Be stingy in a smart way. I'd like a description why you need the storage, an estimation how much and a projection of growth over the next 6 - 12 month, though the latter one can wait for a month or three for something new. Beyond a certain scale we'd need a PO or a project to write up the cost too. And yes, we'll start bugging you again once it starts filling up to 80% or more, because we don't want your systems to fail :)

But this way, I directly get an idea of the increase in storage we will need over the next year in order to plan the next hardware expansion.