File extension
.vhdx
Hyper-V Virtual Hard Disk v2
.vhdx files are Hyper-V Virtual Hard Disk v2 images: a Microsoft virtual disk format supporting disks up to 64 TB with a metadata log for crash resilience.
Known meanings
Formats and reference material for .vhdx
Hyper-V Virtual Hard Disk v2
Microsoft virtual disk image format succeeding VHD, with larger capacity and power-failure protection
Details
Format notes
VHDX
VHDX is the second-generation virtual hard disk format from Microsoft, introduced with Windows Server 2012 and Hyper-V. It replaces the older VHD format for most uses and is the default disk format for Hyper-V virtual machines. Windows can also mount VHDX files directly as drives.
Structure
A VHDX file starts with the ASCII signature vhdxfile. It contains a header
section with redundant headers, a region table, a metadata region, a block
allocation table (BAT), and a log. The log records metadata updates so that the
file can be recovered consistently after a power failure or crash. Improvements
over VHD include a maximum virtual disk size of 64 TB, support for 4 KB logical
sector sizes, larger block sizes, and alignment better suited to modern storage.
As with VHD, there are fixed, dynamic and differencing variants.
Adoption And Tooling
VHDX is supported by Hyper-V, Windows disk management and PowerShell cmdlets such
as Convert-VHD and Resize-VHD. QEMU, VirtualBox and various libraries can read
it, and conversion tools can turn it into raw, qcow2 or VMDK images. Microsoft
publishes the format specification as part of its Open Specifications.
Preservation And Security Notes
Treat a VHDX like a whole disk: it can contain deleted data, credentials and malware. If a differencing disk is used, its parent file must be preserved together with it. Never mount images from untrusted sources on a production system.
Further Reading
- VHDX Format Specification (MS-VHDX):
https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-vhdx/