As memory serves, I recall a report by some Congressional committee from a few years ago that said the US intell infrastructure was generating in the neighborhood of 4 petabytes per month! (although that might have been per year, still a very large bucket ‘o bits).
Still, 4T drives are common these days; that’s a 1000 (or 1024) of them.
When your budget is the NSA’s, even assuming multiple redundancies of the data store on RAID, several 1000 drives per month is nothing.
And people have some really neat answers for cheap storage these days. The BackBlaze Pod is up to V 4.0. $0.051 / GB.
http://blog.backblaze.com/2014/03/19/backblaze-storage-pod-4/
I’m sure the government is using more expensive answers, but still, it shows what can be done.