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VirtualBox: How To Shrink VDI File

One area where Parallels is much better than VirtualBox is in the ease of compacting a VM disk to what's actually in use.

I've found that VM disks just keep increasing in size, regardless of what you might delete. Parallels makes compacting easy - all you do is select "Shrink..." from the Parallels menu.

The situation with VirtualBox is more complicated 😀
While there is a command line "compact" option, this relies on unused stuff being zero - which it won't be for things that got deleted...

However there is a tool (zerofree) which you can run in the VM and it sets all the free space on the disk to zero, which can then be compacted in VirtualBox.

Here are the steps I've been using:

Step 1: Install zerofree in the VM (Linux in my case):

$ sudo apt install zerofree

Step 2: Empty Trash and delete unneeded files

Step 3: Boot into a recovery session

  • Enter root password.

Step 4: Remount disk as read-only

# mount -n -o remount,ro /dev/sda1

Step 5: Run zerofree on disk

# zerofree -v /dev/sda1

Step 6: Shutdown VM

Step 7: Shrink VDI File from Host

$ VBoxManage modifymedium disk <your disk>.vdi --compact

Let me know if there is an easier way?!
In particular, it would be great if the zeroing part could be done from the host environment.
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