Serving up thousands of requests per seconds from 3 TB (while continually adding and updating more data!) is a lot different from just archiving it.
A _lot_. :)
To put it in perspective, 100GB is pretty much the limit of what you can serve from a single mysql machine, for instance. This will vary depending on exact workload but that is a reasonable ball park number.
Of course, in a relational database you wouldn't (generally) be storing the vast majority of the data in question...you'd be querying for it. That's not to trivialize the improvement in performance here, just to point out that this probably would be 100GB in a MySQL database.
