Weird behaviour with external USB3 enclosure
So far, it seems that my MacBook doesn't recognize USB3 before login. If I plug either my Time Machine or clone which are both USB3 into a USB2 hub, both are recognized at boot using either option or command+r. You could also use a regular USB2 cable to force to USB2. This is not unusual as my Windows desktop I built is the same because the BIOS doesn't support USB3 yet. The USB3 functionality is implemented through a separate chip from the Processor or Chipset. I wonder if this is the same for MacBooks....