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I've been using Time Machine over wifi and have had a recurring problem with corrupted sparsebundles. The scenario is a relatively new Airport Extreme, a MacBook with Leopard, and a partitioned Western Digital drive hooked up via USB to the Airport.

The backups work fine, if I'm just around the house, or if I remember to stop Time Machine and give it a few minutes to wind down before leaving. But if I just close the computer and run out the door, and am away from the network when I wake the computer, I come home to a corrupted backup, which generally cannot be repaired with Disk Utility (once or twice Disk Utility has been able to fix it).

This has forced me to delete my entire backup and start from scratch on several occasions. Is there any way around this problem, other than being vigilant about stopping backups before I leave?

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up vote 3 down vote accepted

Sadly this is why the Airport Extreme isn't supported for time machine. It doesn't have the smarts to repair the filesystem or handle a disconnect as reliably. This isn't an issue with time capsules or a server than can clean up when the backup gets interrupted.

You will have to nurse your setup as described, but the lifespan of sparse bundles on airport as USB disk are limited.

Perhaps a firmware update or change to Mac OS X will make things better, but for now it's something to watch.

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Thanks for the confirmation on that. One thing I've noticed is that if I don't wake up the system until I get it back into the network range, it seems to pick up where it left of with no corruption problems. So if I'm correct about that, there ought be a (relatively) simple way to "suspend" the backup until the disk becomes available again. – handsofaten May 20 '11 at 15:38

This may sound like a weird answer, but this same thing (error backing up to an external drive connected to my Airport Extreme - sparse bundle error) happened to me last night. And my setup is very similar (MacBook, Western Digital External (1TB), Airport Extreme, Time Machine over Wifi). After fiddling for a while and searching various forums, I simply turned off the external drive for a few minutes and then turned it back on. The Airport eventually found it on the next Time Machine backup attempt and I am back in business. Who knew. If you are still stuck, try doing that and see what happens. I have my Time Machine settings set to not back up when not on AC power btw. This prevents the backup from running when I am in a room other than my office or for instance at Starbucks. I had the Time Machine backup start once when I was away from my lan with the same type of error.

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I have had the same problem now a couple of times on a Time Capsule even after upgrading to Lion 10.7.3... "Disc image xxx.sparsebundle could not mount". I simply switched the TC off and back on again, and next time Time Machine performed a normal backup without reporting any problems...

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