Boot from external disk on M1 Mac

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Level 1

15 points

Boot from external disk on M1 Mac

About booting from an external disk on Macmini 2020 (M1)

I own an M1 Macmini 2020, but I'm having trouble booting an external disk.

In January, I wanted to install Big Sur beta, and I installed it on an external disk with a USB-C connection with Big Sur 11.1, but I couldn't switch to an external disk after installation.

After that, I searched the Internet information and found the following information.

https://forums.macrumors.com/threads/m1-macs-boot-from-external-drive-possible.2267649/page-4

According to the information here, it is possible to boot an external disk with Thunderbolt or USB-A, so I tried to create external disks on USB-A and Thunderbolt and confirmed installation, switching, and booting on my Mac mini. Finally I created and used Big Sur beta 11.2 on USB-A, but Thunderbolt was to use it for other purposes.

In February, Big Sur 11.2 was released, so I wondered if I could create Big Sur beta 11.2 on a USB-C(named USB-C1) disk as in the previous step, and successfully create and boot. You can now use Thunderbolt, USB-A and USB-C.

However, a new problem was found.

1) I can no longer switch to the USB-A disk I made in January.

2) After initializing this USB-A, creating Big Sur beta 11.2 on USB-A, switching, and confirming startup, it is no longer possible to switch to the above-mentioned created USB-C1 disk!

3) When I re-initialized the USB-C1 disk and created Big Sur 11.2 on USB-C1, I couldn't switch to the above-mentioned created USB-A disk this time!

4) For confirmation, I re-initialized another new disk with the same USB-C(named USB-C2), installed, switched, and confirmed the startup, but the USB-C1 disk created and confirmed in 3) could not be switched. ..

Taken together, isn't switching to an external disk (including installing Big Sur) limited to the last disk created? I feel that.

I've searched Apple and Internet information, but I'm not sure if this is a spec. or a temporary one (Big Sur bug?).

If you have any information that can be used as a clue, please let me know.

Mac mini 2018 or later

Posted on Feb 6, 2021 8:07 PM

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Answer 1

Feb 9, 2021 11:54 AM in response to matsuda0707

FWIW, there have been some long threads here about booting

from an external drive and even in my own experience it was

quite an adventure.

It seems at this point in time, you need "just the right drive" to

get it two work. Some cases USB-C drives connected with

Thunderbolt 3 cables would work but if connected with USB-C

cables they wouldn't. Some cases a drive would seem to boot fine

only to find out later it wouldn't boot. Most of the issues I have

seen had been with any USB based drive as being a toss up as to whether

it would work. Thunderbolt 3 drives seem to have the highest success rate.

It is some quirk in the M1 systems that is causing the issue as it

seems those with Intel systems that have been updated to Big Sur

do not have the issue.

Just for an idea of the "bizarreness", I have a Sandisk Ultra 3D SATA SSD drive

and using a SATA 3 to USB adapter. The only thing that worked was connecting

it to my USB-C port on my M1 MacBook Air using the Apple USB-C/USB-A

adapter. No other "generic" adapters or cables would work, just the Apple one?????

This was something to be flawless and a given on Macs since they supported

external booting, I think all the way back to 68000 based Macs or at the

very least the first Mac OS X 10.0.

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Answer 2

etresoft

Level 9

56,290 points

Feb 9, 2021 10:15 AM in response to matsuda0707

Follow the instructions in this Apple Support document: About Startup Security Utility - Apple Support

I would not recommend taking advice from non-Apple websites, especially when beta versions of the operating system are concerned. There is too much changing and too much incompetence and misinformation.

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Answer 3

matsuda0707 Author

Level 1

15 points

Feb 9, 2021 10:08 AM in response to Sharon_419

Thanks for reply.

I know that the way to switch the startup disk.

The problem is;

1) Why the USB-C disk is not bootable for M1 Macbook air or Pro.

2) Why the startup disk is limitted to the last created disk.

Please read carefully my first post!

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Answer 4

Sharon_419

Community Specialist

Feb 9, 2021 8:26 AM in response to matsuda0707

Hi matsuda0707,

We understand you're looking to boot your Mac from a different startup disk. The following page offers information, including steps specific to your Mac, that we expect to be helpful: Change your Mac startup disk

Take care!

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Boot from external disk on M1 Mac

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