Client had legacy Windows NT application (not connected to Internet, but running legacy system) that was running on VMWARE ESXi.

Client wanted to migrate to KVM/qemu however the old physical system had IDE emulation via Adaptec SCSI->IDE. And client had created the VMWARE emulation the same way. Thus when the VM was converted from VMWARE to KVM/qemu the system would not eboot. Got the infamous BSOD with "INACCESSIBLE BOOT DEVICE" error as it was looking for a SCSI drive controlled as IDE by an adaptec driver that didn't exist anymore.

The system was so old with so many manual updates that re-installation from scratch was not a preferred option.

Tried defining KVM/qemu drives as SCSI or IDE but neither worked as the drives were seen by the system as IDE despite running as SCSI.

Solution:

1. re-installed over old WINNT directory with new installation which overwrote System file and got system running again with disks visible but no services.

2. Attached the old VMWARE drives as additional drives to KVM/QEMU system (e.g. Drives E:,F:)

3. Did a search for all files that referenced aic78 (the adaptec driver) that were changed between new install and old system and found
C:\WINNT\system32\config\System

4. Since you can't copy system files in use on running Windows OS, rebooted into rescue CD and ran ntfs-3g to mount both old and new install drives inside KVM. Copy System file from new install drive to old install hard drives.

5. Deleted new installation disk, made old disk images as primary boot (with the one file changed from the new system)

Migration from ESXi to KVM complete for legacy Windows System.