I have two external western digital hard drives, one a couple years old and one brand new. I have both connected to an airport extreme via a USB hub.

I am using the older one as back up with time machine, it shows up under the airport on shared devices and the time machine back up seems to work fine.

However, I can't seem to get the other one to "show up" on shared devices under the airport extreme.

Same is true of an HP scanner I used to have connected directly.

Any thoughts on how to resolve?