How to maintain the FS of a cold storage HDD

[Coach]

I back up my data, perhaps not as well as I should but that is not the topic of my thread. Rather I would like to ask about hard drives that are used as offline backups. How do I mitigate bit rot or other threats to the data on the hard drive? Periodic passes over the drive with SpinRite???

Thank you very much!

[frontier204]

I haven't seen any data about how long modern drives in practice can maintain data when unplugged, and whether passing over the drive with tooling helps or hinders. (i.e. I haven't found a study where someone wrote stuff to 1000 hard drives and checked if the stuff was damaged after 6 months, 1 year, 2 years) The SpinRite (or badblocks, or other drive test) would tell you something went wrong with the drive, but it won't be guaranteed to fix the data.

If you're using multiple drives in an array instead of individual drives as backup, (make sure you have ECC RAM!) you can do a scrub operation on the array. https://wiki.archlinux.org/index.php/Btrfs#Scrub
Unlike a drive test, the scrub can check if the data is damaged and then restore from the redundant copy in your disk array. I mention ECC RAM because if your RAM is unstable when you do a scrub, the scrub software will freak out and think everything is damaged, ruining your data in the "repair" attempt.