ethereum 2.0 sharding, how does data travel around from one shard to the other

Question

Shard 1 needs to contact shard 2 about a contract it has, how does it go about doing it? What's the "traveling salesman path" of least resistance to get to it?

Or am I misunderstanding how sharding works? I understand there is some sort of central chain, the "root" if you will or something along those lines.

What I am most confused about, is where the data is stored. On the nodes in the shard level or up another level. Who's responsible for keeping all the data intact? Are they compensated? Thanks.

Answer 1

I was reading this a few weeks ago: https://ethos.dev/beacon-chain/ . It explains everything you need to know and a lot more.

To be honest the article got way too deep for me and I didn't manage to finish it but at least the basic idea is relatively simple: there is a chain called Beacon chain which is the communication layer between different shards. This Beacon chain is part of the Eth2.0 phase 0 so in theory it should be launched somewhere around this summer.

I was trying now again to look for clues about exact data storage but didn't see much. As I understand it, nodes will pretty much contain all the data of the shard chain - so similar situation as currently.

Data integrity is the responsibility of validators who are organized in various group sizes and assigned randomly. It requires a 2/3 majority of validators in a group to reach consensus.