Lost ability to boot off external drives? -SOLVED

Original thread here, but too old and locked, so I can't post the solution:

Lost ability to boot off external drives?

Scott Bernard wrote:

Somehow I've lost the ability to boot off of external drives. I can still see and choose the bootable drives in Preferences>StartupDisk but it just reboots to my primary internal drive instead.

If I hold down Option at startup, I only see my internal drives, plus 2 "EFI Boot" drives I never saw before. Neither of these will boot either. They seem to crash and I end up restarted off my primary internal drive again.

How do I get things back to normal?

MacBook Pro 17″

Posted on Oct 22, 2023 10:16 AM

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Scott Bernard Author

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46 points

Posted on Oct 22, 2023 10:29 AM

Scott Bernard wrote:

How do I get things back to normal?

I was wrongly told the external drives needed a dedicated power supply, rather than power from its connection to laptop USB port, so I gave up.

Then yesterday I accidentally solved it:

I had the drives formatted "MacOS Extended (Journaled)" with GUID partition map.

I reformatted to "APFS" with GUID partition map.

I installed High Sierra (sorry, I have old hardware). Restarted, held down option, and the drives now appear and are bootable. "EFI Boot" drives no longer show up. Everything works as expected.

In case any newbies are reading, remember to back up your data before reformatting.

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Lost ability to boot off external drives? -SOLVED

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