New 'MPG' Metric For Data Centers

While data centers consume massive amounts of energy, most data centers have become massively more efficient over the past several years.This is an important point made in a new white paper, Energy Logic: Calculating and Prioritizing Your Data Center IT Efficiency Actions, by Emerson Network Power, which introduces a new metric to measure data center efficiency that Emerson hopes will have some of the same value that the miles-per-gallon (MPG) metric provides as an easily understood and agreed-upon efficiency measure for cars. Adding context to the improvements the computing industry has made in output and efficiency, the white paper notes, "While auto efficiency achieved a modest 0.8 percent compound annual growth rate, data center efficiency grew by 53 percent annually. If fuel efficiency had kept pace with data center efficiency improvements, the current generation of automobiles would average 163 MPG."

Specifically, the new Energy Logic white paper introduces the concept of CUPS, or Compute Units per Second, which is a relative measure of server output, based on average server performance in 2002. Using data from multiple industry sources, Emerson calculated the change in CUPS between 2002 and 2007, showing that while data center energy consumption has risen in recent years, the increases are overshadowed by dramatic gains in output and efficiency. "If data center output had remained flat between 2002 and 2007, the efficiency improvements achieved would have cut 2007 data center consumption to one-eighth the 2002 consumption." CUPS can be the numerator in the equation that determines compute efficiency for individual devices and/or data centers as a whole, with the power draw as the denominator, i.e. Compute Efficiency = CUPS/Watts Consumed. According to the white paper "Server efficiency, measured in CUPS/watt, grew 658 percent (7.6x) between 2002 and 2007. Data center efficiency, aided by infrastructure improvements, achieved even more impressive gains. CUPS/data center watt grew by 738 percent (8.4x) during the same period." Data center professionals can experiment with the new CUPS metric in an online data center efficiency calculator.

The white paper points up several shortcomings in the Power Usage Effectiveness (PUE) metric currently proposed as an interim measure of efficiency and makes a compelling case that any acceptable efficiency metric should meet at least three criteria: