When you implement a cluster using physical hardware, the process is very straightforward.But what if you want to implement a cluster using virtualization?
I was working ona project recently that required just such a solution. The short answer to the question is that you can, but the long answer is that it's not quite as easy as having the real physical equipment.
To implement clustered virtual machines (VMs) with Windows Server 2008, I needed four VMs. The first VM was the Active Directory domain controller, since the new Failover Clustering service in Windows Server 2008 requires a domain. For this VM, I used 1024MB (1GB) of RAM. You should provide more RAM to this machine if you plan to have virtual or physical clients connecting to the machine, but I was not allowing clients to connect in my situation. The second VM ran the iSCSI service software. This software is needed because Windows Server 2008 no longer allows you to configure attached disks as the "shared storage" within a virtual environment. The best solution is, therefore, iSCSI. Two excellent free software-based iSCSI solutions are FreeNAS (www.FreeNAS.org) and OpenFiler (www.OpenFiler.org). I used OpenFiler for my virtual environment because it can be downloaded as a VMware appliance. This made the setup much easier. Finally, the last two VMs ran Windows Server 2008 Enterprise Edition and acted as the Failover Clustering nodes. These nodes connected through iSCSI with the second VM for shared storage.
With a configuration like this, I was able to build a clustered test environment for certification preparation or lab testing without the expense of a hardware-based SAN. The nice thing is that all the virtual machines are backed up so I can rebuild a virtual clustered environment within a few hours anytime I need it.