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).
RAID is redundancy, not backup. The main purpose is to keep your system available while you deal with certain, specific types of failures. Also, for all intents and purposes, RAID2 isn’t a thing. I suspect you were reading about RAIDZ, RAID using ZFS. While it has proponents and advantages, it won’t secure your data any more than the common RAID5/6.
Backup is to make sure you don’t lose data, regardless of what happened. This includes hardware failures, user error, bad/malicious software, and more.
If your data is important to you, setup a backup. If you need 100% uptime, setup a backup, then setup RAID.