Why does my virtual machines convert to AVHDX files?

I have a pc running Windows 8.1.
My plan was to use Hyper-V for some virtual Windows 7 machines.
For some strange reason the virtual hard drives has changed to AVHDX format.
I know that this has something to do with snap shots / recovery points but I don't recall making these.
How do I convert back to VHDX?

Looking forward to your inputs :-)
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Zephyr ICTCloud ArchitectCommented:
VHDX is the Virtual Hard Drive file name used in the 2012 version.  The AVHDX filename is actually the "delta" (difference) file that is created when you make snapshots. Since you say you didn't create any it's strange ... Can you check if you can delete the snapshot (if there is any)? If you delete the snapshot and then power down the VM the files should "dissapear", it can take a moment, since they need to merge...
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Delete the Snapshots.
OhmitAuthor Commented:
how do I find these snapshots? :-)
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Zephyr ICTCloud ArchitectCommented:
You might find some useful info here
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
You don't need to find them, do not delete them from the file system.

remove them through the menu.

Hyper-V Snapshots FAQ
OhmitAuthor Commented:
Hi Andrew - thnx for your input but your link does not work
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Philip ElderTechnical Architect - HA/Compute/StorageCommented:
Someone took a snapshot/checkpoint as mentioned.

When this happens a differencing disk is created for any changes post snapshot/checkpoint. That is the AVHDX file.

For obvious reasons if storage is already thinly provisioned or fully provisioned with fixed VHDX files having a growing differencing disk or disks is perilous to the entire setup. As soon as that storage runs out all VMs with VHDX files on that storage go into a Paused - Critical state.
OhmitAuthor Commented:
Ok I appreciate the information but how do I change this?
Philip ElderTechnical Architect - HA/Compute/StorageCommented:
As mentioned you delete the snapshot in Hyper-V Manager for the VM.

NOTE: You need enough free storage to allow the merge process to create a new VHDX file!

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