I have an early 2009 Mac Pro that has stopped recognizing one of it's internal hard drives. From a little troubleshooting it looks like the problem is with the drive and not the computer, but I thought I'd see if anyone else has had this happen. I've had plenty of drives fail before, but this one isn't reporting failure - it's just not appearing at all. I had been running 2x 3TB drives in a software RAID 1 setup until recently I saw the RAID had been compromised because one of the drives was missing - according to Apple's Disk Utility. I copied everything off the volume and deleted the RAID. This gave me back one of my empty 3TB drives, but the other one still didn't mount. I attached a screenshot showing what the system report shows for the drive bay the missing 3TB drive is in. Right now it's in Bay 2 - but I've tried this drive in all four bays with no luck, and had success mounting other working drives in Bay 2. The only difference I can tell so far is that the missing drive lists Native Command Queuing as "No", where all the others list "Yes". Could this have something to do with it? Not sure what else to try, besides maybe getting a USB/eSATA hard drive dock, but I suspect I'll have the same problem there. Any ideas would be much appreciated!