Mac Mini M4 will not boot from external HD

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.

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.

Thanks for the info. I guess there are these precautions and options to make a bootable external drive on Silicon Macs:

Remove all 3rd party virus apps, "cleaning", "optimizing", "speed-up" and VPN apps that might corrupt the system. Connect the external SSD drive directly to the Silicon Mac. Disconnect any hubs and unneeded external devices that might be incompatible. Erase the external device (not just volumes under it) as APFS, GUID, case insensitive with that Mac's Disk Utility (or use the Disk Utility while in Recovery mode or while booted into USB installer).

#1. Download macOS installer from App Store and use it to install to the external drive.

#2. Boot into Recovery or Internet Recovery and use its installer to install to the external drive (this should bypass any corruption caused by those 3rd party apps). Booting into Recovery is fast but I guess also it must then download the actual installer files from the Internet and that might be slow and unreliable, right?

#3. Download macOS from App Store, prepare a bootable USB macOS installer with the Terminal via Apple's instructions, Option-boot to it, and install to the external drive (this should bypass any corruption caused by those 3rd party apps). The install phase is faster than in #2 because there is no need for further downloads (iCloud stuff can be skipped but I have not tested if can this be done completely off-line).

#4. Use Carbon Copy Cloner's default data-clone or Super Duper to the external disk, and make it bootable by applying a full macOS install with some #1-3 method.

#5. Use Carbon Copy Cloner's "legacy mode" or Super Duper to make a bootable clone to the external disk. Should work on Intel Macs but might not be bootable in Silicon Macs. Might the external drive then be made bootable by applying a full macOS install on top of the old system? Or maybe the "ownership" is then incorrect and the external drive is not bootable anyway?

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.

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).

for what's it's worth.

I purchased a Mac mini M4 base model when it launched. Yesterday I took an external USB C-SSD That I had purchased from CostCo years ago (I connected it to the front USB 3.? connectors as I knew it was USB 3 or slower)

I launched the recovery and formatted the external SSD using Disk Utility from the recovery tools. I loaded the latest MacOS from the recovery to the external drive.

I restarted the recovery and booted into the external drive. The only thing I lost running the external drive was Apple Intelligence will do operate on a external drive (I have no idea why??)

To change boot drives I use the boot drive selector from the System settings...

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.

Coming back to this - I bought a new ssd and enclosure and followed the method of using ccc to clone the drive and installing the os on it, in recovery mode on the new machine. It worked a treat, unfortunately it did mean I had to buy a new ssd and enclosure - but I suppose I have another incase I run into this issue again!

"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."

I tried this and it worked perfectly!

All I can say is that I have a one year old USB 3.0 SSD (Sonoma) and a three week old Thunderbolt NVMe (Sequoia 15.1.1) which my M2 mini can boot from so there doesn't appear to be anything wrong with the M-series architecture.

I haven't tried the M4 but many others on YouTube etc. have and they all appear to work so there must be something different about your setup or modus operandi.

Are you sure you are formatting the Physical Disk and not a Volume? Very often by default, Disk Utility is set to View/Show Only Volumes which you must not use for formatting.

You must select "Show All Devices" which will display Physical Disks which can be corroborated as shown by the arrow.

Yes it does work.

I have installed Sequoia 15.1.1 on an external SSD and even an external Fusion Drive.

When installing the OS directly to a freshly formatted drive ( I tend to use

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

rather than Disk Utility), it works perfectly.

Carbon Copy Cloner nearly works when using Legacy Copy. You still have to install the OS afterward, but that doesn't take too long.

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.

Follow Matti's first suggestion . . . download the macOS installer and install it on the external after you have formatted the PHYSICAL DISK (not volume!) as APFS.

You should have no problem.

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/