I bought an active 7-port-USB-Hub to avoid all the cable mess on my desk. The following devices are plugged in:

* Scanner (which is not being used, actually)
* Keyboard
* Mouse
* Android-Phone

When I now plug in a hard disk (passive, 2.5') as Time Machine device, it is not recognized. I wonder why this is the case, because it's an active hub. Do I really need to buy a hard disk with its own power supply?

Another strange thing is, that when I plug the hard disk directly into the MacBook (beside the hub), it does not work either.