At bash prompt: mlaunch init --sharded 3 --replicaset mongo Note: I'm using mlaunch version 1.1.6 At the mongo shell: for (i=1; i<=1000; i++ ) {x = []; for (j=1; j<=1000; j++) {x.push( { a : i, b : j, c : 1000 * i + j, _id : 1000 * i + j } )}; db.foo.insert(x) } db.foo.ensureIndex( { a : 1, b : 1 }, { name : "first" } ) db.foo.ensureIndex( { b : 1 }, { name : "second" } ) sh.enableSharding( "test" ) sh.shardCollection( "test.foo" , { b : 1 } ) Wait a minute or two, and then run sh.status(). Expected result: Data is in several chunks, and the load is balanced with no errors. Actual result: Migration failures as the load balancer starts: "Failed with error 'chunk too big to move', from shard01 to shard03" and "Failed with error 'chunk too big to move', from shard01 to shard02", though the chunks seem to eventually get where they need to go. Here is the output of sh.status() partway through: mongos> sh.status() --- Sharding Status --- sharding version: { "_id" : 1, "minCompatibleVersion" : 5, "currentVersion" : 6, "clusterId" : ObjectId( "5492159f53be077898567039" ) } shards: { "_id" : "shard01" , "host" : "shard01/cross-mb-air.local:27018,cross-mb-air.local:27019,cross-mb-air.local:27020" } { "_id" : "shard02" , "host" : "shard02/cross-mb-air.local:27021,cross-mb-air.local:27022,cross-mb-air.local:27023" } { "_id" : "shard03" , "host" : "shard03/cross-mb-air.local:27024,cross-mb-air.local:27025,cross-mb-air.local:27026" } balancer: Currently enabled: yes Currently running: yes Balancer lock taken at undefined by undefined Collections with active migrations: test.foo started at Wed Dec 17 2014 19:05:28 GMT-0500 (EST) Failed balancer rounds in last 5 attempts: 0 Migration Results for the last 24 hours: 3 : Success 2 : Failed with error 'chunk too big to move' , from shard01 to shard03 1 : Failed with error 'chunk too big to move' , from shard01 to shard02 databases: { "_id" : "admin" , "partitioned" : false , "primary" : "config" } { "_id" : "test" , "partitioned" : true , "primary" : "shard01" } test.foo shard key: { "b" : 1 } chunks: shard01 4 shard02 2 shard03 1 { "b" : { "$minKey" : 1 } } -->> { "b" : 1 } on : shard02 Timestamp(2, 0) { "b" : 1 } -->> { "b" : 150 } on : shard03 Timestamp(3, 0) { "b" : 150 } -->> { "b" : 300 } on : shard02 Timestamp(4, 0) { "b" : 300 } -->> { "b" : 450 } on : shard01 Timestamp(4, 2) { "b" : 450 } -->> { "b" : 600 } on : shard01 Timestamp(4, 3) { "b" : 600 } -->> { "b" : 899 } on : shard01 Timestamp(1, 2) { "b" : 899 } -->> { "b" : { "$maxKey" : 1 } } on : shard01 Timestamp(1, 3) mongos>