[mceachen]

You can certainly use par2 or something you cook up yourself using SHAs, but it'd be a whole lot easier if you just used a filesystem that handles this for you.

I wrote up a lengthy description of the problem and several different solutions here:

https://photostructure.com/faq/how-do-i-safely-store-files

I personally use a Synology and an Unraid box, both using btrfs, with scheduled data scrubs and periodic SMART health checks.

I also rsnapshot to an external drive, just formatted as ext4, as Yet Another Copy of my stuff.