It's All About Power

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Disaster Recovery Planning

It's All About Power

5/1/2008

By Dian Schaffhauser

From that incident and others like it, Zeller has learned an important lesson: "Any place there’s the potential for a single point of failure, eventually there will probably be a failure."

UT-Knoxville’s data center, which contains hundreds of servers, is housed in a seven-story building. Only Zeller’s floor is hooked up to the generator, a Caterpillar diesel generator set comprising a 3412 diesel engine and an SR4B generator, which provides 750kVA/600kW of coverage. The only service the generator maintains on the other floors is emergency lighting, a small power load compared to the requirements of the data center. If the power stays off for longer than about 10 seconds, says Zeller, the generator starts up and makes the switch. Staff inside the data center notice the switchover only because the lights (which aren’t on a UPS) will go off for a few seconds, then come back on. That’s it. "Everything stays up and running," he says.

Zeller estimates that the generator can sustain an outage of between 24 to 36 hours at full load, without refueling. He’s never had the chance to time it because the campus has never had an outage of that magnitude. But the generator is sized for the capacity to cover services over a holiday, he says- enough time to allow a truck to get to the campus to refuel it.

That doesn’t mean the data center power management setup is foolproof. "There are always those single points of failure," says Zeller, adding practically that "it’s a space-and-money issue to go fully redundant on a lot of these things [UPS, generator, electrical box]." But, he says, "We’re doing much better than we did the prior 10 years when we didn’t have a single UPS."

Still, when the generator finally came in (after several years of delay, due to campus budgetary limits), Zeller made a decision to cut back on the number of batteries in the UPS, from three cabinets’ worth to two. (The data center could run on only half of that, but he prefers to have a level of redundancy.) That saved the school roughly $6,000. (The generator itself cost about $100,000; related hardware and installation costs pushed the entire project to about $500,000.)

Zeller considers cooling and humidity control in the data center a vital aspect of keeping services running. The optimal temperature is 70 degrees, he says; the optimal humidity level 45 percent, plus or minus 5 percent. "If the humidity gets too low, we have a static electricity problem, and if it gets too high, we have a condensation problem," he explains. The data center uses Liebert Deluxe System/3 chilled water environmental control systems, which can humidify and dehumidify, based on sensors in the units.

Right now, the UPS in the data center runs at about 80 percent capacity. Zeller maintains a graph of growth and power usage in the center, and based on the campus’s current rate of growth, he says, "We don’t have too much longer before we’re going to run out of power." By then he hopes to have moved some of the data center equipment that’s part of a research computer cluster, as well as test and development systems, into a building that the university recently purchased, which is already outfitted with a generator. To that end, he’s worked with the facilities people to design what the site will need in terms of wiring and a new UPS.