And what happens if you want to replay one you played before? Hope the store still exists? Pay another £50 for it? What about my save games and mods from a game I was halfway through?
This throwaway culture is exactly why this industry (and all others) is so bad.

Don't replay games, do something else like read a book
throwaway is the best thing , or else we would just rewatch the same movies etc. ruining our economy

Maybe. There's more books, more music, more TV shows, more movies, and more games than we can play in our lifetimes.

Although how many of them aren't shovelware i'm not sure...
Mhmm. Nothing wrong with multiple full dependencies, i just have to balance the cost of having a second full backup price-wise. losing 20% of space for redundancy costs less than losing 50% of space between two drives. But in the end it's a balancing act.

As I already wrote in the post you’re replying to, my local copies are automatically refreshed on a daily basis (at least for GOG, Humble Bundle and itch.io games). So if GOG does close down in 10 years, at this time my local installers would be less than 24h old.

As for the age of the drive itself, it is not related to the age of the backups: my current drive dedicated to game installers is only a bit more than 1 year old. But it includes backups I did as far as 2014. It is most probably going to be replaced with something bigger a couple times in the coming 10 years.

The disk previously used for this purpose is now 3 years old, and the previous one is a bit less than 7 years old. All of them are still in use, the oldest one getting the least critical data (TV series right now). According to SMART reports, even the oldest one is still in very good health.

lots of money wasted
and lots of waste created
+ lots of server and net used for nothing

How to check if a file has been corrupted due to hdd failing. a lot of years passed or for other reasons? Is there a program that scans for damaged files without putting constant pressure on the hdd? Something that can do that fast without taking for example 5 hours.

Anything that does a checksum on files could be used. A checksum is an algorithm which fingerprints a file(s) to ensure they haven’t changed. So you could create a list of checksums and use that. I know there are tools, md5deep for instance will create and check a whole load of md5s.

do what we all do and download all the offline installers of your gog games.

Don't forget shared files - and any data accessible over a LAN (more likely for business users). People need write access to a significant amount of data, which is why a ransomware attack can be so paralyzing (though easy to prevent).
This is moving onto the topic of general (as opposed to game library) backup - but I would agree and my regime involves a combination of full image backups (courtesy of Drive Snapshot) and automatic file versioning (any time a file changes, a copy is taken with previous copies being renamed) of documents and savegames (courtesy of Aphar Backup - although the webpage is Dutch, the software runs in English).
It's been a while since I've seen anyone mention (let alone recommend) a tape drive... (cue images of the ZX Microdrive and C90 cassette).

However the economics here just don't make sense. A single LTO-8 tape cartridge which can store 12TB native (30TB with compression is often quoted) can be purchased for £72/US$94 which compares well with, say, a 14TB Seagate Iron Wolf Pro drive at £372/US$483.

But you then need a £3,700/US$4,810 tape drive to use it. You'd need to be using at least 12 tapes/discs for that option to become worthwhile.
Ultra-HD Blurays can now get up to 128GB with Quad BDXL - however having to swap in 10+ discs to create a single backup of a 1.5TB games library probably isn't practical.

Online backups are another option to consider and this post provides useful insight into the costs involved there.
Also see the Fighting "Bit-Rot" section of my previous post. Note that just creating checksums is not enough - you need to regularly check them (before taking a new backup would be a good time).

I wonder when we'll see more and more COW diffs for shared files and then merging to the final result at a later point. I can see a lot of data needing to be Readable, not sure about writable.

I was looking into tape backup not that long ago, you could do something like 20Tb with current backup tapes...

Yep. It's the big tradeoff.

How much is it per disc? Although quad bluerays do sound very tempting even if they were say $5 per.


Mhmmm... Using ECC both as checksum and as correction would be used, but how often to check... Hard to say. Though the larger and more powerful ECC is, the slower it will be. I modified and made a 16bit Reed Solomon codes as a test. It worked! and in theory covers like 400k area, however it was like 20x slower than the 8bit versions.

ZFS had an option to check and repair errors, but that isn't an obvious option for nearly any other filesystem.

This is why all these personal backups are meh
there should be a common repo where you can just get your games after showing your license for them
I bet many people would even pay for it a few euros each month