Mac Mini M4 will not boot from external HD

I have an external boot drive for my new Mini M4. I use a WD NVME in a TB enclosure. I use carbon Copy Cloner(CCC) to clone the data, then I booted into recovery and installed 15.1 on the external and it works fine. I did not use the CCC legacy bootable tool as that does not work most of the time with Silicon Macs.

There could be several reasons why this problem exists but here is what I would do.

• Reformat the SSD only using Disk Utility. Do not use any so-called maintenance apps which may have come with the SSD. They do cause problems. Make sure the SSD is formatted the same as your Mac's HD is.
• Download and reinstall the OS. The original OS on it my have been corrupted. This will often happen when it is downloaded via Wi-Fi. Better to use a wired Ethernet connection. If that is not possible, then you may have to do multiple downloads to get one that works.
• If the problem still persists, I would replace the SSD.

Those all in one docks have never been a reliable system for a bootable external drive.

You really need to use a standalone external USB4 or Thunderbolt enclosure for a bootable SSD and even then you need to make sure you have the right combination of enclosure and SSD, not just for boot ability but even just to work fast and reliable. Many combinations simply don't work on a Mac (or a PC for that matter).

I have exactly the same problem, got my M4 the day of the release to swap a M1 Mac mini which I have booting from this external drive, when I started the M4 and connect the external WD NVME on a TB Acacis case I get an "SDErrorDomain error 104". Escalate to a senior engineer on Sunday from apple and they haven't get back to me. Getting frustrated because Apple shouldn't block this kind of practice to force people to purchase their savage and expensive storage ! If I don't resolve this in the next days I'll return the machine.

I had the same issue. With the new Mac you need to make a new bootable drive. The previous bootable drive will not work. The Platform is not compatible. I redid my bootable drive using the new M4 Mac and works fine. That being said I did use my previous external clone drive to migrate to my new Mac M4 and had no issues. It just could not be used as a boot drive until I redid it using the new Mac M4.

david3_1415 wrote:

Bootable SSD will boot with iMac and Macbook running 15.1.

Are those machines Intel-based or Apple-Silicon-based?

I would not be too surprised to find that any particular installation of macOS works only with one processor type. Sequoia runs both on Apple Silicon Macs and on some Intel Macs, but that would not necessarily mean that you could take a Sequoia startup drive from an Intel Mac, and boot from it on an Apple Silicon Mac, or vice versa.

I may have changed security settings in a previous version several years ago and it may have carried over with migration assistant with each new Mac I have purchased which is many. I cannot really remember. You can boot into recovery and select security from top menu and change if needed.

tbirdvet wrote:

I had the same issue. With the new Mac you need to make a new bootable drive. The previous bootable drive will not work. The Platform is not compatible. I redid my bootable drive using the new M4 Mac and works fine. That being said I did use my previous external clone drive to migrate to my new Mac M4 and had no issues. It just could not be used as a boot drive until I redid it using the new Mac M4.

Platform issues aside, this is likely a security thing Apple has in place. Any macOS installation has an "ownership" linked not only to an admin user but also to the machine. This is likely to prevent anyone with a "generic" external boot drive from plugging into any Mac, booting it, and then scraping data from a stolen machine.

tbirdvet wrote:

I have an external boot drive for my new Mini M4. I use a WD NVME in a TB enclosure. I use carbon Copy Cloner(CCC) to clone the data, then I booted into recovery and installed 15.1 on the external and it works fine. I did not use the CCC legacy bootable tool as that does not work most of the time with Silicon Macs.

They are all Silicon these days (I guess) but you may mean Apple or Intel processors.

Ian R. Brown wrote:

When you format the SSD make sure you format the Physical Disk and not a Volume.

I made that mistake a year ago and wondered why it would not boot.

This is a sticking point on the route to cleaning and replacing the file system on a new SSD. The instructions on the Apple help site are not clear about navigating the different things Drive/Volume/Volume Group/Container/Media. Selecting the right name/label for such things is quite important.

https://www.seagate.com/gb/en/support/kb/how-to-format-your-drive-apfs-on-macos-big-sur-and-later/

The legacy bootable feature is part of CCC but not very reliable. So you need to boot into recovery to install the OS on the external. This applies mostly to silicon Macs. With Intels the legacy system usually works.