Say with with me: "RAID is not backup!"
Indeed. There is also a difference between backup and archive.
RAID = This is running live, and I need a duplicate that is instantly available so I can keep running in case one drive fails. The trick is that if there is an operation that destroys data (e.g. ransomware infection that encrypts your stuff) then you lose all disks. This is why RAID is not backup.
Backup = Just in case the machine dies, or I accidentally delete a bunch of stuff, or a virus hits, I can restore from the backup. This generally follows the 3-2-1 rule: At least three copies, at least two media, at least one off site. Businesses often use D2D2T systems for this.
Archive = I will probably never look at this again, but I absolutely need to keep a copy around for historic or business reasons. Think about services like Iron Mountain or Amazon Glacier. Tape archives that are quite cheap and almost certainly never reviewed again. This is along the lines of "show me the obituaries from a newspaper published 7 May 1957", or similar.
For the original story, it seems like he is looking for an archival solution rather than a backup solution.