If you are virtualizing your server environment – use NFS as your storage protocol. It’s better, period, end of story. Don't beleive me, ask Nick Triantos at NetApp. If you are ok with limited storage capacity, let a NAS storage controller virtualize your disk and present NFS to your virtual servers. If you want to protect yourself from lock-in and the pain of provisioning beyond a single NAS controller, do your virtualization in the network connecting your storage arrays to your virtualized servers.