Level 4

2,149 points

Mac Mini M1 Using External SSD

Hi, I bought the new Mac Mini M1 and would like to use it with a external 1TB SSD. I recently bought a 2018-2019 Mac Mini and was using my external SSD just fine with it, but now with the M1 it is having all kinds of connectivity issues. I thought I would just plug it in the M1 and it would work, since it has the same OS version as the internal SSD, but it wouldn't let me. It said I needed to reinstall 11.01 all over again, so I tried, but it got halfway and then said there was an error and it stopped installing. It then said I had the wrong version of macOS, even though the internal SSD had the same exact version (11.01).

So I formatted my SSD and reinstalled 11.01 onto it. Guess what, yep, you guessed it, it says I can't use it because it needs to be "updated" - even though it is the current version of macOS (11.01).

BTW, I tried the Startup Security Utility as shown here;

https://support.apple.com/en-us/HT208198

but there was no external drive option.

How can I get this M1 to boot into the external SSD?

Posted on Dec 10, 2020 10:41 PM

Top-ranking reply

MarcoT76

Level 1

14 points

Posted on Dec 27, 2020 6:57 PM

Booting on external drive M1 Mac

For background, I’m Coming from 2018 Intel Mac Mini using an external Plugable Thunderbolt 3 NVMe SSD as my boot drive.

I purchased the M1 Mac Mini in the 16gb with 256 SSD thinking I could save the $400 and keep using my external drive. Boy I did not know what apple had in store for me...

After spending hours unsuccessfully trying to use the drive, I turned to this forum for help. Like many I found help and got as far as booting into the drive but unable to clone or backup from time machine to instal all my apps, files, profile, etc. searing other forums, and piecing advice together, I was finally happily running the M1 Mac mini with my external drive as intended.

Her is how I ended up getting it to work:

I Setup new M1 Mac Mini using internal drive. Used migration assistant to clone external intel drive from my 2018 Mac mini to the internal M1 drive. I then booted into M1 internal drive.

Since the M1 Mac can not use a boot drive that was created from an intel Mac, I had to erase the external drive using disc utility and reformatted to APFS and GUID. You have to do this from your M1 Mac. This is a critical step, intel boot drive won’t work on M1 Mac.

Restarted M1 Mac using the new system restore start up options (hold down power button on the Mac mini until options menu loads) from there I had to change security settings to “low security”on the internal M1 drive. (If you don’t do this, migration assistant won’t work) Then instal fresh copy of Big Sur onto external drive using recovery menu within the startup options screen. (You must instal Big Sur from this menu, you can’t instal it through the App Store).

After an hour or so, the M1 Mac booted from the external drive and I was presented with language selection screen. (Be patient, system will restart several times) From there I continued setup and used migration assistance to clone internal M1 drive to the “new” external drive.

Missing any of the steps above will break the chain that allowed this to work.

Good Luck!!

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52 replies

Dec 14, 2020 7:57 AM in response to Matti Haveri

Matti Haveri wrote:

Ars Technica's Big Sur review:

"Apple does say that Apple Silicon Macs can boot from external volumes without changing the Mac’s security settings, unlike Apple T2 Macs—this is because these security settings can now be set per volume. You can boot your internal disk with all of Apple’s security protections intact and boot in a reduced-security mode from an external disk without needing to change anything."

https://arstechnica.com/gadgets/2020/11/macos-11-0-big-sur-the-ars-technica-review/10/#h2

That may be true but still can't create an externally bootable drive.

My last attempt was simply format GUID/APFS in Recovery Disk Utility

and the installed Big Sur to external (in Recovery) and all progressed

through to the reboot stage. Saw he indicator on the external drive

flash like it was starting to load then all stoped for a long time and

then rebooted to the internal drive. So, it seemed like it wanted to

start the setup process but something borked it.

Once again, went into select Startup Disk in system preferences and tried to select the

external drive there and got the good old need to update blurb to be bootable.

Thanks for the info Matti. At least now I know why the boot/no boot option

is gone in Security dialog.

Dec 15, 2020 10:37 AM in response to MyApple8MyPC

No joy in Mudville!

While the external drive will now appear as bootable,

it gets tossed into boot recovery asking for a the admin

password to verify after which it results in not being

able to verify the drive.

I think the changes to the Startup Utility, along with Big Sur,

and adding the M1s special drive architecture (evidenced by

what appears to be a different boot volume, i.e. no longer

EFI) just has everything totally borked.

I really don't want to really totally on Time Machine for system

recovery because that it is excruciatingly slow and I have been

burned once before (I had a bootable back up then which got

me back).

Peymon

Level 1

8 points

Dec 24, 2020 8:59 PM in response to Peymon

Go buy a Apple brand Thunderbolt 3 usb c cable and connect your SSD in my case as you see in picture 1 T Sandisk extreme

and install from Recovery mode in APFS

sbd you will be fine

it is sad that spent a week ( I learned a lot) but all was needed actual Apple Made Thunderbolt cable .

but hey it all good now

Peymon

Level 1

8 points

Dec 26, 2020 4:38 AM in response to MyApple8MyPC

Make sure you pick up Apple Thunderbolt 3 Data cable (Short one) and Also go to Recovery and change Security for your internal SSD to mid and then Erase the nEW ssd with APFS . then install Big Sur from Recovery mode. If all is well you should see a Speedy install after 52 min all the way down to 28 min and 0 then reboot itself few times and let it do its thing it will be slow and then you should see Country choice , You will know that is new install , I suggest restoring from Your internal SSD if you have all you need there , IF not from Time Machine ..........Goodluck

Dec 11, 2020 6:38 AM in response to MyApple8MyPC

Just an additional tidbit, on the security options I only

see two options, not 3, Full and Reduced.

Dec 11, 2020 6:53 AM in response to woodmeister50

> no option to allow external booting

This must be a just a temporary glitch that is fixed in the next update real soon now... :-|

Dec 13, 2020 1:06 PM in response to Peymon

Have you actually verified that you are booting into the external

by check the "Startup Disk" in "About this Mac" because if it

is a proper clone, it will look identical to what you are running.

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Mac Mini M1 Using External SSD