Not too long ago, I had one of my XenServer hosts crash due to a hardware failure. It was not my Pool Master. When a XenServer host crashes the virtual machines running on the failed server can’t be controlled, so we’re unable to tell them to start up on another host. The XenServer pool still considers them running, however, they’re not listed in XenCenter. Hopefully this can help some of you get back up and running a little quicker.