Catalina - missing firmware partition - external SSD

Here’s my problem:

  • iMac late 2012 model
  • internal HDD dead
  • been running El Capitan on external SSD for several years
  • upgraded to Sierra without issue
  • cannot upgrade to High Sierra, Mojave or Catalina. Get message from installer that "You may not install this volume because the computer is missing a firmware partition.”
  • anybody encounter and solve similar issue? Seems from other forums that it is related to recovery disk partition on OEM internal HDD (which is completely unusable in my case).

Advice welcome.

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Not a Mac expert, so take this with a VERY large grain of salt.

I believe the installer is simply looking for a small partition (EFI) to put the recovery info for the version of the OS you are trying to install. Older versions of Mac OS did not do this. When you upgraded to, say, Mavericks, when you did a system recovery off the hard drive, you always went back to the version that came with your Mac. Newer versions of MacOS seem to update this “hidden” partition to the version you are installing. So, I think that if you give the installer a small partition with the correct name, format, and size, it will be happy.

I haven’t had the chance to try this yet, but I intend to give it a go later today, time permitting. Read the part of the article telling how to create the EFI partition, and decide if you want to give it a go. I do suggest you try this on a spare external drive or memory stick before touching your current operating system. That’s what I intend to try.

Good Luck

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I’m wondering since he doesn’t have access to his original internal hard drive, would Internet Recovery do a full install including the EFI partition?

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I’m of the school, try anything, but I believe it will result in same message. The internet recovery downloads the install app and runs it, so I believe it will still look for the EFI partition as it wants to update it.

Thank you, Bgeeoz. Will give that a try. Appreciate your advice.

Remember in my tome up above I said take it with a grain of salt, well I’m digging my way out slowly.

Spent hours trying to re-create your problem by installing HS on an external drive using every format possible using Disk Utility. No matter what I did, I never got the message you saw. Did learn a bit about Disk Utility.

When you format a drive for GUID, you automatically get an EFI partition on the drive you format.

Also, when I created HS on a GUID formatted drive, I get an Apple Boot Recovery drive on the external disk.

image Screen Shot 2019-10-16 at 9.56.00 am

On the attached list, with HS running on the external drive, the external drive is disk2. Disk0 is HS on my internal drive, Disk1 is Catalina on my internal drive.

Suggest you start by entering “diskutil list” on a terminal window and see what you have.

Don’t know if you are trying to upgrade in place (take current system to upgraded version with all apps and data preserved) or trying to do a clean install. I don’t think you will be able to do the former easily, if at all. I would try the following if you have the resources;

Create a USB install of the Mac version you are trying to get to.
Shut down, disconnect your external drive, and set it aside. If you ever get the upgrade working, you can literally copy all your data and apps from it.
Boot to the USB install drive you created.
Using the MacOS Recovery Disk Utility that comes up, format a large enough, clean external drive or memory stick to APFS. You might have to format the top level disk (usually has manufacturers name as disk name) to GUID before it lets you select AFPS.
Try to install the MacOS on this clean disk.
If it works, you know you can do a clean install.
If it doesn’t work, ??? Think that means it wants something from the internal disk you do not have. Time to get a suction cup, and take apart the iMac.

Good luck

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Great stuff! I’m curious…does he need to upgrade one version at a time? Can he upgrade directly to Catalina from Sierra by downloading Catalina and creating a USB install from that? I don’t think that avoids the main issue but just wondering if he can skip the step by step upgrades?

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If he does a clean install, and has access to the Install app for version he wants, he can install any version he wants.
There was a time you could only get the next version from the App store if you were already running the previous version. I believe High Sierra or Mojave changed that, allowing you to upgrade directly from older versions. Therefore, you could download the Install app.
As an example, my 2010 Macbook Air cannot go to Mojave or Catalina according to Apple. The Apple App store will not let me download the Install app for either.
As a result of this forum, I learned about, where I can download the patcher software, and as a result, get the Install Catalina (and Mojave) download.

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Thanks. I know MACalot personally. I’m thinking about downloading the Catalina installer for him and then sending it to him to give a try.

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Hey, that’s great.

I think it is very important that the current HS drive contents be preserved safely. Backup the entire user folder, and backup the top level Applications folder.

Just in case you do not know it, on a Mac, most applications can literally be copied from the Applications folder on the backup drive, paste it into the new Applications folder, and you’re done.

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When I was installing Catalina onto a brand new SSD for my MacBook Pro, I formatted the new SSD to Mac OS Extended (Journaled) file system as I had done before. I encountered the exact same error. I went back to Disk Utility and formatted the SSD using Apple File System (APFS) and Catalina installed successfully.