Reclaiming Disk Space from Docker's Massive VHDX File on Windows

The post says Docker Desktop on Windows uses WSL 2, and that this creates a dynamic VHDX file that stores images, containers, and volumes. Because the file expands as Docker use grows but does not shrink on its own, free space on the C: drive can disappear even after items are deleted.

Reading notes

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• WSL 2 is described as Microsoft’s lightweight virtual machine tech that runs a real Linux kernel on Windows.
• Docker Desktop uses WSL 2 by default for better performance, including Linux syscalls, faster file I/O, and container isolation.
• The Docker ext4.vhdx file, usually under %LOCALAPPDATA%\Docker\wsl\disk\docker_data.vhdx, acts as the Linux filesystem for WSL 2.
• The VHDX grows when images, containers, and caches are added, but it does not automatically shrink after they are removed.
• The post recommends running Docker Desktop, opening PowerShell as admin, and using docker system prune -a –volumes to remove unused images, stopped containers, networks, and volumes.
• It says pruning can reclaim space immediately, and docker system df can be used to check usage.
• It also says pruning alone does not shrink the VHDX, so the disk must be compacted manually with Optimize-VHD -Path “$env:LOCALAPPDATA\Docker\wsl\disk\docker_data.vhdx” -Mode Full after wsl –shutdown.
• Before optimizing, the post recommends updating to WSL 2.5+ with wsl –update and checking wsl –version.
• It suggests setting a WSL disk limit in %USERPROFILE%.wslconfig, including memory, swap, and diskSize settings.
• When the VHDX reaches 100GB, Docker builds can fail with no space left on device, and the post says to fix that by pruning Docker and optimizing the VHDX.
• The post ends with a PowerShell script that checks Docker, shows disk usage before pruning, optionally prunes unused resources, shuts down WSL, finds the VHDX path, and runs Optimize-VHD.