I have an Unraid server that I have had up and running for over three years. A couple of weeks ago, I attempted to run a parity sync but one of the drives (Drive 4) had read errors during the process. I ran a test for the drive but it apparently seems healthy. I deleted all of the corrupt files that I found on the drive and ran the parity sync again but the drive still has read problems during the process. All in all, I have tried everything and don't know what I should do. What should I do to set things back to normal?

tower-diagnostics-20200529-1310.zip

I don't see any errors on the diags posted, but you're using the Marvell controller and they are a known problem on those boards, not surprisingly disk4 is connected there, so first thing would be to stop using, don't connect anything to the first 4 white SATA ports, there are enough Intel ports for all your devices.