A mongodb cluster is the word usually used for sharded cluster in mongodb. The main purposes of a sharded mongodb are:
- Scale reads and writes along several nodes
- Each node does not handle the whole data so you can separate data along all the nodes of the shard. Each node is a member of a shard and the data are separated on all shards.
A sharded cluster consists of config servers, shards, and one or more mongos routing processes.