How to reduce size of docker data volume in Docker Desktop for Windows v2

Docker Desktop for Windows v2, which uses WSL2, stores all image and container files in a separate virtual volume (vhdx). This virtual hard disk file can automatically grow when it needs more space (to a certain limit). Unfortunately, if you reclaim some space, i.e. by removing unused images, vhdx doesn't shrink automatically. Luckily, you can reduce its size manually by calling this command in PowerShell (as Administrator):

Optimize-VHD -Path c:\path\to\data.vhdx -Mode Full

The docker-desktop-data vhdx is normally in this location:

%LOCALAPPDATA%\Docker\wsl\data\ext4.vhdx

Comments

[Mateusz]

If you get error:

Optimize-VHD : Hyper-V encountered an error trying to access an object on computer 'K48689' because the object was not
found. The object might have been deleted. Verify that the Virtual Machine Management service on the computer is runnin
g.

Run command:

mofcomp %SYSTEMROOT%\System32\WindowsVirtualization.V2.mof

[Barbakadze]

I get an error: Optimize-VHD : 'Local\Docker\data\ext4.vhdx4' is not an existing virtual hard disk file.
Although vhdx4 file is right there.

[Musin Vitaly]

For me help wsl --shutdown

[John Bevan]

Thanks for sharing this.
For anyone who doesn't have this cmdlet / the Hyper-V module, you can add it via Add/Remove Programs, Windows Features, per: superuser.com/a/1307442/156700

[István Földházi]

One-liner:

Optimize-VHD -Path $Env:LOCALAPPDATA\Docker\wsl\data\ext4.vhdx -Mode Full

If the above command fails with "The process cannot access the file because it is being used by another process.", stop services and tasks using that file:

net stop com.docker.service
taskkill /IM "docker.exe" /F
taskkill /IM "Docker Desktop.exe" /F
wsl --shutdown

[Little Red Riding Hood]

Thanks, it was really useful for me!

[Dan Manastireanu]

Thanks, reclaimed 14.5 GB of my ssd :D

[Zvi Cahana]

Thanks for this useful info!

Note that both Docker Desktop and WSL2 need to be stopped before running this, otherwise an error will occur:

Optimize-VHD : Failed to compact the virtual disk.
The system failed to compact 'C:\Users\ZVICAHANA\AppData\Local\Docker\wsl\data\ext4.vhdx'.
Failed to compact the virtual disk.
The system failed to compact 'C:\Users\ZVICAHANA\AppData\Local\Docker\wsl\data\ext4.vhdx': The process cannot access
the file because it is being used by another process. (0x80070020).
At line:1 char:1
+ Optimize-VHD -Path C:\Users\ZVICAHANA\AppData\Local\Docker\wsl\data\e ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ResourceBusy: (:) [Optimize-VHD], VirtualizationException
    + FullyQualifiedErrorId : ObjectInUse,Microsoft.Vhd.PowerShell.Cmdlets.OptimizeVhd```

To stop Docker Desktop, right click its tray icon and choose "Quit Docker Desktop".
To stop WSL2, open a command prompt and run wsl --shutdown.