Resize APFS partition and move it to another hard drive I have a 500 GB external USB disk that contains a 465GB &quot;APFS container&quot;, with Mac OS X Catalina, bootable (with the trick &quot;Press and hold the Option (Alt) key immediately after turning on or restarting your Mac&quot;)
I need to use this disk for something else, and I need to move it to another 320 GB disk.
How to do that?

First how to shrink the 465 GB to 300 GB (only &lt; 100 GB are used)? Is it possible from another Mac OS High Sierra computer or another Linux or another Windows computer?

Then how to copy the partition to the 320GB so that it will still be bootable?
Apple documentation states you should be able to replicate a bootable APFS container to a new drive. Unfortunately, the GUI based software from Apple is wrought with bugs. Below are the steps I preformed to successfully clone Catalina macOS 10.15.5 to a new USB drive. To be honest, I admit this was tested using a VirtualBox virtual machine.

Boot to macOS Recovery. I booted to the macOS Recovery APFS volume on the 465 GB USB drive.

Plug the 320 GB drive in a USB port

Open the Disk Utility.

Under the View pulldown, select Show all Devices.

Highlight the 320 GB Drive, then select the Erase button.

Use the selections shown below, then select the Erase button.


Quit the Disk Utility, then open the Disk Utility.

Highlight the MyNewUSB volume, then select the Restore button. From the Restore from pulldown list, select the existing external USB macOS volume, as shown below. When finished, select the Restore button.

Note: This will replicate the macOS, macOS - Data, hidden Preboot and hidden Recovery volumes.



When finished, quit the Disk Utility, then open the Disk Utility.

Visually, check the results.

Quit the Disk Utility.

Shutdown the Mac.

Unplug the 465 GB USB drive.

Start the Mac and immediately, hold down the option Key until the Mac Startup Manager icons appear.

Hold down the control key and select to boot from the 320 GB USB drive. Note: This first boot took longer than normal.