MongoDB Documentation, Release 3.0.4 the chunks evenly across the shards. To divide the shard key values into chunks, MongoDB uses either range based partitioning or hash based partitioning . See the Shard Key (page 674) documentation for more information. For range-based sharding , MongoDB divides the data set into ranges determined by the shard key values to provide range based partitioning . Consider a numeric shard key: If you visualize a number line that goes from negative infinity to positive infinity, each value of the shard key falls at some point on that line. MongoDB partitions this line into smaller, non-overlapping ranges called chunks where a chunk is range of values from some minimum value to some maximum value. Given a range based partitioning system, documents with “close” shard key values are likely to be in the same chunk, and therefore on the same shard. Range Based Sharding Hash Based Sharding For hash based partitioning , MongoDB computes a hash of a field’s value, and then uses these hashes to create chunks. With hash based partitioning, two documents with “close” shard key values are unlikely to be part of the same chunk. This ensures a more random distribution of a collection in the cluster. Chapter 10. Sharding 664