It depends...
We have a mirrored 1Tb RAID-1 D-Link NAS drive that I put on line every week or so and copy new stuff onto that. (Yes, that's two 1Tb mirrored discs)! The nice thing is that it's small enough to fit into the firesafe - about the size of 2 or 3 paperbacks.
My main problem is photos which at 3-4Mb apiece and videos (1-2Gb each) soon eat up space. Fortunately they don't need version control so they're manageable. I even back up the music library (I once lost the lot with a HDD failure and it took days to recreate).