Time Machine Backing up to the Wrong Disk

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Time Machine Backing up to the Wrong Disk

I have been successfully using a 1TB LaCie disk for Time Machine Backups for over three years now, but the disk just died, almost causing me to loose the backup of my MBP, as its hard drive also just died. I decided it was time for a new disk, and bought a 2TB Iomega drive (which I aptly named "Backup"). I already had one such drive (still under the default name "Iomega HDD"), and now Time Machine is trying to use both of them as the backup drive.

I only plug this new Iomega drive in for backups, so it won't get used if it doesn't need to be, but the other (identical) Iomega drive is on almost all the time, as I have my iTunes and video libraries on it.

For whatever reason, Time Machine backs up to the correct disk (Backup) when it's connected, but when it's not, it backs up to the wrong disk (Iomega HDD).

This results in Time Machine trying to back up to this drive every hour, which I don't need, not to mention the fact that a full backup (which is what it has tried to do) would fill this 2TB drive to the brim, as it already has 1.6TB of used space. Apart from vetoing Time Machine every hour, or turning it off altogether, I don't see a way around this new problem. Is there a way to tell Time Machine not to backup to this disk (Iomega HDD)?

(Time Machine has always made backup easier, until now…)

iMac Intel 20" (Early 2009), MacBook Pro 15" (Early 2010), Mac OS X (10.6.7), 32 GB iPod Touch, 160 GB, 1TB (effectively dead) external LaCie drives, 2 Iomega 2TB external drives

Posted on Apr 12, 2011 6:34 PM

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Answer 1

Best reply

Pondini

Level 8

38,863 points

Apr 12, 2011 8:31 PM in response to Future Progammer

It sounds like both drives have the same UUID (Universally Unique Identifier). We've seen that on a couple of occasions of identical drives that were used "as is" from the factory.

To see the UUIDs, use the +Disk Utility+ app, in your Applications/Utilities folder. Select the line for the partition (indented, under the main line for the drive), and click the Info icon in the toolbar, or select +File > Get Info+ from the menubar.

If both have the same one, you'll have to erase one to change it's UUID. 😟

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Answer 2

Apr 14, 2011 8:49 AM in response to Pondini

It was no problem to erase the backup drive, as it only had backups on it. That immediately fixed the problem, though I did have to go re-tell it which drive to use. Thanks a lot!

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Answer 3

Joel.s

Level 1

15 points

Oct 5, 2011 2:27 AM in response to Pondini

I found this post because I had a pair of 2010 WD drives with identical UUIDs which were preventing me syncing them but I developed a solution suggested by Decimus (who make Synk backup software) that allowed me to change the UUID without erasing the drive.

This suggestion comes with a big health warning about potentially dire consequences of you addressing the wrong drive and the use of the sudo command generally, but if you are careful it might save a lot of trouble restoring the contents of a large drive like mine. If you can make a backup of the drive, then do so. While I did my research, I am not remotely an expert with Terminal and use it infrequently and with caution, so my knowledge is limited but here is what I did:

Firstly, get the name of the drive from Disk Utility by clicking the visible icon name of the drive ("Backup01" or whatever) in the left-hand panel and clicking the Info button in the Toolbar.

The name you want is against the Disk Identifier and will be something like disk1s3. I think disk0 is always your startup drive, so never choose this one. If the name is just "disk1" you have clicked the parent entry in the list.

For the purposes of these commands, the identifier is prefixed with the letter "r" so you would enter "rdisk1s3" where ever you see [rdi] at the ends of the following commands.

I suggest building these commands in a text editor first then copying them into Terminal when you are satisfied they are correct.

Open Terminal.

Check that you can see the current value for the UUID of the drive you want to change:

sudo /System/Library/Filesystems/hfs.fs/hfs.util -k [rdi]

You will probably be prompted for your system password (which is not displayed) and then the UUID for the named disk should be returned.

Unmount (but do not eject) the drive with Disk Utility by clicking the respective button in the Toolbar.

Now issue the command to assign a new UUID:

sudo /System/Library/Filesystems/hfs.fs/hfs.util -s [rdi]

Mount the drive again with Disk Utility and wait a few seconds.

Check the UUID has been changed:

sudo /System/Library/Filesystems/hfs.fs/hfs.util -k [rdi]

or use the Info button in DU (it might take a few moments to show the change)

It should be radically different to the one returned earlier.

Mac OS will immediately start to reindex the drive for Spotlight and when it has finished you are done.

I then checked the drive with DU and DiskWarrior 4.2 (directory and files) and no problems were found. I was then able to mount the two drives and successfully sync between them.

If this does not work, or the commands are not syntactically correct for your system, you may have to erase and restore the drive.

MacBook Pro 3,1, 10.6.8

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