Startup Disk Error...

I have downloaded both Mac Mojave and Mac Catalina from the AppStore and created a bootable installer for macOS in two separate partitions on my external SSD as per this support article:

https://support.apple.com/en-us/HT201372

Both the installers were created successfully and show up under the Startup Disk option in System Preferences.

However, if I choose to restart from any of them, I get this error:

I also tried to shutdown my Mac and then hold down the option key to boot to the startup disk menu. From there if I choose these startup volumes, it tries to boot but eventually goes into a recovery screen.

Any ideas how to create a proper startup disk?

I hope using separate partitions on the same SSD is not a cause for the problem.

MacBook Pro 13", macOS 10.15

Posted on Oct 25, 2019 2:15 PM

Top-ranking reply

i_rina

Community Specialist

Posted on Oct 31, 2019 10:39 AM

Hello Sridhar Ananthanarayanan,

Thanks for posting to the Apple Support Communities. I understand using an external SSD, it is unable to boot into macOS installed on that external drive. I'll do what I can to help.

Look through these suggestions which will focus on the drive itself:

Try plugging the SSD into a separate USB port.
Reformat the SSD in macOS Recovery and try setting up the bootable installer again. This time only use a single partition. Verify it boots. If it does, try creating the other partition and doing the same thing. Partitions may cause these types of errors on certain drives and these steps will determine that.

Take care.

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Startup Disk Error...

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