Increase hard disk size in VirtualBox 4.x

Increase hard disk size in VirtualBox 4.x

0. Shut down virtual machine & quit VirtualBox

1. Locate VDI file

$ VBoxManage list hdds
UUID:        xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
Parent UUID: base
Format:      VDI
Location:    /Users/user/Library/VirtualBox/HardDisks/XP.vdi
State:       created
Type:        normal
Usage:       XP (UUID: yyyyyyyy-yyyy-yyyy-yyyy-yyyyyyyyyyyy)

2. Backup virtual machine

There are two methods:

1. Simply copy the VDI file to another location. (If you try opening this copy in a new VM later, you may receive a "Cannot register the hard disk ... with UUID ... because a hard disk ... with UUID ... already exists in the media registry ..." error. This can be resolved by assigning a new UUID: $ VBoxManage internalcommands sethduuid XPcopy.vdi ^*)
2. Or use the clonehd command, which creates a cloned copy with a new UUID automatically:
   $ VBoxManage clonehd XP.vdi XPclone.vdi

3. Resize drive

Specify the new size in MBs. In this example, we'll expand a 10GB virtual disk to 40GB:

$ sudo VBoxManage modifyhd XP.vdi --resize 40960

The process should complete in a few seconds.

4. Allocate new space 

1. Download Parted Magic
2. Open VirtualBox and select your VM
3. Go to Settings > Storage to select the Parted Magic ISO image:
   
   and then to Settings > System > Motherboard to set the boot order.
4. Start the virtual machine. Once Parted Magic is booted, double click "Partition Editor" on the Desktop. You'll see something like this:
   
5. In this example, you'd resize /dev/sda1 to take up the additional 30GB and click Apply: