With NW 6.5sp5 and backup exc 9.2 I am trying to create a mirrored drive

When I create the pool I have no drives available to pick from the list.

The two drives I have are HP Ultrium 960 and a HP Ultrium 460. I know
they are different capacities, but if I am reading the manual correctly,
this shouldn't be a problem.

Does anyone know what might be wrong? Is it the different capacity
ultrium drives?