Creating a bootable installer on an external SSI drive

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Creating a bootable installer on an external SSI drive

I'm following the instructions posted in Apple Support on "How to create a bootable installer for macOS" using Terminal. This is what happens:

SuperMac@Mac-Pro-3 ~ % sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/AppleSSI

Ready to start.

To continue we need to erase the volume at /Volumes/AppleSSI.

If you wish to continue type (Y) then press return: y

APFS disks may not be used as bootable install media.

An error occurred erasing the disk.

SuperMac@Mac-Pro-3 ~ %

The Mac Pro I'm using currently has Big Sur installed. The SSI is from a late 2013 Mac Pro and is enclosed in a OWC Envoy Media USB enclosure. Any suggestions?

Mac Pro, macOS 11.6

Posted on Dec 19, 2021 1:52 PM

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Answer 1

Top-ranking reply

Barney-15E

Level 10

116,662 points

Dec 19, 2021 2:12 PM in response to Mark Duhamel

You need to erase the drive and format as Mac OS Extended as stated in the instructions.

Do you mean SSD? I’ve never heard of SSI. Regardless, that isn’t the problem as noted in the error message:

APFS disks may not be used as bootable install media.

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Answer 2

Old Toad

Level 10

210,591 points

Dec 19, 2021 3:53 PM in response to Mark Duhamel

Instead of using an external SSD drive try using a Flash Drive that's at least 16GB in capacity or greater. Then following the directions in the Apple document. I've created bootable installers for Monterey, Catalina, Mojave and High Sierra this way.

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Answer 3

Barney-15E

Level 10

116,662 points

Dec 20, 2021 12:09 PM in response to Mark Duhamel

Still not quite there getting the OS to recognize it as bootable, but progress thanks to you.

Can you explain?

Are you trying to boot from a T2 Mac? Have you enabled external boot in Startup Security Utility?

Does it not appear when you hold down the Option key on restart?

-- If it is a Wireless keyboard, wait until you hear the tone or try a wired keyboard.

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Answer 4

Mark Duhamel Author

Level 1

15 points

Dec 20, 2021 12:39 PM in response to Barney-15E

Sure. It's a late 2013 Mac Pro, only the MacPro internal SSD shows up as a choice after holding down the option key on startup, not the external drive. The "external boot" option does not appear in the Startup Utilities menu as the instructions say it should. This is the latest version of Big Sur. I'm doing this to get past the Firmware roadblock caused by a 2tb OWC Aura SSD. I have two of these MacPros and both have an Aura 2Tb SSD installed. One of them apparently was made with the proper Firmware to allow me to upgrade to Monterey. This other Mac Pro will not upgrade. The solution offered by OWC is to install the original Apple SSD, upgrade that, which apparently updates the Firmware, and then re-install the 2tb and it should upgrade. I've done exactly this before, way back in maybe 2016 with a previous version of the Aura SSD.

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Answer 5

Barney-15E

Level 10

116,662 points

Dec 20, 2021 1:58 PM in response to Mark Duhamel

Sure. It's a late 2013 Mac Pro, only the MacPro internal SSD shows up as a choice after holding down the option key on startup, not the external drive.

Is external directly connected to a port on the Mac and not through a Hub? I've seen it not show up if it is connected to a hub. You said you have another Mac, does it show up on that one?

The "external boot" option does not appear in the Startup Utilities menu as the instructions say it should.

That Mac doesn't have a T2 chip, so there are no restrictions on external boot.

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Answer 6

Mark Duhamel Author

Level 1

15 points

Dec 20, 2021 11:47 AM in response to Barney-15E

Thanks Barney! I was able to get the SSD properly formatted. Still not quite there getting the OS to recognize it as bootable, but progress thanks to you.

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