Creating an external Ventura boot drive for a 2017 iMac

I am trying to create an external USB drive running Ventura. I have managed to create a Mojave external drive and have cloned this to another SSD drive. When updating the operating system to Ventura, this fails when it needs to reboot during the install process. This happens despite having set there system to restart on the external drive. How can I ensure that when restarts it restarts the external disk and completes the install process?

iMac 27″ 5K, macOS 10.14

Posted on Feb 17, 2025 2:09 PM

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D.I. Johnson

Level 7

32,165 points

Posted on Feb 17, 2025 3:23 PM

Are you booting from Mojave on the external SSD drive and initiating the upgrade from that? The upgrade installer should apply itself to the boot drive, that being the Mojave external.

If you are being prompted to select a drive to upgrade, do you select the Mojave external SSD?

Have you tried creating a bootable USB installer for Ventura on a flash drive? Create that per the guidance found here: Create a bootable installer for macOS - Apple Support

Once created, you can boot the Mac from the bootable flash drive and apply the installer to whichever external drive you like.

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3 replies

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D.I. Johnson

Level 7

32,165 points

Feb 17, 2025 3:23 PM in response to Tomsheck

Are you booting from Mojave on the external SSD drive and initiating the upgrade from that? The upgrade installer should apply itself to the boot drive, that being the Mojave external.

If you are being prompted to select a drive to upgrade, do you select the Mojave external SSD?

Have you tried creating a bootable USB installer for Ventura on a flash drive? Create that per the guidance found here: Create a bootable installer for macOS - Apple Support

Once created, you can boot the Mac from the bootable flash drive and apply the installer to whichever external drive you like.

Tomsheck Author

Level 1

8 points

Feb 20, 2025 3:30 AM in response to D.I. Johnson

Hi, I have tried all options but the install always fails on reboot and d=gos back to the operating system installed on the 128gb of internal SSD - the other part of the Fusion Drive - a 2TB hdd - appears to have failed completely.

I do not appear to have any security installed on the iMac to prevent the creation of a new bootable SSD. Also using my MacBook Pro, I have not been able to create an external bootable drive on that machine, but I shall try and see whether Apple support is happy to help. I have support contract for the M1 laptop.

dialabrain

Level 10

135,527 points

Feb 20, 2025 3:44 AM in response to Tomsheck

FWIW, you cannot create a bootable Ventura drive on an Apple Silicon Mac that will boot an Intel Mac.

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Creating an external Ventura boot drive for a 2017 iMac