Hi, here is my situation... I was a Snow Leopard holdout for a long time, through Lion / Mountain Lion / Mavericks. I finally decided when Yosemite came out to upgrade (the iOS integration was enough to get me to switch). So, I downloaded Yosemite installer, made a clone of my internal hard disk to an external drive using Super Duper, and booted from the external disk. I then wiped the internal disk, and installed Yosemite from the installer program while booted from the external disk. I don't recall having any problems doing the install; I probably had to point the installer at the internal disk at some point so as make it install there, rather than the external disk I was booted from. So, everything is fine as far as Yosemite is concerned. I have Filevault working, etc. The problem is, I would like to be able to boot from that backup clone of Snow Leopard on the external drive from time to time. However, when I boot the computer with the external drive connected and hold down the option key to get a choice of boot drives, it shows me two drives: my internal (Yosemite) drive, and the external drive shows up as "OS X Installer." Apparently the external drive is marked in some way to boot into the Yosemite installer? How can I make it go back to booting Snow Leopard in the usual way? By the way, I've looked at the external drive while booted into Yosemite, and all my old Snow Leopard files appear to be there. Thank you for any advice you may have.