I recently installed a new SSD into my late 2012 Mini. Install was not a problem and getting everything copied over from the old hard drive to the new one also didn't seem to be an issue. I planned on using the old hard drive as a holding ground for a lot of the files that I don't use very often. The problem that I am running into is that the Disk Utility is not allowing me to unmount and erase the old hard drive. Any ideas on how I can get the old hard drive unmounted so that I can erase it and use it the way I planned on?