Just thought I should share this link:
I have tried this on a HP DL380 G6 and it worked like a charm.
One of the advantages of using that kind of server is that it has internal usb ports so you don’t have to worry about someone accidentally unplugging the usb drive.
Why should I run a server os from a usb drive you may ask. Well, the biggest advantage is that if your storing all virtual machines on e.g. a SAN anyway you don’t have to buy internal disks for your Hyper-V hosts.
Another advantage is that is that usb drives are like ssd disks, they have no movable parts that can break, and they have a much lower power consumption.