It seems that MS doesn't have any decent guidance on how to manually create a DPM replica for Hyper-V backups.
Consider that you have a Hyper-V host in a remote site and want to back it up over a slow WAN link.
e.g. You have a few VMs totaling hundreds of GB or even TB of data and a T1 link or similar. Replicating the initial data over the wire would take several weeks.
You can copy the VMs to disk, ship the disk to the site with the DPM server and import the data. The details how to do this are very badly documented.
Below is what I worked out with a little help from this blog post:
Copy the data from the remote site
1. Attach a removable hard drive to a workstation or server in the source site.
2. Copy the data to be backed up remotely to the USB drive. For a VM you will need to shut down the VM and copy the entire VM folder from the host or CSV.
3. Move this removable hard drive to the destination site and attach to a workstation or server.
Import the data into DPM
1. RDP to the DPM server as a local administrator account (not a domain account)
2. Open DPM as a domain account (shift-rightclick)
3. Under Protection, All Protection groups, expand the new protection group member and under Details, Replica path click on the “Click to view details” link. Right click on the destination and copy.
4. Paste this into notepad
5. Append the full path to your data to be backed up to the end of the path starting with “N_Vol” where N is the drive letter. E.g. for my VM called TESTVM that is on a CSV called TESTCSV1 my full path was "C:\Program Files\Microsoft System Center 2012 R2\DPM\DPM\Volumes\Replica\Microsoft Hyper-V VSS Writer\vol_0c2c97b6-327a-401a-b65f-d253a607fdcd\b20116a3-a646-4480-afe9-aeb322887251\Full\\C-Vol\ClusterStorage\TESTCSV1\TESTVM"
The GUIDs in here will be specific to your config so you must copy these from what you pasted into notepad.
6. Open an elevated CMD prompt and run mkdir and paste the full path from notepad that you just created. Make sure you enclose this in “ “ since it includes a space
7. This path will most likely be too long for Windows Explorer to deal with so we need to mount this folder to a drive letter using command:
and then paste the full path from notepad again. Substitute X for any free drive letter in your system. Make sure you enclose the path in “ “
8. Copy the VM files from the removable media to this drive. You must replicate exactly how the file and folder structure looks on the source.
Start backing up using the copied data as the initial manual copy.
1. In DPM console under Protection, All Protection groups, expand the new protection group member.
2. Right click on the Protection Group member and select Perform Consistency check. This will perform a block level comparison of the files we manually copied with the files on the source system and copy any changed blocks over the wire. Only the changed blocks will be copied.