Green computing is a hot-button issue right now, but not all the ideas out there are practical for data centers. "It's 90% hype," says Ben Stewart, senior vice president of facilities planning at Terremark Worldwide. He's dubious about solar and wind power, for example. But Stewart says 10% of the ideas are win-win: Done right, certain green initiatives can increase energy efficiency, reduce carbon emissions and yield savings.

According to Steve Sams, vice president at IBM Global Technology Services, there's only one way to evaluate green energy options. "If I spent the money, where would I get the best return? That's the question to ask," says Sams. The key is knowing where to start. These four questions and answers can help you develop a plan.

Why should I care about having a green data center?

Data center managers who have run out of power, cooling or space are already motivated to move to greener practices. But many others don't care because they put reliability and performance first - and they don't see the power bills, says Peter Gross, CEO at New York-based EYP Mission Critical Facilities. That's likely to change as electricity consumption continues to rise. "Our data centers are a small fraction of our square footage but a huge percentage of our total energy bill," says Sams.

The cost of electricity over a three-year period now exceeds the acquisition cost of most servers, says Gross. "I don't know how anybody can ignore such an enormous cost. It is the second-largest operating cost in data centers after labor," he says. Gross says that every CIO, facility manager and CEO he meets expresses concern about data center energy efficiency.

"My CEO is beating the drum about cutting power consumption," says John Engates, chief technology officer at hosting company Rackspace Inc. in San Antonio. He says just 50% of power coming into the data center goes to the IT load. The rest is consumed by surrounding infrastructure, including power, cooling and lighting. "If you're using less power, you're spending less money. It's just good business," Engates says.

Returns on investment can be difficult to determine, however, because in most cases, the IT staff in a data center doesn't see the power bill. "The single most important step is to find ways to measure efficiency in your facility," says Gross. "You cannot control what you cannot measure."

One way to determine overall data center energy efficiency and provide a benchmark is to hire professionals to do an analysis. An inspection by IBM Global Technology Services costs US$50,000 to US$70,000 for a 30,000-square-foot data center, says Sams.

But just a one- or two-day engagement might get you most of the benefits for a lot less money, says Rakesh Kumar, an analyst at Gartner.

"You can get 80% accuracy with a small investment in consultancy costs," he says. "That's good enough to make some judgments."

What steps can I take to increase the efficiency of my data center's IT equipment?

The biggest savings come from server consolidation using virtualization technology. Not only does this remove equipment from service, but it also helps raise server utilization rates from the typical 10% to 15% load today, increasing energy efficiency.

Consolidating onto new servers brings an additional benefit. Power-supply efficiencies for servers purchased more than 12 months ago typically range from 55% to 85%, says Gross. That means 15% to 45% of incoming power is wasted before it hits the IT load. Newer servers operate at 92% or 93% efficiency, and most don't drop below 80%, even at lower utilization levels.

Using virtualization, Affordable Internet Services Online consolidated 120 servers onto four IBM xSeries servers. "Now we don't have the power use and cooling needs we had before," says CTO and co-founder Phil Nail.

Using networked storage can also keep energy costs in check. Direct-attached storage devices use 10 to 13 watts per disk. In an IBM BladeCenter, for example, 56 blades can use 112 disk drives that consume about 1.2 kilowatts of power. Those can be replaced with a single 12-disk Serial Attached SCSI storage array that uses less than 300 watts, says Scott Tease, BladeCenter product manager.

IT managers should demand more energy-efficient designs for all data center equipment, says Engates. He says his company standardized on Brocade Communications Systems Inc. switches in part because of their energy efficiency and "environmental friendliness."