The power supply in xenserver2 failed. As I don't have a spare on hand at the moment, I brought it back to life by smacking on the case.
Percussive maintenance being the temporary fix it is, I'm not putting anything critical on this box. I'm going to tee up both of these machines for a power supply replacement, and look at either getting a third machine, or increasing RAM in these two drastically.
As i write this, the filesystem fell out from under xenserver2, so I strongly suspect something far more unseemly is happening, perhaps still power supply related.
So at this point it sits cold in the datacenter for a few days until I get the resources (time/money/etc) together to get this bad boy back to health. If anyone's feeling generous, it's an ATX power supply, pretty standard, actually. It needs the standard compliment of connectors modern supplies have. 450w or better.
and a few test vms of mine.