After failed Big Sur upgrade and manual High Sierra installation, I have two disks : "Update" and "iMac_SSD - Data". How do I fix this?

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ulyssedupac Author

Level 1

11 points

After failed Big Sur upgrade and manual High Sierra installation, I have two disks : "Update" and "iMac_SSD - Data". How do I fix this?

Hi guys,

I am coming to you to ask for your help.

I own an iMac (Retina 4k, 21.5-inch, late 2015

Processor 3.1 GHz Intel Core i5

Memory 8 GB 1867 MHz DDR3

Graphics Intel Iris Pro Graphics 6200 1536 MB)

It must be said that 4 years ago, I brought my iMac in a specialised store, where they changed the main drive (which was slow and sometimes unresponsive), to an SSD drive.

Because I am stupid, I’m unable to remember exactly which OS I was running before the problem happened.

Anyhow, basically, at some point, in a rush leaving for work and trying to turn off my computer, I accepted some update: upgrade to Big Sur.

After that, I was unable to restart my computer: it gets stuck at the loading screen (I tried leaving my iMac on for 48 hours, just to make sure it wasn’t the installation that was taking some time). I tried recovery mode (first aid on both the drive, which I think were iMac_SSD and iMac_SSD - Data ; reinstalling big sur) but to no avail.

I created a bootable installer with macOS Catalina. Unfortunately, I was unable to install Catalina (the iMac_SSD wouldn’t appear in the disk I could install Catalina on). I read somewhere that it was because I needed an APFS-compatible OS.

I created a new bootable installer with macOS High Sierra. Which - sort of - worked. I got asked if I wanted to install High Sierra on the disk “Update” or the disk “iMac_SSD - data”.

I chose the "Update"-disk and it installed High Sierra. Now, I see in the finder “iMac - SSD - Data”. I managed to save most of my data from “the iMac_SSD - Data” drive, on an external drive.

Now I am wondering what to do. How do I reset everything and do a fresh install? I feel like the Big Sur upgrade split my disk in two, with this weird “Update” disk, and the other “iMac_SSD - Data”.

If I go in the Disk Utiliy, I see two internal disks:

"Update" (1.05 TB ; "shared by 5 volumes"), which has 11.85 GB used, 703.36 GB other volumes, 337.45 GB Free. Screenshot 1 ; Screenshot 2

"iMac_SSD - Data" (1.05 TB ; "shared by 5 volumes"), which has 681.57 GB used, 33.63 GB other volumes, 337.45 GB Free. Screenshot 1 ; Screenshot 2

Is there anyway to fix everything while keeping my data? If yes, how?

If not, how do I reset everything ?

Many thanks if you can help me, this would be greatly appreciated!

iMac 21.5″, macOS 11.6

Posted on May 15, 2022 2:48 AM

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Answer 1

Top-ranking reply

PRP_53

Level 10

91,591 points

May 15, 2022 6:41 AM in response to ulyssedupac

First steps first and get the High Sierra installed.

Then and only then consider the computer options.

The Age of this computer will Govern what newer version of macOS it will Qualify to install. Use About this Mac from the Apple Icon on Desktop - the required Information will be there.

With the above information in-hand - follow this How to get old versions of macOS and verify what version this computer Qualifies to install. For Best results use Safari to commence the download as Others may not work.

Safari will open a redirect and open the Apple Store where the download can commence.

macOS Big Sur 11 hardware requirements

Empty Space Requirements specific to the Big Sur. Apple states 35.6 GB Empty Space but suggest 50 GB or more

macOS Catalina 10.15 hardware requirements

macOS Mojave 10.14 hardware requirements

Caution - jumping over all the newer versions and directly to Big Sur / Monterey on Qualifying computers is Technically possible - there are those who have attempted and were successful.

Then there are those who attempted and had less than good results.

If this is a Production or Mission Critical Set-up - a more prudent and measure approach is suggested.

The above is from observations on the Apple Support Community Forums and IMHO

Tips Big Sir Upgrade Released Nov 2020

Make Time Machine Backup is very useful and can be used to Revert to Previous Working macOS

Notation - Mojave is the Last version to support 32 bit applications / extensions and Drivers. Catalina, Big Sur & Monterey supports only 64 bit and there is no workaround.

Suggest using Go64 to find 32 bit application before attempting the upGrade. Some or many of the Application already installed may required update or upGrades to 64 Bit Versions.

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Answer 2

PRP_53

Level 10

91,591 points

May 15, 2022 4:10 AM in response to ulyssedupac

This method will WIPE ALL Data and there is No Recovery - Period.

To perform this action will require booting from a Bootable Installer.

The Bootable Installer can Only be performed on an Apple Computer

This will have to be performed from a Qualifying Computer to run the version of macOS to be made on the Bootable Installer. Example : Bootable Installer of High Sierra would have to be done on a computer that Qualifies to run High Sierra .

Notation: If the computer being used to perform this action is Too New or Too Old to qualify to run the version of macOS - this computer can not be used.

Alternative is, to gain access to a Qualifying Apple Computer from a family member, friend or associate.

Once that is done read on for preparing the Destination computer >> Only works on Intel Based Apple Computers.

1 - Shutdown computer and disconnect all external drive Except the newly created Bootable Installer.

2- Restart and immediately hold the OPTION key until the Startup Manager appears and choose the USB Drive.

3 - It will present options >> Disk Utilities >> View >> View ALL attached Drives.

4 - Choose the Upper Most Drive ( not the volumes indented and list below ).

5 - Formatting for macOS 10.13 High Sierra and below requires HFS Journaled with the GUID Partition Map

6 - Once that is done >> backup out of Disk Utilities and choose install macOS.

7 - Follow the prompts and it may automatically reboot several time.

8 - Upon a final reboot - Setup Assist will present with the newer version of macOS.

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Answer 3

PRP_53

Level 10

91,591 points

May 15, 2022 5:58 AM in response to ulyssedupac

" However, this didn't solve my problem at all (cf. my post)."

If the user had Wiped the Entire Drive as per above, then during the Installation Process fro the USB Installer Drive

How to fix a split Fusion Drive

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Answer 4

ulyssedupac Author

Level 1

11 points

May 15, 2022 5:18 AM in response to PRP_53

Hi there,

Many thanks for your answer.

Because of the failed Big Sur upgrade, I already went through the process of using a bootable installer (with MacOS High Sierra).

However, this didn't solve my problem at all (cf. my post).

To which MacOS should I migrate it? A.k.a which version of MacOS should I use to make a bootable installer?

Then, how do I "fuse" together the 2 disks?

Is there any way to that without wiping the drive?

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Answer 5

ulyssedupac Author

Level 1

11 points

May 15, 2022 6:36 AM in response to PRP_53

Thank you very, very much!

So with the manipulation you mentioned in your first post, I should be able to reinstall High Sierra and have "correct" disks configuration.

How will I manage to upgrade to Big Sur? All this was caused by Big Sur installation getting stuck.

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Answer 6

May 16, 2022 9:58 AM in response to PRP_53

P. Phillips wrote:

First steps first and get the High Sierra installed.

Wise piece of advice. Personnal point of vue ( from someone who tested all recent versions of MacOS from a quality, security and usability standpoint before validating one and using it for professionnal use ): High Sierra is a pretty high level grade of MacOS.

Suggest using Go64 to find 32 bit application before attempting the upGrade. Some or many of the Application already installed may required update or upGrades to 64 Bit Versions.

Check that you really need any of the function of the version starting from Catalina ( 1st 64 one ) which will require finding 64 bit versions and a long and paineful upgrade ( backup and tests ).

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