I've installed macOS Sierra and then Windows 10 on the second partition. I've decided to split Windows partition to another 2 partitions and it doesn't work. Splitting executed using standard Windows disk management utility. Before splitting I've got message that "Your disks become dynamic..." something like this. Have clicked Yes anyway and splitting didn't done, but in disk management partitions become another color. Windows still running until rebooting. Then it won't boot with error "Something wrong with your PC. Try to reboot again". Autofixing problems, check disk etc. didn't help at all. macOS disappeared from boot menu and now has RAW filesystem. I guess splitting disk corrupted its filesystem. Is there a way to back macOS to boot menu? It seems RAW filesystem have to be converted to GPT someway. macOS is on G: partition. Please help.
There is a way I fix this. This is the simplest solution you may use in case you have backup of Windows files and macOS files using via Time Machine or external drive.
- Create a backup image of restored Windows partition. If Windows didn't restore yet use TestDisk util. Example of restoring.
- Boot your Mac in recovery mode and there you'll have option to reinstall macOS or to restore from Time Machine. You're lucky if you have backup. However on my 2011 late MacBook I've got Sierra macOS option to install, instead of default MacOS Lion. This saved me a hour of time to update from Lion to Sierra. NOTE: that installing macOS again will erase your Windows disk. Therefore we made a bit-to-bit backup on step 1.
- After installing Sierra you have an ability to reinstall Windows via Bootcamp. If your Mac newer than 2012 that supports Windows 10 installation you can skip this step. My late MacBook Pro 2011 doesn't support Windows 10 by Bootcamp, so I need to do a trick by installing Windows 7 first. Then convert MBR record from Hybrid to Protective (Win10 doesn't support Hybrid). And only then install Windows 10. Read this perfect post for details.
- Restore Windows 10 from backup we've created on step 1. You have to boot in the recovery mode of Windows and go to Restore from backup step.
Not sure this is the fastest way to restore, but I didn't find another one. This took over 4-5 hours to get back to normal state of booting macOS or Windows 10 on my old MacBook. And get a lesson that to DO NOT SPLIT disk when you have more than one OS installed.