Before deciding to go underground, IT executives need to identify potential limitations, experts say. Even things as simple as ceiling height can be a challenge. Continental's data center space in the Westland bunker has 10-foot ceilings, and putting full-height racks on top of an 18-inch raised floor was a tight fit. "We had to come up with a design to allow us to use full-height racks while providing sufficient airflow," Stelly says.
Another concern: While computer systems may be protected in a bunker, critical infrastructure needed during a disaster, such as generators, fuel tanks and air conditioning cooling towers, may be above ground. That could be a problem if the catastrophe you need to worry about is a tornado, warns Westec's Bolen.
Bolen recounts how one company claimed that its hardened facility could withstand a direct hit from an F3 (158 to 206 mph) tornado. But the air conditioning and generators were outside. "When an F3 hits, those generator and HVAC units are going to come off their pads," he says.
Westec ended up taking space at InfoBunker, about 45 miles away from its offices, Bolen says. The 65,000 square foot Cold War command bunker, designed to withstand a 20-megaton nuclear blast, maintains all infrastructure, including generators, fuel and cooling equipment, 50 feet underground.
Another consideration is that these underground facilities tend to be in rural, out-of-the-way locations. The facilities may be too far away from a company's primary data center, and finding local lodging for staff in a disaster situation may be difficult. Continental had to find office space and lodging accommodations for more than 100 operations staff during Hurricane Ike. Fortunately, Montgomery Westland had hardened above-ground office space as well as access to local lodging.
Underground facilities do have a few other advantages. The limestone floors at The Underground have a virtually unlimited load rating, while the walls maintain a constant temperature of about 55 degrees and act like a heat sink for some of the waste heat that comes off data center equipment. The limestone walls absorb 1.5 BTUs per hour per sq. foot of wall space, Doughty says.
The green aspect of going underground is what attracted Marriott International. It wanted to move from an outsourced "cold site" disaster recovery service to managing its own hot site backup data center. Management wanted a hardened, secure facility in a location that was within a day's drive from Marriott's Bethesda, Md., headquarters. And it wanted to make sure the facility followed the company's focus on environmentally friendly best practices, according to Dan Blanchard, Marriott's vice president of enterprise operations.
Last year, the hospitality business completed the build-out of a 9,000 sq. foot remote backup data center at The Underground. Blanchard says that although the extreme level of security, including armed guards, exceeded his requirements, the idea of reusing an old mine rather than breaking new ground appealed to Marriott. "It's a definition of recycling to use the space that was a mine and convert that fairly inexpensively to its next use, which for us is a data center."
Energy efficiency also factored into Marriott's decision, Blanchard says. While Marriott's data center uses a traditional chiller as its primary cooling system, the backup is a prototype free cooling system. That prototype, designed by Iron Mountain, uses an air-to-air heat exchanger, drawing 55-degree air from the 1,000 acres of unused space within the mine. "The air is the exact temperature of what you would bring in with mechanical cooling," Doughty says. Iron Mountain also is experimenting with a system that would pull cool water from an underground lake within the mine.
An abandoned mine may conjure up images of damp walls and dripping ceilings -- but that's not the case here. "You have pumps and a lot of protective devices," says HP's Gross, and all of the facilities claim that dampness is not a problem. Doughty says The Underground is naturally dry due to its location and the type of limestone above the mine.
Air quality also is good, he says. The air in the Iron Mountain facility is relatively clean and non-condensing, he says. "As soon as you put heat to it moves away from the dew point," and that makes it a good choice for cooling, he says.
Blanchard says the new Recovery and Development Center, which is used for software development until needed in an emergency, costs half as much as he previously spent on power. Some of that is attributable to relatively low cost of power in Pennsylvania (5.5 cents per kWh). The rest comes from efficiencies of design and the characteristics of the underground environment.
Gross cautions, however, that cooling efficiency gains specific to the location are probably not all that significant. A well-designed data center today can cut power consumption in half by using new energy efficient equipment that can run at higher operating temperatures, by optimizing airflow designs to allow intake air temperatures to rise as high as 85 degrees and still keep equipment within operating temperature limits, and by picking a location in a colder climate, where water- or air-side economizers can be used to take advantage of cool outside air as weather permits.
Security, Gross says, is the primary benefit of using an underground facility to host a primary or secondary data center. But for most of his clients, the ability to get people to the backup data center in a hurry, connectivity options, and finding a facility that meets budget are priorities. Underground facilities usually don't beat out above-ground sites in his clients' evaluations, he says.
Still, Continental and Marriott are among a small number of enterprise operations using underground facilities. Rakesh Kumar, an analyst with Gartner Inc., says he is unaware of any Gartner client that is currently leasing space in one. The primary benefit of such sites, he says, is that they are designed to be highly resilient -- often to military specifications. That's important for some government data centers. "But for most commercial enterprises, it probably will not be such a major requirement." IT executives considering underground data center space should check into expansion capability, energy efficiency and how electricity use is metered, he says.
Join the CIO Australia group on LinkedIn. The group is open to CIOs, IT Directors, COOs, CTOs and senior IT managers.