Tuesday, November 20, 2007

Why Leopard’s Time Machine Doesn’t Support AirPort Disks

Recently, I discussed how Time Machine as released in Mac OS X 10.5 Leopard does not support backing up to a hard drive connected to an Airport Extreme despite that having been a feature listed prior to release. Well, now we've got the "why."

Turns out that, as currently configured, Airport Extreme doesn't provide a safe acknowledgment of received packets and therefore data could potentially be lost during a backup without any notice given or corrective action taken. Clearly, not a situation on which you'd want to rely.

According to Alex Curylo (via RoughlyDrafted):

This was explained on one of the developer lists a couple weeks back. The problem is that integrity cannot be guaranteed — the AirPort acknowledges receipt of the data before it’s actually written, and if power is interrupted, the disk disconnected, yadayadayada in the window between the Airport acknowledging receipt and the data actually getting written out to disk, it’s gone forever with no way to recover it or even realize it’s gone missing.
The good news is that this seems fixable in a future update to Airport and so it would seem reasonable to believe that Apple will eventually release updates to both Airport and Time Machine to allow over-the-air file backups. Jump for the deets. Let's hope that comes sooner rather than later, as there are lots of other people out there besides me who think automated wireless file backup to an external hard drive is a great enhancement for laptop users.


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