SOLVED Getting read and write errors while trying to replace old drive.

[The_Ianator]

I've recently begun replacing 4tb WD reds with new 12tb WD drives in my encrypted raid Z2 array. Since I have extra sata ports on my motherboard I've just been plugging in the new drive and replacing while leaving in the old drive, assuming that it will be less hard on the drives if it has the original to work from rather than having to get all the data from the other drives.

This worked perfectly fine for the first three drives but I'm having some trouble with the fourth. The old drive is throwing read and write errors and the resilver has made no progress in twelve hours (the first three all finished in less time.) I did power down the machine and recheck cables but it didn't solve the problem.

Is this as simple as clicking detach on the old drive, forcing the new one to rebuild from the rest of the array? I don't want to just recklessly go ahead without asking first.

Or is this error deceptive and the problem may actually be with the new drive? Why is the old drive getting so many write errors? Why's it being written to at all when it's being replaced?

Could this be explained if the electrical tape had slipped off the 3.3v pins on the new drive while I put it in the machine?

Thanks for any help you can give.

Edit: Just took out the old drive and the array resilvered fine.