MongoDB Documentation, Release 3.0.4 Considerations • Shard key range tags are distinct from replica set member tags (page 590). • Hash-based sharding only supports tag-aware sharding on an entire collection. • Shard ranges are always inclusive of the lower value and exclusive of the upper boundary. Behavior and Operations The balancer migrates chunks of documents in a sharded collection to the shards associated with a tag that has a shard key range with an upper bound greater than the chunk’s lower bound. During balancing rounds, if the balancer detects that any chunks violate configured tags, the balancer migrates those chunks to shards associated with those tags. After configuring a tag with a shard key range and associating it with a shard or shards, the cluster may take some time to balance the data among the shards. This depends on the division of chunks and the current distribution of data in the cluster. Once configured, the balancer respects tag ranges during future balancing rounds (page 684). Manage Shard Tags (page 730) See also: Additional Resource • Whitepaper: MongoDB Multi-Data Center Deployments 14 • Webinar: Multi-Data Center Deployment 15 $^{14}$http://www.mongodb.com/lp/white-paper/multi-dc?jmp=docs $^{15}$https://www.mongodb.com/presentations/webinar-multi-data-center-deployment?jmp=docs 10.2. Sharding Concepts 683