You could deploy a cluster-across-boxes to implement a Microsoft Cluster with a VM on one ESX host and a VM on a different ESX host.  You can do this natively in ESX so you wouldn't need to buy a third-party solution.  You would then implement HA to protect the other VMs that are not part of a Microsoft cluster from a failure of a single ESX host.

Hi George,

As others have pointed out, HA allows you to bring the VM back online on another ESX host. This will protect you against a failure of that ESX host.

You can also use MSCS and cluster two VM's together that reside on two ESX hosts, this gives you the additional software layer protection.

Last but not least, you could use Veritas Cluster Service (now Symantec) for additional functionality.

The benefit to HA is that there is almost no complexity involved. You do not need to be familiar with clustering. Assuming you a running Windows VM's you also can reduce cost as you do not need a Windows Enterprise edition and the same goes for your applications. The other benefit is that with MSCS the application needs to be cluster aware, where HA will work with any OS/application combination.

In short, HA is a very cost effictive solution to get high availability for servers or companies that normally could not cost justify this, but it does not replace clustering technologies.

Last but not least, using VMotion with a MSCS clustered VM is not supported. This also means that an MSCS clustered VM should never be a part of a DRS cluster.

Sincerely,

Daniel Bischops