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User profile for user: dec2636
dec2636 Author
User level: Level 1
8 points

Mac Mini (2014) External Boot Drive

I have searched many support notes. I cannot figure out how to enable external drive booting on my Mac Mini 2014. Or it is just not recognizing the bootable install drive I created to downgrade my Big Sur back to High Sierra. When I am able to get it restarted in Recovery Mode (which is a challenge all on its own), the Startup Security program gives me only the option to set a password and nothing else. Also, there are no other system install options on the main window there except for re-installing Big Sur. I cannot get the device to do anything when I try holding down the Option key while restarting or powering up.


Mac mini, macOS 11.4

Posted on May 28, 2021 11:45 AM

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User profile for user: samtenor
samtenor
User level: Level 4
1,792 points

May 29, 2021 1:32 PM in response to dec2636

  1. Under Big Sur -> go to https://support.apple.com/en-us/HT211683 and follow the direction to download High Sierra 10.13.
  2. Please do not install after download is completed.
  3. Get an USB thumb drive (I think 8gb will do, but stay in safe side, try 16gb). Using direction from here: https://support.apple.com/en-us/HT201372 to make a bootable thumb drive.
  4. Shut off the system
  5. Plug the thumb drive and external drive (intended for Sierra), then turn the power on while holding "option" key. Special Note: try to use wired keyboard due to Wireless keyboard's Bluetooth latency connection issues.
  6. Choose to boot from USB drive -> then do all the routines (erase/partition the external drive, under disk utility) and install 10.13 in the external drive.


Additional Note: Since Big Sur, I no longer can use "System Preference" ->"Startup Disk" to switch between Mojave and Big Sur.

To avoid any headache, I have to use "option" key while booting up system. You will also get some "incompatibility" warning when you boot into 10.13 High Sierra (mine is Mojave) -- just ignore that. I treated both systems (even under the same machine - 2015 iMac 5K) as independent from each other.

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User profile for user: samtenor
samtenor
User level: Level 4
1,792 points

May 29, 2021 7:05 PM in response to samtenor

I want to clarify:

Please set the default boot drive at Big Sur, and use boot option (by holding "option" key) to choose "High Sierra" when need it.


When boot into High Sierra - the MacOS will have trouble to read Big Sur data (on the other drive) and will display "incompatible" warning alike. BY ignoring it, you just go on for what you need to achieve under High Sierra.


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Mac Mini (2014) External Boot Drive

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