Merge Differencing Disk to HyperV Host

Merge differencing disks (AVHD/AVHDX) to boot Hyper-V machine

I have had a torrid time merging differencing disks (AVHD/AVHDX) to the original boot HyperV machine problem. These files occupy most of the space on the host machine causing all the virtual machines running on the host to go into a pause state.

It is imperative to take a backup of the virtual machine concerned before running the merge process. The steps provided below do not guarantee a successful merge of the AVHD/X to the VHD/X.

Please find below steps to resolve the problem at hand:

  1. Select Hyper-V server in Hyper-V Manager
  2. On left-hand side, select Inspect Disk
  3. Browse to location of restored AVHD/AVHDX files
  4. Select one of the AVHD/AVHDX files > OK
  5. Record parent disk name
  6. Repeat steps 2-5 for each AVHD/AVHDX file, and record their order (from newest to oldest)
    • Note: do not use timestamps to determine which files to merge, as this could lead to overwriting the incorrect parent file
  7. Select Hyper-V server in Hyper-V Manager
  8. On left-hand side, select Edit Disk
  9. Next > Select newest AVHD/AVHDX file
  10. Followed by Next > Select Merge
  11. Next To the parent virtual hard disk
  12. Finish
  13. Repeat steps 7-12 for each AVHD/AVHDX disk, until only the VHD/VHDX disk is left for the machine
  14. Mount VHD/VHDX in new virtual machine in Hyper-V and boot

In order to merge the files using PowerShell, you can use the below steps:

  1. Open PowerShell and run command to navigate to directory where AVHDX and VHDX files are located:
    • Note: if files are on different disk than C:, first change to correct disk with disk letter in PowerShell prompt:
      • <disk letter>:
      • For example, if data is located on drive D:, command would be:
        • D:
    • To change to correct directory:
      • cd <directory path where files are located>
  2. Run following command on each AVHDX file:
    • Get-VHD .\<name of AVHDX file>.avhdx
  3. Note name of parent AVHDX file from ParentPath entry in output
  4. Repeat steps 2 and 3 until you have a list of all AVHDX files with their respective parent AVHDX files
  5. Beginning from newest AVHDX file (only AVHDX file with no child file), run following command:
    • Merge-VHD -Path ‘<path to AVHDX>’ -DestinationPath ‘<path to parent AVHDX’
  6. Repeat step 5 on each AVHDX, always starting with newest available file
  7. Once all AVHDX files are consolidated, merge last AVHDX with main VHDX file:
    • Merge-VHD -Path ‘<path to AVHDX>’ -DestinationPath ‘<path to main VHDX disk’

As far as I am aware, the internet calls this a manual method to merge the AVHD/X into VHD/X. Feel free to drop a comment in the comment section below. Thank you πŸ™‚


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