I’m running VirtualBox on a Mac OS X host, and I had one .VDI hard disk file that I needed to duplicate into three and use them all at the same time. When I tried to load them all into different VMs inside VirtualBox, I got an error that a hard disk with that UUID was already in use.
Turns out that you can’t just duplicate the hard disk file–you need to use a command called VBoxManage to do it. But it took me a while to find out how to run that command on a Mac.
Here’s what you need to do in a console window:
/Applications/VirtualBox.app/Contents/MacOS/VBoxManage clonevdi path/to/yourold.vdi path/to/vditocreate.vdi
It will probably take a while, and it will only update the progress indicator every 10% or so, so have some patience and you should be set. Once the duplicate is made, just create a new VM in VirtualBox, and choose your new .VDI file.