Turns out two of my four 14-TB drives have bad blocks and out of spare blocks so the QNAP won't use them. I can still use the drives for manual backups if I'm ok with some data may go bad. As far as I can tell the QNAP's Bad Block Scan does read/write operations on every block in order to let the drive's firmware detect bad blocks and retire them. Otherwise BBS doesn't do anything else -- no bad block redirection in software.

The two 14-TB drives I was using constantly. Writing TBs of data and then deleting them a couple of times a year (with the second drive mirroring the first on a weekly basis). So it makes sense they went bad first. Now I don't have enough drives to have all my data online which I can live with for now. I'm thinking of setting up three RAID 1s.

Storage Pool 1. RAID 1. Two 2-TB drives. System volume, QNAP applications, and enough space for my web site if my Mac mini dies. I want to use my 2-TB drives and wear them out first. Possibly download folder here though that would cut my WiFi throughput in half. Three spare drives.

Storage Pool 2. RAID 1. Two 8-TB drives. Work drive where I add and delete data. Normally has 3 to 4 TB used. I have one spare 8-TB drive so should be fine for now.

Storage Pool 2. RAID 1. Two 14-TB drives. Longer term storage that is mostly store and don't delete. Video, music, software, VODs. Would be about 9 to 10 TB currently. No spare drives.

Offline. About 10 TB of VODs.