kabadisha

Just an update to confirm that the RAM was indeed the issue. Removed it and after one cleanup sync, the second sync returned no errors! Woohoo!

Oh that's excellent to know! Thanks for the tip 🙂

Yeah, that's a good shout - I'd seen that advice elsewhere regarding parity sync errors which is what led me down the RAM research rabbit-hole. Oddly, after ripping out the offending RAM I did attempt to do Memtest as you say, but when I selected that option from the unRaid boot options the machine simply rebooted with apparently no attempt to launch memtest. I suspected it was something to do with my LSI HBA interrupting the boot process, but didn't have time to dig into it. I've just ordered a couple of larger RAM sticks to replace what I am left with right now, so will try again to run Memtest when that arrives.

I just wanted to drop here and say thanks to @garycase and leave this here in the hope that it will help others in the future. I recently started seeing parity sync errors on an array with disks that all seem happy otherwise. I've been tearing my hair out trying to figure out why they keep coming back (around 700 errors on a 30TB, 3 x 14TB disk array). Having stumbled across this thread, I double-checked my RAM and bingo! - I mixed RAM with different specs as it's what I had on-hand. Crucially, half was rated for 1.5v and the other half wanted 1.65v. They also had different timings. I've just removed half of it, manually set the correct voltage & frequency in BIOS and am re-running parity sync now. So far it seems like much lower error rate, so I think I've found the problem 🙂 I'll run another parity check after this one completes and fingers crossed, I'll get zero errors on that run. Thanks again!