Over the past 25 years, I have built a substantial DVD collection, sticking to my absolute favorite movies and TV shows.
A couple of years ago, I discovered that a not insignificant number of my dvd's succumbed to disc rot.
That's when I decided I would create an ISO backup of every dvd I owned. If my dvd was ruined, I borrowed a copy from my library system to make the rip.
All my dvds are now stored in a cool dry place, and I view the ISOs on my home server. I have cold backups as well.
I have graduated to blu-ray for my absolute absolute favorites. For the most part, this is impossible for some of my favorite TV shows, but I do have Star Trek TNG and Miami Vice on Blu-ray. I went through the painstaking exercise of ripping each individual episode of each show to MKVs.
I have a very limited collection of 4K UHD for my absolute absolute absolute (!) favorites. They live on my HTPC data drive as MKVs and are viewed on my 55" 4K TV (not impressive, I know...but until I got it, I was watching movies exclusively on a 27" PC monitor). If I lose those files, I still have the discs. I have 2 Pioneer blu-ray optical drives that are flashed to read 4k UHD discs. I realize they are not being manufactured anymore so I guard and preserve them with all my might. It is not a nice mindspace to be in, knowing that if/when those drives fail, I'm pretty much dead in the water. Secondary market 4K UHD-capable drives are ridiculously priced.