Can Windows open VHD files?

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Can Windows open VHD files

VHD (Virtual Hard Disk) files are virtual hard drives used by virtualization software like VirtualBox and Microsoft Hyper-V. They allow you to create virtual machines that act like real computers, complete with their own virtual hard drives. VHD files contain the file system and data for these virtual drives.

Windows has native support for working with VHD files, allowing you to mount them and access their contents like a real drive. So the quick answer is yes, Windows can open VHD files without any additional software.

What are VHD files?

VHD stands for Virtual Hard Disk. A VHD file represents a virtual hard drive that can be connected to a virtual machine created in virtualization software like VirtualBox, VMware, Hyper-V, Parallels, etc.

Just like a real computer has a physical hard drive where the operating system, applications and data are stored, a virtual machine has a virtual hard drive stored in a VHD file. This allows virtual machines to act just like a real independent computer with its own dedicated storage.

Some key characteristics of VHD files are:

  • They can contain entire operating system installations and applications.
  • Common VHD formats are VHDX and VHD for Microsoft and VMDK for VMware.
  • VHD files are like normal disk image files and behave like physical disks when mounted.
  • Standard VHD sizes range from 32 MB to 2 TB.
  • VHDs can be dynamically expanding or of fixed size.

VHD File Formats

There are a few common file formats used for virtual hard disks:

  • VHDX – An enhanced version of VHD used by Hyper-V on newer Windows versions. Supports larger drive sizes up to 64 TB.
  • VHD – The original VHD format used by Virtual PC and the first versions of Hyper-V. Limited to 2 TB in size.
  • VMDK – Used by VMware virtualization products. Available in different variants like monolithic or split VMDKs.

Mounting VHD files on Windows

Windows provides native support for mounting VHD files without needing any other software. Mounting attaches the VHD as a disk drive so you can access the contents just like a real drive.

Here are the steps to mount a VHD file on Windows:

  1. Open Disk Management (type diskmgmt.msc in the Start menu search).
  2. Click Action > Attach VHD from the menu.
  3. Browse and select the VHD file you want to mount.
  4. The VHD will show up in the Disk Management window as an additional disk drive.
  5. The new drive should get an assigned drive letter and can be accessed in File Explorer.
  6. To detach the VHD when done, right click and select Detach VHD.

Mounting VHDs this way provides read-write access. You can view, edit, copy, delete files on the mounted VHD drive just like a physical disk.

Mounting VHDs via DiskPart

Another option is using the command line tool DiskPart to mount VHD files:

  1. Open an elevated Command Prompt or PowerShell prompt.
  2. Type diskpart and press Enter.
  3. Type attach vhd C:\path\to\file.vhd and press Enter.
  4. The VHD will get mounted as a disk and receive a drive letter.
  5. Type exit when done to close DiskPart.

This achieves the same result of mounting the VHD via the GUI Disk Management utility.

Opening VHD files on Windows

Once mounted on Windows, there are a few ways to open and access the contents of a VHD file:

  • File Explorer – Use Windows File Explorer to browse the mounted VHD drive letter and open files.
  • Command line – Access the VHD using the assigned drive letter from Command Prompt or PowerShell.
  • Disk Management – View details on the mounted VHD in the Disk Management console.
  • Registry Editor – Mounted VHD drives appear under HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices in the Registry.

The main method is using File Explorer. The VHD will appear as another hard disk drive with its own drive letter. You can view files and folders, copy/move data out of the VHD, or open applications and executables stored in the VHD.

For example, if you have a VHD containing a Windows 10 system installation, you could mount it and access the Windows folder to view its contents. Or open the Program Files folder to launch apps installed in the VHD.

Read-only access to VHDs

By default, mounted VHD drives provide full read-write access. To mount a VHD in read-only mode:

  • Use DiskPart to mount with attach vhd C:\file.vhd readonly
  • Or check the Read-only option in Disk Management when attaching the VHD.

This is useful if you only need to access the VHD contents without making any changes.

Differences Between VHD and VHDX

VHD and VHDX are the main VHD formats used by Microsoft for Hyper-V virtual machines. Here are the key differences between them:

VHD VHDX
Older original VHD format used in Virtual PC and Hyper-V Newer enhanced format debuting in Windows Server 2012
Maximum size of 2 TB Supports up to 64 TB VHDX sizes
Does not support TRIM for unused blocks Supports TRIM and is more efficient
Restricted to only Basic GPT partitioning style Permits GUID Partition Table (GPT) partitioning

In summary, VHDX is an improved version of VHD and has replaced VHD as the default format in Hyper-V since Windows Server 2012 and Windows 8. But VHD remains supported for backwards compatibility.

Converting VHD to VHDX

Since VHDX has superseded VHD as the standard Hyper-V virtual disk format, Microsoft provides tools to convert existing VHD files to VHDX:

  • Hyper-V Manager – Right-click a VM and choose Convert to VHDX to convert its disk.
  • PowerShell – Use the Convert-VHD cmdlet to convert VHD to VHDX.
  • Disk Management – The Edit Disk feature can convert between VHD and VHDX.

However, there are some scenarios where a VHDX disk may need converted back to VHD format:

  • To attach it to an older VM that only supports the VHD format.
  • Converting a dynamic VHDX back to fixed VHD when the target platform does not support dynamic VHDs.

This VHDX to VHD conversion can be done via Hyper-V Manager or PowerShell’s Convert-VHD cmdlet as well.

VHD and VHDX Performance

In terms of performance, VHDX generally performs better than VHD. Here are some key differences:

  • Disk space efficiency – VHDX utilizes free space more efficiently thanks to its TRIM support. Unused blocks can be trimmed to reduce size.
  • Faster initial provisioning – A VHDX can be created almost instantly with just metadata first, then dynamically allocated on-demand later as needed by the VM.
  • No performance penalty for dynamic disks – VHD had slower performance for dynamic disks compared to fixed, but VHDX eliminates this penalty.
  • Better performance for large disks – VHD was limited to 2 TB while VHDX can scale to 64 TB with better performance at that size.

In most usage scenarios, VHDX performs the same or better than VHD. The main advantages are seen in dynamic disk allocation scenarios and very large disk sizes above 2 TB where VHD hit limits.

VHD File Compression

VHD and VHDX files can optionally be compressed to reduce their storage footprint. There are a couple ways to enable compression:

  • Hyper-V Manager – Check the option Enable compression on the Hard Drive settings of the VM.
  • PowerShell – Use the -Compressed parameter when creating a new VHD with New-VHD.

Compressing VHD files saves storage space at the cost of some extra processor overhead. The space savings depends on the compressibility of the data inside the VHD. Compression works for both static VHDs and dynamic VHDs.

Some key points about VHD compression:

  • Available on both VHD and VHDX file types.
  • Compression is done in real-time as data is written.
  • Typically results in 30-60% compression savings.
  • Works on Windows Server 2012 R2 or newer.
  • Requires processor support for LZX compression.

The compression savings versus performance tradeoff should be evaluated per workload. Enabling it can help conserve disk space if needed.

VHD File Security

VHD files can be protected with encryption to prevent unauthorized access. The two types of encryption available are:

  • BitLocker encryption – Full BitLocker volumes can be stored inside VHDX. Provides full-disk encryption with TPM for added security.
  • VHD encryption – The virtual disk itself can be encrypted using cert-based or password encryption. Supported on both VHD and VHDX types.

To use VHD encryption, it must be enabled at creation time either in Hyper-V Manager or via PowerShell. It encrypts all content written to the VHD using the specified certificate or password.

Some benefits of VHD encryption include:

  • Prevents offline attacks by requiring a key for access.
  • Data remains encrypted when exported, copied or moved.
  • Centralized encryption across multiple VMs using a common certificate.

Using encryption does add a performance hit, so it should only be used where the security benefits warrant it.

VHD Boot Issues

Booting from a VHD or VHDX is a common task in virtualization scenarios. For example, having a bootable VHDX containing Windows Server that you can boot Hyper-V VMs into.

Some potential issues that may prevent booting from VHD files include:

  • Invalid or missing bootloader – The VHD requires a valid system bootloader like BOOTMGR for Windows or GRUB for Linux.
  • Incorrect boot order – The VM firmware boot order needs to have the hard drive first to boot the VHD system disk.
  • Damaged VHD – File corruption or issues with the VHD itself could cause boot problems.
  • Unsupported mode – Trying to boot UEFI on older VHD formats instead of VHDX.
  • Missing boot partition – Dynamic VHD needs an active primary partition marked bootable to be bootable.

Troubleshooting steps for VHD boot issues include:

  • Check boot order in VM settings to ensure the hard drive is first.
  • Verify the VHD mode (BIOS or UEFI) matches the VM firmware.
  • Examine the VHD contents to confirm the bootloader is intact.
  • Enable boot debugging messages to see where the boot fails.
  • Test mounting the VHD on another OS to rule out file corruption.

Resolve any issues found and test booting again. Multiboot VHD files may require extra configuration like editing the boot menu.

Conclusion

VHD and VHDX files are designed to make virtual disks portable and easily manageable. Windows provides integrated support for mounting these disk images to access them like local drives.

VHDX improves upon VHD format limits and is generally recommended for new VMs. But VHD remains useful for compatibility with older systems.

With the ability to natively mount, open and boot VHD files, Windows provides flexible utility over these virtual disks for administration, content access and VM configuration.