The expected output from `bpimmedia -disk -disk_stu` is a usage statement because you didn't include the name of your DSU ;)
`bpimmedia -disk -disk_stu <name_of_my_DSU>` returned the expected image list for me.
I have to tell you... I think in this case, the -disk switch is probably redundant.
(If you need the name of your DSU, `bpstulist -l` can help you out.)
