I have an rMBP with a 7 port usb hub, 3 usb 3.0 and 4 usb 2.0 The hub is powered and plugged into the usb 3 port on the mac. I have a usb 2 desktop external powered HDD that is seen by the mac when plugged into this hub, and other peripherals are also seen like a wacom tablet and a focusrite audio interface. However I have two WD Mypassport 2.5" external usb3 drives that the mac will not see when plugged into the usb 3 ports. If I plug any other device into these usb 3 ports it is seen so I know the ports are working. When I plug the WD hard drives into the port they boot up and start spinning but will not load to the destop. If I plug them directly into the mac they are seen on the desktop no problems. Any clues as to if there are some cache files or other such nonsense that I could delete to get the mac to see these WD mypassport ultra drives? There was a time in the past when they were seen by the mac through this very same hub, but suddenly not any longer. Naturally I've tried rebooting in various ways, with the hub plugged in and without the hub plugged in and then plugged in after booting. Every other peripheral I have works fine in all the ports excecpt these two WD drives.