Shrink Docker WSL2 vhdx Disk Size

Can also be used to clean up files for regular WSL distributions

When running Docker Desktop with the WSL2 backend on Windows, due to the nature of dynamic VHD disks (docker_data.vhdx), the host machine’s disk space is not automatically released even if we delete a large number of useless images and containers in Docker. Often, the actual container usage is only around 20 GB, but the host’s .vhdx file can swell to 130 GB, or even fill up the C drive.

Core Solution: Directly Compress the VHDX

The most fundamental way to solve this problem is to shut down first, and then use Windows’ diskpart tool to manually compress the bloated virtual disk file. Simply running docker system prune is not enough; you must actually compress the VHD file back.

1. Clean Up Internal Docker Junk (Optional)

Before compressing the disk, it’s best to completely discard unnecessary images and zombie containers to free up space inside the container:

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# View space usage
docker system df

# Clean up all dangling resources, stopped containers, and unused cache volumes
docker system prune -a --volumes

2. Shut Down WSL

After cleaning up, exit Docker Desktop completely. To detach the WSL VHDX from its mounted state, run the following in an Administrator PowerShell:

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wsl --shutdown

3. Compress the Disk

Continue by typing diskpart in the Administrator PowerShell to enter the interactive interface, then execute the following commands in order (replace with the actual path of your local .vhdx):

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# Select your vhdx file
select vdisk file="C:\Users\mioyi\AppData\Local\Docker\wsl\disk\docker_data.vhdx"

# Mount in read-only mode
attach vdisk readonly

# Compress the virtual disk (core operation, this step may take some time)
compact vdisk

# Detach and exit diskpart
detach vdisk
exit

After execution, you will find that the size of the .vhdx file has significantly decreased, close to the actual upper-layer read/write usage of your current Docker system. You can then reopen Docker Desktop and use it normally.

Appendix: One-Click Cleanup Script

Usage: .\Compact-Vhdx.ps1 C:\Users\mioyi\AppData\Local\Docker\wsl\disk\docker_data.vhdx

Compact-Vhdx.ps1

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[CmdletBinding()]
param(
    [Parameter(Mandatory = $true, Position = 0)]
    [ValidateNotNullOrEmpty()]
    [string]$VhdxPath
)

Set-StrictMode -Version Latest
$ErrorActionPreference = 'Stop'

function Test-IsAdministrator {
    $identity = [Security.Principal.WindowsIdentity]::GetCurrent()
    $principal = [Security.Principal.WindowsPrincipal]::new($identity)
    return $principal.IsInRole([Security.Principal.WindowsBuiltInRole]::Administrator)
}

try {
    $ResolvedVhdxPath = (Resolve-Path -LiteralPath $VhdxPath).ProviderPath
} catch {
    Write-Error "VHDX file not found: $VhdxPath"
    exit 1
}

if (-not (Test-IsAdministrator)) {
    if (-not $PSCommandPath) {
        Write-Error 'This script must be saved as a .ps1 file before it can self-elevate.'
        exit 1
    }

    $powerShellExe = (Get-Process -Id $PID).Path
    $arguments = @(
        '-NoProfile'
        '-ExecutionPolicy'
        'Bypass'
        '-File'
        "`"$PSCommandPath`""
        '-VhdxPath'
        "`"$ResolvedVhdxPath`""
    )

    $process = Start-Process -FilePath $powerShellExe -ArgumentList $arguments -Verb RunAs -Wait -PassThru
    exit $process.ExitCode
}

$diskpartScript = [IO.Path]::GetTempFileName()

try {
    $commands = @(
        "select vdisk file=`"$ResolvedVhdxPath`""
        'attach vdisk readonly'
        'compact vdisk'
        'detach vdisk'
        'exit'
    )

    Set-Content -LiteralPath $diskpartScript -Value $commands -Encoding ASCII

    Write-Host "Running diskpart compact for: $ResolvedVhdxPath"
    & diskpart.exe /s $diskpartScript

    if ($LASTEXITCODE -ne 0) {
        throw "diskpart failed with exit code $LASTEXITCODE."
    }
} finally {
    if (Test-Path -LiteralPath $diskpartScript) {
        Remove-Item -LiteralPath $diskpartScript -Force
    }
}

Last updated on June 4, 2026 15:15

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