VHD vs VHDX

Virtual hard disks typically use the .vhd extension. Windows Server 2012 introduces a new type of virtual hard disk that uses the .vhdx extension. Virtual hard disks with the .vhdx format have the following benefits over virtual hard disks that were used in Hyper-V on Windows Server 2008 and Windows Server 2008 R2:

• Virtual hard disks with the .vhdx format can be as large as 64 terabyte (TB), whereas virtual hard disks with the .vhd format are limited to 2 TB.
  
• Virtual hard disks with the .vhdx format are less likely to become corrupt if the virtualization server suffers an unexpected power outage.
  
• The .vhdx format supports better alignment when deployed to a large sector disk.
  
• Virtual hard disks with the .vhdx format can hold larger dynamic and differencing virtual hard disks. This provides for better performance from the dynamic and differencing virtual hard disks.

You can convert a virtual hard disk with the .vhd format to the .vhdx format by using the Edit Virtual Hard Disk Wizard. You might want to do this if you have upgraded a Windows Server 2008 or Windows Server 2008 R2 virtualization server to Windows Server 2012 or Windows Server 2012 R2. You can also convert a virtual hard disk with the .vhdx format to the .vhd format.