Since you say you are using screen and not the preclear plugin, what does it look like in your screen sessions?
It's just frozen.
I looked more into it and it may be related to hardware. It is a new build and those two disk are the first I plug into my AOC-SAS2LP-MV8 card. The other disk are plugged directly on the motherboard (Supermicro X10SL7-FO). I also have 4 Norco SS-500 5-bay and those are the only disk in the 3rd SS-500. It may be a problem with the SAS card or the SS-500. I will do more test.