MongoDB is a Database that supports Sharding
Automatic balancing for changes in load and data distribution
Easy addition of new machines Scaling out to one thousand nodes
No single points of failure
Sharding must be ran in trusted security mode, without explicit security.
Shard keys are immutable in the current version
All (non-multi)updates, upserts, and inserts must include the current shard key.
This may cause issues for anyone using a mapping library since you don't have full control of updates.