Cloning Startup disk to new internal hard drive High Sierra (Continued)

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Cloning Startup disk to new internal hard drive High Sierra (Continued)

This is the same topic as I had started in May but which was closed for some reason before I had resolved all that required resolving.

The original discussion was here:

Cloning Startup disk to new internal hard… - Apple Community

I am at the stage where the 2nd test drive has been cloned using CCC but that the attempt to upgrade the test drive to Mojave is met with the response as per the attached image.I am just looking to get a better understanding of where I am with this process before proceeding.

Firstly is is necessary for mojave to be installed on an AFPS formatted drive?

What does the message from the installer mean and what does it require to resolve the 'internal error' whatever it may be?

Should I erase/format the test drive to AFPS? If I do so then I would not then be able to do the closing of the main drive to the test drive as it would be a different file structure.

Thanks for the previous contributions on the earlier closed thread. Much appreciated. I am here to learn!

Posted on Oct 29, 2025 7:16 AM

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Answer 1

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HWTech

Level 9

68,198 points

Oct 29, 2025 4:18 PM in response to Anthony ÓDoibhailein

Excellent advice by @MartinR. When erasing the drive, make sure to erase the whole physical drive instead of just the "New PRIME" volume. This way a fresh partition table is created by macOS/Disk Utility as well as a clean APFS volume using the Mojave installer. The partitioning from the factory can sometimes have issues for some operating systems....especially for a boot drive, plus doing this can help detect bad or even fake drives.

Unfortunately Disk Utility hides the physical drives from view by default, so you will need to click "View" within Disk Utility and select "Show All Devices" before the physical drives and hidden Containers appear on the left pane of Disk Utility. Here is an Apple article showing the process (unfortunately Apple modified their document to exclude the pictures so I got an older copy from the Internet Archive's Wayback Machine...why Apple why?!?):

https://web.archive.org/web/20250909095655/https://support.apple.com/guide/disk-utility/erase-and-reformat-a-storage-device-dskutl14079/mac

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Answer 2

MartinR

Level 7

24,053 points

Oct 29, 2025 8:21 AM in response to Anthony ÓDoibhailein

My 2¢ ...

An alternative to cloning the internal High Sierra drive & trying to upgrade the clone to Mojave .... would be to install Mojave on the 2nd (new) drive, then run Migration Assistant on the Mojave drive to move over your apps, user accounts, settings, etc. from the internal High Sierra Drive.

BTW, if you choose to do it that way, when you start the Mojave installer, select Disk Utility instead of install Mojave and then format the 2nd (new) drive as APFS, GUID Partition Scheme. APFS changed significantly from High Sierra to Mojave to Catalina and further. It would be better/safer to format the drive from the Mojave installer Disk Utility than the High Sierra Disk Utility.

I assume your interest in cloning is to preserve 32-bit apps from your High Sierra drive without having to reinstall them from scratch on the Mojave drive ... correct?

What hard drive (or SSD) are you using for this? (make & model)

You may still want to make a separate clone of the internal High Sierra drive, however, as a backup!!

And, FWIW, it appears you have a Mac Pro and want the new Mojave drive to be internal. I would do this entire operation with the intended Mojave drive in an external enclosure and thoroughly test it there before placing the drive in the Mac Pro.

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