And if a raid controller fails... no fun. I had data failure when even a replacement identical controller for the raid could not read the data. I stopped using raids that day. And it was the week I was out of town so my only latest project was not backed up. It was that project I needed to deliver to a client. The last minute data recovery was horrendously expensive.
I agree. Most RAID configurations offer some protection against hardware failure, like one drive suddenly going bad. But it is not a backup solution like real redundancy can offer. When the controller of a RAID goes bad, and it is an additional component that can (and ultimately will) fail, then a lot of costly issues can be the result.
While less efficient for storage space, and a bit more work to maintain, IMHO it's hard to beat multiple copies of different drives with duplicates of the same files. The only thing is that they should be periodically refreshed if not used for a long period of time (the level of magnetism slowly decays).
The benefit of Cloud backups is their location independent availability, but it's relatively slow for large volumes of data.