So I'm struggling to work out if this is possible. I've run the installer, selected the external drive during initial drive selection and my macbook then booted from the external drive. But, when I'm asked where to install OSX 10.10 the only option is the internal Macintosh HD drive. Could this because I forgot to check if the external drive had ownership enabled? Or would I need two external drives connected so I can install from one to the other? Any help appreciated..