Interest in modular data centers is growing, fueled by high-profile endorsements from Microsoft and Google. But the model raises new management concerns, and efficiency claims may be exaggerated.

Modular, containerized data centers being sold by vendors such as IBM, Sun and Rackable Systems fit storage and hundreds, sometimes thousands of servers into one large shipping container with its own cooling system. Microsoft, using Rackable containers, is building a data center outside Chicago with more than 150 containerized data centers, each holding 1,000 to 2,000 servers. Google, not to be outdone, secured a patent last year for a modular data center that includes "an intermodal shipping container and computing systems mounted within the container."

To hear some people tell it, containerized data centers are far easier to set up than a traditional data center, easy to manage and more power-efficient. It should also be easier to secure permits, depending on local building regulations. Who wouldn't want one?

If a business has a choice between buying a shipping container full of servers, and building a data center from the ground up, it's a no-brainer, says Geoffrey Noer, a vice president at Rackable, which sells the ICE Cube Modular Data Center.

"We don't believe there's a good reason to go the traditional route the vast majority of the time," he says.

But that is not the consensus view by any stretch of the imagination. Claims about efficiency are over-rated, according to some observers.

Even IBM, which offers a Portable Modular Data Center and calls the container part of its green strategy, says the same efficiency can be achieved within the four walls of a normal building.

IBM touts a "modular" approach to data center construction, taking advantage of standardized designs and predefined components, but that doesn't have to be in a container. "We're a huge supporter of modular. We're a limited supporter of container-based data centers," says Steve Sams, vice president of IBM Global Technology Services.

Containers are efficient because they pack lots of servers into a small space, and use standardized designs with modular components, he says. But you can deploy storage and servers with the same level of density inside a building, he notes.