Re-size VirtualBox Disk-Images

The native disk-file format for VirtualBox is .vdi, but VirtualBox is fully operational with other file formats as well.  ( .vdmk .vhd .ovf .ova .vdi ...)

However, if you need to re-size your virtual disk image, you might need to convert your file. To my knowledge, currently the re-size function within VirtualBox image manager works best with .vdi images.

In my case I was using a vmWare image of Windows 7 on my Ubuntu 12.04 / 14.04 LTS host, so I cloned my disk first to .vdi before re-sizing.

procedure:

1 Clone your .vmdk image to .vdi:

VBoxManage clonehd "source.vmdk" "cloned.vdi" --format vdi

2. Re-size the .vdi image to 50GB:
VBoxManage modifyhd "cloned.vdi" --resize 51200

Will re-size the hard disk up to 50GB (= 50 * 1024 MB).

3. Optional: clone resized .vdi to .vmdk:  

(only needed if you have a particular reason for using .vmdk format, or need to be compatibility with VMware)

VBoxManage clonehd "cloned.vdi" "resized.vmdk" --format vmdk


NOTE: 
Either you use the original source name for the resized.vmdk  (only if you have a backup), or you use a new name, and connect that new drive in VirtualBox to your virtual machine. 


4. Re-size the partition within Windows 7:

Use the disk-manager  (extending the partition)   

Control Panel - System & Security - Administrative Tools - Computer Management - Disk Management.

------- RIGHT MOUSE CLICK ON (C:) DRIVE AND SELECT EXTEND VOLUME --------