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 centre, 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 centre.
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 centre 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 centre."
Energy efficiency also factored into Marriott's decision, Blanchard says. While Marriott's data centre 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 centre today can cut power consumption in half by using new energy efficient equipment that can run at higher operating temperatures, by optimising 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 economisers 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 centre. But for most of his clients, the ability to get people to the backup data centre 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, 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 centres. "But for most commercial enterprises, it probably will not be such a major requirement."
IT executives considering underground data centre space should check into expansion capability, energy efficiency and how electricity use is metered, he says.