System: Dell XPS 15 (9530) with Windows 8.1, non-SSD 1TB HD + 32GB SSD
When I tried to upgrade to Windows 10, I constantly got the error:
WE couldn't install Windows 10 We've set your PC back to the way it was right before you started installing Windows 10.
0xC1900101 - 0x20017 The installation failed in the SAFE_OS phase with an error during BOOT operation
Fix: images from this thread
I struggled with this all last night and I hope somebody will not have to go through the same frustrating experience as me!