How to shrink or compact VirtualBox .vdi images

You have to do the following steps:

1. run defrag in the guest (Windows)

2. nullify free space:

   With Linux guest run this:

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

   With Windows guest, download SysinternalsSuite and run this:

   sdelete –z 

3. shutdown the guest VM

4. now run VBoxManage's compact command

   VBoxManage.exe modifyhd thedisk.vdi --compact 

This reduces the size.

This works for Mac OS X

Open Terminal

Enter the following command:

VBoxManage modifyhd -compact “/Users/user1/VirtualBox VMs/Windows 7/Windows 7.vdi"