I just got a new 18tb exos thinking only one was dying and to replace it, but are both going? parity sync takes 4+ days if I start running it and I suspect it's one or both of these drives.

I should be able to swap both with the 18tb one and use what spare space I have, should I add the 18th drive to the array and just use unbalanced to move everything off them both to it?

I would run an extended SMART test on both then post your diagnostics.

I put my new 18tb drive in and changed my parity drive to the 18tb one temporarily.

I moved everything off the 16tb drive with 3k errors, and the 10tb one that just seemed off.

unfortunately, both are well out of warranty period.

I'm going to get 20tb for the parity drive next that gives me 2tb each upgrade now. won't be for a while though, what's the best time of year to find shucked 22-22TB EXOS on ebay?