Reduce vdisk disk usage

[mgutt]

When you create a VM it's vdisk is a sparse file. A sparse file saves a huge amount of space on your disk, because data which contains nothing (zeros) is "compressed". But after a while it will become bigger as deleted files are not really deleted. To understand this, we use an example. I created a 32G vdisk for my Windows 10 machine:

 

After installation its size is 15G (as it's a sparse file):

file="/mnt/cache/domains/Windows 10/vdisk1.img"
du -h "$file"
15G     /mnt/cache/domains/Windows 10/vdisk1.img

 

After installing the network driver and some updates it grow to 18G:

du -h "$file"
15G     /mnt/cache/domains/Windows 10/vdisk1.img

 

After installing this tool inside the Windows VM:

https://docs.microsoft.com/de-de/sysinternals/downloads/sdelete

 

and executing this command:

sdelete64 -z c:

 

it grow to 30G:

du -h "$file"
30G     /mnt/cache/domains/Windows 10/vdisk1.img

 

And finally after this command:

fallocate -d "$file"

 

It shrunk to 15G again:

du -h "$file"
15G     /mnt/cache/domains/Windows 10/vdisk1.img

 

 

 

The same can be reached with a Linux VM and the command "zerofree".

 

 

This could be executed once every month.

 

[JonathanM]

https://forums.unraid.net/topic/51703-vm-faq/?tab=comments#comment-557606