My first thought was, how long did it take to write and read this data? I don't expect exceptional speed, but I do wonder about throughput and seeking.
OK, so assuming 1 hour for 3 billion bases, it's 1000 hours for 3 trillions bases (3 Terabits) or 1 million hours for ~3 petabits (or 400TBs of data). Yeah, that's a long time, roughly 100 years :)
Seeking can be performed through entirely different means, as DNA is content-addressable. You can put in a magnetic bead attached to a strand complementary to what you're seeking, and pull that out of the mix. This is still a physical process that can take quite a bit of time.