When using the Backup Exec MSVS agent to backup the Hyper-V virtual images it will backup the complete hard drive and not the actual data on the drive. I mean if you have created a VHD of 100 GB and have only 30 GB used, when we backup it the VHD it will backup complete 100GB and not 30 GB this is because Unlike VMware, MS doesnot provide any utilty like VCB which inturn compress the data and lets the Backup Exec backup the only data and not the free space.
hence when backing up Hyper-V images it will backup the complete VHD though you donnot have that much data on the drive.....
Let me know if some has any other answer to this question.