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Sharded Cluster Behavior

These documents address the distribution of data and queries to a sharded cluster as well as specific security and availability considerations for sharded clusters.

Shard Keys
MongoDB uses the shard key to divide a collection’s data across the cluster’s shards.
Sharded Cluster High Availability
Sharded clusters provide ways to address some availability concerns.
Sharded Cluster Query Routing
The cluster’s routers, or mongos instances, send reads and writes to the relevant shard or shards.