Think of it like the skin of a 3d shape sliced apart and stretched over a 2d plane, because that it what you are looking at.
The space is continuous in 3d.
The plot you show changes as you change the ratios of l,c,h
When you click the ‘show 3d’ button you can see the cut out areas correspond to colors that are not on the surface of the color volume.


Lto tape. But I only have 15tb
It quickly becomes cost effective when you actually need the data to be safe. Far easier to have off site backups. I have never had a problem , but I like to have offline backup. Most of the time my data is static. So I am only backing up projects files ans changes for the most part.
If you have 40+ tb of dynamic data I can’t help there.
Edit: I buy used drives that are usually 2 generations old, so I got lto-5 drives when lto 7 was new. The used drives may be less reliable but used drives can be 1/10th the price of the newest ones.