Hi @orac31, your best option is something like Crashplan. I gave up on RAID a long time ago because it's simply not reliable for backups. If a hard drive dies, fine, but what if the RAID controller dies? What if the RAID controller's software is faulty and fails to recover after a drive dies? I've lost data because of both scenarios. RAID sucks for backups, so I would advise against going with a NAS solution. RAID is the technology they use to prevent data loss.
Crashplan is basically an online backup service. Assuming you don't have metered Internet or anything, there's no better solution. Backs up everything to the cloud, gradually over time. I've backed up over 12 TB (yes, that's 12 terabytes) to Crashplan and I've had to restore hundreds of gigs over the years due to failed drives. Never had an issue, saves me every time. Restores do take a while, but in an emergency they can ship you a hard drive with your data for $$$.
Of course it's not free, but they have an unlimited storage amount per computer. You pay per computer, basically. It's worth every penny.