There is more to a database than a raft implementation. A raft implementation would provide data replication between members and leader election. That is just one piece in a distributed database architecture. You then need a storage engine to persist the data, and a query engine to query the data.

To be able to scale, the database would most likely be composed of several raft clusters which brings couple of other challenges: - You need a sharding layer so that the queries can be routed to the right cluster - You need an orchestrator to be able to manage these clusters

It gets trickier as you try to run transactions across multiple raft clusters. You end up needing to implement 2PC.

FoundationDB solves all of the above except for the query engine part (given it is a KV).