How to start up your M1 Mac from an external drive

It’s not as easy as it used to be, as it likely requires that you purchase new hardware.

- GLENN FLEISHMAN

Apple’s relatively new M1 Macs that rely on Apple silicon have a number of usability differences from previous Intel-based Macs. One difference that’s tripped up some readers is how to start up or boot the M1 Mac from an external drive. Intel Macs generally make this easy.

You might want to use a bootable external drive to have a higher-capacity SSD than is offered or affordable via Apple’s pricing. Or you may want one for backup in case something goes very pear shaped with your M1 Mac.

Testing indicates that the following are required to start up from an external volume:

A Thunderbolt 3 drive. That’s not just one that uses the USB-C connector, but one that is a native USB 3.1 or 3.2 drive. Nor can you use a Type A adapter for a USB 3.0 or later drive. Success appears to require a native Thunderbolt 3 drive.

Erasing the drive completely, and then formatting it as APFS.

Obtaining a Big Sur installer, and then installing Big Sur from your M1 Mac directly onto the external drive. (This will allow only an M1 Mac to boot from the drive; Intel Macs will be unable to start up from your M1-prepared external drive.)

Let’s expand on each point.

THUNDERBOLT 3 DRIVE