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User profile for user: Heathej2
Heathej2 Author
User level: Level 1
4 points

Mac 27inch 15.1 running Big Sur 11.6.8 refuses to recognise bootable USB drives as bootable

I bought an external USB SSD drive to run Big Sur as the original drive is getting slow and I can prolong the life of the machine. I have read loads of info about creating bootable installers, recovery mode et al but it still won't boot to that drive OR a new USB thumb drive I bought. They just will not appear in System Preferences / Startup disk.

So here is what I have tried

NVRAM reset

SMC reset

Recovery mode with and without internet

Safe boot

Startup disk selection (hold down Alt)

Reinstall of Big Sur on the original drive

Deselecting the ownership tick box on the external drive

Cloning the disk with CCC with the boot box selected

NB the Startup security option in Recovery mode only has the firmware password option available - I think this is because Big Sur has the startup disk app?


So I am stumped. Anybody got any other options beyond



iMac 27″, macOS 11.6

Posted on Aug 23, 2022 2:56 AM

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User profile for user: PRP_53
PRP_53
User level: Level 10
91,243 points

Posted on Aug 23, 2022 6:46 AM

Suggestion and Only if the User is absolutely certain the USB Installer Drive was created properly.


Below is what I have used and it has worked every time.


With the Full Version of " Install Big Sur " Application located in the Applications folder and nowhere else.


Terminal command below where the Untitled below is the name given the Destination Drive for the installer drive is given that name


sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled


Once done, shutdown the computer and disconnect ALL External Drive except the USB Installer Drive


Restart and hold the Option key and this should present option to boot into the Internal Drive or the External Bootable Installer Drive.


Choose the USB Installer Drive and pause and attached the Intended External Drive where you what to point the Installer to install Big Sur onto.


Sometimes, have more than one External Drive attached at the same time and starting from a Cold Boot and the Computer test confused and will auto start from Internal Drive - from observations over the years on these Forums.

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User profile for user: PRP_53
PRP_53
User level: Level 10
91,243 points

Aug 23, 2022 6:46 AM in response to Heathej2

Suggestion and Only if the User is absolutely certain the USB Installer Drive was created properly.


Below is what I have used and it has worked every time.


With the Full Version of " Install Big Sur " Application located in the Applications folder and nowhere else.


Terminal command below where the Untitled below is the name given the Destination Drive for the installer drive is given that name


sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled


Once done, shutdown the computer and disconnect ALL External Drive except the USB Installer Drive


Restart and hold the Option key and this should present option to boot into the Internal Drive or the External Bootable Installer Drive.


Choose the USB Installer Drive and pause and attached the Intended External Drive where you what to point the Installer to install Big Sur onto.


Sometimes, have more than one External Drive attached at the same time and starting from a Cold Boot and the Computer test confused and will auto start from Internal Drive - from observations over the years on these Forums.

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User profile for user: Heathej2
Heathej2 Author
User level: Level 1
4 points

Aug 23, 2022 11:31 AM in response to PRP_53

Many thanks, that worked just as described with a couple of additions.

At the first reboot during the BigSur build of the target drive I had to restart and use the same technique to get the build to continue as it had booted to the internal drive.


Then once everything was built, the data was imported and I had plugged in my backup disk a simple restart to see what would happen made it boot to the internal drive even though the external was finally successfully visible and selected in the startup disk app.

This was again resolved a controlled reboot. It seems I will be doing that for the foreseeable future but at least I have a solution.



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Mac 27inch 15.1 running Big Sur 11.6.8 refuses to recognise bootable USB drives as bootable

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