I have a multi shared environment (3 shards), and I'm doing load test on it. I have an infinite loop inserting and deleting small document in a collection. I have a random integer shard key that allow me to spread the load on the 3 shards, and that works pretty well, except that when I monitor the mongos with mongostat I have a 12k/s insert and 12k/s delete rate, and each mongostat on shard gives me a 4k/s insert and 12k/s delete rate. The 12k/s on each does not make sense. My script does 1 insert and 1 delete in sequence in a infinite loop.