Shrink VirtualBox image

Some steps to reduce the size of VirtualBox image files. Originally for VirtualBox’s VDI format, but it can be applied for some other formats as well (OVA, OVF, … ) .

Given we have a VirtualBox image harddisk file called my_hd.vdi , which is used for running a guest OS on your VirtualBox. We’ll try to compact the size of the file by following steps:

Zero out the unnecessary spaces of the hard-disk

If the guest OS is Linux, we can use the dd tool, it can be applied to not only all Linux distributions but also other Unix-based OS (like OpenBSD, FreeBSD, . . . ) . Although you should be careful as a typo in the command with dd may result in formatting the hard disk or similar issues.

$ dd if=/dev/zero of=/bigemptyfile
$ sudo rm -rf /bigemptyfile

If the free space on the guest OS is not much left, you can use the following alternative:

$ cat /dev/zero > zero.fill;sync;sleep 1;sync;rm -f zero.fill

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Another way (if you are in single mode, or have root priviledge) is to use zerofree tool: Install it with apt-get (Ubuntu/Debian) or yum (CentOS/SUSE) :

$ sudo apt-get install zerofree

Then utilize zerofree for the mounted hard disk (usually /dev/sda1 or /dev/hda1 ) :

$ zerofree /dev/sda1

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If the guest OS is Windows, you can use either nullfile.exe or sdelete.exe to zero out the partitions (drives) :

> sdelete -c -z C:\

Ok, now shutdown the guest OS completely and resize the image hard disk on the host OS.

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Use the tool of VirtualBox to shrink the size

You can do that with the VBoxManage.exe (Win) or VBoxManage (Linux), by this command:

VBoxManage modifyhd --compact my_hd.vdi

Example on Windows:

C:\Program Files\Oracle\VirtualBox> VBoxManage modifyhd --compact "D:\VirtualBox\my_hd.vdi"

Examples on Linux:

$ VBoxManage modifyhd "/home/ducquoc/my_hd.vdi" --compact

Besides, you may use the old tool of VirtualBox ( vditool ) , or the clonehd feature of VBoxManage to compact the hard disk image, too.

vditool shrink my_hd.vdi

VBoxManage clonehd my_hd.vdi my_hd_clone.vdi 
VBoxManage clonehd my_hd.vdi my_hd_new.vmdk --format VMDK

In new versions of VirtualBox (4.x+) , there is also has a GUI for clonehd to clone the VDI instead of using command-line. The decrease in that VDI size can be up to 70% , I’ve seen myself : 15.3GB -> 9.3GB, 11.9 GB -> 6.0 GB, 7.2 GB -> 2.4 GB, etc. . .

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UPDATED: For VMWare fans, there is a counterpart for VMDK images too. After zero out the unnecessary spaces, we can use vmware-vdiskmanager to shrink the image size:

vmware-vdiskmanager -k my_hd.vmdk

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Example on Windows:

C:\Program Files\VMWare\VMWare Server> vmware-vdiskmanager.exe -k "D:\Virtual Machines\my_hd.vmdk"

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Examples on Linux:

$ vmware-vdiskmanager -k "/home/ducquoc/my_hd.vmdk"

And for VMWare ESX(i) the tool is vmkfstools .

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Good luck,

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