I’ve just got my hands on a new server to store backups and archived files before being sent offsite, and it wouldn’t boot off my USB key. Even after many dd, dd with skip and FreeNAS installations, I was getting a “GPT table corrupt” message. Finally, the fix was easy enough:

  1. boot FreeNAS installation CD and choose Shell instead of Install
  2. type gpart show, it listed my device and that GPT table was corrupt
  3. type gpart destroy -F <thedevice>
  4. return to the menu
  5. choose Install
  6. when it’s finished, go back to the shell
  7. type gpart show again to check that it’s not corrupt anymore
  8. reboot
  9. enjoy your FreeNAS

That’s it.