diff --git a/weed/shell/command_ec_common.go b/weed/shell/command_ec_common.go
index c49ab7611..209d8a733 100644
--- a/weed/shell/command_ec_common.go
+++ b/weed/shell/command_ec_common.go
@@ -134,6 +134,14 @@ func NewErrorWaitGroup(maxConcurrency int) *ErrorWaitGroup {
 	}
 }
 
+func (ewg *ErrorWaitGroup) Reset() {
+	close(ewg.wgSem)
+
+	ewg.wg = &sync.WaitGroup{}
+	ewg.wgSem = make(chan bool, ewg.maxConcurrency)
+	ewg.errors = nil
+}
+
 func (ewg *ErrorWaitGroup) Add(f ErrorWaitGroupTask) {
 	if ewg.maxConcurrency <= 1 {
 		// Keep run order deterministic when parallelization is off
diff --git a/weed/shell/command_ec_encode.go b/weed/shell/command_ec_encode.go
index afbf90b44..d9e3a88c6 100644
--- a/weed/shell/command_ec_encode.go
+++ b/weed/shell/command_ec_encode.go
@@ -118,33 +118,42 @@ func (c *commandEcEncode) Do(args []string, commandEnv *CommandEnv, writer io.Wr
 	if err = doEcEncode(commandEnv, *collection, volumeIds, *maxParallelization); err != nil {
 		return fmt.Errorf("ec encode for volumes %v: %v", volumeIds, err)
 	}
-	// ...then re-balance ec shards.
+	// ...re-balance ec shards...
 	if err := EcBalance(commandEnv, balanceCollections, "", rp, *maxParallelization, *applyBalancing); err != nil {
 		return fmt.Errorf("re-balance ec shards for collection(s) %v: %v", balanceCollections, err)
 	}
+	// ...then delete original volumes.
+	if err := doDeleteVolumes(commandEnv, volumeIds, *maxParallelization); err != nil {
+		return fmt.Errorf("re-balance ec shards for collection(s) %v: %v", balanceCollections, err)
+	}
 
 	return nil
 }
 
-func doEcEncode(commandEnv *CommandEnv, collection string, volumeIds []needle.VolumeId, maxParallelization int) error {
-	var ewg *ErrorWaitGroup
-
-	if !commandEnv.isLocked() {
-		return fmt.Errorf("lock is lost")
-	}
-
-	// resolve volume locations
-	locations := map[needle.VolumeId][]wdclient.Location{}
+func volumeLocations(commandEnv *CommandEnv, volumeIds []needle.VolumeId) (map[needle.VolumeId][]wdclient.Location, error) {
+	res := map[needle.VolumeId][]wdclient.Location{}
 	for _, vid := range volumeIds {
 		ls, ok := commandEnv.MasterClient.GetLocationsClone(uint32(vid))
 		if !ok {
-			return fmt.Errorf("volume %d not found", vid)
+			return nil, fmt.Errorf("volume %d not found", vid)
 		}
-		locations[vid] = ls
+		res[vid] = ls
+	}
+
+	return res, nil
+}
+
+func doEcEncode(commandEnv *CommandEnv, collection string, volumeIds []needle.VolumeId, maxParallelization int) error {
+	if !commandEnv.isLocked() {
+		return fmt.Errorf("lock is lost")
+	}
+	locations, err := volumeLocations(commandEnv, volumeIds)
+	if err != nil {
+		return nil
 	}
 
 	// mark volumes as readonly
-	ewg = NewErrorWaitGroup(maxParallelization)
+	ewg := NewErrorWaitGroup(maxParallelization)
 	for _, vid := range volumeIds {
 		for _, l := range locations[vid] {
 			ewg.Add(func() error {
@@ -160,9 +169,9 @@ func doEcEncode(commandEnv *CommandEnv, collection string, volumeIds []needle.Vo
 	}
 
 	// generate ec shards
-	ewg = NewErrorWaitGroup(maxParallelization)
-	for _, vid := range volumeIds {
-		target := locations[vid][0]
+	ewg.Reset()
+	for i, vid := range volumeIds {
+		target := locations[vid][i%len(locations[vid])]
 		ewg.Add(func() error {
 			if err := generateEcShards(commandEnv.option.GrpcDialOption, vid, collection, target.ServerAddress()); err != nil {
 				return fmt.Errorf("generate ec shards for volume %d on %s: %v", vid, target.Url, err)
@@ -174,30 +183,13 @@ func doEcEncode(commandEnv *CommandEnv, collection string, volumeIds []needle.Vo
 		return err
 	}
 
-	// ask the source volume server to delete the original volume
-	ewg = NewErrorWaitGroup(maxParallelization)
-	for _, vid := range volumeIds {
-		for _, l := range locations[vid] {
-			ewg.Add(func() error {
-				if err := deleteVolume(commandEnv.option.GrpcDialOption, vid, l.ServerAddress(), false); err != nil {
-					return fmt.Errorf("deleteVolume %s volume %d: %v", l.Url, vid, err)
-				}
-				fmt.Printf("deleted volume %d from %s\n", vid, l.Url)
-				return nil
-			})
-		}
-	}
-	if err := ewg.Wait(); err != nil {
-		return err
-	}
-
 	// mount all ec shards for the converted volume
 	shardIds := make([]uint32, erasure_coding.TotalShardsCount)
 	for i := range shardIds {
 		shardIds[i] = uint32(i)
 	}
 
-	ewg = NewErrorWaitGroup(maxParallelization)
+	ewg.Reset()
 	for _, vid := range volumeIds {
 		target := locations[vid][0]
 		ewg.Add(func() error {
@@ -214,9 +206,37 @@ func doEcEncode(commandEnv *CommandEnv, collection string, volumeIds []needle.Vo
 	return nil
 }
 
+func doDeleteVolumes(commandEnv *CommandEnv, volumeIds []needle.VolumeId, maxParallelization int) error {
+	if !commandEnv.isLocked() {
+		return fmt.Errorf("lock is lost")
+	}
+	locations, err := volumeLocations(commandEnv, volumeIds)
+	if err != nil {
+		return nil
+	}
+
+	ewg := NewErrorWaitGroup(maxParallelization)
+	for _, vid := range volumeIds {
+		for _, l := range locations[vid] {
+			ewg.Add(func() error {
+				if err := deleteVolume(commandEnv.option.GrpcDialOption, vid, l.ServerAddress(), false); err != nil {
+					return fmt.Errorf("deleteVolume %s volume %d: %v", l.Url, vid, err)
+				}
+				fmt.Printf("deleted volume %d from %s\n", vid, l.Url)
+				return nil
+			})
+		}
+	}
+	if err := ewg.Wait(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
 func generateEcShards(grpcDialOption grpc.DialOption, volumeId needle.VolumeId, collection string, sourceVolumeServer pb.ServerAddress) error {
 
-	fmt.Printf("generateEcShards %s %d on %s ...\n", collection, volumeId, sourceVolumeServer)
+	fmt.Printf("generateEcShards %d (collection %q) on %s ...\n", volumeId, collection, sourceVolumeServer)
 
 	err := operation.WithVolumeServerClient(false, sourceVolumeServer, grpcDialOption, func(volumeServerClient volume_server_pb.VolumeServerClient) error {
 		_, genErr := volumeServerClient.VolumeEcShardsGenerate(context.Background(), &volume_server_pb.VolumeEcShardsGenerateRequest{