To echo what I've seen quickly, RAID is not backups. If something (like cryptolocker) suddenly encrypts all your files... you're still completely utterly FUCKED.
If your domicile burns to the group, you're fucked. You need something that'll keep your data consistent, and keep it safe from theft/fire/destruction.
I'm going to ignore any cost considerations... whatever.
Build two identical boxes. The first box is going to sit in your place of residence, the second is going to sit elsewhere (like your parents house, or a buddies)
Each box is running your OS dejour that naively supports ZFS, a pair of 4TB drives, setup as a ZFS mirror volume. Use whatever software you use to copy data to the local box, rsync, crashplan, whatever, once that task is completed, you'll drop a snapshot of all the pertinent file systems you care about. You now, remotely drop a snapshot on our offsite box and then kick off an rsync that catch any changes.
1. If something has drastically gone wrong with your data locally, you can always revert (in this case promote) your latest snapshot (or whatever snapshot you like best). Plus you can thumb through all your snapshots and see what you like...
2. Even if something hasn't gone wrong, but you liked an old version of something, you have that too... though you'll have to decide on a strategy for how many snapshots you're willing to keep. zfs snapshots are now scm but sometimes you realize you don't have something under control and then you wish you did.
3. You've got a full duplicate of this elsewhere in case fire/flood/theft/etc.
4. Monthly do scrubs of your file system just to make sure everything is healthy. Want to expand your volume? Add two more disks and you can tack on another mirror. Yeah, it won't be balanced but you'll suddenly have more space.