When in recovery mode on Windows 2016 2019, it might happen that the bootdrive is not visible.
Apparently Windows recovery mode does not load the drivers.
You can solve it the following way:
Load the Virtio driver CD in you VM.
Boot in Recovery mode.
Choose command promp.
First step: Check what drives you have
X:\wmic logicaldisk get caption
If you do not see the bootdrive (C: probably) find and browse to the driver on the cd (d:\vioscsci\2k19\amd64)
Then type: drvload vioscsi.inf
Check if you see the C: drive now.
If not, also load the driver of d:\viostor\2k19\amd64\viostor.inf
Assumed is that the Virtio driver CD is the D: drive and C: the bootdrive that is missing.