Just power loss. It'd start clicking on and off every now and then. Do that in the middle of a write and your raid has some repairs to do.

I know what RAID 1 is. My point mainly was that I would not get much of benefit from it since I am already keeping my data on two separate places (either two separate hard drives that I manually rsync, or an online server and one local HDD).

Using RAID 1 mirroring has both benefits and drawbacks compared to manual rsync. Extra read performance by RAID 1 is not important to me as this is not a database or other data that is constantly read, but archives I only occasionally need to access.

You're right... and even if you wait a certain amount of time before deleting the old installer (checking community feedback), a 'serious' issue can still be found by other people after you think it's safe to delete the old one.
Still, I only download a new version when there's a changelog that mentions a good reason to download that version.

How are some other file systems a solution? Isn't versioning by the file system the same as just not deleting your old offline backup installer(s)? (the latter just being a bit messier)

If you're paranoid enough to want data on more than one drive, my recommendation would be two separate backup devices rather than RAID. Aside from the fact that RAID is a hassle to configure and maintain, none of the configurations will adequately protect you from a PC BBQ and that has about the same chance of happening as a hard drive failure.

And FFS, keep one of them offsite or in a fire resistant box. Otherwise you're just doing it wrong.

or just use a cloud storage , they are getting cheaper:P

Hey, it's your data... if you want to keep it in cold storage only to discover after you plug your USB drives back in that they're both dead that's your issue. You're the one placing all your faith in SMART (and hilariously enough BTRFS.)

Why do you do it manually? Why not backup software that does it daily/weekly, according to the schedule you set up?

I don't have experience with RAID in home use, the main issue being that it is always an extra cost, buying some RAID controller/chassis into which put HDDs... I rather save that money to buy yet another, and/or bigger, hard drive instead. Also aren't you restricted to using similarly sized HDDs with RAID setups anyway? So if you have set up some RAID-system with several 2TB HDDs, you can't just replace one or few of them with 3TB or 5TB HDDs?

Sure the higher RAID levels offer parity etc., but using filesystems like BTRFS and OpenZFS seem to offer similar RAID-like features, without having to buy extra hardware/controllers.

I personally see RAID more relevant for data that is accessed often (like keeping some database), rather than personal offline archives.

I meant for those who only have one local backup disc A and rely on the cloud as their "B" copy, if the local disc fails, the only newest cloud version available might not be the one you want. Aside from unfixed bugs, I can think of : 1. A new version of a game breaks compatibility with an older mod that hasn't been updated and you feel that keeping the mod compatible outweighs whatever the new version brings, and 2. You own a "base game" but don't want the DLC for that game. However a updated version of the base game which is much larger to accommodate that DLC performs worse than the old one. I've experienced both of these in the past.

The more local drives you have the more likely it is you can keep an older version around at least until the new one has been thoroughly tested to avoid "surprises", or even "time-delay" an entire drive (eg, mirror to A & B but also keep C out of date deliberately). GOG installers aside, doing this for personal data (documents, photos, etc) instead of instantly overwriting all drives with new data can provide significantly increased resilience vs newly undetected ransomware.

Agreed. A friend who went to university had a 4x drive RAID, ie 4x mirrored copies and boasted how totally resilient it was. Whilst he was in class, someone broke in and stole the NAS walking off with all 4x copies at once. He had no other backup to restore from. As much as I love NAS's, if you're going to use one, then it's definitely still worth having something else in addition that's at least in a less visible location apart from the NAS, not just for GOG games but irreplaceable personal data in general.

Since when is 20TB (my case) cloud storage inexpensive?
Anyway, nothing wrong with an EXTRA (encrypted) cloud backup. But there are several downsides to having it as your only backup (or even worse: single storage):
- Internet access is needed.
- Servers can have downtime.
- Other provider issues.
- Depending on which company that provides the cloud storage (especially smaller ones): bankruptcy = high chance oof losing all your data.

And like I said before: if you care about DRM free, it means having full control of your data - and you don't control someone else's servers.

Yeah, RAID makes a lot of sense if you're running a bunch of servers when there's more than one drive's worth of data in play and someone's getting paid to keep things running. It's not so hot for an individual desktop situation.

Yup, the dragon's breath *alone* has more lines of code than every cyberpunk mob combined

I'd argue that it's better to have more total storage (no matter how many drives) than just "more drives". Because: why wouldn't you want to duplicate those old versions, for data safety reasons?

Theft (or fire) 'can' be equally bad for (multiple) external drives. The only real protection is an offsite backup (=keep an extra backup drive at a different location - or have an extra cloud backup).
I don't have an offsite backup myself... I have no outside location available (in any case - it's not very practical to keep data up-to-date this way), and (like I said before) 20TB of cloud storage is pretty expensive (+I try to minimise fixed costs).

I find a NAS more useful for centralised storage (and other duties of course) than as a (scheduled) backup system. You'd probably only use it for backup if you have multiple computers - but... are those always turned on all the time? (ok, if they are - it's handy to have control (/access) of(/to) any backup from any system)
One day I'll get a NAS - I'll use it as media/file server, offload some data from other computers, but still connect USB drive(s) to backup the NAS.

1. How much would e.g. 6 terabytes of cloud storage cost me? (My GOG game installer data size is already beyond 5 TB).

2. What benefit would such cloud storage to offer from downloading the same files from GOG servers? What I mean by this is that at this point I consider GOG servers as my "cloud storage", I can download my GOG game installers from there any time I want.

Because I don't keep my archive hard drives connected (online) all the time, and it isn't much of an extra effort to run the rsync command manually myself while I'm at it. I keep those hard drives connected only if I need some data from them, or want to add/modify something on them, which is more like monthly, rather than daily or even weekly.

It's getting confusing again... I was thinking of 'backup' (duplicating), not archiving (offloading data). To make things extra confusing - they're not necessarily mutually exclusive; you could always backup an archive.