3 copies of your data (original and 2 backups)

2 different media. (pick 2: Raid, jbod, ssd, tape, managed cloud)

1 off-site

I’m gonna add in: one offline

So

original data on a mirror raid or raid 5

External disc disconnected backup trued up whenever you can

Syncthing/rsync/b2/S3 whatevs to get it off-site.

The nice part about syncthing is it will stop if a certain percentage of you data changes. It has a good chance to stop ransomware as long as it’s not too slow at the encryption.