Can I connect a 6tb my book to the usb expansion port of a 4tb my cloud?

I recently purchased a 4tb my cloud. Its all hooked up running good.  I filled it up fast with movies and such so i am looking to purchase a usb 3.0 external drive to connect to expansion port. What drives are recommended usb powered or ac powered drives?  Also am I limited to a 4tb size drive or can I use a 6tb my book  Thank you

Hi there and welcome to the WD community.

You can use either or, its more of a matter of preference for you, i have personally tried Mobile drives as well as ac powered drives and they have work with my unit. I hope this helps you out.