I am mainly hosting Jellyfin, Nextcloud, and Audiobookself. The files for these services are currently stored on a 2TB HDD and I don't want to lose them in case of a drive failure. I bought two 12TB HDDs because 2TB got tight and I thought I could add redundancy to my system, to prevent data loss due to a drive failure. I thought I would go with a RAID 2 (or another form of RAID?), but everyone on the internet says that RAID is not a backup. I am not sure if I need a backup. I just want to avoid losing my files when the disk fails.
How should I proceed? Should I use RAID2, or rsync the files every, let's say, week? I don't want to have another machine, so I would hook up the rsync target drive to the same machine as the rsync host drive! Rsyncing the files seems to be very cumbersome (also when using a cron job).
2 disks in the same machine is not a backup whether the data is copied between them using RAID or rsync or anything else.
Sounds like for this machine, just use the two disks in RAID1, or a ZFS mirror, or something. And figure out something else for backups. Probably a cloud solution.
Also, RAID2 requires a minimum of 3 disks, and is rarely used.
I'd argue it is a backup as long as something is doing snapshots of some kind to the other disk, and not realtime sync like raid. Obviously that should not be your only backup though.
It’s been literally a couple decades now but I once had to troubleshoot multiple RAID failures in a number of identical servers that were all running 6 disk RAID-5. Long story short the power supplies in each server was slowly losing its ability to power all the drives at the same time, so random drives started throwing errors. By the time we figured out the root cause, most of the drives had generated enough errors that the RAID controller couldn’t rebuild the volumes.
So, no, as others have said RAID is not a backup and should never be treated as such. A single point of failure like the power supply can easily cause the loss of the entire volume without warning.