Why VirtualBox harddisk is always growing even though I delete files from virtual drive?

Question

I have seen it with both VBox native VDI format and VMDK format. Even though I delete files from virtual drive, I see it always keeps growing. I have some vague idea that file zero-ing doesn't happen with the virtual drives from this link. When I tried to do that with SDelete (as said in the link) it didn't reduce the VDi disk size. I have applications which once installation grows the disk to 10GB each time. I believe there should be some simple way to zero it than going through the tedious process, is there any? Is there any option in VirtualBox to keep virtual drive small?

Solution

Here is a batch script I use to compact all the VDI files:

@echo off
for /d %%d in (*.*) do (
    cd "%%d"
    for %%f in (*.vdi) do (
        echo Compacting %%f . . .
        echo Initial size:      %%~zf
        "C:\Program Files\VirtualBox\VBoxManage.exe" modifymedium --compact disk "%%f"
        echo Post compact size: %%~zf
        echo.
    )
    cd ..
)

Just save it in the folder containing the Virtual Machines and run...

Comments

[DeathByTensors]

O wow, this is neat! I didn't know this functionality existed

[Ajayvignesh]

Should I do SDelete before running this batch file? I see there is no difference between Initial Size and Post Compact Size after running this batch.

[phuclv]

@Ajayvignesh you must run sdelete or any tools like zerofree to zero the free blocks, because virtualbox/vmware work in raw blocks and have no idea about the underlying filesystem. Hence if it sees a non-zero block, it thinks that the block is has some data and cannot remove it from the file