Chase Jarvis has written about how he manages his backups. you can find it here: http://blog.chasejarvis.com/blog/2010/06/workflow-and-backup-for-photo-video/

Doing backups to DVD's works for smaller libraries, but as you've found, as it grows, it becomes impossible to maintain reliably. There are also issues with how long DVDs last before you risk starting to lose bits and possibly have them become unreliable, unless you use the more expensive archival disks. (see here to start: http://photo.net/digital-darkroom-forum/00W6MR but there's lots of discussion on this all over the net)

The beginning answer is to use three disks: Your data disk, a disk you back up your data disk to, and a second backup disk that you store offsite somewhere and rotate with your backup disk on a regular basis. Backing up disk to disk is the only real solution today for large data sets, and the only way to make sure your backups are reliable is to retire disks before they get too old (and fail), and to have a copy somewhere offsite for those catastrophic failures (like theft or the building burning down).

As your data size keeps growing, even managing disks becomes a pain. when I hit that point I went with a NAS (Network Attached Storage). Some info on that here: http://www.chuqui.com/consider-upgrading-home-network-nas/

And for general "how the heck do I set up a reliable backup?" you can start here: http://www.chuqui.com/want-know-backups-2013-edition/

Bottom line: multiple copies of the data you want to protect. At least one copy offline and offsite. Make sure you do backups regularly. the best practices that I've found is to use multiple drives, not trying to manage with DVDs or other optical media. It's less hassle, more reliable and most cost effective over time.

(cloud backups? I keep exploring them, I keep deciding it's not worth the hassle/cost yet. But it's coming. Your mileage my vary, but also take time to think about how you'll restore from a cloud backup and how long it'll take to replace a catastrophic, complete loss). Most cloud backups don't handle that as well as I want yet.