nexus 7 2013 has out-of-box support for otg wired mouse and keyboard, if you root it and install stickmount, you can mount usb thumb drive, but not your hard drive, the reason is pretty simple, your hard drive need a 5V voltage drive to work, but that otg cable from your tablet can’t provide that. some people suggested hack open a otg cable and wire a extra usb head just for 5V power, connect that usb head to your computer ‘s usb port(which has standard 5V power), and it works. i don’t have tools for that but found my own way:
just buy a 3 headed usb cable that use 1 of the heads to draw power if needed
the good thing about this is 3 headed usb cable is a standard product, you can buy it easily, you don’t have to hack open a existing cable to make your own gear.
i thought this was a obvious solution, not sure if anyone has find it before me, but i can confirm it did works, for my nexus 7 2013.