I've converted a VMWare VMDK to a VHDX. The guest is a Windows 8.1 VM.
When this is attached to a generation-1 Hyper-V VM as an IDE drive, it boots up fine.
When the same VHDX is attached to a generation 2 Hyper-V VM (forced to use SCSI), it fails to boot off the same disk (checked boot order, it fails disk and hits CDROM and network).
The Hyper-V host is a Windows Server 2012 R2 (+updates/patches).
Does anyone know how to get this working as a generation 2 Hyper-V VM. I'm hoping it's not a limitation that I must use IDE (flashback 90s) in order to order to do something as basic as ... boot!
You can't just take a boot disk from a generation 1 guest and have it boot in a generation 2 guest. Your generation 1 disk is likely still using the MBR, your generation 2 disk requires an GPT/EFI partition or converted to GPT/UEFI to boot.
There are some documented manual and scripted methods to convert the virtual machine from generation 1 to generation 2, however these methods would be used at your own risk.
The first link from the manual method is actually from a series of articles on generation 1/generation 2 virtual machines and is a good read.