The Storage Planet was presumably once home to an alien ? race until they were throughly eradicated by the Irkens into total extinction. The storage planet was counquered and made addition to the Irken Empire at an unknown point in time possibly even before Operation Impending Doom 1 the planet's sole purpose in the Irken Empire is for storing supplies such as stealth weapons like the megadoomer combat stealth mech it also stores malfunctioning SIR units due to the planets size it should also likely store other essentials that Irkens use other than warfare weapons the Storage planet is entirely artificall like other planets in the Irken Empire such as Callnowia its surface is littered in mega skyscrapper sized Towers with giant spheres on top of each of them the planets surface seems to be out in the vacum of space hinting that the planets actual natural surface has been built way over into space over time. The planets interior is filled with large storage vaults which can probably only be opened by the use of a laser scanner as seen in episode Megadoomer.
The Storage Planet is only ever seen once in the Invader Zim series in the episode Megadoomer when the Almighty Tallest are looking for useful equipment to send to the Invaders to help them counquer their assigned planets they decide to send Invader Tenn a robot combat stealth mech to help her counquer planet Meekrob and decide to send Zim a dozen malfunctioning SIR units but due to Smikka Smikka Smoodo a screwhead? of the ? counquered Conveyor Belt Planets futile attempt to start a rebellion against the Irken Empire the packages get beamed to the wrong destinations resulting with Zim being sent the megadoomer instead of the malfunctioning SIR units this ultimately leads to Invader Tenns discovery and her being held hostage on planet Meekrob by its inhabitants made of pure energy because of the noticeable wreaked the malfunctioning SIR units were making which captured the attention of the Meekrob.