This the setup I had
- iMac 21 inch
- HDD (500GB) for macOS installation
- SSD (256GB) for Windows 10 installation
This was working perfectly, until I upgraded to High sierra.
After upgrading to High Sierra, macOS stuck at the booting process and shows the spinning wheel all the time. Therefore I used the recovery mode and re-installed high sierra again but no luck. During that time I have erased the Windows 10 SSD via Disk Utility as well.
Then I used a Time Machine back up (2 years old) and reinstalled OS X El Captain. After three and half hour installation process, it booted and shows the white screen with the cursor. In safe mode it worked, but when I use normal mode it didn't. Then I followed these steps:
- Tried to reset the NVPRM, in the restart process Windows BSOD came up and displays the recovery options. In startup disk the boot volume was set to Macintosh HD.
- Then used the Internet recovery, opened the terminal and entered
diskutil list. It shows disk0 as Windows partition, disk1 as Macintosh and disk2 as recovery partition.
But I can see partitions up to disk20 each having ~1 MB allocated space.
diskutils cs list, it shows no CoreStorage logical volume groups found
Now I am running out of idea about how to recover the system. I have created an image of the Macintosh HD before using Internet recovery therefore I'm not worrying data loss.
The image below was taken after I erased the Macintosh partition to install macOS again – I haven't installed it yet.