Lemmy

and they’re not exchanging data, in the sense that if there’s community jimbo on instance rambo, all comments are stored there.

No. The comments are saved by every instance that has at least one user subscribed to !jimbo@rambo.com. If Rambo.com goes down, you wouldn't be able to make new content but I'm pretty sure everyone else could view what was there.

if there’s multiple jimbos on different instances is there some aggregation type of deal or do I have to subscribe to all the jimbos out there? and if I have something important to say about topic jimbo, I just spam/crosspost my idea to all the jimbos out there?

On Reddit there was /r/tech and /r/technology. One of those became the big, go-to sub.

Same will happen here, just give it a bit of time.

so if the operator of rambo goes “man fuck this” and shuts it down, the posts/comments are gone? there’s no way to replicate them or sync them or whatever?

My understanding is that if a user on a different instance is subscribed, then that second instance will keep copies of previous post / comments.

But there also appears to be a download limit, so over time the non-original instances will lose those copies.

It's a strange new world over here!