We are experiencing poor write performance on a large collection. The collection has 390 millions documents with "avgObjSize" : 842.5387 and 4 indexes. In the test environment, we can insert at 4000 documents per second with similar size of the collection. In the production environment, we can only get 1000/s. We tried the write concern setting with (w: 0) but it didn’t help. Here are more details of the data load:

App : Java (Spring Batch)
Bulk insert (1000/batch)
2 shard servers with 200GB of physical memory and 2TB storage for Mongo
3 config/query servers and 1 arbiter server