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Need help external booting using thunderbolt 3 interface with an M1 Mac

Dear experts, I have a M1 MacBook Air with no recovery partition. I am not able to boot it externally with an SSD containing the Mac OS 11.2.3 Big Sur installer created via instructions provided here: https://support.apple.com/en-us/HT201372

The SSD is in an OWC Thunderbolt 3 NVME enclosure.

If I restart the MacBook with the power key pressed, I don't see the external drive.

Please advice on what I can try to boot via the external drive and reinstall Big Sur. thanks

MacBook Air 13″, macOS 11.1

Posted on Mar 12, 2021 11:03 AM

Best reply

Krysler Author

Level 1

10 points

Posted on Mar 13, 2021 11:02 PM

Solved!

To make an external boot device, having a thunderbolt 3 interface is not enough. The device must be using APFS with Mac Big Sur installed in recovery mode of the host computer which has to be using an M1 processor. I restored the recovery partition first and then was able to install Big Sur on an external SSD. and boot from it.

If you don't have a recovery partition and need to reinstate it then follow the Apple Configurator 2 approach and use the option restore. More here: https://mrmacintosh.com/restore-macos-firmware-on-an-apple-silicon-mac-boot-to-dfu-mode/

Tip: to avoid multiple tries, make sure your M1 mac is in DFU mode by frequently checking System Preferences

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Need help external booting using thunderbolt 3 interface with an M1 Mac

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