9 Replies Latest reply: May 10, 2012 10:25 AM by BDAqua
legolas-woodelf Level 1 (0 points)

This is a slightly weird problem.


My setup is basically this:


iMac with Internal HD

Physical External Drive 1 (CrossFire) is an External Drive with two partitions used for keeping work

Physical External Drive 2 (LaCie) is a Second External Drive with six partitions, one of which is used for Time Machine backup.


Having heard that Time Machine doesn't always restore a disk as identical (I gather it is a bit clever at missing out some root level stuff?), as well as Time Machine backups, I clone my main drives once a month on their respective opposite partitions on the Time Machine physical disk. In other words my physical backup drive has everything backed up in both Time Machine and clone format - the best of all worlds. It also enables me to boot from the backup drive in the event of an Internal HD failure.


Attached is a basic diagram of the drive and partition layout.


So far I've been using Time Machine to only backup my Internal Drive on my iMac. However I want to add one of the partitions from CrossFire so that it too gets backed up on Time Machine (see the red line on the diagram).


My problem is this:


When I add the external drive I want to backup it all works perfectly and Time Machine is flawless. But if I disconnect that drive (CF-2) and the clone of that drive (LC-2) is still connected, when Time Machine does its next backup, it thinks the clone of that drive (LC-2) is actually the drive I want backed up (CF-2) and merrily copies all 100gb of data, even though the clone is on a different partition of a different physical drive and has a different disk name. If I look in the "Exclude Items" list, with the drive I want backed up connected (CF-2), the clone (LC-2) is listed as needing to be excluded, but when the drive I want backed up is disconnected, the clone of it disappears from the "Exclude" list. In other words the external drive I want to be Time Machine backed up pulls its opposite clone in and out of the "Exclude" list as it gets mounted and unmounted. And no amount of going in and adding the clone to the "Exclude" list will make that setting stick.


How do I convince Time Machine to ignore the clone and only work with the original?

Is there some identification tag that Time Machine uses (rather than simply the disk name) which fools it into thinking that the clone is the original?

And if so, how do I override it?


As ever, any thoughts or advice most gratefully received.


Drive Layout.gif

Mac OS X (10.5.8), 17" iMac PPC G4 1.25 GHz 10.5.8
  • legolas-woodelf Level 1 (0 points)

    I've just done a bit more googling and learnt about UUIDs (Universally Unique Identifiers). I thought maybe the two drive partitions share the same one, but I've checked via Disk Utility and they're both unique.


    Any other possible causes as to why TM would backup a clone of a drive once the original of that clone was ejected?

  • legolas-woodelf Level 1 (0 points)

    I just looked through TM's log (via the Dashboard widget) and the first time it backed up the clone it even acknowledges that the UUID is wrong, but rather than conclude that it's got the wrong drive and shouldn't back it up, it ploughs on with a "Node requires deep traversal".


    I'm sure I'm circling round the problem, but I don't understand enough about drives, partitions and how TM identifies them to find he answer.


    It seems to hinge round the fact that the drive to be backed up is cloned and if the first drive isn't availabl, TM will back up the clone instead. But I would have thought that since the clone has a unique disk name (both in terms of user name and in terms if Disk Utility's "disk1s5" type identifier) and a unique UUID that TM would leave it alone.


    What else is there that TM can use to distinguish one disk from another?

  • BDAqua Level 10 (121,655 points)

    The only thing I can think of is locking the file that TM uses for exclusions, or...





  • legolas-woodelf Level 1 (0 points)



    OK, I think I may have worked this out, although I only partially understand it.


    I reformatted LC2 (the clone) and started again. Only this time I just cloned the two principle files from my work drive (CF2) onto it (Movies and my iPhoto Library) rather than cloning the entire drive. Now when I Time Machine backup the work drive (CF2), it all seems to work as it should.


    It would appear that Time Machine uses something other than UUIDs and disk names to identify a drive. This means that cloning a drive clones the identifier that TM relies upon, causing TM to go for the clone if the original is absent in the mistaken belief that the clone is the original.


    I hope this thread makes sense to someone. I wrote it and I barely understand it!!!


    Anyway, I think I've sorted it. I'll post up any problems if they arise.

  • BDAqua Level 10 (121,655 points)

    Good work, thanks for the report!

  • legolas-woodelf Level 1 (0 points)

    Doh, just when I thought it was safe to backup...


    When I tested it all yesterday, I ran through various combinations of having the external work drive (CF2) mounted/unmounted, poweredup/powered down etc.


    However having shutdown my computer overnight, I booted up this morning without booting the CF2 work drive, set Time Machine backing up and it dived straight for the clone again. I looked in the TM control panel and sure enough the clone had been pulled out of the exclude list again.


    I'm a bit flummoxed.


    I've been cloning my internal hard drive like this for ages and TM has never gone for that clone.


    Does TM look at files rather than drives maybe?

    Will I have to remember to rename the files on the clone drive every time I update the clone to prevent TM getting confused?

    Would that even work?

    It looks like any solution I find is going to be clunky and inelegant.

    As long as the work drive is always powered up and mounted, it won't be a problem, but the moment Mrs. Woodelf or Woodelf Junior switch the Mac on without first powering up the work drive, TM will go for the clone (which is too big to fit in the remaining TM drive space) and cause all sorts of problems like clearing out old backups that I want to keep.


    Someone out there must know what TM uses to identify a drive and how it can be getting confused?

  • BDAqua Level 10 (121,655 points)

    Have you looked through Pondini's extensive TM help site?



  • legolas-woodelf Level 1 (0 points)

    Hi BD,


    I looked through Pondini's page as I'm aware he is a leading authority on Time Machine, but nothing really touches on my problem.


    However I think I may have sorted it ... again ... sort of.


    First off, I've worked out why the problem has never manifested itself with the clone of my internal hard drive - it's because I always boot from the internal drive meaning it's always mounted and TM will always find it first before it has a chance to see the clone and get confused by it.


    Re. the external drive I want to add to my TM backup, so long as it stays mounted all the time, everything works. But if it's unmounted with its associated clone still mounted, TM will go for the clone. (I've also noticed little things rippling back causing the Finder to get a bit confused too).


    The problem seems to be centred around Carbon Copy Cloner somehow flagging the clone identically to the original drive. (Perhaps unsurprising for cloning software). Even if you only clone certain folders onto the clone drive, you can only clone onto a drive, not into another folder. CCC seems to run it very much as creating a cloned drive with selected files omitted rather than cloning selected files onto a drive, and it's this that seems to be confusing TM.


    So my solution - which seems to have worked so far but it's early days - is to reformat the clone so that it is, as it were, its own drive once more. Then create an empty folder on the top level, and then create synchronized/backed up copies of the folders I want backed up into that top level folder. I did this using SilverKeeper (freeware - my copy came with my LaCie hard drive but you can download it too). This lets you clone/sync/backup individual folders into other individual folders, presumably without touching the actual drive ident tags that TM uses. In other words it can be set to deal with folders not drives.


    Thereafter you can setup a schedule to update the backups weekly using the scheduling feature within SilverKeeper. I've tried making a change to my iPhoto Master (from within iPhoto of course) and updating the backup does work and is pretty quick.


    There are a couple of considerations:


    Firstly the iPhoto library won't like being synchronized two ways. My system works as a one-way backup but that's all. (The SilverKeeper instructions do actually touch on this issue with iPhoto and iTunes libraries). Start using the copied iPhoto Library and changing it and then trying to sync it back to the original and you'll run into problems.


    Secondly, if you try and tell SilverKeeper to use the iPhoto Library as a source, it will be greyed out. The way round it is to put the iPhoto Library inside another folder and set that folder as the source.


    In turn however this means that the next time you open iPhoto you'll need to tell it where the iPhoto Library is as the path will have changed. Secondly it means that Time Machine, if you've alreay been backing up with it previously, will think you've deleted the iPhoto Library and created a new folder with a new library inside it, which means it will re-back up your entire iPhoto Library. It's not a problem if you have a big drive or a small library, but in my case I let it run then deleted all backups of the iPhoto Library that were outside the new folder from within Time Machine to get that space back.


    Other than that, I'm hopeful that this will prove to be the winning solution. If anyone is patient enough to have hung in there to the end of this thread, I hope it makes sense.

  • BDAqua Level 10 (121,655 points)

    Good work, thanks for the report!