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Story URL: http://www.silicon.com/research/specialreports/leanandgreen/0,3800014367,39251526,00.htm

Google: Server efficiency needs different approach
Can't treat them like mobile devices

By Stephen Shankland

Published: Wednesday 25 June 2008

Chipmakers have been applying lessons learned in mobile computing to servers in an effort to increase efficiency by lowering power consumption. But a noted Google engineer has argued the two styles of computing are too different.

Luis Barroso, a Google engineer who closely studies the company's power consumption, speaking at the O'Reilly Velocity conference in California, said: "The data centre is a different device than the key targets for mobile electronics, laptops and mobile devices."

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Naturally, with at least hundreds of thousands of servers in operation and its data centres placed near power plants to cut electricity costs, Google is trying to get computing-equipment makers more excited about efficiency.

The basic problem is that mobile devices and servers have different modes of activity.

Mobile devices have been improving through better exploitation of the fact that they spend a lot of time dormant, with occasional bursts of activity. That lets processors and other electronics save power by spending most of the time in low-power sleep modes, snapping awake for peak-power, high-performance modes when necessary.

The opposite applies to the activity of Google's servers, however: they spend most of their time doing modest amounts of work, with frenzied moments of peak activity and complete lulls a rarity, Barroso said. The measurements are based on measurements of about 5,000 servers performing four different Google applications, he added.

The company's servers simply can't go to sleep: each machine is "rarely fully idle", Barroso said. "The fraction of time the servers are actually doing exactly nothing is very small."

Google is urging electronics designers to create products that more gracefully reduce power demands as activity diminishes. Servers naturally consume peak power at peak activity but still consume about half of peak power when at zero activity.

Processors have come in for criticism for squandering ever more energy. Barroso himself, once a chip designer for Digital Equipment, has expressed such concerns previously. But chips are actually better than hard drives, memory and network adapters at reducing power consumption during periods of moderate activity.

Some sophisticated hard drives, for example, can slow down their rotational speed to save power during periods of lower activity. However, Barroso said: "They need to bump to higher RPM to do something useful", to read and write, unlike processors, which can still process data when in low-activity modes.