External USB Hard Drives dont mount (Samsung Galaxy Tab 10.1)

Hi everybody,
Trough a Canon OTG Connector (Power supply-usb) I try to connect to my Tablet "Galaxy Note 10.1 2014 Edition" 2 different brand external usb hard drives, both 500 gb, one is USB 2.0, the other 3.0, and the tablet doesn't reconize them, they dont mount.
I own both extrenal Hard Drives since long time, I used to connect them to my last tablet, broken now, an Asus Transformer TF300TG , and they where working fine, I connected them in the exact same way, trough an Asus Connector (Power supply-usb).
I tried also to connect to my Galaxy tab some flash usb pens of different size, from 3 mb until 16 mb, I dont own any bigger than these and they are working fine, the tablet mounts them without any problem.
So there is a limitation in size, bigger external usb hard drives than "? gb" could not be mounted on my Tablet Galaxy Note 10.1, or someone out there could be so kind, explain to me why this Samsung tablet doesn't mount my external Hard Drives that could be mounted easily in other brand tablet as I explained?
Thanks a lot for ytour help!

 

If it connected to your Transformer it should connect to your Galaxy Tab the same way. I think you're saying you have attached a powered USB HUB. What happens if you attach the drive directly?

 

Thanks a lot for the answer!
It is impossible to connect any hard drives or any other usb external devices directly cause both tablets, my old Asus and my new Samsung object of this thread, dont have an usb port.
Usb external device could be connected trough an OTG cable, my otg cable is Canon brand, it connects trough the power supply plug "Tablet power supply-usb"
Thanks!