Chapter 1 What’s New for FortiOS 5.0 : New features in FortiOS 5.0 Patch 5 : Secure disk erasing
  
Secure disk erasing
All data on the FortiGate boot device and any hard disks installed in a FortiGate unit can now be securely and permanently erased using the execute erase-disk command. This command performs a low-level format and also overwrites every block on the device with random data three times.