Mac Mini M4 will not boot from external HD

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.

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 got same issue with my m2 Mac mini bootable external drive. I used to use external macOS 15.1.1 on my m2 Mac mini. When I upgraded to m4 pro Mac mini. I couldn’t boot my from my old drive. At last I have to transfer it to my internal SSD on the m4 pro Mac mini. Based on the reports that m4 macs cannot virtualize macOS version earlier than 13.4. I guess the macOS 15 on M1-3 and M4 chips are not exactly the same one.

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.

There is no real problem as long as you format the external drive the same as the internal one and install Sequoia on it (I use an Orico 2Tb SSD in an USB-c Orico enclosure with heat sink and fan – probably necessary). I found it better to transfer manually my contents and apps rather than use the legacy option. The only thing is that Time Machine won't work with the external drive – I spent a frustrating 3 1/2 hours on the phone with Apple technicians before giving up the ghost. The way I found around that is that before going to bed, I restart from the internal drive with the TM option set to "Save once a day". When I get up in the morning, I restart from the external drive... and the Time Machine has done its job, the new restoration perfectly accessible from the external drive. Not such a big price to pay for a much faster and roomier system disk.

Guys.....It does NOT work...Everything installs properly. The drives are all recognized as they should be, but when we actually try to re-boot to an EXTERNAL drive using OSX 15.xxxx and a M1 -M4 CPU it will not boot to that external drive.

I spent way to much time on this, changing cables, changing SSD drives, changing external enclosures............still it does not boot..

Mike S

Apologies --

sudo diskutil partitionDisk drive(xx) 1 gpt jhfs+ DriveName 100%

should read

sudo diskutil partitionDisk drive(xx) 1 gpt apfs DriveName 100%

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.

David & Luis,

I am raising my hand as well. I have an M1 MacMini, and I have spent the last 4 days reading and watching every source possible, to learn how to boot from my external SSD drive. I get the exact same error - " OS needs to be Updated"...This is basically inexcusable from Apple. Why are we all rushing to expand our external bootable storage????

Booting from an external drive( until now) has been beyond-simple....Now they have made it impossible..to make matters worse :>> If they knew that it cannot be done, it would be nice if they let us all know that....

Guys, will a "patch" or update allow us to use an external SSD... or do you think this is a permanent situation for all Silicon CPUs ?

Thank you both very much for your comments above, to inform us on the situation.

Cheers,

Mike

[Edited by Moderator]

I use WD either Blue or Black series NVME. The fastest is the WD SN850X in my Acasis TB enclosure

I’ve been fighting the same issue all day and realised I have a crucial ssd.. like you say - worked fine with my m2 so thought that wouldn’t be an issue. Ball ache