The Hypervisor Commodity is a Fairy Tale
I agree on most of the storage comments here. There is one thing I have to answer on: it won't really help running the same storage layer in different Hypervisors if the Hypervisor is not a commodity to the VM. Today there are at least 3 proprietary parts of the VM that make this impossible:
* the VM config file is proprietary to the hypervisor
* the VM disk format is proprietary to the hypervisor
* the VM guest drivers are proprietary to the hypervisor
So as long as the VM is not a standard, which it probably never will and the way people want to solve this is with even more layers on top, I'd rather use a VSA model for distributed storage over multiple hypervisors than having the storage vendors design their storage controller code for different kernels (Linux, ESX, Windows).