Chapter 20 Virtual FortiGate Units for FortiOS 5.0 : FortiGate VM Overview : Deployment package contents : OpenXEN
  
OpenXEN
The FORTINET.out.OpenXen.zip file contains only fortios.qcow2, the FortiGate VM system hard disk in qcow2 format. You will need to manually:
create a 30GB log disk
specify the virtual hardware settings