MongoDB Documentation, Release 3.0.4 10.3.3 Sharded Cluster Data Management Create Chunks in a Sharded Cluster Example The following documents provide information in managing data in sharded clusters. Pre-splitting the chunk ranges in an empty sharded collection allows clients to insert data into an already partitioned collection. In most situations a sharded cluster will create and distribute chunks automatically without user interven- tion. However, in a limited number of cases, MongoDB cannot create enough chunks or distribute data fast enough to support required throughput. For example: These operations are resource intensive for several reasons: Warning: Only pre-split an empty collection. If a collection already has data, MongoDB automatically splits the collection’s data when you enable sharding for the collection. Subsequent attempts to manually create splits can lead to unpredictable chunk ranges and sizes as well as inefficient or ineffective balancing behavior. To create chunks manually, use the following procedure: To create chunks for documents in the myapp.users collection using the email field as the shard key , use the following operation in the mongo shell: Chapter 10. Sharding 722 1. Split empty chunks in your collection by manually performing the split command on chunks. • Chunk migration requires copying all the data in the chunk from one shard to another. • MongoDB can migrate only a single chunk at a time. • MongoDB creates splits only after an insert operation. • If you want to partition an existing data collection that resides on a single shard. • If you want to ingest a large volume of data into a cluster that isn’t balanced, or where the ingestion of data will lead to data imbalance. For example, monotonically increasing or decreasing shard keys insert all data into a single chunk. Shard GridFS Data Store (page 734) Choose whether to shard GridFS data in a sharded collection. Merge Chunks in a Sharded Cluster (page 725) Use the mergeChunks to manually combine chunk ranges. Modify Chunk Size in a Sharded Cluster (page 727) Modify the default chunk size in a sharded collection Clear jumbo Flag (page 728) Clear jumbo flag from a shard. Manage Shard Tags (page 730) Use tags to associate specific ranges of shard key values with specific shards. Enforce Unique Keys for Sharded Collections (page 732) Ensure that a field is always unique in all collections in a sharded cluster. Migrate Chunks in a Sharded Cluster (page 724) Manually migrate chunks without using the automatic balance process. Split Chunks in a Sharded Cluster (page 723) Manually create chunks in a sharded collection. Create Chunks in a Sharded Cluster (page 722) Create chunks, or pre-split empty collection to ensure an even dis- tribution of chunks during data ingestion.