I have a mid-2009 MBP that I am now installing a Samsung 830 256 GB SSD in the optical bay, while leaving the HDD in its main bay. I currently have Lion on my HDD but plan to to do a fresh install of Mountain Lion on my SSD (using a USB key). I only plan to move my pictures, music, and movies to the HDD (not my whole home folder) and leave the rest on the SSD. I have a current backup on an external HD, which is what I will use for the process. The question I have is on how I should format my HDD after I have installed Mountain Lion on my SSD. Do I not need an OS on my HDD as well? If so, can I leave Lion on my HDD, and have Mountain Lion on the SSD. Anyone?