There are two different techniques DPM uses when it backs up a Hyper-V guest on a host. DPM backs up the guest using a backup using child partition techniques (Online) or backup using saved state (offline).
In the next coming minutes I will try to explain why it differentiates.
Ever seen this, you got a 2008R2 server that gets backed up using saved state? Why, There are VSS’es that are in a stable state running on the virtual machine and all Hyper-V VSS’es looks fine on the host side also.
Let’s try to explain how a backup of a virtual environment works. First you install a DPM agent on the Hyper-V host, that’s the server hosting all the virtual machines. After you have done all necessary configurations in DPM to start protecting your Hyper-V environment you will create the replica. This is where the VSS’es comes in place. The DPM agent on the host will initiate a VSS-Requestor. This will send a VSS request to the virtual machine, the virtual machine will answer to that requests and say what present VSS’s are running within the virtual server.
So, if you are running a Hyper-V server with a server technology that hasn’t any VSS’es that can backup your server technology within the virtual operating system you will end up with a backup that will run only using saved state.
But there’s more.
Online protection is not possible when;
• Backup (Volume Snapshot) Integration Service is not installed or disabled.
• VM has one or more dynamic disks.
• VM has one or more non-NTFS based volumes.
• The VM Cluster Resource Group in a cluster setup is offline.
• VM is not in a running state.
• Shadow storage assignment of a volume inside the VM is explicitly set to a different volume other than itself.