Airport and time machine

For those of us that have an Airport base station (especially the new one with 802.11/n) there’s a bit of good news if you were hoping to use an attached disk for wireless Time Machine backups: A simple hack will enable the feature. However, I should point out that there is a good reason Apple disabled support for Airport disk backups in the first place.

Basically, the firmware in the current Airport base station does not provide adequate confidence that transmitted data has been written to disk. Essentially, the Airport acknowledges receipt of the data with an “ok, I got the data” message. However, if something goes wrong between the Airport getting the data and actually having it written to the disk, there’s no way to know. The Airport already accepted the data, so you’re just out of luck. What’s needed is a firmware upgrade that lets the Airport respond with “ok, I got the data, and I wrote it to the disk, and I verified that it was written.” Hopefully that’s coming in the near future.

Until then, you can make a judgement call on whether or not this level of risk is a concern in your book. I’ve gone ahead and enabled support for my attached disk—but, it’s a risk I understand and am comfortable living with.

So the usual disclaimer applies: If you try this, it’s your own fault if something goes horribly wrong. Here’s the hack. Open up a Terminal window and type the following (on a single line, it’s just wrapped because of the page width):

defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1

After that, all you have to do is mount the Airport disk in your Finder, and Time Machine will see it and happily (and perhaps a bit blindly) use it for backups.

If you’re less inclined to work with an unsupported and potentially risky feature, be patient. Word is that Apple has classified the lack of Time Machine over Airport support as a bug. I’m hopeful we’ll see a real fix sometime in the near future.