How I successfully Made an M1 External Boot Drive.
Several weeks ago I bought a new M1 Mac mini. One of the first things that I needed to do was to set-up a bootable external drive. I thought that this would be straight forward just like on an intel Mac, but it was not.
No matter what I tried to do I always ran into issues/errors, and upon doing a lot of research I quickly learned that I was not alone. Many other people, both here, and on other Apple forums were having the same frustrating issues trying to make a M1 bootable external drive for their M1 also.
After thinking about what might be going wrong, I decided today to take a different approach to the issue. Everyone was being told to copy over their data partition, either by using CCC or by using Migration Assistant, and then once that process was completed to go into Recovery and install a fresh new copy of 11.1 to their external drive. This always ended up with the above mentioned issues/errors.
So today I decided to strip the process down so that I could learn what might be going wrong. My goal was to simply make a bootable drive, with no saved data on it. I simply wanted to externally boot into a fresh copy of 11.1. I figured that if I could get that far, then I could copy all of my old files over later.
Well guess what? It worked!
Here’s how I did it, but keep in mind that you need to perform every step from your M1. First I formatted my external drive down to the bone. Then you need to log into Recovery by doing the following;
Make sure that your Mac is turned off. If it is not off then click on the Apple logo (upper left corner or your screen) and choose Shut Down.
Next press the power button on your M1 and keep pressing the power button down until you see a message on your screen saying that it is loading Options. You can now let go of the power button.
Next, click on Options (far right side) then click on Continue.
If asked, select a user, click on Next, and enter in your Administrator Password.
You are now successfully logged into the M1’s Recovery mode.
Now choose Reinstall macOS Big Sur as shown above, and follow the prompts after you choose which external drive you want to boot from. It can take up to several hours for Mac Big Sur to install, but once it does it will reboot (several times) and then it will open up your desktop. Enter in your admin password and that’s it, you now have a bootable external M1 drive!
From there I simply used CCC to copy over my data from my backup hard drive. All that is left is to use Migration Assistant to copy over your user account. That is were I am currently at. It keeps saying that I need to update before Migration Assistant can run, so I’m looking for a way to get around that, or I’ll just wait until 11.2 is released (see screenshot below).
For my external boot drive I am using an Inland Professional NVMe M.2 PCIe SSD, and it is crazy fast. For the SSD Enclosure I am using an Trebleet Thunderbolt 3 enclosure, which comes with a Thunderbolt 3 cable. BTW, I have tried using several top shelf Thunderbolt 3 cables with this same set-up, and they all seem to work great. I will post performance data later, but I already know it is extremely fast and buttery smooth.
If anyone knows how to get around the Migration Assistant error mentioned above, please post. If you are successful making a M1 boot drive, please also share your success here with everyone. I sincerely hope that this helps others.
Mac mini, macOS 10.13
