Hi, I have had a couple crashes here and there where the screen just freezes or won't come back up after the display has fallen asleep. I am booting off a USB 3 drive that is a samsung 840 pro SSD plugged into a dock. I wonder if anyone here knows if having the energy settings to put hard drives to sleep when available can cause issues with booting from an external drive? And are there any other issues I should know about with booting from an external drive? So far when everything is up and running the system is great and fast. It is a 2013 iMac 27 inch i5 3.4.