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10.5: Use multiple drives for Time Machine backups
Authored by: palahala on Feb 14, '09 06:12:38AM

Another side note, just for the archives: one can easily use multiple drives for backup.

I am not using Time Machine for disaster recovery only: since I have learned that Time Machine has a perfect integration with Apple Mail (and Address Book, and iPhoto '08) I really like being able to go back in time. However, I am a bit too lazy to set up a (rsync, ...?) backup copy of my Time Machine drive. So, I swap two USB drives every now and then -- thus keeping that weekly backup even if one of the drives fails or is somehow erased.

To make that work without the need to select a different drive in the Time Machine preferences each time you swap the drive: just make sure that all drives use the very same contents of that .001122334455 cookie file, and of course match the file /var/db/.TimeMachine.Cookie.

I did NOT try this with attaching the drives to the MacBook directly: in my set up, both drives also have the same name, and I attach them (one at a time) to a Mac Mini -- so Time Machine on my MacBook always uses the same AFP share name. The second drive initially was a full copy of the first, to preserve existing history.

When the CONTENTS of the hidden .001122334455 files do not match, one will get the "Volume at path [..] does not appear to be the correct backup volume for this computer. (Cookies do not match)" error I mentioned in my previous comment. At that point one could still continue using that drive by manually selecting it (which would not create a new full backup then, assuming the file NAME of the .001122334455 file matches the MAC address, even though the file CONTENTS do not match /var/db/.TimeMachine.Cookie). Ensuring that the contents match as well, eliminates the need to manually select another drive.

When in need to restore a file that only existed for a short period, I might need to search both drives, but well... In fact, I never investigated if the weekly backups (which are kept until the drive is full) do hold all files that ever existed during the daily backups of that week -- I guess not?



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10.5: Use multiple drives for Time Machine backups
Authored by: palahala on Feb 14, '09 08:04:54AM

(As per the original hint, it is of course not sufficient to have a file name that matches the MAC address, and contents that match /var/db/.TimeMachine.Cookie, to make a drive being used for a specific computer. The extended attributes must be set as well. All of these will be fine when copying an existing backup onto a second drive.)



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10.5: Use multiple drives for Time Machine backups
Authored by: palahala on Jun 04, '09 01:00:55PM
10.5: Use multiple drives for Time Machine backups
Authored by: palahala on Jun 08, '09 02:28:43PM

As for the 10.5: Use multiple Time Machine disks for redundancy hint mentioned above: be sure to read its comments for more insight about, for example, the extended attribute com.apple.backupd.SnapshotVolumeLastFSEventID. Ars Technica also features a well-known technical article, explaining how Time Machine uses the logs maintained by fseventsd.

And for whoever is reading these comments (about using multiple drives) through deep links posted on some other sites: please note that these comments are part of a much longer story: 10.5: Repair Time Machine after logic board changes. (Reading the whole story you will learn many more details, like how you might run into "Volume at path /Volumes/TM does not appear to be the correct backup volume for this computer. (Cookies do not match)", and like selecting another drive for Time Machine (through System Preferences) might change the timestamp and contents of /var/db/.TimeMachine.Cookie as well.)

If you initially want to clone a drive to get your second backup drive, then see A Bigger Time Machine without Changing History.



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10.5: Use multiple drives for Time Machine backups
Authored by: palahala on Jun 10, '09 02:34:25AM
...but after cloning a Time Machine disk you may want to take the extended attribute com.apple.backupd.SnapshotVolumeUUID into account as well.

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