Using an Airport Extreme Disk for Time Machine

[Winter Charm]

Hello everyone, I'm having trouble getting this to work. I want to use a Western Digital 3TB Hard drive with my airport extreme base station as a wireless backup point for all the macs we have. Here is my current setup:

Latest Gen Airport Extreme; latest firmware update, connected to external HDD.
Macbook pro
Mac mini
iMac

All of them are running OS X Lion, again, fully updated.

Now, I have connected the WD 3TB external hard drive to the USB port on my airport extreme. It shows up with all my other drives on all the macs, but time machine is not recognizing it as a disk...

What can I do to make time machine let me back up all my macs wirelessly to this hard drive.

Basically, the way I have it right now, I want to be able to back up all my macs to their own external hard drives, but also want them to back up to the networked drive when/if the external drives are not available.

and yes. I'm paranoid about losing data

 

[lexvo]

Maybe your external HD is wrong formatted.
Time Machine requires that destination volumes be formatted as Mac OS Extended (Journaled).

http://www.macworld.com/article/132140/2008/02/timemachine2.html

 

[andyboutte]

I would highly suggest not using your external hard drive with an airport extreme, especially if your paranoid about losing data. You WILL have problems with it.