diff --git a/weed/shell/command_volume_fix_replication.go b/weed/shell/command_volume_fix_replication.go
new file mode 100644
index 000000000..6a76ba458
--- /dev/null
+++ b/weed/shell/command_volume_fix_replication.go
@@ -0,0 +1,194 @@
+package shell
+
+import (
+	"context"
+	"fmt"
+	"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"
+	"io"
+	"math/rand"
+	"sort"
+)
+
+func init() {
+	commands = append(commands, &commandVolumeFixReplication{})
+}
+
+type commandVolumeFixReplication struct {
+}
+
+func (c *commandVolumeFixReplication) Name() string {
+	return "volume.fix.replication"
+}
+
+func (c *commandVolumeFixReplication) Help() string {
+	return `add replicas to volumes that are missing replicas
+
+	-n do not take action
+`
+}
+
+func (c *commandVolumeFixReplication) Do(args []string, commandEnv *commandEnv, writer io.Writer) (err error) {
+
+	takeAction := true
+	if len(args) > 0 && args[0] == "-n" {
+		takeAction = false
+	}
+
+	var resp *master_pb.VolumeListResponse
+	ctx := context.Background()
+	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 all volumes that needs replication
+	// collect all data nodes
+	replicatedVolumeLocations := make(map[uint32][]location)
+	replicatedVolumeInfo := make(map[uint32]*master_pb.VolumeInformationMessage)
+	var allLocations []location
+	for _, dc := range resp.TopologyInfo.DataCenterInfos {
+		for _, rack := range dc.RackInfos {
+			for _, dn := range rack.DataNodeInfos {
+				loc := newLocation(dc.Id, rack.Id, dn)
+				for _, v := range dn.VolumeInfos {
+					if v.ReplicaPlacement > 0 {
+						replicatedVolumeLocations[v.Id] = append(replicatedVolumeLocations[v.Id], loc)
+						replicatedVolumeInfo[v.Id] = v
+					}
+				}
+				allLocations = append(allLocations, loc)
+			}
+		}
+	}
+
+	// find all under replicated volumes
+	underReplicatedVolumeLocations := make(map[uint32][]location)
+	for vid, locations := range replicatedVolumeLocations {
+		volumeInfo := replicatedVolumeInfo[vid]
+		replicaPlacement, _ := storage.NewReplicaPlacementFromByte(byte(volumeInfo.ReplicaPlacement))
+		if replicaPlacement.GetCopyCount() > len(locations) {
+			underReplicatedVolumeLocations[vid] = locations
+		}
+	}
+
+	if len(underReplicatedVolumeLocations) == 0 {
+		return fmt.Errorf("no under replicated volumes")
+	}
+
+	if len(allLocations) == 0 {
+		return fmt.Errorf("no data nodes at all")
+	}
+
+	// find the most under populated data nodes
+	keepDataNodesSorted(allLocations)
+
+	for vid, locations := range underReplicatedVolumeLocations {
+		volumeInfo := replicatedVolumeInfo[vid]
+		replicaPlacement, _ := storage.NewReplicaPlacementFromByte(byte(volumeInfo.ReplicaPlacement))
+		foundNewLocation := false
+		for _, dst := range allLocations {
+			// check whether data nodes satisfy the constraints
+			if dst.dataNode.FreeVolumeCount > 0 && satisfyReplicaPlacement(replicaPlacement, locations, dst) {
+				// ask the volume server to replicate the volume
+				sourceNodes := underReplicatedVolumeLocations[vid]
+				sourceNode := sourceNodes[rand.Intn(len(sourceNodes))]
+				foundNewLocation = true
+				fmt.Fprintf(writer, "replicating volume %d %s from %s to dataNode %s ...\n", volumeInfo.Id, replicaPlacement, sourceNode.dataNode.Id, dst.dataNode.Id)
+
+				if !takeAction {
+					break
+				}
+
+				err := operation.WithVolumeServerClient(dst.dataNode.Id, commandEnv.option.GrpcDialOption, func(volumeServerClient volume_server_pb.VolumeServerClient) error {
+					_, replicateErr := volumeServerClient.ReplicateVolume(ctx, &volume_server_pb.ReplicateVolumeRequest{
+						VolumeId:       volumeInfo.Id,
+						Collection:     volumeInfo.Collection,
+						SourceDataNode: sourceNode.dataNode.Id,
+					})
+					return replicateErr
+				})
+
+				if err != nil {
+					return err
+				}
+
+				// adjust free volume count
+				dst.dataNode.FreeVolumeCount--
+				keepDataNodesSorted(allLocations)
+				break
+			}
+		}
+		if !foundNewLocation {
+			fmt.Fprintf(writer, "failed to place volume %d replica as %s, existing:%+v\n", volumeInfo.Id, replicaPlacement, locations)
+		}
+
+	}
+
+	return nil
+}
+
+func keepDataNodesSorted(dataNodes []location) {
+	sort.Slice(dataNodes, func(i, j int) bool {
+		return dataNodes[i].dataNode.FreeVolumeCount > dataNodes[j].dataNode.FreeVolumeCount
+	})
+}
+
+func satisfyReplicaPlacement(replicaPlacement *storage.ReplicaPlacement, existingLocations []location, possibleLocation location) bool {
+
+	existingDataCenters := make(map[string]bool)
+	existingRacks := make(map[string]bool)
+	existingDataNodes := make(map[string]bool)
+	for _, loc := range existingLocations {
+		existingDataCenters[loc.DataCenter()] = true
+		existingRacks[loc.Rack()] = true
+		existingDataNodes[loc.String()] = true
+	}
+
+	if replicaPlacement.DiffDataCenterCount >= len(existingDataCenters) {
+		// check dc, good if different from any existing data centers
+		_, found := existingDataCenters[possibleLocation.DataCenter()]
+		return !found
+	} else if replicaPlacement.DiffRackCount >= len(existingRacks) {
+		// check rack, good if different from any existing racks
+		_, found := existingRacks[possibleLocation.Rack()]
+		return !found
+	} else if replicaPlacement.SameRackCount >= len(existingDataNodes) {
+		// check data node, good if different from any existing data nodes
+		_, found := existingDataNodes[possibleLocation.String()]
+		return !found
+	}
+
+	return false
+}
+
+type location struct {
+	dc       string
+	rack     string
+	dataNode *master_pb.DataNodeInfo
+}
+
+func newLocation(dc, rack string, dataNode *master_pb.DataNodeInfo) location {
+	return location{
+		dc:       dc,
+		rack:     rack,
+		dataNode: dataNode,
+	}
+}
+
+func (l location) String() string {
+	return fmt.Sprintf("%s %s %s", l.dc, l.rack, l.dataNode.Id)
+}
+
+func (l location) Rack() string {
+	return fmt.Sprintf("%s %s", l.dc, l.rack)
+}
+
+func (l location) DataCenter() string {
+	return l.dc
+}