I don't like raid controllers, because they are typically stubborn. Requires drives of the same size, and if too many fail, everything is dead and gone.
I use SnapRaid for software parity to protect against up to two simultaneous drive failures currently. And even if 3 shall fail at the same time, I only lose the data that was on those discs, and nothing else. The big plus of SnapRaid for me is that its not even a driver or anything like that, its just an application and it reads and writes the file system like any other app, so there is very little chance that it would somehow fight against the OS or anything like that.
But as others have said, such a hardware or software raid is not a backup, its just a first level of protection against single harddrive failure. For my ripped Blu-ray collection this backup currently is the optical discs I have stored away, just from the sheer volume of the data - which isn't going to get any smaller with UHD BDs. I don't have room for a second onsite storage box, and a cloud solution would require at least double my current upload bandwidth to not feel totally off-base.