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Data centers drunk on power! Crunching numbers with HP

Each new generation of servers brings a 30 to 50 percent increase in power requirements, said Jeff Otchis, marketing manager of the rack and power systems group for the enterprise servers and storage division of Hewlett-Packard Co. These are numbers to keep in mind for the years to come, especially with the skyrocketing costs of electricity.

As we reported a few months back, managers of agency data centers are facing the twin problems of keeping their data centers cooled as well as keeping them supplied with enough power. Actually, the two problems are different aspects of a single concern. The more power your gear consumes, the more heat you have to dispel (which, in turn, jacks the power bill even higher). When building out a data center you have to balance cooling and electricity consumptions.

When we talked with the data center experts at HP, they broke the problem down into a fascinating set of interrelated numbers.

The average rack of servers used to consume 3-5 kilowatts per hour per rack, according to Ron Mann, director of HP's rack and power systems group. Thanks to more power-hungry processors, though, today it is not unusual for a rack of servers to consume 7, 15, or even 30 kW these days (and count 40 kW for blade servers). These are expensive numbers, what with commercial electricity prices inching towards 15 cents kW and beyond.

Such numbers are worth keeping in mind because, 'you design a data center based on how much power you pack in per square foot,' Bob Periera, infrastructure solutions engineer for HP told us.

HP estimates that most older data centers today use about 50 watts for every square foot of floor space. According to HP's own calculations, the optimum cost of building out a data center is right about 100-150 watts per square foot.
One might be tempted to spread the servers out over a wider range of floor space to save in cooling costs, but then you run into greater real estate costs. But if you pack your servers even more densely, the costs for additional cooling and other various support issues start the skyrocket.

So aim for 100-150 watts per square foot. You may not actually need all that wattage now, but be sure to factor in increases in power needs for the years to come. 'As a general rule of thumb, we tell customers to plan for a minimum of 25 percent power increase year over year.' HP's Otchis said.

You should also consider what kind of power to use. Most juice running along the utility company power lines is three phase (a phase is a flow of current). Before it hits the data center though, it is stepped down into single phase current, by use of a local transformer. U.S. homes use single phase power.

You could, however, use the three-phase power instead, which is actually the most optimal way to use the power, Mann said. An appliance that requires 160 watts to operate will gobble 3 amps from a single-phase 120 volt connection, but will use only half that'1.5 amps'from the 208 volts of a three phase connection.

'It's all about amps,' Mann said.

'Posted by Joab Jackson

Posted by Brad Grimes, Joab Jackson on Jun 14, 2006 at 9:39 AM


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