After exporting hyper-v vmcx, vhdx avhdx will not be automatically merged

Question

After exporting hyper-v vmcx, vhdx avhdx will not be automatically merged

Tim 0

I use root\virtualization\v2 ExportSystemDefinition, and I have the following settings:

exportSettingData["CopySnapshotConfiguration"] = 1;
exportSettingData["CopyVmRuntimeInformation"] = false;
exportSettingData["CopyVmStorage"] = false;
exportSettingData["CreateVmExportSubdirectory"] = true;
exportSettingData["CaptureLiveState"] = 0;

Once I successfully export, any checkpoints taken after that and deleted will not be merged until I shut down the virtual machine or Restart-Service vmms. Can anyone help me? Thank you very much.

2 answers

Your answer

Answer 1

HenryMai-3878 6,585 Independent Advisor

Hello Tim, I am Henry and I want to share my insight about your issue

The behavior you're seeing is by design. When you run ExportSystemDefinition with CopyVmStorage = false, Hyper-V intentionally places a temporary lock on the VM's disk chain. This is done to guarantee the consistency of the exported configuration and its associated checkpoints. This lock, however, is what prevents the live merge process from running.

My recommendation to handle this without restarting the VM or the service is to isolate the lock to a temporary checkpoint that you create and then immediately delete.

Create a Temporary Checkpoint: Before running your export script, create a new checkpoint for the VM. Let's call it "TempExportCheckpoint".
1. PowerShell: Checkpoint-VM -Name "MyVM" -SnapshotName "TempExportCheckpoint"
Run Your Export Script: Execute your existing C# code as-is. The export will now reference the state of the VM at the moment "TempExportCheckpoint" was created. The persistent lock is placed on the chain including this new checkpoint.
Delete the Temporary Checkpoint: Immediately after the export is complete, delete the "TempExportCheckpoint".
1. PowerShell: Remove-VMSnapshot -VMName "MyVM" -Name "TempExportCheckpoint"

Because the export's lock was tied to the temporary checkpoint you just deleted, the lock is cleanly released from the running VM. Any other checkpoint deletions you perform after this will trigger their live merges correctly without any delay.

I hope this information is helpful.

Tharindu De Zoysa 0 Reputation points

2025-08-07T16:27:35.97+00:00

I agree with your answer, y creating and then deleting a temporary checkpoint before exporting, you avoid locking the main VM disk chain. This allows normal checkpoint merging to continue without requiring a VM shutdown or vmms service restart.
Tim 0 Reputation points

2025-08-08T01:45:50.3166667+00:00

I followed your steps, but it still won't merge automatically.
HenryMai-3878 6,585 Reputation points Independent Advisor

2025-08-08T03:03:59.7+00:00

I sincerely apologize that the initial recommendation did not resolve the issue. My suspicion that your script is deleting the temporary checkpoint before the export job has fully completed in the background.

When you call ExportSystemDefinition, it initiates an asynchronous job. The method returns control to your script almost immediately, but the Hyper-V VMMS service is still working on the export in the background. If your script proceeds to delete the snapshot while that export job is still active, the lock on the disk chain will remain until the job finishes, defeating the purpose of our workaround. Whether you try to modify the script to wait for the export job to complete before deleting the temporary checkpoint.

Besides that, please check the following:

Check for Other Locks: Is there any other backup software (Veeam, Windows Server Backup, etc.) that might have failed and left a persistent VSS lock on the machine? Open an Administrator PowerShell and run vssadmin list writers. Look for any writers that are in a Failed or unstable state.

Hyper-V Event Logs: Check the event logs on the Hyper-V host immediately after running the script. The most important log is in Event Viewer -> Applications and Services Logs -> Microsoft -> Windows -> Hyper-V-VMMS -> Admin. Look for any errors or warnings related to the export (ExportSystemDefinition), snapshot deletion, or disk merges.

Windows Updates: Ensure your Hyper-V host is fully patched with the latest Windows Updates. It is possible this is a bug that has been resolved in a recent cumulative update.

Answer 2

Tharindu De Zoysa 0

Hi Tim,

Based on your description, you're experiencing an issue where checkpoint (AVHDX) files aren't automatically merging after deletion when using the ExportSystemDefinition method with your current settings.

Root Cause Analysis

The behavior you're seeing is expected with your current configuration because:

You've set CopyVmStorage to false, which means the export isn't creating full copies of your VHDX files
When you delete checkpoints after export, the merge operation requires exclusive access to the virtual disks
The VM's running state prevents the merge from occurring immediately

Recommended Solution

Modify Export Settings

Try adjusting your export settings to include storage:

exportSettingData["CopyVmStorage"] = true;

Tim 0 Reputation points

2025-08-08T01:48:33.6133333+00:00

But I just want to export the settings file, or is there a better way to do this? Thank you.

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After exporting hyper-v vmcx, vhdx avhdx will not be automatically merged

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