Can't Update iMac Due To "Missing Firmware Partition"

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Can't Update iMac Due To "Missing Firmware Partition"

I am currently using a Late 2012 21.5 Inch iMac, running macOS Sierra using an external SSD plugged in by USB. This is because the internal hard drive the Mac originally came with has failed (sometime around 2016), and so it is not recognised. I've been trying to update to the latest versions compatible with my device (namely High Sierra, Mojave and Catalina), but they all produce the same error banner when I try to install the update on an external SSD - "You may not install to this volume because the computer is missing a firmware partition".

I've tried formatting another external SSD as APFS on newer Macs and attempting to install from there but another variation of the message appears, so that method doesn't work. I've tried to create a bootable installer using terminal, that also doesn't work.

Any help or advice would be greatly appreciated. Thanks in advance.

iMac 21.5″, macOS 10.12

Posted on Mar 27, 2024 1:47 PM

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Answer 1

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HWTech

Level 9

55,604 points

Mar 28, 2024 6:30 PM in response to ko_ldn

Unfortunately the macOS 10.13+ installers require a properly partitioned & formatted internal drive. The internal drive can otherwise be empty, but the computer must contain an internal drive with a GUID partition and MacOS Extended (Journaled) file system in order for the macOS installer to be able to update the computer's system firmware. I don't know if this requirement extends to later reinstallation of the same version of macOS since the system firmware would no longer need to be updated since I don't recall if I ever tested for it.

Theoretically it may be possible to manually trigger a system firmware update outside of the macOS installer, but that is not easy to do because of the requirements of the firmware updater (there are instructions for updating the system firmware from a Monterey installer, but even those instructions required a certain firmware level for them to work). Plus there is more risk updating the system firmware from an external USB drive than from the internal drive.

The "easiest" thing would be to replace the internal drive with an SSD. Fortunately the macOS 10.13 - 11.x installers do not require an Apple OEM drive. Of course the easiest option may be to only reinstall macOS 10.12 Sierra (or earlier) to the external drive.

Unfortunately it is not easy to open an iMac. You can check out OWC for SSD upgrade kit options where they also provide video instructions you can review on the product upgrade page. The video makes the process look easier than it really is.

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Answer 2

BDAqua

Level 10

239,009 points

Mar 27, 2024 3:04 PM in response to ko_ldn

See Tesserax'sanswer here..

Missing firmware partition - Apple Community

Tesserax

User level:

Level 10

148,213 points

Posted on Sep 1, 2021 8:34 AM

By "firmware partition" are you referring to the recovery partition? If so, there could be a number of reasons why it got deleted. The key now, of course, is how to recreate it. The "simplest" way would be to fully erase your Mac's drive, and then, install a clean copy of macOS on it. However, it still may be possible to recreate it without having to go through those steps.

As such, see if any of the following articles can help. Note that each of these articles refer to a script utility, called: Recovery Partition Creator. The issue is that this utility may no longer be available since these articles were written. Just providing them to you as an option.

macOS: Putting a Recovery Partition on Your Mac (Without Reinstalling macOS) - the Mac Observer
How to Recreate Recovery Partition in Mac OS X - OSXDaily

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