diff --git a/weed/shell/command_ec_encode.go b/weed/shell/command_ec_encode.go
index 80a0ccf5c..4647c2507 100644
--- a/weed/shell/command_ec_encode.go
+++ b/weed/shell/command_ec_encode.go
@@ -5,10 +5,15 @@ import (
 	"flag"
 	"fmt"
 	"io"
+	"sort"
+	"sync"
 
 	"github.com/chrislusf/seaweedfs/weed/operation"
+	"github.com/chrislusf/seaweedfs/weed/pb/master_pb"
 	"github.com/chrislusf/seaweedfs/weed/pb/volume_server_pb"
+	"github.com/chrislusf/seaweedfs/weed/storage/erasure_coding"
 	"github.com/chrislusf/seaweedfs/weed/storage/needle"
+	"github.com/chrislusf/seaweedfs/weed/wdclient"
 	"google.golang.org/grpc"
 )
 
@@ -53,18 +58,28 @@ func (c *commandEcEncode) Do(args []string, commandEnv *commandEnv, writer io.Wr
 
 	ctx := context.Background()
 
+	// find volume location
 	locations := commandEnv.masterClient.GetLocations(uint32(*volumeId))
-
 	if len(locations) == 0 {
 		return fmt.Errorf("volume %d not found", *volumeId)
 	}
 
-	err = generateEcSlices(ctx, commandEnv.option.GrpcDialOption, needle.VolumeId(*volumeId), locations[0].Url)
+	// generate ec shards
+	err = generateEcShards(ctx, commandEnv.option.GrpcDialOption, needle.VolumeId(*volumeId), locations[0].Url)
+	if err != nil {
+		return fmt.Errorf("generate ec shards for volume %d on %s: %v", *volumeId, locations[0].Url, err)
+	}
+
+	// balance the ec shards to current cluster
+	err = balanceEcShards(ctx, commandEnv, needle.VolumeId(*volumeId), locations[0])
+	if err != nil {
+		return fmt.Errorf("balance ec shards for volume %d on %s: %v", *volumeId, locations[0].Url, err)
+	}
 
 	return err
 }
 
-func generateEcSlices(ctx context.Context, grpcDialOption grpc.DialOption, volumeId needle.VolumeId, sourceVolumeServer string) error {
+func generateEcShards(ctx context.Context, grpcDialOption grpc.DialOption, volumeId needle.VolumeId, sourceVolumeServer string) error {
 
 	err := operation.WithVolumeServerClient(sourceVolumeServer, grpcDialOption, func(volumeServerClient volume_server_pb.VolumeServerClient) error {
 		_, genErr := volumeServerClient.VolumeEcGenerateSlices(ctx, &volume_server_pb.VolumeEcGenerateSlicesRequest{
@@ -76,3 +91,136 @@ func generateEcSlices(ctx context.Context, grpcDialOption grpc.DialOption, volum
 	return err
 
 }
+
+func balanceEcShards(ctx context.Context, commandEnv *commandEnv, volumeId needle.VolumeId, existingLocation wdclient.Location) (err error) {
+
+	// list all possible locations
+	var resp *master_pb.VolumeListResponse
+	err = commandEnv.masterClient.WithClient(ctx, func(client master_pb.SeaweedClient) error {
+		resp, err = client.VolumeList(ctx, &master_pb.VolumeListRequest{})
+		return err
+	})
+	if err != nil {
+		return err
+	}
+
+	// find out all volume servers with one volume slot left.
+	var allDataNodes []*master_pb.DataNodeInfo
+	var totalFreeEcSlots int
+	eachDataNode(resp.TopologyInfo, func(dn *master_pb.DataNodeInfo) {
+		if freeEcSlots := countFreeShardSlots(dn); freeEcSlots > 0 {
+			allDataNodes = append(allDataNodes, dn)
+			totalFreeEcSlots += freeEcSlots
+		}
+	})
+	if totalFreeEcSlots < erasure_coding.TotalShardsCount {
+		return fmt.Errorf("not enough free ec shard slots. only %d left", totalFreeEcSlots)
+	}
+	sort.Slice(allDataNodes, func(i, j int) bool {
+		return countFreeShardSlots(allDataNodes[j]) < countFreeShardSlots(allDataNodes[i])
+	})
+	if len(allDataNodes) > erasure_coding.TotalShardsCount {
+		allDataNodes = allDataNodes[:erasure_coding.TotalShardsCount]
+	}
+
+	// calculate how many shards to allocate for these servers
+	allocated := balancedEcDistribution(allDataNodes)
+
+	// ask the data nodes to copy from the source volume server
+	err = parallelCopyEcShardsFromSource(ctx, commandEnv.option.GrpcDialOption, allDataNodes, allocated, volumeId, existingLocation)
+	if err != nil {
+		return nil
+	}
+
+	// ask the source volume server to clean up copied ec shards
+
+	// ask the source volume server to delete the original volume
+
+	return err
+
+}
+
+func parallelCopyEcShardsFromSource(ctx context.Context, grpcDialOption grpc.DialOption,
+	targetServers []*master_pb.DataNodeInfo, allocated []int,
+	volumeId needle.VolumeId, existingLocation wdclient.Location) (err error) {
+
+	// parallelize
+	var wg sync.WaitGroup
+	startFromShardId := 0
+	for i, server := range targetServers {
+		if allocated[i] <= 0 {
+			continue
+		}
+
+		wg.Add(1)
+		go func(server *master_pb.DataNodeInfo, startFromShardId int, shardCount int) {
+			defer wg.Done()
+			copyErr := oneServerCopyEcShardsFromSource(ctx, grpcDialOption, server, startFromShardId, shardCount, volumeId, existingLocation)
+			if copyErr != nil {
+				err = copyErr
+			}
+		}(server, startFromShardId, allocated[i])
+		startFromShardId += allocated[i]
+	}
+	wg.Wait()
+
+	return err
+}
+
+func oneServerCopyEcShardsFromSource(ctx context.Context, grpcDialOption grpc.DialOption,
+	targetServer *master_pb.DataNodeInfo, startFromShardId int, shardCount int,
+	volumeId needle.VolumeId, existingLocation wdclient.Location) (err error) {
+
+	if targetServer.Id == existingLocation.Url {
+		return nil
+	}
+
+	for shardId := startFromShardId; shardId < startFromShardId+shardCount; shardId++ {
+		fmt.Printf("copy %d.%d %s => %s\n", volumeId, shardId, existingLocation.Url, targetServer.Id)
+	}
+
+	return nil
+}
+func balancedEcDistribution(servers []*master_pb.DataNodeInfo) (allocated []int) {
+	freeSlots := make([]int, len(servers))
+	allocated = make([]int, len(servers))
+	for i, server := range servers {
+		freeSlots[i] = countFreeShardSlots(server)
+	}
+	allocatedCount := 0
+	for allocatedCount < erasure_coding.TotalShardsCount {
+		for i, _ := range servers {
+			if freeSlots[i]-allocated[i] > 0 {
+				allocated[i] += 1
+				allocatedCount += 1
+			}
+			if allocatedCount >= erasure_coding.TotalShardsCount {
+				break
+			}
+		}
+	}
+
+	return allocated
+}
+
+func eachDataNode(topo *master_pb.TopologyInfo, fn func(*master_pb.DataNodeInfo)) {
+	for _, dc := range topo.DataCenterInfos {
+		for _, rack := range dc.RackInfos {
+			for _, dn := range rack.DataNodeInfos {
+				fn(dn)
+			}
+		}
+	}
+}
+
+func countShards(ecShardInfos []*master_pb.VolumeEcShardInformationMessage) (count int) {
+	for _, ecShardInfo := range ecShardInfos {
+		shardBits := erasure_coding.ShardBits(ecShardInfo.EcIndexBits)
+		count += shardBits.ShardIdCount()
+	}
+	return
+}
+
+func countFreeShardSlots(dn *master_pb.DataNodeInfo) (count int) {
+	return int(dn.FreeVolumeCount)*10 - countShards(dn.EcShardInfos)
+}
diff --git a/weed/storage/erasure_coding/ec_encoder.go b/weed/storage/erasure_coding/ec_encoder.go
index dbfe5858b..da0cfcde8 100644
--- a/weed/storage/erasure_coding/ec_encoder.go
+++ b/weed/storage/erasure_coding/ec_encoder.go
@@ -15,6 +15,7 @@ import (
 const (
 	DataShardsCount             = 10
 	ParityShardsCount           = 4
+	TotalShardsCount            = DataShardsCount + ParityShardsCount
 	ErasureCodingLargeBlockSize = 1024 * 1024 * 1024 // 1GB
 	ErasureCodingSmallBlockSize = 1024 * 1024        // 1MB
 )
@@ -93,7 +94,7 @@ func encodeData(file *os.File, enc reedsolomon.Encoder, startOffset, blockSize i
 }
 
 func openEcFiles(baseFileName string, forRead bool) (files []*os.File, err error) {
-	for i := 0; i < DataShardsCount+ParityShardsCount; i++ {
+	for i := 0; i < TotalShardsCount; i++ {
 		fname := baseFileName + ToExt(i)
 		openOption := os.O_TRUNC | os.O_CREATE | os.O_WRONLY
 		if forRead {
@@ -138,7 +139,7 @@ func encodeDataOneBatch(file *os.File, enc reedsolomon.Encoder, startOffset, blo
 		return err
 	}
 
-	for i := 0; i < DataShardsCount+ParityShardsCount; i++ {
+	for i := 0; i < TotalShardsCount; i++ {
 		_, err := outputs[i].Write(buffers[i])
 		if err != nil {
 			return err
@@ -154,7 +155,7 @@ func encodeDatFile(remainingSize int64, err error, baseFileName string, bufferSi
 	if err != nil {
 		return fmt.Errorf("failed to create encoder: %v", err)
 	}
-	buffers := make([][]byte, DataShardsCount+ParityShardsCount)
+	buffers := make([][]byte, TotalShardsCount)
 	outputs, err := openEcFiles(baseFileName, false)
 	defer closeEcFiles(outputs)
 	if err != nil {
diff --git a/weed/storage/erasure_coding/ec_test.go b/weed/storage/erasure_coding/ec_test.go
index 625f4e9a6..ecf73ac96 100644
--- a/weed/storage/erasure_coding/ec_test.go
+++ b/weed/storage/erasure_coding/ec_test.go
@@ -153,9 +153,9 @@ func readFromOtherEcFiles(ecFiles []*os.File, ecFileIndex int, ecFileOffset int6
 		return nil, fmt.Errorf("failed to create encoder: %v", err)
 	}
 
-	bufs := make([][]byte, DataShardsCount+ParityShardsCount)
+	bufs := make([][]byte, TotalShardsCount)
 	for i := 0; i < DataShardsCount; {
-		n := int(rand.Int31n(DataShardsCount + ParityShardsCount))
+		n := int(rand.Int31n(TotalShardsCount))
 		if n == ecFileIndex || bufs[n] != nil {
 			continue
 		}
diff --git a/weed/storage/erasure_coding/ec_volume_info.go b/weed/storage/erasure_coding/ec_volume_info.go
index c26269158..ef8cc4ed4 100644
--- a/weed/storage/erasure_coding/ec_volume_info.go
+++ b/weed/storage/erasure_coding/ec_volume_info.go
@@ -36,6 +36,10 @@ func (ecInfo *EcVolumeInfo) ShardIds() (ret []ShardId) {
 	return ecInfo.ShardBits.ShardIds()
 }
 
+func (ecInfo *EcVolumeInfo) ShardIdCount() (count int) {
+	return ecInfo.ShardBits.ShardIdCount()
+}
+
 func (ecInfo *EcVolumeInfo) Minus(other *EcVolumeInfo) (*EcVolumeInfo) {
 	ret := &EcVolumeInfo{
 		VolumeId:   ecInfo.VolumeId,
@@ -69,7 +73,7 @@ func (b ShardBits) HasShardId(id ShardId) bool {
 }
 
 func (b ShardBits) ShardIds() (ret []ShardId) {
-	for i := ShardId(0); i < DataShardsCount+ParityShardsCount; i++ {
+	for i := ShardId(0); i < TotalShardsCount; i++ {
 		if b.HasShardId(i) {
 			ret = append(ret, i)
 		}
@@ -77,6 +81,13 @@ func (b ShardBits) ShardIds() (ret []ShardId) {
 	return
 }
 
+func (b ShardBits) ShardIdCount() (count int) {
+	for count = 0; b > 0; count++ {
+		b &= b - 1
+	}
+	return
+}
+
 func (b ShardBits) Minus(other ShardBits) (ShardBits) {
 	return b &^ other
 }
diff --git a/weed/topology/data_node_ec.go b/weed/topology/data_node_ec.go
index e8ead5511..63c8f2127 100644
--- a/weed/topology/data_node_ec.go
+++ b/weed/topology/data_node_ec.go
@@ -30,11 +30,11 @@ func (dn *DataNode) UpdateEcShards(actualShards []*erasure_coding.EcVolumeInfo)
 		} else {
 			// found, but maybe the actual shard could be missing
 			a := actualEcShards.Minus(ecShards)
-			if len(a.ShardIds()) > 0 {
+			if a.ShardIdCount() > 0 {
 				newShards = append(newShards, a)
 			}
 			d := ecShards.Minus(actualEcShards)
-			if len(d.ShardIds()) > 0 {
+			if d.ShardIdCount() > 0 {
 				deletedShards = append(deletedShards, d)
 			}
 		}
diff --git a/weed/topology/topology_ec.go b/weed/topology/topology_ec.go
index eb52b44b4..050a0b901 100644
--- a/weed/topology/topology_ec.go
+++ b/weed/topology/topology_ec.go
@@ -7,11 +7,9 @@ import (
 	"github.com/chrislusf/seaweedfs/weed/storage/needle"
 )
 
-const shardCount = erasure_coding.DataShardsCount + erasure_coding.ParityShardsCount
-
 type EcShardLocations struct {
 	Collection string
-	locations  [shardCount][]*DataNode
+	locations  [erasure_coding.TotalShardsCount][]*DataNode
 }
 
 func (t *Topology) SyncDataNodeEcShards(shardInfos []*master_pb.VolumeEcShardInformationMessage, dn *DataNode) (newShards, deletedShards []*erasure_coding.EcVolumeInfo) {