honst VS scorch

The method I use is to run scorch every night to compute hashes for new files and check around 12% of old files for hash errors every night. Even if your backup is the same day as a ransomware attack, you will still catch it if the attack hits enough files for one to get randomly scrubbed. Also scorch is designed around making the hash database small and independent from the rest of the system, so you can automate copying it to a bunch of different places.

Lastly, you could just point scorch (https://github.com/trapexit/scorch) at your drives and run it on a cron or systemd timer - just have the script alert you with an e-mail or whatever your preferred method is. Not ideal but probably less work than rebuilding two arrays because you don't like the format of error messages.

If you really care, you can use something like scorch or file-digests to get the hashes of your files and just store that in a text file, recalculating monthly. No need to get fancy with it. Hell, write your own simple script that hashes, outputs to file, and checks previous versions.

Not exactly what you're looking for but close -> https://github.com/trapexit/scorch

Scorch should fit the bill (https://github.com/trapexit/scorch)