I have 3 configsvr, 70 shardsvr:
1. enableSharding the database;
2. shardCollection by mongo shell `load("shard.ms")`, the content:
sh.shardCollection('test.info150831', {_id: 'hashed'});
....
sh.shardCollection('test.info150915', {_id: 'hashed'});
3. Such as the title. After I shard these collections, I run mongo shell `sh.status()`. I find that shard0000 have much more chunks than others, why?