Virtual Server 2005 R2 (free)
- The host clustering whitepaper that includes a script to implement virtual machines as cluster resources. This whitepaper can be downloaded from the Microsoft site.
Check out the entire article and read his conclusions on the subject, here.