MongoDB Bench marking/Limitations

Most of us have these questions in mind when we go MongoDB on boarding – here you go. 

Max No. of Shards :-
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The MongoDB software imposes no limit here, so theoretically the number of shards can be infinite.
However, practically speaking, the largest production deployments have had hundreds of shards, and the largest test deployments we’ve exercised have had 1000 shards.

Max No. of Config servers :-
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The number of config servers must be exactly 3 in all production deployments.
That number has no bearing on or relationship to the number of shards or mongos processes; it’s just a fixed detail in the sharding architecture.

Max No. of Mongos (Routers) :-
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The MongoDB software imposes no limit on number of mongos processes, but typically no more than 10 or 20 are called for, even in the largest clusters.

(To be candid, under certain odd circumstances, a large number of mongos processes can cause performance degredations, e.g., due to excessive network connections to shard members.
So you can consider mongos processes to act as “concentrators” for resources such as network connections in addition to acting as routers.
However, note that the degredation cases are rare, and there exist production clusters with hundreds of mongos processes which don’t experience any degredation related to the number of mongos processes.)

Max No. of nodes in a RS (Replica Set) :-
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Each shard must be a replica set for all production systems, and the number of nodes within a replica set is limited to 12.

See: http://docs.mongodb.org/manual/reference/limits/#Number-of-Members-of-a-Replica-Set

Max amount of data size in a node (mongod) :-
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Each node within a replica set is a mongod, and the amount of data each mongod can store turns out to be limited by operating system (specifically, the maximum virtual memory size a process may have on the OS). On Linux the limit is 64TB per node; on Windows the limit is 4TB per node.

See: http://docs.mongodb.org/manual/reference/limits/#Data-Size