Share via

What is .avhd file and what do I do with it?

  • Article

Question

Wednesday, May 18, 2016 4:02 PM

I have a Hyper-V VM that has a .vhd file attached to it as data disk. I want to transfer this file off that server and copy it to an Azure storage account so that I can attach it to an Azure VM.

There are 2 other files beginning with the same name as the actual .vhd file appended with some string and .avhd extension.

What are those files?

What should I do with them?

Thanks - Esmail

All replies (3)

Thursday, May 19, 2016 10:31 AM

Hi,

Thank you for posting here! We are happy to assist you.

An AVHD (or AVHDX) file is essentially a differencing disk that's a child of another VHD (or VHDX) file. The "A" in AVHD stands for Automatic VHD as in Automatically Managed VHD--that is, it's managed by Hyper-V.

The AVHD files are differencing disks which work in conjunction with the parent VHD file. At the point the snapshot of the VM was created, the parent VHD essentially became read-only and all the changes or additions to disk made by the VM were actually being written to the AVHD file. This allows snapshots to do their job by giving the flexibility to dump all those changes and return the VM to its original state at the top of the snapshot tree.

For more information, related to. avhd file; refer to the below mentioned link.

https://blogs.msdn.microsoft.com/charles_sterling/2008/08/06/what-are-all-these-avhd-files-and-how-to-magically-make-them-go-away-hyper-v/  

Regards,

Sumanth BM

Thursday, May 19, 2016 5:15 PM

Thank you Sumanth,

I am wondering if all .avhd files are Snapshots and if I need to merge them with .vhd file.

If you have any link to help with that, I appreciate it.

Monday, May 30, 2016 12:49 PM

Hi Esmail,

Sorry for the delay in response, If the issue still occurs; Please try the below mentioned suggestions.

You attach the VHD to the VM and then mount the disk. You have to update the fstab in order for the VHD to be mounted again if the VM is rebooted.

Also, You can refer to the below mentioned links.

https://azure.microsoft.com/en-in/documentation/articles/virtual-machines-windows-classic-attach-disk/

http://social.technet.microsoft.com/wiki/contents/articles/6257.manually-merge-avhd-to-vhd-in-hyper-v.aspx

For more information.Click here

Regards,

Sumanth BM