After recently having some issues with an 8TB Seagate drive, I bought a new replacement to backup, and realised I have this dock sitting here with dual bays that can clone a disk far faster than any software copy I can do with my meagre USB 3 connections. So I've tried this clone function only a couple of times and realised when I try and mount one of the cloned volumes it couldn't show both to compare files, so on research I realise the byte for byte copy cloned the unique code for the volume and the system can't handle having two of the same connected. So after searching for some time and not getting any clear answers I've come here for some expert advice.

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It took at least 12 hours to copy the drive, I really don't want to start again using Carbon Copy Cloner or SuperDuper as I suspect it will take 3 days through software.

Is there any way of changing the unique code, is it safe to do so?

  • Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.
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    Commented Jun 3 at 22:48
  • I think it is fairly clear what Lee is asking, but it may be a duplicate. This Q&A shows how to change the GUID, I believe. However not being a disk partition guru I could be wrong, but worth checking out, I believe. apple.stackexchange.com/questions/305706/… Commented Jun 3 at 23:05
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    The answer depends on the type of filesystems. Can you specify what types of volume are on your Seagate drive. Also are any of the volumes bootable? Commented Jun 4 at 11:06
  • Thanks for your replies, file system = Mac OS Extended (journaled), no system, so won't be used for booting, just storage for media files and my precious photo library. Commented Jun 4 at 11:20
  • @SteveChambers That link might have the answer, but looks like its for a slightly more complicated problem? I'm nervous after previously using mdutil commands on a drive and then getting errors messages back that I couldn't solve, so ended up wiping a drive. Commented Jun 4 at 11:29

1 Answer 1


The command is hfs.util. I believe you can find this command in the following folder.


The syntax is given below for getting the current UUID.

/System/Library/Filesystems/hfs.fs/Contents/Resources/hfs.util -k device; echo

The syntax is given below for setting a new unique UUID.

/System/Library/Filesystems/hfs.fs/Contents/Resources/hfs.util -s device

You can see man hfs.util for more information.

Note: When using either the -k or -s options, a return value of 253 means success.

  • Thank you David, took a couple of attempts for some reason, but I got there in the end thanks to you, what seemed complicated in the end was quite trivial! Commented Jun 5 at 8:58
  • If my post answered your question, then you should accept my answer. This will put a green checkmark next to the answer. Other will then know an answer was found. Commented Jun 5 at 10:45

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