Merge-VHD Question and vmgs non bootable vm question

[merrittr]

I have a vm where the main disk is defined in Hyperv management as disk0-snapshot.vhdx and there is another disk0.vhdx in that folder that is larger in size , when I try and boot the vm I get a message <random charachters>.vmgs does not exist message. but there is a
<random charachters>.vmgs.<morechars>. How do I rehabilitate this into a bootable vm?

 

[ChatGPT]

Hi merrittr — this sounds like two separate Hyper‑V issues:

1. The VM is trying to resume from a missing .vmgs guest state file.
2. The VM disk currently points to disk0-snapshot.vhdx, which is likely a differencing/checkpoint child disk whose parent is disk0.vhdx.

Do not simply attach disk0.vhdx and boot it yet. If disk0-snapshot.vhdx contains newer writes, booting from the parent may appear to “roll back” the VM.

Recommended recovery path​

1. Power off the VM and make a full folder backup​

Before merging or changing anything:

1. Shut down/turn off the VM if possible.
2. Stop any backup software that may be touching the VM.
3. Copy the entire VM folder somewhere safe, including:
   • disk0.vhdx
   • disk0-snapshot.vhdx
   • any .avhdx, .vhdx, .vmcx, .vmrs, .vmgs files

This is important because a bad merge can make the chain unrecoverable.

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2. Delete the broken saved state​

The missing .vmgs message usually means Hyper‑V is trying to restore a saved/running state that no longer exists.
Try this first:

1. Open Hyper‑V Manager.
2. Right-click the VM.
3. If available, choose Delete Saved State.
4. Try starting the VM again.

If Hyper‑V Manager will not do it, use elevated PowerShell:
Remove-VMSavedState -VMName "Your VM Name"
Then try starting the VM.
Do not rename the existing <random>.vmgs.<morechars> file to match the missing .vmgs unless you have no other choice and have a backup. It may be a stale/temp/state-related file and not valid for this VM state.

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3. Inspect the VHDX chain​

Run this from an elevated PowerShell window on the Hyper‑V host:
Get-VHD -Path "C:\Path\To\disk0-snapshot.vhdx" | Select-Object Path,VhdType,ParentPath
Expected result if it is a checkpoint/differencing disk:

VhdType    : Differencing
ParentPath : C:\Path\To\disk0.vhdx

Also check the parent:
Get-VHD -Path "C:\Path\To\disk0.vhdx" | Select-Object Path,VhdType,ParentPath
If disk0-snapshot.vhdx has disk0.vhdx as its parent, then the active boot disk is probably the snapshot child.

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4. If the disk chain is healthy, keep the VM pointed at the child disk​

If disk0-snapshot.vhdx is healthy and points to disk0.vhdx, the quickest recovery may be:

1. Delete the saved state.
2. Leave the VM attached to disk0-snapshot.vhdx.
3. Start the VM cold.

If it boots, you can later clean up/merge the checkpoint properly.

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5. If you want to merge the snapshot into the parent​

Only do this after the VM is off and backed up.
If disk0-snapshot.vhdx is a differencing disk and disk0.vhdx is its parent, run:
Merge-VHD -Path "C:\Path\To\disk0-snapshot.vhdx" -DestinationPath "C:\Path\To\disk0.vhdx"
After the merge completes:

1. Open the VM settings.
2. Change the hard drive path from:

disk0-snapshot.vhdx
to:
disk0.vhdx

1. Start the VM.

Warning: After a successful merge, the child snapshot disk is no longer useful as an independent disk.

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6. If Hyper‑V still refuses the VM config, create a new VM shell​

If the VM configuration is damaged because of the missing .vmgs/state files, the cleanest option is often to create a new VM and attach the recovered disk.

1. Create a new VM with the same generation as the old one.
2. Do not create a new virtual disk.
3. Attach the correct recovered disk:
   • Use disk0-snapshot.vhdx if you did not merge.
   • Use disk0.vhdx if you successfully merged.
4. Match the old VM settings as closely as possible:
   • Generation 1 vs Generation 2
   • Memory
   • vCPU count
   • Network switch
   • Secure Boot setting if Gen 2
5. Boot the new VM.

If it is a Generation 2 Windows VM and fails to boot, check:

1. VM Settings > Firmware
2. Make sure the VHDX is first in boot order.
3. If needed, temporarily disable Secure Boot to test.

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My suggested order for your case​

1. Back up the whole VM folder.
2. Run:

Remove-VMSavedState -VMName "Your VM Name"

1. Check the disk chain:

Get-VHD -Path "C:\Path\To\disk0-snapshot.vhdx" | Select Path,VhdType,ParentPath

1. If the chain is valid, try booting again while still attached to disk0-snapshot.vhdx.
2. If it boots, then decide whether to leave it or merge it.
3. If the config remains broken, create a new VM and attach the correct VHDX.

If you can paste the output of:

Get-VMHardDiskDrive -VMName "Your VM Name" | Select VMName,Path

Get-VHD -Path "C:\Path\To\disk0-snapshot.vhdx" | Select Path,VhdType,ParentPath

I can tell you exactly whether you should boot from the snapshot, merge it, or rebuild the VM config.