I have lots of movies and songs saved on hard drives. I recently changed my OS to Yosemite. i want to change the bootable hard drives I have as backups. My thought? I'll take one, have it wiped clean and replaced with my computer (so it has the right apps, OS, library folders), and then literally copy the music and movies folder I have from the other backup to it. At that point, my first backup should have both the new OS and the music and movies. I can then completely copy that external to the other external. Is it bad to just copy the whole music folder? I dont know exactly how itunes folder and library files work. Are they OS specific? Thoughts on this plan?