Mac OS X Mavericks backup to Airport Extreme

Mac OS X Mavericks doesn't show my USB HDD that's attached to my Airport Extreme

(or backing up to a airport extreme with Mavericks)

So you've upgraded to the latest mavericks, and you thought you;d attach a spare USB HDD to the airport your have to use as a time capsule.
It used to show in Snow leopard (10.6), but for some reason it doesn't show in Mavericks.... why?

Apple fucked you over - it's specifically disabled in Mavericks.
I've read posts that you it has to be a specific format (http://support.apple.com/kb/PH14168) which I did, but it still didn't show up...

So what you need to do is this

Terminal , then run:
 defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1

 

Reboot your machine, then go to Time Machine -> add disk, and it should display!!! Woo!

From: Hacked Potatoes