The short answer
- VHDX is a Microsoft virtual-disk format that stores a disk abstraction in one file, with a maximum virtual-disk capacity of 64 TB.
- On Windows 10, Windows 11, or a supported Windows Server version, open Disk Management and use its attach-VHD action to select the VHDX file. After attachment, the image appears as a local disk; existing partitions and file-system volumes normally receive drive letters. Use DiskPart's readonly attachment option for an untrusted image.
- A VHDX is not a script, but it can contain a complete disk and arbitrary files that become visible to the host when attached. Read-only attachment prevents host writes to the image; it does not establish that contained files are safe. Use an updated, bounds-checking implementation, and verify the header signature instead of trusting the extension alone.
VHDX file: identify, open, mount, and convert
Microsoft introduced Virtual Hard Disk v2 with Windows Server 2012, primarily for Hyper-V virtual machines. It supports fixed, dynamically expanding, and differencing disks, plus metadata journaling, custom metadata, larger blocks, 4 KB logical sectors, and space-reclamation notifications.
Convert-VHD can copy a source VHD or VHDX into a new target file while changing format, disk type, or block size. The disk must be offline and detached when conversion starts. Converting VHDX to legacy VHD may sacrifice equivalent support for VHDX-only capacity, journaling, 4 KB logical sectors, and space reclamation, so check target capacity, sector, and platform requirements first.
How to open it
On Windows 10, Windows 11, or a supported Windows Server version, open Disk Management and use its attach-VHD action to select the VHDX file. After attachment, the image appears as a local disk; existing partitions and file-system volumes normally receive drive letters. Use DiskPart's readonly attachment option for an untrusted image.
On Windows 10, Windows 11, or a supported Windows Server version, open Disk Management and use its attach-VHD action to select the VHDX file. After attachment, the image appears as a local disk; existing partitions and file-system volumes normally receive drive letters. Use DiskPart's readonly attachment option for an untrusted image.
Convert-VHD can copy a source VHD or VHDX into a new target file while changing format, disk type, or block size. The disk must be offline and detached when conversion starts. Converting VHDX to legacy VHD may sacrifice equivalent support for VHDX-only capacity, journaling, 4 KB logical sectors, and space reclamation, so check target capacity, sector, and platform requirements first.
File safety
A VHDX is not a script, but it can contain a complete disk and arbitrary files that become visible to the host when attached. Read-only attachment prevents host writes to the image; it does not establish that contained files are safe. Use an updated, bounds-checking implementation, and verify the header signature instead of trusting the extension alone.
An unknown sender, a name ending in two extensions, or contents that do not match the extension — check before you open it.
Converting it
Convert-VHD can copy a source VHD or VHDX into a new target file while changing format, disk type, or block size. The disk must be offline and detached when conversion starts. Converting VHDX to legacy VHD may sacrifice equivalent support for VHDX-only capacity, journaling, 4 KB logical sectors, and space reclamation, so check target capacity, sector, and platform requirements first.
Convert a copy, never the original, then compare quality, metadata, and layout against what you started with.
Common questions
What is a VHDX file format, and what is it used for?
VHDX is Microsoft's Virtual Hard Disk v2 format. It provides a virtual-disk abstraction in one file and is used primarily by Hyper-V virtual machines.
How do I open a VHDX file?
On a supported Windows system, attach the file through Disk Management. It then appears as a local disk, and existing volumes normally receive drive letters.
How do I mount a VHDX in Windows 11 with Disk Management?
Open Disk Management, choose its attach-VHD action, and select the VHDX. Detach it through Disk Management when finished.
Why will a VHDX file not open even though it has a .vhdx extension?
The extension is insufficient. A loader must verify that offset 0 contains 76 68 64 78 66 69 6C 65, the ASCII/UTF-8 text “vhdxfile”; failure indicates that the file is not valid for loading or is damaged.
Should I use VHDX or legacy VHD for a Hyper-V disk?
VHD may be needed for earlier Hyper-V compatibility. VHDX supports up to 64 TB and adds metadata journaling, 4 KB logical sectors, and space-reclamation capabilities that VHD cannot preserve equivalently.
How do I convert VHDX to VHD offline with Convert-VHD?
Detach the virtual disk and keep it offline, then use Convert-VHD to copy its data to a new VHD target. Confirm capacity, sector, and destination-platform requirements before conversion.
Is an emailed or downloaded VHDX file safe to mount?
Do not assume so. It may contain arbitrary files, and attachment exposes its volumes to the host. Prefer DiskPart's readonly option and use an updated implementation; read-only mode protects the image from host writes but does not make its contents safe.
What is the VHDX file vhdxfile signature?
The File Type Identifier begins at offset 0 and contains the required “vhdxfile” signature. After a VHDX is created, its first 64 KB must not be overwritten.
Can I inspect a VHDX without uploading it to a server?
Yes. Disk Management and DiskPart attach the image locally on supported Windows systems. Use readonly attachment when the image is untrusted.
Can a VHDX virtual disk be larger than 64 TB?
No. The maximum virtual-disk capacity defined for VHDX is 64 TB.
Related formats
Sources
[MS-VHDX]: Virtual Hard Disk v2 (VHDX) File Format · Microsoft Open Specifications
[MS-VHDX] 2.2.1 File Type Identifier · Microsoft Open Specifications
Hyper-V storage I/O performance · Microsoft Learn
Manage Virtual Hard Disks (VHDs) · Microsoft Learn
Convert-VHD · Microsoft PowerShell documentation
attach vdisk · Microsoft Windows command documentation