Not too long ago a few software engineers figured out that a server running a single application is wasteful because a significant amount of power is consumed by the server, yet only a small fraction of the processing capability is being used. Today one of the many reasons IT departments leverage server virtualization is to reduce the electrical usage in the data center. Unfortunately, they stop there and are unaware that their data center efficiency has suffered for the same reason that drove them to virtualize in the first place. Why does doing something good like virtualization result in a negative impact on data center efficiency? This article will help bring some understanding to this paradox and provide suggestions on how to avoid it.

A server has a power supply, memory, drives, fans, cards, a processor, and other components that consume electricity, all so that some type of valuable computing is produced. All these components draw power immediately upon plugging the server into a receptacle, even at 0% processor utilization - this is known as fixed losses. Fixed losses in servers are typically 33-50% of a server's maximum power consumption. As processor utilization increases, so does the power consumption, but the fixed losses remain. Unfortunately, unvirtualized servers typically run a single application with a processor utilization averaging around 5-10%. This means that it is costing much more per kW-hour to run that application compared to a host server that is running 10 applications / operating systems (i.e., 10 virtual machines).