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Downgrading from Big Sur to Mojave

After several attempts I have managed to downgrade from Big Sur to Mojave using Recovery, all seems to work fine.

However, there are 2 changes:

1/ When I start my MacBook I get a message "Incompatible disk. This disk uses features that are not supported on this version of macOS." I have no idea which disk it is referring to and what features. I assume there are still some remains of Big Sur.

2/ Before upgrade to Big Sur I used to have just one disk - Macintosh HD (on desktop and in Storage Tab in About This Mac). Now, after downgrade back to Mojave, I have 3 disks - Macintosh HD, Macintosh HD - Data and Update. Is there a way to get rid of these 2 extra disks or it is irrelevant and I shouldn't be bothered by this. Or maybe I should do recovery process in some different way?

Would be great if you could help.

Thanks, Margaret

MacBook Air 13″, macOS 10.14

Posted on Dec 19, 2020 4:38 AM

Top-ranking reply

tbirdvet

Level 6

14,423 points

Posted on Dec 19, 2020 5:22 AM

The reason you have extra volumes is because the drive was not erased completely when you did the reinstall. You can go to disk utilities and use the - sign to delete one or two of the volumes but not sure what this will do to the operating systemm. I have done this myself and all was fine but no guarantee. I would delete the "data" and "update" vol. You may have to start over in erasing your drive and reformatting again. the "incompatible disk" error is because you have some Big Sur vol. left over.

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Downgrading from Big Sur to Mojave

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