Not everything should be plugged into the UPS

My last entry detailed the fun that can ensue when a power failure occurs, but things such as the KVM switch, emergency lights and the monitor aren’t plugged into a UPS. This entry is much shorter and deals with what happens when too many things are plugged into a UPS.

I heard this story during a Windows NT 4 training course back in 1997.

A datacenter was being set up on one of the upper floors of a newly constructed office building in the Darwin CBD. The datacenter design included a large UPS array. The design was such that any power outlet on the datacenter floor ran directly to the UPS array. The array was large enough that the twenty or so servers the datacenter would hold could continue to run for 30 minutes if the building lost power.

For those of you that aren’t great with Australian geography, Darwin is only a couple of degrees off the equator. It goes without saying that in an equatorial climate like Darwin’s, every room, not just the server room, needs air-conditioning. For those that aren’t acclimated, it can be like living in a sauna. During the hottest months, the outside temperature at three in the morning can be well over 90 F. Air conditioners for most buildings in Darwin are located on the roof.

After servers and networking equipment had been moved into the datacenter, a wandering member of the management classes asked a systems administrator why the area was kept so cold. The systems administrator informed them that servers generated a lot of heat which could lead to component failure if the environment became to warm. If the building’s air conditioners failed, the systems administrator continued, the servers would have to be shut down until such time until the climate system could be repaired.

The air conditioners were located on the floor above the datacenter. After thinking about this, the manager got an idea. Without talking it over with anyone, he organized for the building’s air conditioners to also be connected to the UPS array. Whoever did the connection apparently did not ask too many questions.

Air conditioners draw significantly more power than servers do. When the power finally did fail, rather than 30 minutes of leeway, the building’s air conditioners sucked the UPS array dry in a matter of seconds.

I think that it was fair to say that although the servers did not shut down gracefully, they also didn’t have a chance to heat up the datacenter to the point where components failed.