It's a more expensive investment to get started, (as opposed to something like CrashPlan, Carbonite, etc.) but I definitely recommend having a Drobo product hooked up to your network, with regularly scheduled backups to it.

If you got one of the five drive boxes, you could dump 5 2TB drives into it, and likely have enough capacity to store all 5TB of photos, and be able to flip on the option to have two drives crash simultaneously without you losing any data. (you definitely lose space using them, as I have a 1TB and 2TB in mine right now and only have ~900GB available) If you're using a mac, it can even act as a Time Capsule so you can direct Time Machine to back up directly to it. (my wife and I do this, it tends to back up about once a day rather than every hour like Apple promises) Yes, I know it's expensive, but it's nice to know I have a local box (nothing in the cloud!) with all my (and my wife's) data backed up to it, where if a hard drive decides to go kaput, neither of us lose anything.