VHD vs. VHDX: Virtual disk format differences

Microsoft's new virtual hard disk format, VHDX, has some important advantages over the legacy VHD format, as this VHD vs. VHDX comparison describes.

The release of Windows Server 2012 brought many new virtualization improvements, but one that caught the eye of many IT pros was the introduction of the VHDX file format. Windows Server 2012 supports the new format but also lets Hyper-V administrators use the legacy VHD format. With two virtual hard disk formats to choose from, let's take a minute to talk about VHD vs. VHDX.

A look at VHD vs. VHDX
One of the biggest advantages of VHDX compared with the legacy VHD format is virtual disk storage capacity. Before Windows Server 2012, Hyper-V virtual hard disks had a 2 TB limit. VHDX files have a 64 TB capacity. The advantages of VHDX aren't limited to improved capacity, however; VHDX files were designed to work with today's modern hardware and have a 4 KB logical sector size that improves performance compared with VHD files.

The VHDX format also provides protection against file corruption related to power failures by continuously keeping track of updates in the metadata, a feature not available with the VHD format. Larger block sizes for dynamic and differencing disks, as well as the ability to store custom metadata, also give the new format the edge in the VHD vs. VHDX comparison.

Converting to VHDX
First, it's important to note that while you can create and use both formats with Windows Server 2012, VHDX files are not compatible with Windows Server 2008. Microsoft recommends that most Windows Server 2012 users upgrade VHD files to VHDX to take advantage of these benefits. However, if you expect you might want to move a VM to a previous version of Windows Server, it could be easier to keep your VHD files. Users can convert VHD files to VHDX through the Edit Virtual Hard Disk Wizard found in Hyper-V.

This was first published in January 2013

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