I currently have 3 750GB drives for my mac pro. I have one drive in Bay-1, which is backed-up daily to the drive in Bay-2. About every two weeks I swap out the drive in Bay-2 with the third drive and use it as the back-up. That way I can keep an off-site back-up and it will never be more than ~2 weeks old. I am beginning to run out of drive space so I need to think about a new paradigm. I could buy 3 more 750GB drives and do the same thing again. This would run ~$730 (seagate from newegg). I think the 1TB drives are interesting, but still priced at a premium so I've kind of ruled those out. Alternately, I could keep the cost down and get 3x 500GB drives for ~$360 (again, seagate at newegg), which is appealing for the cost savings, but I might end up with a RAID card in the next year and it might be nice to have all drives with the same capacity. I've also considered doing something similar with a group of raptors, but the $/GB is high and I don't think I need the speed for what I do. So I guess the main question is....am I insane to have SIX drives in play, but really only using 2 at one time (four more serve as backup!). My data is valuable (many many man hours, expensive experiments etc.) So I am pretty insistent on an off-site back-up, but it occurs to me that maybe I should just by a ~1TB external drive and haul it into work every two weeks to make a copy. Anyone want to help with the cost/benefit analysis? Any thoughts?