Figured to finally run some tests with High Sierra (yeah late to the game, had some other priorities)
So I set out to put a macOS Sierra VM on an external USB disk and began the upgrade process within that VM.
About half way during the process I end up with the following screen:
Don't be fooled by the Fusion icon, this is a guest OS that I also happen to run Fusion in for testing
Will rerun this from a local disk now, but if needed I can rerun this as a test later on from USB.
It should not be a hardware issue as I have used the USB disk to run guests from without issues in the past, but who knows.. figured to at least report that I bumped into this.
After the above error I would only cancel (other options didn't work) and I was warned about that the disk might be corrupt.
Don't worry I have backups
Host OS: 10.12.6
Hardware: mac mini 2014
Fusion Tech Preview: Professional Version e.x.p (6048684)