The Repair-VHD cmdlet is a built-in PowerShell utility included in the Hyper-V module on Windows systems. It’s specifically designed to scan, diagnose, and repair corrupted or inconsistent virtual hard disk (VHD/VHDX) files. These virtual disks are essential components in virtual machine environments, storing operating systems, applications, and user data.
When a VHD becomes damaged, it can prevent virtual machines from starting or accessing their data. The Repair-VHD cmdlet provides a safe and efficient way to attempt recovery and get the virtual disk back into a usable state.
Purpose of this article:
In this guide, we’ll explore common VHD errors that Repair-VHD can fix, explain how it works, and share best practices for using it safely. Quick recovery is vital—every minute of downtime can lead to lost productivity, data loss, and costly delays.
Getting to Know VHD and VHDX Virtual Disks
VHD (Virtual Hard Disk) and VHDX are file-based virtual disks used in Hyper-V virtual environments. They act like physical hard drives to a virtual machine, storing its operating system, software, and user files.
- VHD – the original format, with a size limit of 2 TB.
- VHDX – the newer format, supporting up to 64 TB, more resilient to corruption, and offering better performance on modern storage.
Even though VHD and VHDX are stable formats, corruption can occur due to various reasons:
- Improper shutdowns or power failures while the VM is running.
- Physical disk errors or bad sectors on the host machine.
- Interrupted export/import operations of virtual machines.
- Hyper-V snapshot chain issues from failed or incomplete merges.
- Malware or aggressive antivirus interference that damages disk data.
Understanding these causes can help prevent issues and make it clear when to use Repair-VHD.
Overview of the Repair-VHD Cmdlet
Location and availability
Repair-VHD is part of the Hyper-V PowerShell module. You can use it on Windows systems where the Hyper-V role is installed. It works on both VHD and VHDX files.
Basic syntax
The basic command structure looks like this:
Repair-VHD -Path <path_to_vhd> -Mode <mode>
- Path – The full path to the VHD or VHDX file.
- Mode – The type of operation to perform.
Repair modes explained
There are two main modes:
- Scan – Performs a read-only scan to detect errors without making changes.
- Restore – Attempts to fix detected issues and recover readable data.
Tip: Always run Scan mode first to assess the damage safely before attempting Restore.
Common Errors Fixed by Repair-VHD
The Repair-VHD utility can address several common issues that often prevent virtual disks from mounting or functioning correctly. One of the most frequent problems is a corrupted VHD footer or header, which can occur after sudden power loss or interrupted writes and prevents the disk from being recognized. The tool can validate and reconstruct this structural metadata. It also helps fix broken differencing disk chains, which happen when a parent VHD is moved, deleted, or becomes corrupted, causing “parent not found” errors. Another common issue is an invalid Block Allocation Table (BAT), often caused by file system corruption or incomplete merge operations; Repair-VHD can analyze and rebuild this table to restore disk functionality.
In addition, Repair-VHD can resolve snapshot merge failures that arise from unexpected shutdowns during checkpoint deletion, ensuring all data is properly consolidated. It can correct inconsistent size metadata created by abrupt crashes during disk resizing, allowing the VM to start again. Lastly, when a disk shows an “Invalid VHD format” error due to a missing footer signature, the tool can reconstruct the signature based on the existing data. By handling these issues, Repair-VHD provides a reliable way to restore access to corrupted virtual disks without requiring full data recovery tools.
Steps to Run Repair-VHD Safely
Precautions before using Repair-VHD
- Work on a copy of the disk instead of the original file to avoid making corruption worse.
- Ensure sufficient free space on the host drive for temporary files and recovery data.
- Back up VM configuration files (like .vmcx, .vmrs, or snapshot files) before starting.
Example commands
Scan mode:
Repair-VHD -Path “C:\VMs\Disk1.vhdx” -Mode Scan
Restore mode:
Repair-VHD -Path “C:\VMs\Disk1.vhdx” -Mode Restore
Always start with Scan mode to understand the severity of the issue before attempting to fix it.
When Repair-VHD Cannot Help
While Repair-VHD is highly effective for fixing logical and structural corruption within VHD and VHDX files, it does have limitations. It cannot repair issues caused by physical disk failures or severe sector damage on the underlying storage device. If the host drive itself is malfunctioning, the data within the virtual disk may be inaccessible until the physical problems are addressed. Likewise, repair-vhd cannot help if the VHD file has been deleted from the system and has not yet been recovered.
In such cases, alternative approaches are necessary. You can use specialized VHD recovery tools like DiskInternals, R-Studio, or UFS Explorer to extract data from damaged or lost VHD files. If the file has been deleted, first recover the raw VHD from the host disk using general data recovery software, and only then run Repair-VHD on the recovered copy to fix any internal corruption. This two-step approach ensures the virtual disk is physically retrievable before attempting logical repairs.
Post-Repair Best Practices
After running Repair-VHD successfully:
- Verify VHD integrity by mounting it in Hyper-V or Windows Disk Management.
- Run chkdsk inside the guest OS to check and fix any file system errors.
- Create fresh backups of the repaired virtual disk to avoid future data loss.
- Monitor the health of the host storage using SMART tools or monitoring software to prevent future corruption.
Conclusion
The Repair-VHD utility is a powerful built-in tool for resolving common VHD/VHDX errors, helping administrators quickly recover virtual disks and minimize downtime. By fixing issues like corrupted footers, broken differencing chains, and invalid metadata, it can bring virtual machines back online in minutes instead of hours.
However, prevention is still key: always back up virtual disks, handle snapshots carefully, and maintain healthy storage hardware. With proper precautions, Repair-VHD can serve as a valuable safety net when things go wrong.