I am on Mountain Lion with a 2010 imac 27" QC i7. I have a 3TB western digital drive that keeps unmounting itself, but the WD SmartWare can see the drive powered on. So I just select to mount the drive. I have been working with Apple on this issue and have tried several resets, unplug/replug, as well as reloading ML entirely.
Tonight, I put a DVD into the drive and it almost instantly spit it back out. I tried it with a couple DVDs and it spits it back out sometimes after 2-3 seconds and other times 10-15 seconds later. I can see the DVD mount on the desktop and then a pop up. Then it goes away.
Its HAS to be something with ML and the 2010 imacs. Apple is to call me back tomorrow at 11am. Its going to be interesting as they were telling me last time that more than likely its a Western Digital problem with drives. But since DVDs wont stay mounted.... Now I am starting to see my Time Machine backup having issues as well as my SYSTEM.log just keeps growing and growing. I cant even read it in the console since it keeps scrolling text.