Ok so whenever I press option/alt when I turn my MBP on and go to disk utility, I click on the 500GB HD and erase it I always get an error/failed and says something like failed/error unmounting. I'm erasing it and making it Journaled of course But when I try to erase the Macintosh HD, it works and lets me erase it with no problem. I bought this MBP used and I just want to make sure it's completely wiped. Is there any way I can erase the 500gb without the error? Or am I completely wiping it clean when I format the Macintosh HD?