The only way I've ever been able to find a bad drive is to connect to the RTC console (either via puTTY in RAW mode to port 2002, or straight to the serial port on the front of the controller), and watch for 10-15 minutes for error messages, usually containing something line "dma_access_error" or "drive_read_error". If you see those, your drive is probably toast.
Also on those older releases, a monthly programmed reboot clears up a lot of odd problems.