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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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! :)
 
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Joined
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Messages
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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! :)
Did I guess right, from there being no mention of it, that you don’t have a Time Machine backup? If you don’t have any form of backup and if you do have vital information in your drive, find someone with another Mac and see if you can retrieve your information using Target Disk Mode transfer. For your information, your iMac’s model identifier is iMac16,2.

You can connect in Target Disk Mode using USB or Thunderbolt 2. The former is probably your best bet for connecting to another Mac. Reboot your iMac and immediately hold down the “T” key. Your screen should indicate if it’s in that mode. Connect the two Macs with a USB (or Thunderbolt 2) cable and your iMac should show up on the other computer as an external drive. If successful, do what you must to copy all that information to the other Mac. Then you will be ready to proceed to the next step.

The “Update” volume you see in Disk Utility is just a temporary volume created with the previous failed installation. There is no need to copy that over. When you are again ready, reboot the iMac into Recovery (command-R). You need an internet connection to do a reinstallation.

First open Disk Utility (in Recovery). It will help if you choose “Show All Devices” from the View pulldown menu. The top category is the internal SSD. Select it and click on Erase. The prompt will allow you to give it a name. I would use “Macintosh HD” as it’s still the default label for all Mac internal drives. Format should be APFS, GUID Partition Map.

Afterwards, exit Disk Utility and from the main window, choose to install macOS. It will probably offer to install macOS Monterey since that is the newest macOS that your iMac can run. Recovery will not give you a choice to install any other version. If you are determined to install an older version, you can do it using an external bootable installer disk, or perform the operation from the other Mac while in Target Disk Mode. You will need a copy of the macOS installer file.

Good luck. By the way, if I guessed wrong and you do have a Time Machine backup, you will be spared of the earlier steps. After the system installation, Migration will ask for the data transfer source, so your Time Machine drive should already be connected for you to choose.
 

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