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A2115 / 2019 / Processors from 3.0 GHz 6-core i5, up to 3.6 GHz 8-core i9. Released March 19, 2019.

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The volume is not compatible with [Sonoma]

Recently had to reformat the 3TB HDD in a 2019 27" iMac and reinstall the OS. I made a bootable Sonoma installer USB stick and booted the machine.

I formatted the HDD as APFS. When I tried to install Sonoma I got the error: "This volume is not compatible with this update."

I found I had to go back and format the HDD as APFS (case sensitive) in order to get it to install. I looked on Apple's requirements site and do not see this documented anywhere.

Can someone confirm that this is a requirement or did I just have something funny going on with this machine?

Note that the HDD did have an issue where it would no longer boot the machine so the drive may have issues. It formatted and tested normally though.

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Update (10/29/23)

Just wanted to follow up with this.

It turns out this was a fusion drive machine. I had incorrectly assumed that the 3TB HDD was the issue and simply pulled it and replaced with a 2TB SATA SSD and did not remove the 128GB blade SSD (because I did not remove the logic board).

What finally clued me in was that the machine would randomly fail to complete the boot up even though it initially setup and installed macOS just fine on the new SSD.

I noted that when I formatted the new SSD, the 128GB drive that was part of the original fusion drive DID NOT show - this is why I did not think it had one. I eventually did pull the logic board out and found the SSD.

Knowing that Disk Utility didn't see it I assumed it was bad. So I removed it, reassembled the machine, and found the machine works 100%. As for the Bug that @danj thinks might be present, I wasn't able to replicate the issue. So I can't comment on that. I'm thinking maybe the failed blade SSD was causing some issues with the installer??

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@larry767 - No, I think your discovery is the true issue! The Blade SSD is not a normal drive which is why you don’t see it in Disk Utility. The blade is a cache to the HDD which is only accessed by the OS kernal.


@danj Well, OK, let's back up to the beginning. This machine was originally a 3TB Fusion Drive (but I didn't think it was). It would stall part way through the startup process. Disk Utility would not repair the disk. Disk Utility did reformat the drive (it did not report as fusion drive which is odd) and I was able to reinstall the OS on the HDD and get it to boot. But after a reboot, the stalled boot condition returned. So I pulled the 3TB HDD out and installed a 2TB SSD in its place. Same issue. Able to install macOS fine and boot to it at least once. But upon a restart, it would not complete the startup. Reinstall the OS and it would be fine for at least that initial boot but subsequent restarts it would always fail. That's when I finally thought to physically confirm there wasn't a corrupt fusion drive behind the logic board and the rest is history.


The reason I'm confused is because I've had experience converting a non fusion drive machine to a fusion drive machine. After installing a blade SSD in that slot on the back and restarting, Disk Utility showed the drives as a seperate SSD and HDD and I had to recreate the fusion drive using terminal commands. So I was expecting this to be the same - if I removed the HDD and the SSD in the back was still there, would it not be seen by Disk Utility because it is now a "split" fusion drive? I've heard of cases where the fusion drive somehow gets split back into seperate drives which is why the diskutil resetFusion command exists.


Either way, I'm guessing the system was trying to boot from that bad SSD and because I couldn't see it in Disk Utility, I couldn't just erase it and let it live there forever. Only physically removing it allowed the system to boot off the new SSD I had installed.


Hi Larry,

Glad you found a solution!

May I ask you how is your iMac performing with Sonoma, compared to Ventura? Can't decide to upgrade... that's why I'm looking for how many advises as possible from people that actually did it.



I'm having the same problem with Sonoma but I gave up and installed Ventura instead. My iMac is a late 2012 iMac13,2. The last Apple supported OS was Catalina for my machine. I installed Big Sur years ago using OpenCore Legacy Patcher. I needed to upgrade the OS because of software updates that required a newer MacOS. So I wanted to go directly from Big Sur to Sonoma but I could not because I got the "volume is not compatible with this update" error. So I decided to try to install Ventura instead. Ventura installed fine with OpenCore Legacy Patcher and is working great. I did not reformat my drive at all to do this. It is still the APFS that was formatted under Big Sur. I would still like to upgrade to Sonoma but I think there is something definitely off with the Sonoma that causes that error to occur. I thank god for OpenCore though. I was able to skip Monterey. My machine is fast because I maxed out the memory and I replaced the hard drive with a 4TB SSD.


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@larry767 - No, I get it! The issue is you messed up the Fusion Drive as you took away the HDD the cache was bonded to. The system got into a battle between the cache drive trying to impose its role when your new SSD is also trying to grab attention too!

Apple now requires full removal of there cache drive. I often slide in an OWC blade SSD. Setting it up as a dual dive config with the blade as the boot drive for advanced amateurs, pro’s and students which are in the Arts all three in music & video work.

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Larry Jorgenson zal eeuwig dankbaar zijn.

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