Make a bootable external drive
QHow can I make an external bootable clone of the internal SSD in my M1 MacBook Pro? I’ve tried using Carbon Copy Cloner, but just get an error 108. Is this impossible on Apple silicon Macs? byJOEREID
AApple silicon Macs are designed to be able to start up from external drives, but creating them using cloning techniques is no longer reliable, and not recommended. Instead, it’s much better to install macOS on them using Apple’s full installer app. This is because of the way macOS always starts up from the internal SSD in an Apple silicon Mac, and how external boot disks require secure ownership, but unlike T2 models don’t need any change in startup security, in Recovery mode.
Start by formatting the external drive in APFS, then either download and run the current macOS installer from the App Store, or start up in Recovery and go to Install macOS there. Opt to install to your external SSD, and leave the process to complete. You’ll be asked to select a user to make the owner of the new startup volume, and should then copy the account settings for that user when invited. At the end of the first phase of installation, time will stand still when the installer says there’s only a minute or so remaining. Give it ample time, and your Mac will then go through the usual sequence of black screens and progress bars as the installation completes. Once those are done, your Mac should start up from your external drive, and will complete personalisation, setup, and two-factor authentication.