Hyper-V R2 and storage location for snapshot differencing disks

I recently worked with a Hyper-V case, where the differencing disk files (.AVHD) for snapshots didn`t appear at the expected location. As we figured this out, I would like to share the experience we had regarding this.

A virtual machine has two important directories, the VM root and the snapshot root. The VM root is where we store the virtual machine configuration file (XML) and the saved state files (.BIN and .VSV). The snapshot root is where we store the config and saved state files for each snapshot of a virtual machine.

Virtual hard disks (.VHDs) are stored where ever the user specifies when creating the virtual machine (or when creating a new virtual hard disk).

What has changed in Hyper-V between Windows Server 2008 and Windows Server 2008 R2 is the placement of .AVHD files (these are the differencing disks created for each snapshot). In Windows Server 2008 the .AVHD is always created in the snapshot root location, which by default are located at C:\ProgramData\Microsoft\Windows\Hyper-V\Snapshots. This caused a lot of people problems – as they would run out of space on the partition where the snapshot root folder was. In Windows Server 2008 R2 the .AVHD file is always created in the same location as its parent virtual hard disk.

This means that with R2 .AVHD files will always appear beside their respective .VHD files. The one exception to this is if you bring across a Windows Server 2008 virtual machine with .AVHDs already in the snapshot root. In this case new .AVHDs will be created beside their parent .AVHDs (in the snapshot root).

 

Microsoft TechNet Resources

Hyper-V in Windows Server 2008
Hyper-V R2 in Windows Server 2008 R2