BackupHyperVDisks

A PowerShell script that creates backups of stopped Hyper-V virtual machines using timestamp-based change detection with three different backup methods.

What it does

The script automatically backs up Hyper-V VMs by:

• Backing up stopped VMs using one of three configurable methods
• Only backing up VMs when their disk files have changed since the last backup
• Keeping a configurable number of recent backups per VM
• Cleaning up old backups automatically
• Skipping VMs that are not turned off

How it works

The script checks the LastWriteTime of each VM's VHD/VHDX files against the timestamp of the most recent backup folder. If any disk file is newer than the last backup, it creates a new backup using the configured method.

Backup Methods

1. Export-VM ($BackupMethod = "Export")

   • Creates complete VM backups including configuration and disks
   • Uses Hyper-V's built-in Export-VM command
   • Stored in BackupRoot\<VMName>\<timestamp>\Export\
   • Largest backup size but includes everything needed to restore the VM

2. !!! NOT TESTED !!! Robocopy ($BackupMethod = "Robocopy")

   • Copies only VHD/VHDX disk files
   • Uses robocopy for fast, reliable file copying
   • Stored in BackupRoot\<VMName>\<timestamp>\Disks\
   • Faster than Export-VM, smaller backup size, but no VM configuration

3. 7-zip ($BackupMethod = "7zip")

   • Compresses VHD/VHDX disk files into a single archive
   • Uses fastest compression setting with multithreading
   • Stored as BackupRoot\<VMName>\<timestamp>\<VMName>.7z
   • Smallest backup size, moderate speed, no VM configuration

Backups are stored in folders named with timestamps (yyyy-MM-dd_HH-mm-ss format) under BackupRoot\<VMName>\.

Requirements

• Windows with Hyper-V role installed
• PowerShell with Hyper-V module
• Administrator privileges
• Sufficient disk space at the backup destination
• 7-zip command line utility (only if using 7-zip backup method)

Configuration

Edit the variables at the top of the script:

$BackupRoot = "T:\Arhiv\VM"                     # Backup destination path
$MaxBackupsPerVM = 2                            # Number of backups to keep per VM
$TimestampFormat = "yyyy-MM-dd_HH-mm-ss"        # Folder naming format
$BackupMethod = "Export"                        # "Export", "Robocopy", or "7zip"
$RobocopyFlags = "/E /Z /B /MT:8 /R:3 /W:10"    # Robocopy parameters
$SevenZipPath = "7z"                            # Path to 7z.exe
$SevenZipFlags = "a -t7z -mx=1 -mmt=4 -ms=off"  # 7-zip parameters

Usage

1. Stop the VMs you want to back up
2. Run PowerShell as Administrator
3. Execute the script:

   .\BackupHyperVDisks.ps1

You can of course create a desktop shortcut to run the script. In this case, the PowerShell switch -NoExit is recommended, so you can inspect the script output when it's done.

For the Export-VM and Robocopy methods, you might want to enable NTFS compression on the backup folder to save space. The 7-zip method already provides compression.

Performance Tips

• Antivirus exclusions: Real-time antivirus scanning can significantly slow down backup operations. Consider adding exclusions for:

  • The backup destination folder ($BackupRoot)
  • The VM disk files being backed up
  • The PowerShell script itself

• 7-zip optimization: The default 7-zip flags use -ms=off (non-solid mode) which significantly speeds up writing to spinning drives. Additional optimizations:

  • For fast CPUs with slow target drives, consider higher compression (-mx=3 to -mx=5) for better space efficiency
  • Adjust thread count (-mmt=4) based on your CPU cores

Notes

• Only stopped VMs are backed up
• Running or paused VMs are listed but skipped
• The script uses atomic operations (temporary folders) to prevent incomplete backups
• Failed backups are automatically cleaned up
• Change detection is based on disk file timestamps, not VM configuration changes
• Export-VM method creates complete backups that can be imported directly
• Robocopy and 7-zip methods only backup disk files - VM configuration must be recreated manually
• 7-zip method requires 7z.exe to be installed and accessible in PATH or specify full path in $SevenZipPath