WSL Sparse does not work at all.

[PeterTucker]

Windows Version

Microsoft Windows [Version 10.0.19045.4894]

WSL Version

2.2.4.0

Are you using WSL 1 or WSL 2?

• [X] WSL 2
• [ ] WSL 1

Kernel Version

5.15.153.1-microsoft-standard-WSL2

Distro Version

Ubuntu 22.04

Other Software

No response

Repro Steps

Sparse does not work.

Ubuntu disk space (.vhdx file) shows 118gbs in windows 10. In Ubuntu: /ncdu / --exclude /mnt shows 64gbs

Powershell(admin): notepad "$env:USERPROFILE/.wslconfig" .wslconfig:

[experimental]
sparseVhd=true

Powershell(admin):

wsl --list # list distros
wsl --manage <distro> --set-sparse true # enable sparse on vdisk
wsl --shutdown # restart wsl
wsl # restart wsl 

Then when I check the size, it has not changed at all, still 118gbs.

SOLUTION (MANUAL SHRINKING):

for anyone who finds this in the future. Here is a way to resize the disk manually.

Powershell (admin):

FIRST BACKUP YOUR VHDX FILE
wsl --list # list distros
wsl --shutdown # Be patient and wait a bit for wsl to shutdown. It will eventually shutdown.
wsl --manage <DISTRO_NAME> --set-sparse false
optimize-vhd -Path "<VHDX_FILE>" -Mode full
wsl --manage <DISTRO_NAME> --set-sparse true

Then test if the VHDX file (wiztree) has shrunk and your distro can run.

Expected Behavior

Reclaim disk space in Windows 10.

Actual Behavior

The sparseVhd setting does not reclaim disk space in Windows 10.

Diagnostic Logs

No response

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View similar issues

Please view the issues below to see if they solve your problem, and if the issue describes your problem please consider closing this one and thumbs upping the other issue to help us prioritize it!

Open similar issues:

• wsl --manage Alpine --set-sparse true # No result for auto disk space clean up (Set sparse VHD) (#10703), similarity score: 0.80
• Using the SparseVhd option causes High CPU, RAM, and Disk usage (#10991), similarity score: 0.73

Closed similar issues:

• The ext4.vhdx file size grew too fast than actual use（swap or caches） (#8695), similarity score: 0.73
• WSL2 distro rapidly expands to fill drive without using space and cannot be shrunk (#8226), similarity score: 0.72
• The WSL 2 ext4.vhdx file keeps growing for no good reason (#10353), similarity score: 0.71

Note: You can give me feedback by thumbs upping or thumbs downing this comment.

[PeterTucker]

/question

[PeterTucker]

Why does it not work?

[github-actions[bot]]

Diagnostic information

Found '/question', adding tag 'question'

[elsaco]

@PeterTucker after wsl --manage <DISTRO_NAME> --set-sparse false do a wsl --shutdown again, and it should work.

Notice the FileSize before and after running the command:

PS C:\Users\elsaco> Get-VHD -Path "G:\vms\sid\ext4.vhdx"

ComputerName            : ELEVEN
Path                    : G:\vms\sid\ext4.vhdx
VhdFormat               : VHDX
VhdType                 : Dynamic
FileSize                : 1081081856
Size                    : 549453824000
MinimumSize             :
LogicalSectorSize       : 512
PhysicalSectorSize      : 4096
BlockSize               : 1048576
ParentPath              :
DiskIdentifier          : 40545B0A-6EE6-483B-AE7D-B64B4EF39DB1
FragmentationPercentage : 100
Alignment               : 1
Attached                : False
DiskNumber              :
IsPMEMCompatible        : False
AddressAbstractionType  : None
Number                  :

PS C:\Users\elsaco> Optimize-VHD -Path "G:\vms\sid\ext4.vhdx" -Mode full
PS C:\Users\elsaco> Get-VHD -Path "G:\vms\sid\ext4.vhdx"

ComputerName            : ELEVEN
Path                    : G:\vms\sid\ext4.vhdx
VhdFormat               : VHDX
VhdType                 : Dynamic
FileSize                : 1067450368
Size                    : 549453824000
MinimumSize             :
LogicalSectorSize       : 512
PhysicalSectorSize      : 4096
BlockSize               : 1048576
ParentPath              :
DiskIdentifier          : 40545B0A-6EE6-483B-AE7D-B64B4EF39DB1
FragmentationPercentage : 100
Alignment               : 1
Attached                : False
DiskNumber              :
IsPMEMCompatible        : False
AddressAbstractionType  : None
Number                

[tusharsnx]

~It wasn't working for me on stable. After updating to the latest pre-release (2.4.8), it seems to work as expected: deleting files inside wsl shrinks the vdhx (after wsl shuts down).~

Edit: Doesn't seem to work reliabily. The size doesn't go down when files are deleted.

[PeterTucker]

@tusharsnx Well, that's good to hear. I just transferred all my stuff to Cygwin. Might have to do a test with docker tonight. Thanks for the update!

[dporf]

Just tried 2.4.10, works partially. Ubuntu, ext4.

• wsl --shutdown & wsl --manage Ubuntu --set-sparse true

test1

• start wsl
• create large files -> host free space reduced
• remove files
• wsl --shutdown -> host free space restored ok

test2

• start wsl
• crete large files -> host free space reduced
• wsl --shutdown
• start wsl
• remove files
• wsl --shutdown -> host free space is not restored

[dporf]

wsl 2.5.9.0 still the same

[SultanovIlnur]

It doesn't work for me either. I had to use sudo fstrim -av (in Linux terminal) first, then disable sparse mode (wsl --manage Debian --set-sparse false) and then optimize-vhd -Path "<vhdx_file>" -Mode full to reduce the disk image from 211 GB to 20 GB.

[tusharsnx]

There hasn't been any confirmation from the WSL team for why sparse vhds are failing to shrink on its own. Is something wrong with our setup? Or is --set-sparse just broken as of today?

Can we get a simple manual command to optimize WSL vhdx files (that works for Win Home users)? For example, wsl --manage Ubuntu --optimize-vhd

[dporf]

Does anyone know which part of code may do the job? Is it in this or some other repo? As far as I understand WSL should hook trim/discard kernel calls and make FSCTL_SET_ZERO_DATA request

[slo617]

Devices needs to be mounted with discard option enabled. (Seems to be default for Ubuntu, not sure if this is default for Debian.) In addition sudo fstrim -av can trigger trimming manually.

Both works for me more or less with WSL-Version 2.6.1.0, Ubuntu 22.04 and 24.04. Also I noticed that not all space seems to be freed. Used space reported by df -h is 191G, ext4.vhdx size is 312GB. But after deleting large files, docker containers or the like ext4.vhdx shrinks - at least a bit.

[dporf]

@slo617

can trigger trimming manually

For me it just triggers vhd purge on wsl shutdown in some cases. What is really should do is to force host system to mark regions of vhd as empty and free allocated space imediately, this is what sparse files for.

Current behaviour may be easily tested with command fsutil file layout ext4.vhdx (may require admin rights). Just compare file size and allocated size before and after deleting files + fstrim. Allocated size should change immediately after executing fstrim but it does not.

You can mark some regions as empty manually (BE CAREFUL! IT ERASES DATA REGIONS!):

# set sparse flag
fsutil sparse setflag "1.bin"
# print file layout
fsutil file layout 1.bin
# mark a region as empty
fsutil sparse setrange 1.bin 0 999999999
# pring file layout again
fsutil file layout 1.bin

So WSL should catch BLKDISCARD ioctl in VM and execute symmetrical FSCTL_SET_ZERO_DATA ioctl in the host system.

[zillur01]

this does not work for me either wsl --shutdown & wsl --manage Ubuntu --set-sparse true also vhd opmtize not available on windows 11 home