A recent article by Judy Keen in USA Today, takes an in-depth look at the proliferation of huge data centers across the country: “Buildings house secret servers that keep Net humming.” While the existence of these big data centers might be news to many who don’t ever think about the sprawling aisles of servers that power their Facebook profiles or Gmail accounts, the tech community is, of course, all too familiar with the idea. Still, Keen’s profile of various data centers — both urban and rural — and the degree of security and secretiveness involved in some locations, makes for an interesting read.

There are about 13,000 large data centers around the world, 7,000 of them in the USA, says Michelle Bailey, a vice president at IDC, a market research company that monitors the industry. Growth stalled during the recession, but her company estimates about $22 billion will be spent on new centers worldwide this year.

I thought it was interesting how old facilities, from water tanks to former mines to refurbished manufacturing plants, are being reborn as modern data centers. Security measures are also of interest:

Some data centers have “traps” that isolate intrusions by unauthorized individuals, technology that weighs people as they enter and sounds an alarm if their weight is different when they depart, bulletproof walls and blast-proof doors, Bailey says.

The video below profiles the underground Iron Mountain Data Center, site of an old limestone mine, in Butler County, PA.