Hyper-V Gen2 SCSI boot issues with legacy IDE converted machines

I was converting a Windows 2012R2 server from a VMDK to a VHDX, creating a new Hyper-V Gen2 host and struggling to get it to boot.  I could mount the drive, read from it from a safe CMD prompt, tried to make sure the correct partition was active using DISKPART, even used BOOTBCD to try but with no luck.

I eventually found that the issue was because I was creating Gen2 Hyper-V machines rather than the Legacy Gen1.   Whilst Gen2 will support Win2012R2 they do not support the booting of IDE drives connected as a virtual SCSI controllers can only be recognized after installing Hyper-V Integration Services on the guest OS on the VM. If this is not the case then the guest OS cannot boot from a SCSI disk.

Running up a Gen1 machine and connecting the drive to the IDE booted first time...!

References: 

The Differences Between Hyper-V Generation 1 vs. 2 VMs

https://docs.microsoft.com/en-us/windows-server/virtualization/hyper-v/plan/should-i-create-a-generation-1-or-2-virtual-machine-in-hyper-v#windows-guest-operating-system-support