If you perform either of the above setups and find that on reboot one member of the array is not present and the command "mdadm --detail /dev/md0" shows that the array is degraded, the following may help.
In a Fedora forum thread, - http://www.fedoraforum.org/forum/showthread.php?t=255048 it was found that some makes of hard drives can cause this problem as they take a while to spin up so the system ignores one of them and carries on with the degraded array.