Thomas Wenisch, assistant professor in the department of Electrical Engineering and Computer Science, and students David Meisner and Brian Gold will present a paper about improving the energy efficiency of data centre computer systems on March 10 at the International Conference on Architectural Support for Programming Languages and Operating Systems in Washington, D.C.

Thomas Wenisch and the students analysed data centre workloads and power consumption and used mathematical modelling to develop their approach. The approach includes PowerNap, the plan to put idle servers to sleep, and RAILS, a more efficient power supplying technique. RAILS stands for Redundant Array for Inexpensive Load Sharing.

The Environmental Protection Agency expects the energy consumption of the United States' data centres to exceed 100 billion kWh by 2011, for an annual electricity cost of $7.4 billion. Those figures are about twice what they were in 2006, when data centres already drew more electricity than 5.8 million U.S. households.

Data centres waste most of the energy they draw. The facilities are inefficient because they must be ready for peak processing demands much higher than the average demand. "For the typical industrial data centre, the average utilization is 20 to 30 percent. The computers are spending about four-fifths of their time doing nothing", Thomas Wenisch stated. "And the way we build these computers today, they're still using 60 percent of peak power even when they're doing nothing."

Techniques employed today such as dynamic frequency and voltage scaling don't do enough to conserve power, the researchers said. Instead, servers could sleep periodically like ordinary laptops. They would have to slumber and wake exceedingly fast, Thomas Wenisch said. His detailed analysis of 600 servers illustrates the sporadic and sparse demands on data centre servers. Their average idle period is mere hundreds of milliseconds. Their average busy period is even shorter, at tens of milliseconds. A millisecond is one-thousandth of a second.

While PowerNap would require a new operating system to co-ordinate the instantaneous sleeping and waking, most of the other technologies that would make this possible already exist, Thomas Wenisch stated. "There aren't really technological barriers to achieving this", Thomas Wenisch stated. "The individual components know how to go to sleep fast. Engineers have developed that technology for laptops and smart phones. But the pieces haven't been used in servers where you don't have a user closing the lid. The components are out there, but the system needs to be redesigned."

While the computer parts might not be hard to find, the power supply would need to be overhauled for PowerNap to work properly, the researchers say. Their new RAILS technique addresses this problem.

Today's power supply technique for stacking "blade-based" servers connects about 16 computers to a handful of 2,250-watt power supplies. The arrangement is inefficient unless the machines are running full steam.

To cut down on the power loss, RAILS would replace the one 2,250-watt power supply with a bunch of smaller, 500-watt power supplies. RAILS would be a necessary complement to PowerNap because without it, even sleeping servers would waste energy. "Together, these approaches can help make data centers green and solve these big energy efficiency challenges", Thomas Wenisch stated.

This research is funded by the National Science Foundation and Intel. The paper is called "PowerNap: Eliminating Server Idle Power". David Meisner, first author of the paper, is a doctoral student in the U-M division of Computer Science and Engineering. Brian Gold, a co-author of the paper, is a doctoral student in electrical and computer engineering at Carnegie Mellon University.

University of Michigan has filed for patent protection on the technology, and is currently seeking an industry partner to help bring the technology to market. Simple data centre and server initiatives underway at the University of Michigan are reducing computing energy levels by 10 percent, which equals $500,000 annually, said Tim Slottow, University of Michigan executive vice president and chief financial officer.

"Green computing is a wide-open environmental frontier and through Climate Savers Computing Initiative, the University is implementing data centre and server green computing best practices. More sophisticated solutions such as PowerNap and RAILS could exponentially increase our energy savings", Tim Slottow stated.