OK, it turns out that the second drive had once been part of a RAID as was not being recognised. Using: sudo dmraid -E -r /dev/sda as described on this page: http://ubuntuforums.org/showthread.php?t=2003675 fixed it.
OK, it turns out that the second drive had once been part of a RAID as was not being recognised. Using: ubuntuforums. org/showthread. php?t=2003675
sudo dmraid -E -r /dev/sda
as described on this page:
http://
fixed it.