Hyper-V VM backup size

[liuyang]

Hi, my master and media servers are all NBU 7.1 on Windows 2008 R2 SP1. We would like to back up VMs in the Hyper-V servers (NBU 7.1, Windows 2008 R2 SP1). We have configured the Hyper-V servers to be SAN media servers and we want to do full VM backups. My question is:

What is the backup size of a VM? Is it the size of disk allocated to the VM  or the data size inside the VM?

Thanks in advance.

[Marianne]

Please forgive us if we are slow to respond to your posts...

Trying to assist you is quite difficult and demotivating, as you hardly give feedback when we request additional information. It also seems very difficult for you to mark anyone else's post as solution, even when we point you in the right direction. (e.g. https://www-secure.symantec.com/connect/forums/how-configure-hyper-v-server-enterprise-client )

In all honesty - you are the best person to answer the questions in your post.
The first successful backup will tell you how much data was backed up.

NBU for VMware has an option in policy to 'Exclude unused and deleted blocks'. 
I cannot find a similar option in NetBackup for Hyper-V Administrator's Guide  http://www.symantec.com/docs/DOC3662

So, my gut-feel tells that the backup will probably be the size of disk allocated to the VM.

[liuyang]

The actual backup size varies based on our testing. Sometimes it is close to the disk size allocated to the VMs.Sometimes it is close to the actual data size in the VMs.

[V4]

is it same VM which you point as different backup size ?

What type of Disk are assigned to Guest VM (Fixed or Differencing)?

Any LDM or any pass through device mappings?