Xen is cool. Xen is so cool, I don't feel that I can give it a summary to do it justice. But, I like failure, so I will try. Basically, xen is a hypervisor (all the geeks in the room just went "ahhh", all their girlfriends just rolled their eyes).
Basically, it lets you run multiple instances of an operating system on top of another operating system with minimal performance hit. I saw one article that stated the performance crunch for Xen was about 3%. That's pretty dang slick considering that Vmware on my box is a painful ugly dog. Anyways, I was trying to create a very minimal image to run in Xen to do some network testing, and I kept getting the following error.
moses auto # xm create ttylinux Using config file "ttylinux". Error: Device 2049 (vbd) could not be connected. Backend device not found.
How frustrating is that?!!? Well, I joined up to #xen on freenode, and lo and behold, someone pointed out that my configuration said:
disk = ['file:/usr/xenbase/ttyroot/,xd0,w']
Notice that I say "file" and then point to a directory. Apparently, in Xen, you can choose between an actual disk partition or a disk image formatted with something nifty like efs2. So anyways, converting that to a disk image fixed the problem.