I just bought the Mi Box yesterday and didn't see much on where the drives plugged into the Mi Box mount at. So, just to be a resource for people the drives put into the Mi Box mount at /storage. If you don't see it there, it didn't mount. I've had some issues with an ExFAT drive I had, but was able to get a flash drive working after formatting it as MBR instead of GPT. When I get home I'm going to try out all of the combinations.
I have one unit that doesn't recognize any USB device until I perform FACTORY RESET. PITA. Works fine afterwards.