Various issues with installing Windows

Loner T wrote:

Is there a specific reason they are not?

Thanks for all your help so far. No specific reason on why they aren't configured as a Fusion drive. I'm pretty new to Apple products and I am still learning about this system. I could see the benefit in setting up a NVME/SSD and mechanical drive in a Fusion drive configuration, but from my (limited) understanding, there are no performance benefits in having a NVME and SSD configured in a Fusion drive configuration. Also, I've read somewhere that Fusion drive configuration only works when one drive is a solid state and the other is a mechanical drive. Not sure if that's true or not.

Not an easy one. You have to physically disconnect the drive you do not want to participate in Windows, install Windows which also means that this drive must also have macOS, and then connect the second drive. The designated Windows drive must be in the main 'slot/bay' of the Mac, otherwise it will not boot in Windows correctly. Also, after you connect the second drive, it is very hard to repair Windows, if there is any issue with the installation.

Be aware that third-party NVMe or SSD storage may not work properly with Windows.

This was something I didn't want to resort to, but I guess I'll have to. So just to be clear (before I open it up) - after I disconnect the second drive (non OS), Windows is installed and set up correctly, and finally, reconnect the second drive, there shoudn't be any issues with booting into either MacOS or Windows?

Loner T wrote:

On APFS systems, there is an additional requirement that the -secondary should be larger in size than the -main disk. I assume that is the case on your iMac.

Both my main and secondary are the same size as shown in the diskutil list output:

/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                 Apple_APFS Container disk3         1000.0 GB  disk0s2

/dev/disk1 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk1
   1:                        EFI EFI                     209.7 MB   disk1s1
   2:                 Apple_APFS Container disk2         1000.0 GB  disk1s2

/dev/disk2 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +1000.0 GB  disk2
                                 Physical Store disk1s2
   1:                APFS Volume Stuff                   43.3 GB    disk2s1

/dev/disk3 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +1000.0 GB  disk3
                                 Physical Store disk0s2
   1:                APFS Volume Macintosh HD — Data     40.3 GB    disk3s1
   2:                APFS Volume Preboot                 283.4 MB   disk3s2
   3:                APFS Volume Recovery                626.2 MB   disk3s3
   4:                APFS Volume VM                      1.1 MB     disk3s4
   5:                APFS Volume Macintosh HD            15.3 GB    disk3s5
   6:              APFS Snapshot com.apple.os.update-... 15.3 GB    disk3s5s1

Just to double confirm - due to the above, I will not be able to create a Fusion APFS configuration with the NVME and SSD? Meaning I definitely have to perform unnecessary repair work to get this sorted out?

Was able to resetFusion successfully, rebooted and installed macOS. Ran diskutil first aid, reset PRAM, then without restoring any backups, I ran Boot Camp Assistant and an error popped up saying something along the lines of "there is 0 bytes of free space to partition the drive..."

Diskutil shows 1.98TB free.

Checked diskutil resizecontainer limits and it shows that the Minimum, Recommended Minimum and Maximum figures were all the same, which was odd. Tried to resize manually and it wouldn't work.

Tried deleting snapshot and rebooted. Boot Camp Assistant popped up with the same error.

Ran resetFusion again and went through the install process again. Same result.

I needed Windows set up for some of my work, so didn't have much time left to troubleshoot. I ended up splitting the Fusion, pulled the screen off just enough to reach my hand in to disconnect the SATA plug to my SSD. Then installed macOS, ran Boot Camp Assistant and Windows successfully installed without a single problem. Pulled the screen off again to plug the SSD back in. Tested everything to make sure there were no errors, then finally replaced the adhesive for the screen. This ended up being a much quicker way to resolve the issue for me.

Thanks for all your help, Loner T! Have learnt a lot and I'm glad it's finally resolved.

No, they are not configured as Fusion drive. Is there another way?

I will try this and report back. Thanks!