I have had it in mind for a long time to write up a storage and backup article on the site. It’s a topic that many folks are often interested in, I think, and it can hopefully provide some value.
I would personally recommend thinking of the 3-2-1 rule for data backup:
- 3 copies of your data
- 2 different types of media
- 1 copy in a different physical location
Sometimes I might relax the 2 different types of media (I keep everything on spinning drives personally).
@paperdigits makes a valid point: current HDD prices are quite cheap. At the roughly $100 for 4TB price point, this is only about $0.03/GB. Because I’m paranoid I always try to have a pair of HDD to rsync between - so buy two if you can… 
I really should sit down and write an article for folks.