Do they have a scale/redundancy option for write scaling beyond shard + mirror set? I think my bigger issue with mongo, is you really need 6+ servers for a production deployment in many scenarios. It's great for getting a single developer instance up and running. But if I'm sticking to one instance or a couple mirrors for production, I may just reach for ms-sql or postgresql.

Aside: I'm sad that RethinkDB didn't get more of a foothold.

MongoDB supports a combination of shards and replica sets. Each replica set uses a protocol similar to raft for strong consistency. The replicas are a lot better than just active-secondary mirroring

https://docs.mongodb.com/manual/replication/

There's also Atlas which is the hosted version and makes it very easy to scale up https://www.mongodb.com/cloud/atlas

They also just added a free tier if you want to play with that https://docs.mongodb.com/manual/tutorial/atlas-free-tier-set...

Yeah, sorry for using mirrored instead of replica. I've worked with 3+ replica sets where I needed read scaling, and that worked well enough. But there are cases where I want read scaling and don't want to have a full copy of all data on all servers, but do want redundancy.

I really like, by comparison, how RethinkDB, Cassandra and others do it with clustering that has sharding + replication. It seems to be a better model in a lot of ways when you want to spread things out (read/write) but also want some replication of data. It's just a different way of working with things.

Thanks for pointing out Atlas.

Thanks for posting that; I haven't had a good reason to look at it in quite a while. It makes sense that they're adding those features as they all exist in SQL DBMS's because they're a need.