Symptoms

Hyper-V backups of certain VMs may fail with messages similar to the following: avhypervvss Warning <42496>: Virtual machine 'EMC <GUID>' has one or more virtual disks with same ID and will not be backed up with image level backup. ... avhypervvss Error <43105>: Virtual machine 'EMC' does not have valid vhd chains and will not be backed up with image level backup avhypervvss Warning <41605>: The following Virtual Machines have failed: avhypervvss Warning <41604>: [1] EMC <GUID>

Cause

This problem occurs if one of the VHDs attached to the VM was created by copying the contents of a physical hard drive. In this scenario, the new virtual hard drive contains the same disk signature as the physical hard drive in the parent partition. During a backup process that uses the Hyper-V VSS Writer, the virtual hard disks are mounted in the parent partition. This process fails for the affected VMs because of the disk signature collision.

Resolution

Power off the affected VM.For each of the VHDX files attached to the VM, run this cmdlet from an elevated PowerShell prompt (run as Administrator): Get-VHD -path "<directory of the VHD files>" Example: Get-VHD -path "D:\Hyper-V\EMC.vhdx" Get-VHD -path "D:\Hyper-V\EMC1.vhdx" Check the DiskIdentifier field for each VHD. If they are not unique, change the disk IDs so that they are different from each other Set-VHD -ResetDiskIdentifier -Path "location of VHDX file" This command changes the disk identifier attribute on the VHDX file. Do this for the other VHDX files attached to the affected VM. Power the VM back on.Run the following PowerShell command: Get-VHD -path "<directory of the VHD files>" Do this for each of the VHDX files for the affected VMs and confirm that the disk identifier value is different for each file.

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