There is no catch, there is a caveat. We backup as big of a drive as you can cram into your computer, so if your D: drive is a Terabyte, or two, or ten, we will back it up for the same price. The caveat is you can backup one drive. 99% of all computers come from the factory with all the data stored on one drive (usually the D: Drive) so if you are a high end geek with a computer that has 12 drives, you have to pick one drive letter to have File to backup. We don’t care how big it is.