MongoDB Documentation, Release 3.0.4 db.settings.save( { _id:"chunksize", value: <sizeInMB> } ) Note: The chunkSize and --chunkSize options, passed at startup to the mongos , do not affect the chunk size after you have initialized the cluster. To avoid confusion, always set the chunk size using the above procedure instead of the startup options. Modifying the chunk size has several limitations: If MongoDB cannot split a chunk that exceeds the specified chunk size (page 688) or contains a number of documents that exceeds the max , MongoDB labels the chunk as jumbo (page 687). If the chunk size no longer hits the limits, MongoDB clears the jumbo flag for the chunk when the mongos reloads or rewrites the chunk metadata. In cases where you need to clear the flag manually, the following procedures outline the steps to manually clear the jumbo flag. Divisible Chunks The preferred way to clear the jumbo flag from a chunk is to attempt to split the chunk. If the chunk is divisible, MongoDB removes the flag upon successful split of the chunk. Step 2: Find the jumbo Chunk. Run sh.status(true) to find the chunk labeled jumbo . Step 1: Connect to mongos . Connect a mongo shell to a mongos . For example, the following output from sh.status(true) shows that chunk with shard key range { "x" : 2 } -->> { "x" : 4 } is jumbo . --- Sharding Status --- sharding version: { ... } shards: ... databases: ... test.foo shard key: { "x" : 1 } chunks: sh.status( true ) Procedures Clear jumbo Flag • Automatic splitting only occurs on insert or update. • If you lower the chunk size, it may take time for all chunks to split to the new size. • Splits cannot be undone. • If you increase the chunk size, existing chunks grow only through insertion or updates until they reach the new size. • The allowed range of the chunk size is between 1 and 1024 megabytes, inclusive. Chapter 10. Sharding 728