Problems with the Power Usage Efficiency (PUE) metric
This is one of my slides from a recent talk I gave on Cloud Computing in Athens (full talk is at www.slideshare.net/TomRaftery/cloud-computings-green-pote...).
PUE (en.wikipedia.org/wiki/Power_usage_effectiveness) is a widely used metric to measure how efficient data centers are. However it is a poor measure.
Consider the example above - in the first row, a typical data center has a total power draw of 2MW. Of which 1MW goes to the IT equipment. This results in a PUE of 2.0.
If the data center owner then goes on an efficiency drive and reduces the IT equipment energy draw by .25MW (by turning off old servers, virtualising, etc.), then the total draw drops to 1.75MW but the PUE goes up to 2.33.
When lower PUE's are considered better (1.0 is the theoretical max), this is a ludicrous situation.