Users also taking steps to dial down server heat

By Deni Connor and Jennifer Mears, Network World
May 31, 2004 12:08 AM ET

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As server vendors roll out systems that are increasingly powerful - and increasingly small - IT managers need to consider the heat output and power demands of new configurations that pack more processing power into less space.

In the past, companies could feel comfortable installing more air conditioning units in data centers as their cooling needs grew. But as servers become faster and more compact, the issues of heat and power aren't answered by adding more air conditioning.

Consider Virginia Polytechnic and State University, in Blacksburg, which recently deployed a supercomputing cluster of about 1,100 Apple G5-based systems. To adequately cool the cluster, the university's engineering firm recommended the school use traditional air conditioning units and spread the servers across a 10,000-square-foot area, the entire floor space for the university's main data center.

"[Spreading the cluster across] a 10,000-square-foot design really wasn't an option," says Kevin Shinpaugh, director of research and cluster computing at Virginia Tech and associate director of the Virginia Tech Terascale Computing Facility, which manages the Terascale cluster. He couldn't allocate the entire data center for the cluster because of other systems the university had installed.

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Shinpaugh looked for other options for cooling the servers and finally settled on precision cooling systems from Liebert that suck hot air out of racks and use rack- or ceiling-mounted air conditioning units.

"We had about 3,000 square feet of available space [for the cluster] and the [Liebert] extreme cooling option allowed us to do what we needed to do," he says. "Our only other option would have been to build another building."

Shinpaugh says the school spent about $2 million for the cooling devices and adding power, but says now the data center has excess power and cooling capacity, and will be able to handle additional systems over the next few years.

"The $2 million investment allows us to better use the space we already have," he says. "Once we get over the upfront costs, adding to the cluster or building new clusters will be easy."

Mark Nelson, project manager at Applied Materials in Austin, Texas, says he too designed his data center to accommodate increasingly dense configurations. Today, the data center is designed to handle about 75 watts per square foot of power, but only uses about 39% of that capacity.

"We anticipate as we put in more equipment and as equipment is replaced with newer technology that our wattage per square foot is going to start creeping up. We'll start approaching 75%," he says.

Nelson says he runs a redundant power system so there is immediate failover in case of problems and has an extra air conditioner on hand in case heat output spikes above his worst-case scenario.

According to the Uptime Institute, a consortium of corporations focused on reducing downtime in data centers, the average heat density output in today's data centers is about 28 watts per square foot.

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Having dense servers means more heat and more power consumption in smaller spaces. As corporations deploy these new systems, they must work closely with their facilities teams to ensure their data centers can stand the heat. A few tips:

•	First things first: Do a realistic analysis of cooling capabilities and power availability before planning new deployments.
•	Make room: Ensure that there is enough room in the back of racks so that cables don’t obstruct airflow.
•	Look up: Consider technology that moves hot air out of the top of racks and cools from the top down.
•	AD/DC: Evaluate DC power alternatives, which are typically less expensive.
•	The dotted line: Don’t overdo it with perforated tiles; focus them in cool aisles.
•	Plug holes: Be sure cable cutouts behind or underneath racks don’t let too much air escape, reducing airflow pressure.
•	Spread things out: In some cases, having more open space to ease power and cooling requirements makes more sense than pushing for maximum density.
•	Keep your eye on advances: Vendors are introducing servers with multithreading and multicore technologies, which provide performance improvements without big jumps in heat and power.

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Brill says some blade users have reported as much as 14 kilowatts of heat output per rack, about the same amount of heat given off by two household electric ovens.

Cees de Kuijer, infrastructure manager at Capgemini, a consulting and outsourcing firm, says he'll wait for blade server technology to evolve before bringing the compact slices of computing power into his data center.

"Blade servers present several problems - one of them is heating, the other is powering," de Kuijer says. "We basically have a ban on blade servers at this moment on the procurement side."