How to get Hyper-V virtual machines to merge ?

Microsoft’s Hyper-V supports a technology called “live migration” that lets you move running virtual machines from one physical server to another with no downtime.

But what if you want to move a bunch of virtual machines of an old server onto a new one? You can’t just pick them up and carry them over — you have to export them first.

Exporting a virtual machine creates a portable copy of it that you can import onto another Hyper-V server.

The process is not complicated but time-consuming, so it’s best to plan ahead and do it when you have some downtime. Here’s how to export and import virtual machines in Hyper-V.

If your application or system has just completed a backup or other I/O-intensive task, you may find that the machine’s storage utilization is unacceptably high.

One way to reduce storage utilization is to merge snapshots. Merging converts the differencing disk that contains the snapshot changes into a regular disk and then commits those changes to the parent disk.

The parent disk must be online and have enough free space to receive the contents of all child disks.

If you have ever used Hyper-V, you will know that creating a new VM using the Quick Create option in the Hyper-V manager makes not one but two virtual disk files; a VHDX and an AVHDX.

The VHDX is the virtual hard disk that contains the files for your operating system and any applications you have installed.

At the same time, the AVHDX is effectively a differencing disk that points to the VHDX and only stores blocks that have changed since the parent disk (the VHDX) was created.

If you have a virtual machine that is running on Hyper-V and you want to merge its checkpoint, you can do so by following the steps below:

1. Make sure that the virtual machine is turned off. If it is not, turn it off now.
2. Right-click on the virtual machine and choose “Edit Settings.”
3. Select the “Checkpoints” tab.
4. Select the checkpoint that you want to merge and click “Delete.”
5. Click “OK” to confirm the deletion of the checkpoint.

If you’re running Hyper-V on Windows 10, version 1709 or later, you can quickly use the new merge command to merge your different disks. For example, to merge a different disk named avhdx to its parent vhdx, you can run this command:

Merge-VHD -Path avhdx.vhdx -DestinationPath vhdx.vhdx

If you’re running an earlier version of Hyper-V, you can still use the built-in disk management tools to perform the merge operation manually.

When you delete a snapshot in Hyper-V, the snapshot files (.avhdx) are not deleted. Instead, they are left behind as “orphaned” files. While these files don’t take up a lot of space, they can eventually add up if you’re constantly creating and deleting snapshots.

To remove these orphaned files, you can use the following PowerShell cmdlet:

Remove-Item -Path ‘C:\Hyper-V\VM1\Virtual Machines*.avhdx’ -Recurse

“You can delete a checkpoint without merging by right-clicking the checkpoint and selecting Delete Checkpoint.

If you have made changes to a virtual machine since the checkpoint was created and you do not want to keep those changes, you should select Delete Checkpoint and then choose Changes Discard when prompted.”

There are two types of snapshots in Hyper-V, standard snapshots and production checkpoints. You can convert an ordinary snapshot to a production checkpoint, but you can’t restore a production checkpoint to a normal snapshot.

1. Ensure that you have a reliable backup solution before creating any checkpoints.
2. Test your backup solution regularly to ensure that it is working correctly.
3. Delete any checkpoints that are no longer needed.
4. Merge any checkpoints that are no longer needed.
5. Do not create too many checkpoints, as this can impact performance.

I have a question regarding Hyper-V virtual machine file merging. I have seen posts that say to use the Edit Virtual Hard Disk Wizard to merge the files, but when I try this option, it is grayed out.

The other post I saw said to defrag the guest OS, but that did not work either.

I have also tried restarting the VM, taking snapshots and then deleting them (per Microsoft’s suggestion), and running disk cleanup on the guest OS.

I am running Windows Server 2012 R2 Datacenter on a Dell PowerEdge R620 server with two Intel Xeon E5-2650 processors and 256GB of RAM.

We have tried to cover all possible options on how to get Hyper-V virtual machines to merge and all its pros and cons. Do let us know your thoughts about the topic in the comment section below.