Migration failed because of `already exists with different options`

Create a shared cluster Step1: enable sharding for test database sh.enableSharding( "test" ) Step2: create index for some colletion mongos> db.coll.createIndex({x: 1 }) { "raw" : { "mymongo02/r101072137.sqa.zmf:9665" : { "createdCollectionAutomatically" : true , "numIndexesBefore" : 1 , "numIndexesAfter" : 2 , "ok" : 1 , "$gleStats" : { "lastOpTime" : Timestamp( 1504497721 , 2 ), "electionId" : ObjectId( "58eeece962cc998e3a94975d" ) } } }, "ok" : 1 } Shard1 (primary shard for test database) db.coll.getIndexes() [ { "v" : 1 , "key" : { "_id" : 1 }, "name" : "_id_" , "ns" : "test.coll" }, { "v" : 1 , "key" : { "x" : 1 }, "name" : "x_1" , "ns" : "test.coll" } ] Shard2 db.coll.getIndexes() [ ] Step3: shardCollection for test.coll sh.shardCollection( "test.coll" , {x: 1 }) { "collectionsharded" : "test.coll" , "ok" : 1 } Step4: create index again with different option mongos> db.coll.createIndex({x: 1 }, {safe: null }) { "raw" : { "mymongo02/r101072137.sqa.zmf:9665" : { "ok" : 0 , "errmsg" : "Index with name: x_1 already exists with different options" , "code" : 85 }, "mymongo03/r101072137.sqa.zmf:9666" : { "createdCollectionAutomatically" : true , "numIndexesBefore" : 1 , "numIndexesAfter" : 2 , "ok" : 1 , "$gleStats" : { "lastOpTime" : Timestamp( 1504497768 , 2 ), "electionId" : ObjectId( "59acc73aacadfa7926c9cabb" ) } } }, "code" : 85 , "ok" : 0 , "errmsg" : "{ mymongo02/r101072137.sqa.zmf:9665: \"Index with name: x_1 already exists with different options\" }" } Shard1 (primary shard) db.coll.getIndexes() [ { "v" : 1 , "key" : { "_id" : 1 }, "name" : "_id_" , "ns" : "test.coll" }, { "v" : 1 , "key" : { "x" : 1 }, "name" : "x_1" , "ns" : "test.coll" } ] mymongo02:PRIMARY> Shard2 db.coll.getIndexes() [ { "v" : 1 , "key" : { "_id" : 1 }, "name" : "_id_" , "ns" : "test.coll" }, { "v" : 1 , "key" : { "x" : 1 }, "name" : "x_1" , "ns" : "test.coll" , "safe" : null } ] Now two shards have the same index with different IndexOption, the migration will never success.