How to compact VirtualBox's VDI file size?

vdi-file-compacting.md

Source: StackOverflow

1. Run defrag in the guest (Windows only)

2. Nullify free space:

With a Linux Guest run this:

sudo dd if=/dev/zero | pv | sudo dd of=/bigemptyfile bs=4096k
sudo rm -rf /bigemptyfile

or

telinit 1
mount -o remount,ro /dev/sda1
zerofree -v /dev/sda1

With a Windows Guest, download SDelete from SysInternals and run this:

sdelete.exe c: -z

(replace C: with the drive letter of the VDI)

3. Shutdown the guest VM

4. Now run VBoxManage's modifyhd command with the --compact option:

With a Linux Host run this:

vboxmanage modifyhd /path/to/thedisk.vdi --compact

With a Windows Host run this:

VBoxManage.exe modifyhd c:\path\to\thedisk.vdi --compact

With a Mac Host run this:

VBoxManage modifyhd /path/to/thedisk.vdi --compact