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roninpawnee Author

Level 1

8 points

Unable to boot 2015 iMac from external SSD with APFS + Catalina

My mid-2015 iMac's internal drive is dead.

I got an external SSD (SanDisk Portable) and created a bootable copy of Catalina - APFS format , using my laptop (2019 MacBook Pro). I can boot my laptop from this SSD bootable copy fine.

But the 2015 iMac does not recognize the APFS SSD as a bootable drive. Command + R + Disk Utilities sees the drive but Startup Disk will not let me select it.

So then I created another partition on the SSD, formatted as MacOS Extended Journaled and installed a bootable copy of Yosemite. The iMac can boot from this!

Question: Is there any way to make my mid 2015 iMac (no functioning internal drive) boot from an APFS external SSD?

Posted on Aug 10, 2020 6:36 AM

Top-ranking reply

steve626

Level 6

11,501 points

Posted on Aug 10, 2020 8:37 AM

There is probably something about the way the Catalina bootable external drive was created with the newer Mac that is incompatible with the older Mac.

Instead of troubleshooting that, perhaps you can start from your Yosemite external bootable system and simply upgrade that to Catalina? Then that external drive can boot the older Mac? This is not finding the root cause of the issue (which could be very involved), but it might be a relatively quick empirical workaround.

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Unable to boot 2015 iMac from external SSD with APFS + Catalina

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