As you probably know, "the cloud" in Internet parlance isn't an actual cloud. The Internet's cloud refers to remote storage of information and the network that connects to it. What tech companies pitch as a nebulous intangibility is really just stacks and stacks of servers with direct connections to the rest of the world. Things that take up physical space, in other words.
For the National Security Agency to do its spying, they need servers. They need buildings, perhaps ones clad in black, patrolled by guards, in remote places across the country. Indeed, the NSA is building a massive facility in Utah. But they need big buildings to hold the data infrastructure. But just how big, physically, is the NSA's privacy invasion? We decided to try and figure that out.
But to answer that question, we needed to answer three other questions. What information is being collected in the surveillance operations? How much of that information is the NSA housing? And, how much space would saving that much information actually take up? What we learned from talking to a variety of experts is that the calculus is not simple, and any answers are largely estimates. But we got answers.
For the rest of the story: http://www.theatlanticwire.com/national/2013/06/nsa-datacenters-size-analysis/66100/