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

MyApple8MyPC Author

Level 4

2,149 points

Dec 26, 2020 4:28 AM in response to woodmeister50

woodmeister50 wrote:

I am going to pick up and give a Sandisk NVMe based drive

USB-C drive a shot today sometime. It is much less costly

than a TB3 solution and if it doesn't work, it will serve as

my photo library storage for 2021 (which I have been

looking to pick up anyway). If I bought a TB3 drive and it

didn't work, it would be way to costly for that purpose and

could only be directly connected to the MBA instead of

just sitting on my USB3 hub.

The price difference between a USB3 drive and a TB3 drive is only around $70.

HWTech

Level 9

68,606 points

Dec 26, 2020 9:34 AM in response to AdossiMac

AdossiMac wrote:

I use an external SSD via the Thundebolt port from WD and do not have any issues. It's 2TB, so 1TB is dedicated to Time Machine, and the other 1TB is for my files, so I don't tax the SSD that came with the computer.

If the files in the second partition are important & unique you need to make sure to back them up as well. However, backing them up to the same physical drive is not a backup if (and when) this external drive fails as you will lose all copies of that data.

MarcoT76

Level 1

14 points

Dec 27, 2020 4:13 AM in response to MyApple8MyPC

Congrats on getting it working. Can you please sim up how you got it to work? About ready to return this M1 mini back to Apple. I’ve tried most of what was mentioned and no luck for me. Hearing in one post how you got it to work would be hugely helpful. Thanks for the update!

MyApple8MyPC Author

Level 4

2,149 points

Dec 14, 2020 1:47 PM in response to woodmeister50

Apple engineers may have found a fix. I will know more tomorrow.

MyApple8MyPC Author

Level 4

2,149 points

Dec 24, 2020 10:12 PM in response to Peymon

Yes, we did that. Still no joy.

https://support.apple.com/en-us/HT208368

MyApple8MyPC Author

Level 4

2,149 points

Dec 25, 2020 12:14 PM in response to tbirdvet

So far mine is booting repatedly.

Peymon

Level 1

8 points

Dec 25, 2020 3:21 PM in response to AdossiMac

MyApple8MyPC Author

Level 4

2,149 points

Dec 25, 2020 4:04 PM in response to Peymon

Peymon are you beta testing 11.2?

Peymon

Level 1

8 points

Dec 25, 2020 6:13 PM in response to MyApple8MyPC

Yes , I am , but that doesn’t have much todo with install , since now that I have external

working , I zap the internal and installed

11.1 on that

MyApple8MyPC Author

Level 4

2,149 points

Dec 25, 2020 6:14 PM in response to Peymon

OK, Thanks.

Peymon

Level 1

8 points

Dec 26, 2020 4:47 AM in response to MyApple8MyPC

BTW that is Scandisk Extreme with transfer rate off 1001 , there are cheaper ones , But get this or Ultra which is more expensive , But gives you 2000 Transfer speed. Mine is 1000 (Just Extreme).

Dec 26, 2020 11:18 AM in response to MyApple8MyPC

MyApple8MyPC wrote:

....

The price difference between a USB3 drive and a TB3 drive is only around $70.

But that $70 is a few cases of beer or a few bottles of wine!

Dec 11, 2020 12:32 PM in response to MyApple8MyPC

I tried a few times my self with the last time saying the drive needed a software

update??? Another time it stopped installing and said it could not make the

required permissions update??? One time, all seemed to go well with the install,

but it was never visible.

Installed from recovery and claimed to be 11.0.1?

Each attempt at reinstalling yielded something different. Seems this operation

is no ready for prime time on M1 Macs. I'm going to give support a call and

have them generate a support ticket.

BTW, Recovery is downloading the full installer every time! I thought an installer

would be local unless that is yet another bug.

MyApple8MyPC Author

Level 4

2,149 points

Dec 11, 2020 6:20 PM in response to woodmeister50

woodmeister50 wrote:

I tried a few times my self with the last time saying the drive needed a software

update???

Yes, when the Startup Security Utility is not set to allow external drives, it tells you to update.

The problem is it doesn't show the "External Boot" section of the Startup Security utility, so you can't select "Allow booting from external media". This is a huge bug that Apple should have known about during their beta testing of the M1.

See below what it is supposed to look like. On a M1 the lower half (everything below medium security) of the utility is completly missing.

Peymon

Level 1

8 points

Dec 13, 2020 6:17 AM in response to MyApple8MyPC

I was using T5 Samsung and didn’t work , then I used My G technology External 1T and worked perfectly to startup externally

steps

1- hold power to get to options

2 - disk utilities and erase and partition

3 - reinstall Os from recovery.

57 min and be patient and it will work.

now I am migrating from TIme machine to new drive.

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Mac Mini M1 Using External SSD