STEP bring the shard key to the top level

gistfile1.txt

var cursor = db.messages.find({},{_id:1, 'headers.Date':1})

while(cursor.hasNext()){
    var doc = cursor.next();
    var id = doc._id;
    var dt = doc.headers.Date;
    db.messages.update({_id:id},{$set:{date:dt},$unset:{'headers.Date':1}})
}


sh.getBalancerState()
//true


// stop the balancer
sh.setBalancerState(false)

db.messages.ensureIndex({date:1})
sh.shardCollection('enron.messages',{date:1})

mongos> sh.status()
--- Sharding Status --- 
  sharding version: {
	"_id" : 1,
	"version" : 3,
	"minCompatibleVersion" : 3,
	"currentVersion" : 4,
	"clusterId" : ObjectId("5314f1487abd6cb2803696d6")
}
  shards:
	{  "_id" : "shard0000",  "host" : "Rohit-MacBook-Pro.local:30000",  "tags" : [ 	"current" ] }
	{  "_id" : "shard0001",  "host" : "Rohit-MacBook-Pro.local:30001",  "tags" : [ 	"archive" ] }
	{  "_id" : "shard0002",  "host" : "Rohit-MacBook-Pro.local:30002",  "tags" : [ 	"archive" ] }
  databases:
	{  "_id" : "admin",  "partitioned" : false,  "primary" : "config" }
	{  "_id" : "test",  "partitioned" : false,  "primary" : "shard0000" }
	{  "_id" : "enron",  "partitioned" : true,  "primary" : "shard0000" }
		enron.messages
			shard key: { "date" : 1 }
			chunks:
				shard0000	13
			{ "date" : { "$minKey" : 1 } } -->> { "date" : ISODate("2001-02-16T10:55:00Z") } on : shard0000 Timestamp(1, 0) 
			{ "date" : ISODate("2001-02-16T10:55:00Z") } -->> { "date" : ISODate("2001-03-06T10:04:00Z") } on : shard0000 Timestamp(1, 1) 
			{ "date" : ISODate("2001-03-06T10:04:00Z") } -->> { "date" : ISODate("2001-03-20T22:12:00Z") } on : shard0000 Timestamp(1, 2) 
			{ "date" : ISODate("2001-03-20T22:12:00Z") } -->> { "date" : ISODate("2001-04-03T13:37:14Z") } on : shard0000 Timestamp(1, 3) 
			{ "date" : ISODate("2001-04-03T13:37:14Z") } -->> { "date" : ISODate("2001-04-17T13:50:16Z") } on : shard0000 Timestamp(1, 4) 
			{ "date" : ISODate("2001-04-17T13:50:16Z") } -->> { "date" : ISODate("2001-04-27T16:29:00Z") } on : shard0000 Timestamp(1, 5) 
			{ "date" : ISODate("2001-04-27T16:29:00Z") } -->> { "date" : ISODate("2001-05-09T12:27:00Z") } on : shard0000 Timestamp(1, 6) 
			{ "date" : ISODate("2001-05-09T12:27:00Z") } -->> { "date" : ISODate("2001-05-18T07:46:00Z") } on : shard0000 Timestamp(1, 7) 
			{ "date" : ISODate("2001-05-18T07:46:00Z") } -->> { "date" : ISODate("2001-05-30T19:21:00Z") } on : shard0000 Timestamp(1, 8) 
			{ "date" : ISODate("2001-05-30T19:21:00Z") } -->> { "date" : ISODate("2001-06-08T12:49:56Z") } on : shard0000 Timestamp(1, 9) 
			{ "date" : ISODate("2001-06-08T12:49:56Z") } -->> { "date" : ISODate("2001-07-12T20:25:00Z") } on : shard0000 Timestamp(1, 10) 
			{ "date" : ISODate("2001-07-12T20:25:00Z") } -->> { "date" : ISODate("2001-08-20T19:34:00Z") } on : shard0000 Timestamp(1, 11) 
			{ "date" : ISODate("2001-08-20T19:34:00Z") } -->> { "date" : { "$maxKey" : 1 } } on : shard0000 Timestamp(1, 12)