Backup and restore WSL2 vhdx, avoid 256GB vhdx limit for docker desktop WSL2 native

setupDevEnv_workaroundWSL2vhdxLimit.md

Determine the expected size of the docker-desktop-data volume

• Get the base image size + additional + all docker volumes using docker system df
• Add raw uncompressed size for alpine (50MB), docker for your version of windows (700MB) and linux (80MB)

docker system df

Get info for the docker-desktop-data VHD

PS C:\Users\windows-admin\AppData\Local\Docker\wsl\data> Get-VHD -Path C:\Users\windows-admin\AppData\Local\Docker\wsl\data\ext4.vhdx


ComputerName            : WINDOWS10PRO
Path                    : C:\Users\windows-admin\AppData\Local\Docker\wsl\data\ext4.vhdx
VhdFormat               : VHDX
VhdType                 : Dynamic
FileSize                : 115GB <in bits>
Size                    : 256GB <in bits>
MinimumSize             :
LogicalSectorSize       : 512
PhysicalSectorSize      : 4096
BlockSize               : 1048576
ParentPath              :
DiskIdentifier          : A9****
FragmentationPercentage : 10
Alignment               : 1
Attached                : False
DiskNumber              :
IsPMEMCompatible        : False
AddressAbstractionType  : None
Number                  :

Quit docker in windows or via

taskkill /F /IM "Docker Desktop.exe"

Stop the docker service

net stop com.docker.service

Shutdown wsl

wsl -shutdown

Create a backup of the docker-data virtual disk. -VHDType Fixed will set the size to fixed volume the max size of the volume, the size attribute returned by Get-VHD. Ensure you have enough HD space to proceed, you can use an external volume but it will be slow.

# PS>
Convert-VHD -Path C:\Users\windows-admin\AppData\Local\Docker\wsl\data\ext4.vhdx -DestinationPath C:\Users\windows-admin\AppData\Local\Docker\wsl\data\ext4_fixed.vhdx -VHDType Fixed

Compact the fixed disk... the size will not change

# PS>
Optimize-VHD -Path C:\Users\windows-admin\AppData\Local\Docker\wsl\data\ext4_fixed.vhdx 

Delete the dynamic disk

# PS>
Remove-Item -Path C:\Users\windows-admin\AppData\Local\Docker\wsl\data\ext4.vhdx 

Rename the fixed disk to ext4.vhdx

# PS>
Rename-Item -Path C:\Users\windows-admin\AppData\Local\Docker\wsl\data\ext4_fixed.vhdx -NewName ext4.vhdx 

Export the docker-desktop the docker-desktop-data wsl distros. This should bring their .vhdx with them, and only bring the data from the in-use portion of the volume.

wsl --export docker-desktop E:\docker-desktop.tar # 57MB
wsl --export docker-desktop-data E:\docker-desktop-data.tar # 115GB

Optionally compress the distro tars to save filespace and backup elsewhere

bash # can also use 7zip via windows
tar cvzf docker-desktop.tar docker-desktop.tar.gz # 17MB
tar cvzf docker-desktop-data.tar docker-desktop-data.tar.gz # 13GB

Import the docker-desktop-data wsl distros

# wsl.exe --import <DistributionName> <InstallLocation> <FileName>
wsl --import docker-desktop-data %APPDATA%/Docker

Move in either direction to restore or backup the image. Convert to larger than 256GB fixed volume to surpass WSL limits.

Start docker

• Can use .exe it wil restart the docker service
• Docker pre-configured in wsl2 mode will also start wsl
• Pull or run a large amount of stuff without fearing the native wsl2 256GB limit that cannot be reconfigured using the Microsoft method because docker appears to have left docker-desktop-data 'shell-less'
• Monitor that you do not broach the >256GB limit, much like you did using WSL1. When reach <your size in GB above 256GB>, you may not be able to start or recover your data. There is no built-in altitude warning.
• If you reach the <your size in GB above 256GB> limit and cannot start docker, you can attempt to export the docker-desktop-data wsl distro and run it natively with some linux filesystem utilities and hyper-v .vhdx drivers, it may be possible to prune the image manually then remount it.