I usually use hard drives for backing up. I have two backups of everything (on separate HD's). This has been OK until the Mac froze during a back-up and the back-up HD would not mount afterwards. Luckily I had a second back-up. I have a lot of information (over 600Gig). Thus it is very laborious to keep all that stuff on DVD's (and even they are not 100% foolproof). Are there any other REASONABLY ECONOMIC and fast alternatives to hard drives for backing up?