Hi, I just got my new iMac 27" and want to set up an external SSD drive as my boot drive. I didn't get the Fusion Drive. I have an external 480GB SSD in a USB3 enclosure from OWC to use as the boot drive. I'm just not sure how to start or what to do. Can someone explain or send me a link on how to do this? Thanks for any help you can provide.