Update: Apple has released this update that fixes the problem. After installing the update Time Machine will see and use USB drives attached to an Airport Extreme Base Station. No more hacks required.
Update 2: For an easy to follow guide on how to get this running see Michael’s post here.
Here’s the old post, you can pretty much ignore all the below now:
Time Machine is supposed to be ‘backup for the rest of us.’ You plug it into your Mac and it does everything for you. That is the rub of the problem though. Plug it into your Mac. Most Macs are laptops and plugging your external disks into your laptop can be a pain, both in terms of logistics and remembering.
If you are using NAS or Apple’s own AirPort Extreme Base Station this shouldn’t be a problem, should it. Your laptop should back up over wireless to your NAS or the USB disk in your AirPort Extreme Base Station. You would think, but no. Apple has disabled that functionality in Time Machine.
Rather than introduce new hardware, in the form of TimeCapsule, that addresses this issue, lets fix the old software. We all know that it is a ‘simple’ software fix, so do it already – Apple please fix Time Machine right now.
Until the fix appears, and I’m not sure it will now that Apple is selling a ‘hardware fix’, here’s a workaround for getting your Time Machine to backup to NAS or AirPort Extreme Base Station USB disks; iTimeMachine.
iTimeMachine is a utility, the only utility, that enables the use of AirDisks and Network Disks in Time Machine. Even with the new release of TimeCapsule, users can still not use AirDisks with Time Machine. You can do it with iTimeMachine.
What’s New: iTimeMachine v1.1 now checks if you have network drives enabled. It also uses a toggle button instead of the old UI design. It now includes a progress indicator. It also automatically opens up the Time Machine preference pane and gives tells the user that it has enabled AirDisks.