I have all my backup hard drives encrypted with LUKS. Currently, the passphrase is some 25+ random password that I store in my password manager KeePassX. Since I have the backup drives for the case that a single one of the is the only working drive left, I have a small unencrypted partition on them where I have this password manager file. That way, I only have to remember my long password for the passwort manager and use a strong password for the disk encryption and a different password for every disk.'
A friend pointed out that in effect this is not better than just having the same password on all the disks that I can memorize.
Are there reasons to pick one approach over the other one? I have no idea whether the password on LUKS or KeePassX would be harder to crack. What I thought about is that each LUKS drive probably has the a different crypto key, which might not be good if those different keys are protected with the same password?
All those backups disks contain the exact same data, so it only matters whether one of the drives is brached.