[Santiago]

Is it possible to have two (or more) external HDs connected through a USB hub to Airport Extreme and to use one for storage and one for back up?. I know it is possible to have more than one HD connected with airport to use as storage, but the question is wether is possible to back up those external HD use for storage to another external HD to be used only for back ups. If I want to free space in my MAC internal HD, for instance transferring my Iphoto or Itunes library to an external HD connected to Airport, I also want to make sure that those files will automatically be copied using TM. Ideas? MAC support's answers are only that they don't provide support for that. Many, many thanks.

[Albertr]

If you have pictures in large format such as raw format your airport will be so busy slowing things up. You would be better off getting a larger HD since the cost today is very minimal.
That is what I did and back up my HD to an external using Super Duper and leave Airport to connecting to the net, printing and maybe to an Apple TV.