I'm getting ready to install OS X 10.10 on my macbook. I don't expect anything to go wrong, but I've learned all too well the importance of a physical backup. I have dual hard drives; an SSD for the OS and apps, and an HDD for media and files. Is it necessary to backup my HDD when installing the OS on my SSD? I figured its safe as its an entirely separate drive but I just wanted to make sure before continuing. Thank You.