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Sharding Mechanics

The following documents describe sharded cluster processes.

Sharded Collection Balancing
Balancing distributes a sharded collection’s data cluster to all of the shards.
Chunk Migration Across Shards
MongoDB migrates chunks to shards as part of the balancing process.
Chunk Splits in a Sharded Cluster
When a chunk grows beyond the configured size, MongoDB splits the chunk in half.
Shard Key Indexes
Sharded collections must keep an index that starts with the shard key.
Sharded Cluster Metadata
The cluster maintains internal metadata that reflects the location of data within the cluster.