Here’s a short tutorial to copy VirtualBox image for backup or cloning. I have successfully used this method to clone an existing VDI to make 2 Windows XP virtual machines, one running IE6 and the other IE8 on a MacBook Pro.
Step-by-step to Copy VirtualBox image on Mac OS X
Step 1: VBoxManage clonehd Master.vdi Clone.vdi
You will need to run the above command in the Terminal. First, at the command prompt,
cd ~/VirtualBox\ VMs/Windows\ XP
VBoxManage clonehd Windows\ XP.vdi Windows\ XP\ IE6.vdi
You will have to wait a while for the new VDI is being created.
Step 2: Creat a New Virtual Machine for the newly Cloned VDI
Run the VirtualBox Manager and create a new virtual machine.
You will be promoted to enter a name for the new virtual machine and select the OS type as show in the screenshot above.
Next, allocate the amount memory for your new virtual machine. I used the same setting as the original virtual machine.
At the Virtual Hard Disk prompt, select “Use existing hard disk”. Then click at the folder icon to select the VDI which you’ve just cloned and use it for the new virtual machine.
In my case, the newly created virtual machine would be running Windows XP with IE 6 and I would upgrade my original virtual machine to IE 8. Now I have both IE 6 and IE 8 running on my MacBook Pro for cross-browser testing.