There is an issue with VHD(X) images containing ext formatted partitions.
Windows recognizes the partitions but does not assign any Volume-GUIDs to them.
The VHD(X) mount logic in nbksrv-->libvhd requires the presence of a Volume-GUID in order to mount a partition.
We'll treat this as a known issue for these reasons:
• there don't seem to be a practicable fix for the problem
• development of NovaStor's proprietary image format (svx) as alternative for both VHD(X) and VMDK is about to begin
• there is a workaround for the customer: use VMDK for Hyper-V VMs with linux guests
Here is how you set VMDK as image format for Hyper-V backups:
Edit $(GIRPOOL_DATA_DIR)/pool.conf and set imageProvider.hpv="VMW"