My rMBP currently has Yosemite on it. I want to run Mavericks for a few things. If I run it in a VM its terribly pixelated due to lack of retina support. I have an 8GB USB with a functioning Mavericks bootable drive that I used a few times in the past. I also have a 1TB USB 3.0 external hard drive that I'd like to partition and install Mavericks on as a fully functioning bootable drive. I read about people doing this for Yosemite, can it be done with Mavericks? Would I simply attach both drives and hold "Option" at startup to access my installer and then install Mavericks on the HDD? Thank you.