diff --git a/Makefile b/Makefile
index 52c2ef8ca..14c07fa86 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 BINARY = weed
 
-GO_FLAGS = #-v
+GO_FLAGS = -race #-v
 SOURCE_DIR = ./go/weed/
 
 all: build
diff --git a/go/topology/data_center.go b/go/topology/data_center.go
index 9d992a2cd..a2063f2f4 100644
--- a/go/topology/data_center.go
+++ b/go/topology/data_center.go
@@ -14,11 +14,11 @@ func NewDataCenter(id string) *DataCenter {
 }
 
 func (dc *DataCenter) GetOrCreateRack(rackName string) *Rack {
-	rack := dc.GetChildren(NodeId(rackName)).(*Rack)
-	if rack != nil {
-		return rack
+	n := dc.GetChildren(NodeId(rackName))
+	if n != nil {
+		return n.(*Rack)
 	}
-	rack = NewRack(rackName)
+	rack := NewRack(rackName)
 	dc.LinkChildNode(rack)
 	return rack
 }
diff --git a/go/topology/data_node.go b/go/topology/data_node.go
index b6090fb76..f0f261ea1 100644
--- a/go/topology/data_node.go
+++ b/go/topology/data_node.go
@@ -7,16 +7,17 @@ import (
 	"github.com/chrislusf/seaweedfs/go/glog"
 	"github.com/chrislusf/seaweedfs/go/storage"
 	"net"
+	"time"
 )
 
 type DataNode struct {
 	NodeImpl
 	volumes   map[storage.VolumeId]*storage.VolumeInfo
+	lastSeen  int64 // unix time in seconds
+	dead      bool
 	Ip        string
 	Port      int
 	PublicUrl string
-	LastSeen  int64 // unix time in seconds
-	Dead      bool
 }
 
 func NewDataNode(id string) *DataNode {
@@ -29,7 +30,33 @@ func NewDataNode(id string) *DataNode {
 }
 
 func (dn *DataNode) String() string {
-	return fmt.Sprintf("Node:%s, volumes:%v, Ip:%s, Port:%d, PublicUrl:%s, Dead:%v", dn.NodeImpl.String(), dn.volumes, dn.Ip, dn.Port, dn.PublicUrl, dn.Dead)
+	dn.mutex.RLock()
+	defer dn.mutex.RUnlock()
+	return fmt.Sprintf("Node:%s, volumes:%v, Ip:%s, Port:%d, PublicUrl:%s, Dead:%v", dn.NodeImpl.String(), dn.volumes, dn.Ip, dn.Port, dn.PublicUrl, dn.dead)
+}
+
+func (dn *DataNode) LastSeen() int64 {
+	dn.mutex.RLock()
+	defer dn.mutex.RUnlock()
+	return dn.lastSeen
+}
+
+func (dn *DataNode) UpdateLastSeen() {
+	dn.mutex.Lock()
+	defer dn.mutex.Unlock()
+	dn.lastSeen = time.Now().Unix()
+}
+
+func (dn *DataNode) IsDead() bool {
+	dn.mutex.RLock()
+	defer dn.mutex.RUnlock()
+	return dn.dead
+}
+
+func (dn *DataNode) SetDead(b bool) {
+	dn.mutex.Lock()
+	defer dn.mutex.Unlock()
+	dn.dead = b
 }
 
 func (dn *DataNode) AddOrUpdateVolume(v *storage.VolumeInfo) {
diff --git a/go/topology/node.go b/go/topology/node.go
index d403ea68f..6d018fe39 100644
--- a/go/topology/node.go
+++ b/go/topology/node.go
@@ -326,9 +326,9 @@ func (n *NodeImpl) CollectDeadNodeAndFullVolumes(freshThreshHold int64, volumeSi
 	if n.IsRack() {
 		for _, c := range n.Children() {
 			dn := c.(*DataNode) //can not cast n to DataNode
-			if dn.LastSeen < freshThreshHold {
-				if !dn.Dead {
-					dn.Dead = true
+			if dn.LastSeen() < freshThreshHold {
+				if !dn.IsDead() {
+					dn.SetDead(true)
 					n.GetTopology().chanDeadDataNodes <- dn
 				}
 			}
diff --git a/go/topology/rack.go b/go/topology/rack.go
index 4f4b3b573..66725fc2f 100644
--- a/go/topology/rack.go
+++ b/go/topology/rack.go
@@ -3,7 +3,6 @@ package topology
 import (
 	"net"
 	"strconv"
-	"time"
 )
 
 type Rack struct {
@@ -24,14 +23,17 @@ func (r *Rack) FindDataNode(ip string, port int) *DataNode {
 		dn := c.(*DataNode)
 		return dn.MatchLocation(ip, port)
 	})
+	if n == nil {
+		return nil
+	}
 	return n.(*DataNode)
 }
 
 func (r *Rack) GetOrCreateDataNode(ip string, port int, publicUrl string, maxVolumeCount int) *DataNode {
 	if dn := r.FindDataNode(ip, port); dn != nil {
-		dn.LastSeen = time.Now().Unix()
-		if dn.Dead {
-			dn.Dead = false
+		dn.UpdateLastSeen()
+		if dn.IsDead() {
+			dn.SetDead(false)
 			r.GetTopology().chanRecoveredDataNodes <- dn
 			dn.UpAdjustMaxVolumeCountDelta(maxVolumeCount - dn.maxVolumeCount)
 		}
@@ -48,7 +50,7 @@ func (r *Rack) GetOrCreateDataNode(ip string, port int, publicUrl string, maxVol
 	}
 	dn.PublicUrl = publicUrl
 	dn.maxVolumeCount = maxVolumeCount
-	dn.LastSeen = time.Now().Unix()
+	dn.UpdateLastSeen()
 	r.LinkChildNode(dn)
 	return dn
 }
diff --git a/go/topology/topology.go b/go/topology/topology.go
index 04c69de9c..b8a22e94f 100644
--- a/go/topology/topology.go
+++ b/go/topology/topology.go
@@ -22,7 +22,7 @@ type Topology struct {
 	Sequence           sequence.Sequencer
 	CollectionSettings *storage.CollectionSettings
 	configuration      *Configuration
-	RaftServer         raft.Server
+	raftServer         raft.Server
 
 	chanDeadDataNodes      chan *DataNode
 	chanRecoveredDataNodes chan *DataNode
@@ -51,24 +51,36 @@ func NewTopology(id string, confFile string, cs *storage.CollectionSettings, seq
 	return t, err
 }
 
+func (t *Topology) GetRaftServer() raft.Server {
+	t.mutex.RLock()
+	defer t.mutex.RUnlock()
+	return t.raftServer
+}
+
+func (t *Topology) SetRaftServer(s raft.Server) {
+	t.mutex.Lock()
+	defer t.mutex.Unlock()
+	t.raftServer = s
+}
+
 func (t *Topology) IsLeader() bool {
 	if leader, e := t.Leader(); e == nil {
-		return leader == t.RaftServer.Name()
+		return leader == t.GetRaftServer().Name()
 	}
 	return false
 }
 
 func (t *Topology) Leader() (string, error) {
 	l := ""
-	if t.RaftServer != nil {
-		l = t.RaftServer.Leader()
+	if t.GetRaftServer() != nil {
+		l = t.GetRaftServer().Leader()
 	} else {
 		return "", errors.New("Raft Server not ready yet!")
 	}
 
 	if l == "" {
 		// We are a single node cluster, we are the leader
-		return t.RaftServer.Name(), errors.New("Raft Server not initialized!")
+		return t.GetRaftServer().Name(), errors.New("Raft Server not initialized!")
 	}
 
 	return l, nil
@@ -106,7 +118,7 @@ func (t *Topology) Lookup(collection string, vid storage.VolumeId) (vl *VolumeLo
 func (t *Topology) NextVolumeId() storage.VolumeId {
 	vid := t.GetMaxVolumeId()
 	next := vid.Next()
-	go t.RaftServer.Do(NewMaxVolumeIdCommand(next))
+	go t.GetRaftServer().Do(NewMaxVolumeIdCommand(next))
 	return next
 }
 
@@ -179,11 +191,11 @@ func (t *Topology) ProcessJoinMessage(joinMessage *operation.JoinMessage) {
 }
 
 func (t *Topology) GetOrCreateDataCenter(dcName string) *DataCenter {
-	dc := t.GetChildren(NodeId(dcName)).(*DataCenter)
-	if dc != nil {
-		return dc
+	n := t.GetChildren(NodeId(dcName))
+	if n != nil {
+		return n.(*DataCenter)
 	}
-	dc = NewDataCenter(dcName)
+	dc := NewDataCenter(dcName)
 	t.LinkChildNode(dc)
 	return dc
 }
diff --git a/go/topology/volume_location_list.go b/go/topology/volume_location_list.go
index 901d27ce0..ec71d6115 100644
--- a/go/topology/volume_location_list.go
+++ b/go/topology/volume_location_list.go
@@ -65,7 +65,7 @@ func (dnll *VolumeLocationList) Remove(loc *DataNode) bool {
 func (dnll *VolumeLocationList) Refresh(freshThreshHold int64) {
 	var changed bool
 	for _, dnl := range dnll.list {
-		if dnl.LastSeen < freshThreshHold {
+		if dnl.LastSeen() < freshThreshHold {
 			changed = true
 			break
 		}
@@ -73,7 +73,7 @@ func (dnll *VolumeLocationList) Refresh(freshThreshHold int64) {
 	if changed {
 		var l []*DataNode
 		for _, dnl := range dnll.list {
-			if dnl.LastSeen >= freshThreshHold {
+			if dnl.LastSeen() >= freshThreshHold {
 				l = append(l, dnl)
 			}
 		}
diff --git a/go/weed/weed_server/master_server.go b/go/weed/weed_server/master_server.go
index 62ec5c9aa..07d9a4722 100644
--- a/go/weed/weed_server/master_server.go
+++ b/go/weed/weed_server/master_server.go
@@ -86,17 +86,17 @@ func NewMasterServer(r *mux.Router, port int, metaFolder string,
 }
 
 func (ms *MasterServer) SetRaftServer(raftServer *RaftServer) {
-	ms.Topo.RaftServer = raftServer.raftServer
-	ms.Topo.RaftServer.AddEventListener(raft.LeaderChangeEventType, func(e raft.Event) {
-		if ms.Topo.RaftServer.Leader() != "" {
-			glog.V(0).Infoln("[", ms.Topo.RaftServer.Name(), "]", ms.Topo.RaftServer.Leader(), "becomes leader.")
+	ms.Topo.SetRaftServer(raftServer.raftServer)
+	ms.Topo.GetRaftServer().AddEventListener(raft.LeaderChangeEventType, func(e raft.Event) {
+		if ms.Topo.GetRaftServer().Leader() != "" {
+			glog.V(0).Infoln("[", ms.Topo.GetRaftServer().Name(), "]", ms.Topo.GetRaftServer().Leader(), "becomes leader.")
 		}
 	})
 	if ms.Topo.IsLeader() {
-		glog.V(0).Infoln("[", ms.Topo.RaftServer.Name(), "]", "I am the leader!")
+		glog.V(0).Infoln("[", ms.Topo.GetRaftServer().Name(), "]", "I am the leader!")
 	} else {
-		if ms.Topo.RaftServer.Leader() != "" {
-			glog.V(0).Infoln("[", ms.Topo.RaftServer.Name(), "]", ms.Topo.RaftServer.Leader(), "is the leader.")
+		if ms.Topo.GetRaftServer().Leader() != "" {
+			glog.V(0).Infoln("[", ms.Topo.GetRaftServer().Name(), "]", ms.Topo.GetRaftServer().Leader(), "is the leader.")
 		}
 	}
 }
@@ -105,16 +105,16 @@ func (ms *MasterServer) proxyToLeader(f func(w http.ResponseWriter, r *http.Requ
 	return func(w http.ResponseWriter, r *http.Request) {
 		if ms.Topo.IsLeader() {
 			f(w, r)
-		} else if ms.Topo.RaftServer != nil && ms.Topo.RaftServer.Leader() != "" {
+		} else if ms.Topo.GetRaftServer() != nil && ms.Topo.GetRaftServer().Leader() != "" {
 			ms.bounedLeaderChan <- 1
 			defer func() { <-ms.bounedLeaderChan }()
-			targetUrl, err := url.Parse("http://" + ms.Topo.RaftServer.Leader())
+			targetUrl, err := url.Parse("http://" + ms.Topo.GetRaftServer().Leader())
 			if err != nil {
 				writeJsonError(w, r, http.StatusInternalServerError,
-					fmt.Errorf("Leader URL http://%s Parse Error: %v", ms.Topo.RaftServer.Leader(), err))
+					fmt.Errorf("Leader URL http://%s Parse Error: %v", ms.Topo.GetRaftServer().Leader(), err))
 				return
 			}
-			glog.V(4).Infoln("proxying to leader", ms.Topo.RaftServer.Leader())
+			glog.V(4).Infoln("proxying to leader", ms.Topo.GetRaftServer().Leader())
 			proxy := httputil.NewSingleHostReverseProxy(targetUrl)
 			director := proxy.Director
 			proxy.Director = func(req *http.Request) {
diff --git a/go/weed/weed_server/master_server_handlers_admin.go b/go/weed/weed_server/master_server_handlers_admin.go
index 748c98fda..b06440d85 100644
--- a/go/weed/weed_server/master_server_handlers_admin.go
+++ b/go/weed/weed_server/master_server_handlers_admin.go
@@ -171,7 +171,7 @@ func (ms *MasterServer) deleteFromMasterServerHandler(w http.ResponseWriter, r *
 	if ms.Topo.IsLeader() {
 		deleteForClientHandler(w, r, ms.selfUrl(r))
 	} else {
-		deleteForClientHandler(w, r, ms.Topo.RaftServer.Leader())
+		deleteForClientHandler(w, r, ms.Topo.GetRaftServer().Leader())
 	}
 }
 
diff --git a/go/weed/weed_server/master_server_handlers_ui.go b/go/weed/weed_server/master_server_handlers_ui.go
index af7261ab3..8bbc34461 100644
--- a/go/weed/weed_server/master_server_handlers_ui.go
+++ b/go/weed/weed_server/master_server_handlers_ui.go
@@ -21,8 +21,8 @@ func (ms *MasterServer) uiStatusHandler(w http.ResponseWriter, r *http.Request)
 	}{
 		util.VERSION,
 		ms.Topo.ToMap(),
-		ms.Topo.RaftServer.Leader(),
-		ms.Topo.RaftServer.Peers(),
+		ms.Topo.GetRaftServer().Leader(),
+		ms.Topo.GetRaftServer().Peers(),
 		infos,
 		serverStats,
 	}