Data Center Density Hits the Wall

Why the era of packing more servers into the same space may have to end.

Computerworld |

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Belady wants equipment to be tougher, but he also thinks servers are more resilient than most administrators realize. He believes that the industry needs to rethink the highly controlled environments that host distributed computing systems today.

The ideal strategy, Belady says, is to develop systems that optimize each rack for a specific power density and manage workloads to ensure that each cabinet hits that number all the time. In this way, both power and cooling resources would be used efficiently, with no waste from under- or overutilization. "If you don't utilize your infrastructure, that's actually a bigger problem from a sustainability standpoint than overutilization," he says.

What's Next

Belady sees a bifurcation coming in the market. High-performance computing will go to liquid cooling, while the rest of the enterprise data center -- and Internet-based data centers like Microsoft's -- will stay with air but move to locations where space and power costs are cheaper so they can scale out.

Paul Prince, chief technology officer of the enterprise product group at Dell Inc., doesn't think most data centers will hit the power-density wall anytime soon. The average power density per rack is still manageable with room air, and he says hot aisle/cold aisle designs and containment systems that create "superaggressive cooling zones" will help data centers keep up. Yes, densities will continue their gradual upward arc. But, he says, it will be incremental. "I don't see it falling off a cliff."

At Industrial Light & Magic, Clark sees a move to liquid, in the form of closely coupled cooling, as inevitable. Clark admits that he and most of his peers are uncomfortable with the idea of bringing liquid into data centers. But he thinks that high-performance facilities will have to adapt.

"We're going to get pushed out of our comfort zone," Clark says. "But we're going to get over that pretty quickly."

How-to

Energy-Saving Tips for the Data Center

Refresh your servers. Each new generation of servers delivers more processing power per square foot -- and per unit of power consumed. For every new BladeCenter rack Industrial Light & Magic has installed, it has been able to retire seven racks of older blade technology. Total power savings: 140 kW.

Charge users for power, not just space. "You can be more efficient if you're getting a power consumption model along with square-footage cost," says Ian Patterson, CIO at Scottrade. Use hot aisle/cold aisle designs. Good designs, including careful placement of perforated tiles to focus airflows, can help data centers keep cabinets cooler and turn the thermostat up.

Look for the most efficiently designed servers. Hardware that meets the EPA's Energy Star specification offers features such as power management, energy-saving power supplies and variable-speed fans. It may cost more upfront, but it typically costs less to operate over the long haul.

Consider cold-aisle containment. Once you have a hot aisle/cold aisle design, the next step for cabinets exceeding about 4 kW is to use cold-aisle containment techniques. This may involve closing off the ends of aisles with doors, using ducting to target cold air and installing barriers atop rows to prevent hot air from circulating over the tops of racks.

Use variable-speed fans. Computer room air conditioning systems rely on fans, or air handlers, to push cold air in and remove hot air from the space. A reduction in fan speed of 12.5% cuts power use in half.

Turn on power management. Most servers ship with energy-saving technologies that do things like control cooling-fan speeds and step down CPU power during idle times, but it's not turned on by default -- and many data centers still don't enable it. Consider enabling it by default, except in environments where high availability and fast response times are mission-critical.

Create zones. Break the data center floor into autonomous zones, where each block of racks has its own dedicated power and cooling resources. Zoning involves careful separation of hot and cold air but usually doesn't require that an area be physically partitioned off.

Douse hot spots with closely coupled cooling. A series of high-power-density racks can create a hot spot that the room air conditioning system can't handle, or that forces IT to overcool the entire room to address a few cabinets. In those cases, consider supplemental spot-cooling systems. These require piping chilled liquid -- either water or glycol -- to a heat exchanger that's either attached or adjacent to a high-density cabinet.

Retrofit for efficiency. While new data center designs are optimized for cooling efficiency, many older ones still have issues. If you haven't done the basics, optimizing perforated-tile placements in the cold aisle or putting blankets over cabling in the floor space are good places to start.

Install temperature monitors. It's not enough to monitor the room temperature. Adding more sensors allows better control in the row or rack.

Turn up the heat. The key to raising efficiency is increasing your intake temperatures on the cabinets. The higher the intake temperature, the more energy-efficient the data center. While you probably can't cool an entire cabinet with the room set at 81 degrees at the intake, you probably don't need to be setting the temperature as low as 65, either.

— Robert L. Mitchell

This story was originally published in Computerworld's print edition. It was adapted from an earlier version that first ran on Computerworld.com.

Robert L. Mitchell is a freelance writer and editor. Previously, he was a national correspondent for Computerworld. He also served as an editor at Network World and BYTE magazine, and was part of the editorial team that launched TechBeacon.com.

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