Power is the great uptime equalizer. Show me the most elegant HA design you can dream up and chances are I'll show you a system that's one unexpected power failure away from failure.
Indeed, I can remember us all feeling quite nice and smug with our racks having dual A and B feeds from separate mega UPSs generators etc.
We didn't feel quite so smug when we actually found out that some of the racks actually had both sides plugged into the A feed - which was probably confusion between us, the data center owner and the electrician installing the feeds.
