Setting boot drive

I have a new Dell Poweredge R940. It has one SSD drive that I want to use as boot drive, and 14 drives I'll use for storage. I was able to install a virtual disk on the SSD drive, and was able to install Xen Hypervisor there and set up the other drives as storage. The problem now is that i can't figure out how to boot from that virtual disk. I don't see an easy way to do it. How would I go about it? Thanks.