So my plan... unplug two of the five drives. Start the computer. See who is missing. If J is there, then I get to conveniently check what is on it before I shut down again, and then shut down. Unplug another two, keeping note of which two were just unplugged, restart. If J is still there, voila, I have it. If not, plug back in one of the last removed two, and J will be found.