Avamar: Hyper-V VSS Plug-in Backups Missing VMs Without Errors

Backups complete without errors but some VMs are omitted from the restore list.

• Only a subset of VMs defined in the dataset appear in the Avamar Administrator restore window.
• Log shows the following VMs are specified for backup:

  <path backup="true" name="AvamarVM1_Cluster" />
  <path backup="true" name="AvamarVM2_Cluster" />
  <path backup="true" name="AvamarVM3_Cluster" />
  <path backup="true" name="AvamarVM4_Cluster" />

• However, only "AvamarVM1_Cluster" and "AvamarVM2_Cluster" VMs are available from the restore window.
• In the log of the missing VMs, the problematic VM is listed without a GUID after the name:

  avhypervvss Info <13970>: Components selected in Avamar Administrator:
  avhypervvss Info <7084>: target[0]=AvamarVM3_Cluster<XXXXX-XXXXX-XXXX-XXXX-XXXXXXXXA1>

   
• In the successful log with all the VMs backed up, it shows the GUID:

  avhypervvss Info <13970>: Components selected in Avamar Administrator:
  avhypervvss Info <7084>: target[0]=AvamarVM3_Cluster

   
• In the log, you may see warning messages similar to the following:

  avhypervvss Warning <41730>: VM: AvamarVM3_Cluster<> specified in the target list is invalid and will be skipped from the backup.

The Hyper‑V VSS plug‑in parses VM information from the Failover Cluster Manager’s Cluster Group configuration. It expects the VM name in the dataset to match the Cluster Group name exactly. When a VM’s name differs between Failover Cluster Manager (for example, AvamarVM3_Cluster) and Hyper‑V Manager (for example, AvamarVM3), the plug‑in cannot resolve the GUID and treats the entry as invalid.

• VM name mismatch between Failover Cluster Manager and Hyper‑V Manager.
• Plug‑in relies on the GUID present in the Cluster Group entry; missing GUID leads to skip.
• Log entries show the target without a GUID and a warning “VM: AvamarVM3_Cluster:

  avhypervvss Info <0000>: Got the basic info for the target VM with Name AvamarVM3, GUID XXXXX-XXXXX-XXXX-XXXX-XXXXXXXXA1, Cluster Group Name AvamarVM3_Cluster

Temporary Workaround

Edit the backup dataset to remove the problematic VMs and then add them back.

Permanent Fix

Rename the VMs so that the names are identical in both Failover Cluster Manager and Hyper‑V Manager.

• Ensure the VM name in the Cluster Group matches the Hyper‑V Manager name exactly.

Once the names are consistent, the plug‑in will include the GUID and the VMs will be backed up successfully.