I’ll be real with you: I’ve had a look at the database schema and tables exactly once. It’s a bowl of spaghetti in there. We just sort of view it as a single entity and don’t really separate it out in any granular view.
What I can tell you is that the bulk of the storage is federated content. When a user subscribes to a community on another instance, the aussie.zone database caches content from it here for them. So, lemmy.world for example uses a lot more storage than the user messages. Or aussie.zone content if I’m being honest. We really aren’t that big an instance. We are pretty engaged though. Our user base is small but active.