I know, i did the numbers too - but it's still an almost unthinkable amount of data to try and make sense of. If we conservatively say that there are 5 others like linx, that's nearly half a million 3TB drives. And that's only for 3 days!
edit: clarity
I struggle to believe that GCHQ has the ability to store 3 or even 30 days worth of internet traffic flowing through the UK borders and also make reasonable sense of it all. It's such a mind boggling amount of data. I looked at some bandwidth graphs from places like LINX, which is just one of presumably many, and they are moving around a terrabyte a second - how can you possibly store, let alone sift through that kind of volume? 30 days at a terrabyte a second is nearly 3,000 petabytes of data. And that's just in one exchange. Is this kind of thing feasible? Facebook allegedly deals with 200PB of photo data - 3000PB is a lot more than that.