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MacintoshHD space lost after Catalina downgrade

I just downgraded MacBook Pro from Catalina to Mojave. I did not transfer any files from old computer. I therefore expected a clean disk with lots of space. However, Macintosh HD now shows it has a capacity of 250GB. Out of those, 11.18 GB is used. But only 24.18GB is available. Where is the rest of the space and how can I get it back

Please help

MacBook Pro 13″, macOS 10.15

Posted on Nov 3, 2020 3:42 AM

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Question marked as Top-ranking reply

Posted on Nov 3, 2020 11:50 PM

The problem you are having is that you did not erase your disk correctly, you have erased the Volume Macintosh HD

and installed Mojave on that leaving the Macintosh HD- Data disk intact with your Catalina files still on it.


You have to erase the entire Disk not just any one Volume to downgrade to Mojave.


Boot to your bootable USB installer with Mojave on it.

Open Disk Utility, click View in the menubar and select Show All Devices.

The left hand panel of Disk Utility will now show the Disk and all of its Volumes

which are indented.

Highlight the Disk (probably called Apple SSD ........) and click Erase.

Give the Disk a name.

Format: APFS

Scheme: GUID Partition Map

Click Erase.

When done quit Disk Utility.


Click on Install OS and press Continue, the installation process should begin

follow the prompts.

The you are ready to restore from Time Machine remember to only restore your

personal files and data. Do not restore any system or library files as this will put

Catalina back on your mac. Do not restore any apps as these may have been

updated to work on Catalina and will not work on Mojave.

10 replies
Question marked as Top-ranking reply

Nov 3, 2020 11:50 PM in response to manmserious

The problem you are having is that you did not erase your disk correctly, you have erased the Volume Macintosh HD

and installed Mojave on that leaving the Macintosh HD- Data disk intact with your Catalina files still on it.


You have to erase the entire Disk not just any one Volume to downgrade to Mojave.


Boot to your bootable USB installer with Mojave on it.

Open Disk Utility, click View in the menubar and select Show All Devices.

The left hand panel of Disk Utility will now show the Disk and all of its Volumes

which are indented.

Highlight the Disk (probably called Apple SSD ........) and click Erase.

Give the Disk a name.

Format: APFS

Scheme: GUID Partition Map

Click Erase.

When done quit Disk Utility.


Click on Install OS and press Continue, the installation process should begin

follow the prompts.

The you are ready to restore from Time Machine remember to only restore your

personal files and data. Do not restore any system or library files as this will put

Catalina back on your mac. Do not restore any apps as these may have been

updated to work on Catalina and will not work on Mojave.

Nov 3, 2020 5:20 AM in response to manmserious

Catalina creates two Volumes, one for the OS, and another for your Data.

Mojave has no idea what the - Data volume is besides another volume.

That is why you see all of the space used up. Your data is using the space.

If you transferred all of your data from a backup or otherwise, you can just Remove that volume in Disk Utility.

If you haven't transferred all of your data, you can transfer the documents manually from the Macintosh HD - Data Volume to your Macintosh HD volume, then remove it.

Nov 3, 2020 4:13 PM in response to manmserious

manmserious wrote:

How do I delete the volume? In Disk Utility, Macintosh HD Data has the - (minus) disabled. Erase is also disabled. The both of them are enabled if I select the other volume in the container ie Macintosh HD

Are you sure you are not still running Catalina? Nothing in Mojave should be using it unless you installed Mojave on that Volume.

Nov 3, 2020 9:27 PM in response to Barney-15E

I am running Mojave. Now there is a new problem. A user said I boot in recovery mode and delete Macintosh HD Data from there. I did delete. Now the macbook is booting to a flashing question mark. Other times it is booting only in recovery mode.

If I try to reinstall Mojave from my bootable disk, I am told not possible because a newer version of it is already installed.

If I try to exit the recovery mode screen, I get the option to restart. Nothing happens when I hit restart.

MacintoshHD space lost after Catalina downgrade

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