VHD and VHDX are two commonly used virtual machine disk image file formats used to virtualize a computer’s hard drive. Primarily used with Microsoft’s Hyper-V virtualization platform, the two disk image formats sound similar but have some key differences you should be aware of before firing up your virtual machine.
What Is VHD?
First off, we’ll begin explaining the older of these two formats, VHD.
VHD stands forVirtual Hard Driveand is a type of file format used to represent a virtual hard disk drive. It is essentially a disk image file format that comprises the entire contents of a virtualized hard drive. VHD files are mainly utilized in virtualization environments, where they simulate the functionality of physical hard drives within virtual machines. VHD files can store the operating system, applications, and data, making them an integral part of virtualization technologies, and these VMs use and recognize these files as actual hardware drives—you can mount them, unmount them, and store other files on them.
It’s a format that was first created by a company called Connectix back in 2003, with the company making the file’s specification available to use by third parties since 2005. The format was mainly used by Microsoft for its Virtual PC and, then, onits Hyper-V virtualization platform, but it’s also used bythird-party virtualization programssuch as Virtualbox and VMware.
What Is VHDX?
VHDX, on the other hand, is basically just a newer version of VHD. Microsoft decided to release a successor of sorts to VHD that could fix some of VHD’s shortcomings and issues, as well as make it more flexible to use. Microsoft currently uses VHDX files for Hyper-V, but unlike VHD, VHDX is not widely supported by third-party virtualization software. At the time of writing, Virtualbox and VMware instruct users to convert their VHDX files to VHD if they want to use them on their virtual machines.
VHDX was first deployed in 2012 with the launch of Windows 8 and Windows Server 2012 and has since become the go-to format for all Microsoft virtualization.
How Do VHD and VHDX Differ?
There are some differences between VHD and VHDX. The most immediately noticeable one is the maximum drive size. Whereas VHD allows for up to 2TB drives, VHDX brings the bar up to 64TB. While you’ll unlikely need that much unless you’re a business user, it might help if you want more than 2TB in your virtual machine.
There are also several other differences. VHDX files support larger block sizes and better performance, especially with modern hardware and applications with advanced storage features. VHDX files are also more resilient, including features like protection against data corruption during power failures and a “log” mechanism to keep track of changes before they are committed to the file.
Since it’s an enhanced version of VHD, there are really no downsides to VHDX. However, the one downside we would mention is that you can only really use VHDX files on Hyper-V, with most third-party virtualization software not supporting them as yet.
VHD vs. VHDX: Which One is Better?
If you’re going to use Hyper-V, then VHDX is a no-brainer. It’s the newer format, as well as the most flexible one and the one that’s most secure and most feature-rich. But the fact that it’s barely compatible with third-party virtualization software means that you’re limited to just Hyper-V with that format.
On the other hand, VHD is an older format. Still, it’s also a widely documented one and one that’s used by basically all virtualization software out there, so if you have a VHD file, you can use it on any virtual machine out there.
The main differences between VHD and VHDX come down to what you value most: using a newer specification or keeping your files in a specification that can be used in third-party software. It’s really up to you. We should also mention that in addition to VHD and VHDX, there are also other formats, including VMware’s VMDK files and VirtualBox’s VDI files, so it’s a matter of what works better for you.
