The double-edge blade

When you build, keep power consumption in mind

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One size fits all?

It's an overlooked side effect of blade servers: increased power consumption. While consolidating computing resources onto blades can make sense in terms of IT efficiency, it requires planning to maximize power efficiency.

The average rack of servers used to consume between 3 and 5 kilowatts per hour per rack, according to Ron Mann, director of Hewlett-Packard Co.'s rack and power systems group. However, thanks to more power-hungry processors, today a rack of servers could eat 7, 15 or even 30 kW per hour.

And blade servers? They consume as much as 40 kW per hour, Mann said. These are expensive numbers considering commercial electricity prices have been inching toward 15 cents per kW and higher.

'You design a data center based on how much power you pack in per square foot,' said Bob Periera, infrastructure solutions engineer at HP. According to HP's calculations, the optimal data center consumes 100-150 watts per square foot. Agencies might be tempted to spread out servers over more floor space to save cooling costs, but that could mean higher real estate costs. If you pack servers more densely, the costs for additional cooling and other support issues start to skyrocket.

When you aim for 100-150 watts per square foot, you may not need all the wattage right away, but it should cover your power needs in future years. For its part, HP tells customers to plan for a minimum 25 percent power increase each year.

About the Author

Joab Jackson is the senior technology editor for Government Computer News.

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