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10.5: Reconnect Time Machine backup after drive swap
Authored by: palahala on Feb 19, '09 11:07:39PM

In the comments of the aforementioned hint, 10.5: Repair Time Machine after logic board changes, I wrote about the value of the cookie which has to be the same on both drives, and should match the contents of the file /var/db/.TimeMachine.Cookie on your Mac. Maybe the UUIDs are important too, but in my case I simply used Finder to copy the sparse bundle and the hidden cookie file, and that was it.

Note that my set up uses a sparse bundle on USB drives connected to a Mac Mini, which are used for my MacBook Time Machine -- I never tried with attaching the drives directly to the MacBook.

If these cookies do not match then the logs will show Volume at path /Volumes/TM does not appear to be the correct backup volume for this computer. (Cookies do not match), so for whoever sees that message: for you the UUIDs are not important (and fixing those might not help); see the earlier hint.



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10.5: Use multiple drives for Time Machine backups
Authored by: palahala on Feb 19, '09 11:17:02PM

By the way: I swap those two drives all the time; I use Time Machine with multiple disks. No problems (but, again: things may be different when connecting the drives directly to your Mac -- post your results here!).



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10.5: Reconnect Time Machine backup after drive swap
Authored by: only_solutions on Feb 20, '09 02:03:59AM
You seem to refer to a different situation.

Basically I can think of three different issues here:

- Swapping the motherboard (that was your hint)

- Swapping the backup disks (that seems to be what you're referring to above)

- Swapping the original disks (that is my hint above)

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10.5: Reconnect Time Machine backup after drive swap
Authored by: bll on Feb 20, '09 04:39:36AM

I faced the same problem by just reinstalling the system on the same drive, after reformating the drive. Reformating updated the UUID and Time Machine wanted to redo a full copy. By using the same trick (shame on me, I did not publish it), I was able to get the intended behavior.



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10.5: Reconnect Time Machine backup after drive swap
Authored by: only_solutions on Feb 20, '09 05:47:53AM

Well, at least that's an independent confirmation! ;-)


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10.5: Reconnect Time Machine backup after drive swap
Authored by: palahala on Feb 20, '09 12:19:03PM

Aha, indeed it was not clear to me that you swapped the (source) disks in your Mac that uses Time Machine (not the target disks that you use to store your Time Machine backup).

Now that you explained about this UUID, I'd imagine that the content of /var/db/.TimeMachine.Cookie might somehow be related to the UUID of the drive that is the source for the backup. On the other hand, in the Unix world, I'd expect Time Machine to back up file systems that are actually located on multiple drives (like /home could be on some other drive than the other folders). If that were true then the UUID of a single partition should not matter. But given your hint, I assume that Time Machine in fact does rely on that UUID, and thus cannot create backups of file systems that use multiple drives...

Just for the record: the 10.5: Repair Time Machine after logic board changes hint was not mine; I just commented on it.



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10.5: Reconnect Time Machine backup after drive swap
Authored by: only_solutions on Feb 20, '09 10:07:05PM
palahala: Aha, indeed it was not clear to me that you swapped the (source) disks in your Mac that uses Time Machine

Okay.

palahala: Now that you explained about this UUID, I'd imagine that the content of /var/db/.TimeMachine.Cookie might somehow be related to the UUID of the drive that is the source for the backup.

That sounds plausible... It is probably used to detect the connection of the currently selected backup drive ("Change Disk" in Time Machine preferences probably re-sets it).

palahala: On the other hand, in the Unix world, I'd expect Time Machine to back up file systems that are actually located on multiple drives (like /home could be on some other drive than the other folders). If that were true then the UUID of a single partition should not matter. But given your hint, I assume that Time Machine in fact does rely on that UUID, and thus cannot create backups of file systems that use multiple drives...

Or at least not directly... especially when I think of FileVault I would expect that that is intentional. But since Time Machine is ultimately based on a souped-up version of rsync, maybe a closer look to its manual can give some information about that aspect.

And with the imminent introduction of ZFS the entire Time Machine mechanism may get a significant overhaul anyway.

palahala: Just for the record: the 10.5: Repair Time Machine after logic board changes hint was not mine; I just commented on it.

Yeah, I've just noticed that after posting. :-)

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