Error partitioning a Fusion Drive

You say you have a 1TB Fusion drive (which makes sense), but the diskutil output indicates a much smaller drive and the sizes are inconsistent.

I can't find anything about fixing a Fusion drive short of this: https://support.apple.com/en-us/HT207584

But that doesn't sound like what you are seeing.

I started Internet Recovery and erased the Macintosh HD and installed macOS again. But again the same error.

If you are running Sierra, did you use the special key combo (Command + Option + Shift + R) while booting up? If not, you're in the regular recovery, not in internet recovery and it will not work the same.

https://support.apple.com/en-us/HT204904

Hi, I have the same/similar problem. Tried this solution (How to fix a split Fusion Drive - Apple Support) but I still have the partitions and the same problem.

History:

- It all started when I did a clean install. I didn't know that APFS wasn't supported for Fusion drives only during installation I got a message to join a beta program. Didn't want to do that, so I tried to reformat the drive back but got an error: "Unrecognized file system."

- Then did the macOS Recovery. This installed macOS Sierra (not High) but run into the same problem as with High Sierra: "An error occurred while preparing the installation. Try running this application again." (I did that multiple times).

- So then I partitioned the drive (didn't know that was an issue too) and I could install macOS on the 2nd partition, but it skipped the SSD drive, so all benefits of a fusion drive lost.

Now:

I tried the (How to fix a split Fusion Drive - Apple Support) but that didn't solve my problem. If I use Disk Utility and click on partition and remove one (disk0 is not allowed to delete) and click "Apply" I get the error: "Unrecognized file system."

How can I fix this?

See if this helps …

How to fix a split Fusion Drive - Apple Support

I have found trying to either partition or re-partition a fusion drive to be a more than frustrating experience (which refused to work no matter what I tried for 2 days). In my case, I returned the Mac after one week due to some other problems and I decided I want a hard drive I can control. In any case, you can only create one partition on a fusion drive. Second, you may want to try to recreate the fusion drive by using internet recovery > Disk Utility > erase > reinstall the OS. The best way out of this would be if you had made a bootable clone before all of this: boot into it, erase the internal, and clone back the system. When all of this is done and your fusion drive is back to normal, you can try to create one partition.

No problem - just wanted to clarify. And "original" refers to what the Mac came with (except that pre-download versions such as Snow Leopard can't ever be downloaded, so the system will install the next possible version). That process usually will fix fusion drive problems as it will take it back to factory specs, but you must use internet recovery and, depending on which OS you're on, there are different key combos now.

Contacted Apple support:

There is a "mistake" in the manual: "How to fix a split Fusion Drive - Apple Support" It reads:

1. Turn on your Mac and immediately hold down Command-R or Option-Command-R to start up from macOS Recovery. Release when you see the Apple logo or a spinning globe.

This should be changed to only: "Option-Command-R". for Internet macOS Recovery mode.

Once I followed the manual using Option-Command-R at startup, it worked.

Yeah, I'm not sure how to recover from where you are besides trying to split and erase each, then merge them again.

There might be a way, but I don't know it.

That key combo works only if you are running Sierra 10.12.4 or higher and will reinstall the original OS which usually recreates the fusion drive.