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Non-Apple AFP can be dangerous with time machine...
Authored by: dbs on Sep 24, '09 11:58:57PM
Everyone should be aware that using Time Machine on a Non-Apple AFP volume via these hints may put their backup data at risk. Here's why:

The technical reason why Apple limits Time Machine to 10.5+ AFP volumes appears to be to prevent disk image corruption. There were additional features added to AFP in 10.5 to support Time Machine. These presumably allow the disk image engine to force disk image journal data to write out all the way to the disk. Without such features, a network interruption can result in a corrupted filesystem on the disk image despite journaling. Remember, journaling relies on the journal being written all the way to disk before the changes take place. If you can't guarantee that (e.g., because of network/NAS buffering) then the journal is useless. Time Machine appears to rely heavily on disk journaling to deal with network drop-outs, interrupted backups, and the like. Take this away and your data is at risk.

If the NAS you are using supports these features it should report them to the OS and you should natively be able to choose that volume. If you have to trick the OS to use the volume it means the NAS does not support it.

To summarize: if you care about your backup data you should avoid using non-natively supported AFP servers.

(There is a less-than-satisfactory work-around: backup to a Mac, then use rsync to copy the disk image to the NAS manually. This is what I do to have an off-site copy of my backup.)

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Non-Apple AFP can be dangerous with time machine...
Authored by: sunkid on Sep 25, '09 09:47:15AM
Thanks for the caveats! Can you clarify whether a network interruption would lead to a corrupted disk image or just to a corrupted backup?

There is also another issue users should be aware of that has to do with the size of the disk containing your backup image.

That said, I have a couple of backups to non-OSX based AFP shares running successfully now for about a year and I have not yet had any problems. One of these is from a laptop over WiFi with many of the backups interrupted due to the laptop being put to sleep.

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