Why Replicate Data?
We just talked about storing data across multiple servers—horizontal scaling, partitioning. Now we have multiple servers, each holding a subset or a copy of the data. That already improves scale. But we also want redundancy: if one server dies, we should still be able to access the data from another. Database replication is how we get that. We duplicate data across multiple servers so we have backups and avoid a single point of failure.