Hmm, actually researching this more, I don't think it's actually legal for a regular individual or corporation to make a copy of a DVD movie for backup purposes. I don't think it actually falls under fair use.

You can backup software[1][2] (allowed by law, not fair use) but not movies.

[1] https://www.southerncaliforniapatents.com/articles/2014/10/0...

[2] https://www.law.cornell.edu/uscode/text/17/117

Well once the disk was worn out, and you had a backup, you could re-sell the backup

Of course this may be abuse of the fair use backup copy, but when talking digital, we are anyways inventing philosophies.

Other way could be the backup could be entitled to "one last rental" to recoup last 4 bucks or so. I think that would be fair use but others may not.