Reported by @leftwo. Alan noticed that we don't prevent you from adding two disks to create with the same name, but the API doesn't like it, so you get an error on submit. We should prevent duplicates from being added.

It's even worse than Alan said — something very odd happens when I have a create and an attach with the same name and try to delete it. I have a video but it looks like I'll have to upload it later when I'm off airplane wi-fi.