Disk issue in Hyper-V environment, differential data missing?

Question

Virtualization

Good afternoon!
The situation is as follows:
There is a physical server on which Windows Server 2012 with Hyper-V is installed.
Inside Hyper-V there is a virtual machine with Windows Server 2008 with 2 virtual disks (the first for the system, the second for data storage).

Disk C - DBS.vhdx (97 GB) and DBS_D21CAE00-BA4C-482E-898A-27F288BD8126.avhdx (21 GB)
Disk D - DFS.vhdx (800 GB) It was

necessary to back-up the virtual machine (several .vhdx and .avhdx).

Turned off the virtual machine for the time of copying, started copying the file copy files (.vhdx and .avhdx) to an external USB drive.

After a successful full copy, I restarted the virtual machine, HOWEVER, all files in the virtual machine (both drives C: and D:) contained data as of March 25, 2021, and all other files (changes and additions) since March 26, 2021 have disappeared to this day.

I read the forums for a long time and realized that the problem is probably in .avhdx files containing differential data.
Perhaps the file DBS_D21CAE00-BA4C-482E-898A-27F288BD8126.avhdx (21 GB) contained differential data from both C and D drives.

Please help me resolve the issue of data loss for the last 4 months (from March 26, 2021 to today)

Answer 1

Perhaps the file DBS_D21CAE00-BA4C-482E-898A-27F288BD8126.avhdx (21 GB) contained differential data from both C and D drives.

check the parent disk in Hyper-V Manager (execute Inspect Disk on your AVHDX and see the line Parent) or Powershell ((Get-VHD -Path "AVHDX").ParentPath)
Then run the Merge disks, again in Hyper-V Manager (execute Edit Disk on the desired VM, follow the steps of the wizard) or Powershell (Merge-VHD -Path "AVHDX" -DestinationPath "Parent AVHDX / VHDX")
If you have a VHDX - AVHDX1 - AVHDX2 - AVHDX3 - AVHDX4 - run Merge multiple times from last to first