Shrink Docker WSL2 vhdx Disk Size

When using Docker Desktop with the WSL2 backend on Windows, the dynamic VHD disk (docker_data.vhdx) automatically grows as data is dumped. However, when you delete unused images or containers inside Docker, the host file does not shrink automatically. It is a common occurrence to see the .vhdx file bloated up to massive sizes like 130GB, even though the actual Docker usage is only a fraction of that.

Core Solution: Directly Compact the VHDX

The most effective way to reclaim your host machine disk space is to use the Windows diskpart tool to manually compact the bloated virtual disk file. Simply running docker system prune is not enough to shrink the container file on the host side.

1. Clean up unused Docker data

Before compacting the disk, it’s highly recommended to clean up any unwanted images, containers, and build caches to maximize the space savings:

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# Check space usage
docker system df

# Remove all dangling resources, stopped containers, and unused volumes
docker system prune -a --volumes

2. Shut down WSL

Fully exit Docker Desktop. To safely release the VHDX file from its mounted state, run the following in an Administrator PowerShell:

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wsl --shutdown

3. Compact with Diskpart

While still in your Administrator PowerShell, open diskpart and run the following commands sequentially (replace the file path with your actual setup if different):

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

# Attach as read-only
attach vdisk readonly

# Compact the virtual disk (This is the core action and might take some time)
compact vdisk

# Detach and exit
detach vdisk
exit

Once completed, the massive .vhdx file size will dramatically decrease, matching your actual internal Docker filesystem usage again! You can now restart Docker Desktop and resume your work.