Migrate VM to Managed Disks Fails

Question

Hi,

Successfully migrated exiting production VM and Data storage from classic to ARM. Now, when attempting to migrate disks from unmanaged to managed I get this error: Failed to migrate the virtual machine 'VM'. Error: VHD footer 'Current Size' field validation failed. VHD for disk 'VM_os_dsk.vhd' with blob https://blah.blob.core.windows.net:8443/vhds/os_dsk.vhd specifies size (37762367488) which does not match VHD blob size (37763416576) - VHD Footer Size (512). The VM is currently working fine.

I've tried downloading the vhd using Azure Storage Explorer multiple times, but it fails right before it completes because a size mismatch issue. Even turning off the MD5 check option... I get the same problem.

After trying multiple times I was able to download the VHD using a SAS url, however now when I use resize-vhd, I'm getting error message that the VHD is corrupt and unreadable, even though the VM in azure is running perfectly fine. I've tried downloading the VHD a couple of times, still the same error.

What am I doing wrong, can someone help? How can I migrate this VM to managed disks?

Thanks for your help.

Answer 1

@Bruno-8416 It appears you will need to resize the VHD in order for this to work properly. You can try using VHD Resizer to accomplish this. Please note I recommend to not run this on the production system.

https://blogs.msdn.microsoft.com/devkeydet/2012/07/05/resizing-an-azure-vm-vhd-file/

Hopefully this helps!

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Answer 2

@Bruno This document walks through identifying and mitigating this issue. Please try the mitigation steps and see if it fixes your issue.

https://learn.microsoft.com/en-us/azure/virtual-machines/windows/migration-classic-resource-manager-errors#vm-with-data-disk-whose-physical-blob-size-bytes-does-not-match-the-vm-data-disk-logical-size-bytes

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Answer 3

Thank you! I was able to successfully resize the vhd and create managed disks from it.