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10.5: Reconnect Time Machine backup after drive swap
Authored by: Soybean on Feb 19, '09 09:09:30AM

Interesting. I simply cloned my hard drive (using Carbon Copy Cloner) when I was upgrading my MacBook Pro from a 250GB to a 500GB drive. Time Machine performed an incremental backup without any issue (other than my having to unplug and replug the drive into my Airport Express Base Station).



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10.5: Reconnect Time Machine backup after drive swap
Authored by: only_solutions on Feb 19, '09 09:22:48AM
You probably had it make an identical disk copy block-by-block which does indeed keep the connection to the backup but it could produce problems when both drives are present at the same time or alternatingly while the "hinted" solution still keeps them apart properly.

If it's just about 1:1 replacement with immediate removal / erasing of the old partition, that is certainly an option if you're really careful. It would get problematic when you chose to swap the drives again later on — Time Machine would then "back up" the difference between the newer drive and the older one, probably "removing" all the files in the newer backup which you had created since the switch to the new drive. And Jobs only knows what would happen if both drives were present at the same time!

In my case I simply wasn't inclined to spend another several hours on a new copy of the disk after I had already been through it with Disk Utility.

There just had to be another way around the problem, and indeed there seems to be! ;-)

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10.5: Reconnect Time Machine backup after drive swap
Authored by: only_solutions on Feb 19, '09 09:41:25AM
I forgot to add: The "hinted" solution probably also works on a file copy of a partition, not just on a block copy. I have not tried that one out myself, but from the way things work it is conceivable that even a file-copied partition could be re-connected which would certainly not work otherwise.

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10.5: Reconnect Time Machine backup after drive swap
Authored by: wch on Mar 02, '09 07:28:23PM

I just did a file copy of a partition using Carbon Copy Cloner, and the new partition received a new UUID, so I used the hint above. It seems to have worked -- the first backup size is only 60.7MB, after maybe 25 minutes of "preparing". The backup is running now, although it seems to be going quite slowly; after about 10 minutes, 5.5MB has been backed up. Hopefully things will be faster the next time around....



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10.5: Reconnect Time Machine backup after drive swap
Authored by: wch on Mar 02, '09 09:25:36PM

Update to my previous post: subsequent backups seem to run at normal speed.



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10.5: Reconnect Time Machine backup after drive swap
Authored by: only_solutions on Mar 10, '09 09:06:27PM

That is because OS X keeps a record of files which have been changed recently, but this record is not infinite.

Time Machine uses this record if it can — but when it suspects that the record does not contain all the changes made since the last backup it will do a "deep traversal", basically looking at every file on both disks and checking whether it needs to be backed up or not.

After you've made your copy, the change record on the copy was not deemed consistent and complete, so it took the long road on the first backup.

After that, however, Time Machine was back in sync and on the following backup it could use the change record which was much faster.

If you should have a long gap between subsequent backups, Time Machine may still revert back to deep traversal, but that is normal and will "fix" itself automatically when the backups are closer together again.

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