While there seems to be a lot of information around explaining how to migrate an existing disk image to VirtualBox from both Xen and VMWare, I couldn’t find a single article explaining how to migrate away from VirtualBox. After a lot a google searches (most revealing an obsolete program called “vditool”) and reading quite a lot of documentation I found the VBoxManage clonehd command which allows you to convert a VDI disk image into a RAW disk image that is able to be used by Xen. To save everyone else the time, the syntax is:

VBoxManage clonehd image1.vdi image1.raw —format RAW