diff --git a/weed-fs/src/pkg/replication/volume_growth.go b/weed-fs/src/pkg/replication/volume_growth.go
index 28dca68b4..41d7bd18c 100644
--- a/weed-fs/src/pkg/replication/volume_growth.go
+++ b/weed-fs/src/pkg/replication/volume_growth.go
@@ -126,9 +126,9 @@ func (vg *VolumeGrowth) GrowByCountAndType(count int, repType storage.Replicatio
 func (vg *VolumeGrowth) grow(topo *topology.Topology, vid storage.VolumeId, repType storage.ReplicationType, servers ...*topology.DataNode) error {
 	for _, server := range servers {
 		if err := AllocateVolume(server, vid, repType); err == nil {
-			vi := &storage.VolumeInfo{Id: vid, Size: 0}
+			vi := storage.VolumeInfo{Id: vid, Size: 0}
 			server.AddOrUpdateVolume(vi)
-			topo.RegisterVolumeLayout(vi, server)
+			topo.RegisterVolumeLayout(&vi, server)
 			fmt.Println("Created Volume", vid, "on", server)
 		} else {
 			fmt.Println("Failed to assign", vid, "to", servers)
diff --git a/weed-fs/src/pkg/topology/data_center.go b/weed-fs/src/pkg/topology/data_center.go
index 5edf7c6eb..c661090e8 100644
--- a/weed-fs/src/pkg/topology/data_center.go
+++ b/weed-fs/src/pkg/topology/data_center.go
@@ -13,6 +13,7 @@ func NewDataCenter(id string) *DataCenter {
 	dc.id = NodeId(id)
 	dc.nodeType = "DataCenter"
 	dc.children = make(map[NodeId]Node)
+  dc.NodeImpl.value = dc
 	return dc
 }
 
diff --git a/weed-fs/src/pkg/topology/data_node.go b/weed-fs/src/pkg/topology/data_node.go
index 2305dddd2..cb625a41b 100644
--- a/weed-fs/src/pkg/topology/data_node.go
+++ b/weed-fs/src/pkg/topology/data_node.go
@@ -7,7 +7,7 @@ import (
 
 type DataNode struct {
 	NodeImpl
-	volumes   map[storage.VolumeId]*storage.VolumeInfo
+	volumes   map[storage.VolumeId]storage.VolumeInfo
 	Ip        string
 	Port      int
 	PublicUrl string
@@ -19,15 +19,12 @@ func NewDataNode(id string) *DataNode {
 	s := &DataNode{}
 	s.id = NodeId(id)
 	s.nodeType = "DataNode"
-	s.volumes = make(map[storage.VolumeId]*storage.VolumeInfo)
+	s.volumes = make(map[storage.VolumeId]storage.VolumeInfo)
+  s.NodeImpl.value = s
 	return s
 }
-func (dn *DataNode) CreateOneVolume(r int, vid storage.VolumeId) storage.VolumeId {
-	dn.AddOrUpdateVolume(&storage.VolumeInfo{Id: vid})
-	return vid
-}
-func (dn *DataNode) AddOrUpdateVolume(v *storage.VolumeInfo) {
-	if dn.volumes[v.Id] == nil {
+func (dn *DataNode) AddOrUpdateVolume(v storage.VolumeInfo) {
+	if _, ok := dn.volumes[v.Id]; !ok {
 		dn.volumes[v.Id] = v
 		dn.UpAdjustActiveVolumeCountDelta(1)
 		dn.UpAdjustMaxVolumeId(v.Id)
diff --git a/weed-fs/src/pkg/topology/node.go b/weed-fs/src/pkg/topology/node.go
index 52315ca2f..044b832ef 100644
--- a/weed-fs/src/pkg/topology/node.go
+++ b/weed-fs/src/pkg/topology/node.go
@@ -17,7 +17,7 @@ type Node interface {
 	GetActiveVolumeCount() int
 	GetMaxVolumeCount() int
 	GetMaxVolumeId() storage.VolumeId
-	setParent(Node)
+	SetParent(Node)
 	LinkChildNode(node Node)
 	UnlinkChildNode(nodeId NodeId)
 	CollectDeadNodeAndFullVolumes(freshThreshHold int64, volumeSizeLimit uint64)
@@ -25,6 +25,8 @@ type Node interface {
 	IsDataNode() bool
 	Children() map[NodeId]Node
 	Parent() Node
+	
+	GetValue()interface{} //get reference to the topology,dc,rack,datanode
 }
 type NodeImpl struct {
 	id                NodeId
@@ -36,6 +38,7 @@ type NodeImpl struct {
 
 	//for rack, data center, topology
 	nodeType string
+	value interface{}
 }
 
 func (n *NodeImpl) IsDataNode() bool {
@@ -59,7 +62,7 @@ func (n *NodeImpl) Id() NodeId {
 func (n *NodeImpl) FreeSpace() int {
 	return n.maxVolumeCount - n.activeVolumeCount
 }
-func (n *NodeImpl) setParent(node Node) {
+func (n *NodeImpl) SetParent(node Node) {
 	n.parent = node
 }
 func (n *NodeImpl) Children() map[NodeId]Node {
@@ -68,6 +71,9 @@ func (n *NodeImpl) Children() map[NodeId]Node {
 func (n *NodeImpl) Parent() Node {
 	return n.parent
 }
+func (n *NodeImpl) GetValue()interface{}{
+  return n.value
+}
 func (n *NodeImpl) ReserveOneVolume(r int, vid storage.VolumeId) (bool, *DataNode) {
 	ret := false
 	var assignedNode *DataNode
@@ -130,14 +136,14 @@ func (n *NodeImpl) LinkChildNode(node Node) {
 		n.UpAdjustMaxVolumeCountDelta(node.GetMaxVolumeCount())
 		n.UpAdjustMaxVolumeId(node.GetMaxVolumeId())
 		n.UpAdjustActiveVolumeCountDelta(node.GetActiveVolumeCount())
-		node.setParent(n)
+		node.SetParent(n)
 		fmt.Println(n, "adds child", node)
 	}
 }
 
 func (n *NodeImpl) UnlinkChildNode(nodeId NodeId) {
 	node := n.children[nodeId]
-	node.setParent(nil)
+	node.SetParent(nil)
 	if node != nil {
 		delete(n.children, node.Id())
 		n.UpAdjustActiveVolumeCountDelta(-node.GetActiveVolumeCount())
@@ -150,15 +156,15 @@ 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.LastSeen < freshThreshHold {
 				if !dn.Dead {
 					dn.Dead = true
 					n.GetTopology().chanDeadDataNodes <- dn
 				}
 			}
 			for _, v := range dn.volumes {
-				if uint64(v.Size) < volumeSizeLimit {
-          n.GetTopology().chanFullVolumes <- v
+				if uint64(v.Size) >= volumeSizeLimit {
+          n.GetTopology().chanFullVolumes <- &v
 				}
 			}
 		}
@@ -175,5 +181,5 @@ func (n *NodeImpl) GetTopology() *Topology{
   for p.Parent() != nil {
     p = p.Parent()
   }
-  return p.(*Topology)
+  return p.GetValue().(*Topology)
 }
diff --git a/weed-fs/src/pkg/topology/rack.go b/weed-fs/src/pkg/topology/rack.go
index bbcd594a2..16520d14a 100644
--- a/weed-fs/src/pkg/topology/rack.go
+++ b/weed-fs/src/pkg/topology/rack.go
@@ -15,6 +15,7 @@ func NewRack(id string) *Rack {
 	r.id = NodeId(id)
 	r.nodeType = "Rack"
 	r.children = make(map[NodeId]Node)
+	r.NodeImpl.value = r
 	return r
 }
 
diff --git a/weed-fs/src/pkg/topology/topology.go b/weed-fs/src/pkg/topology/topology.go
index 3943f9555..fc2c902b0 100644
--- a/weed-fs/src/pkg/topology/topology.go
+++ b/weed-fs/src/pkg/topology/topology.go
@@ -2,6 +2,7 @@ package topology
 
 import (
 	"errors"
+	"fmt"
 	"math/rand"
 	"pkg/directory"
 	"pkg/sequence"
@@ -32,16 +33,20 @@ func NewTopology(id string, dirname string, filename string, volumeSizeLimit uin
 	t := &Topology{}
 	t.id = NodeId(id)
 	t.nodeType = "Topology"
+	t.NodeImpl.value = t
 	t.children = make(map[NodeId]Node)
 	t.replicaType2VolumeLayout = make([]*VolumeLayout, storage.LengthRelicationType)
 	t.pulse = int64(pulse)
 	t.volumeSizeLimit = volumeSizeLimit
+
 	t.sequence = sequence.NewSequencer(dirname, filename)
+
 	t.chanDeadDataNodes = make(chan *DataNode)
 	t.chanRecoveredDataNodes = make(chan *DataNode)
 	t.chanFullVolumes = make(chan *storage.VolumeInfo)
 	t.chanIncomplemteVolumes = make(chan *storage.VolumeInfo)
-  t.chanRecoveredVolumes = make(chan *storage.VolumeInfo)
+	t.chanRecoveredVolumes = make(chan *storage.VolumeInfo)
+
 	return t
 }
 
@@ -102,16 +107,10 @@ func (t *Topology) RegisterVolumes(volumeInfos []storage.VolumeInfo, ip string,
 	rack := dc.GetOrCreateRack(ip)
 	dn := rack.GetOrCreateDataNode(ip, port, publicUrl, maxVolumeCount)
 	for _, v := range volumeInfos {
-		dn.AddOrUpdateVolume(&v)
+		dn.AddOrUpdateVolume(v)
 		t.RegisterVolumeLayout(&v, dn)
 	}
 }
-func (t *Topology) SetVolumeReadOnly(volumeInfo *storage.VolumeInfo) {
-	//TODO
-}
-func (t *Topology) UnRegisterDataNode(dn *DataNode) {
-	//TODO
-}
 
 func (t *Topology) GetOrCreateDataCenter(ip string) *DataCenter {
 	for _, c := range t.Children() {
@@ -155,14 +154,41 @@ func (t *Topology) StartRefreshWritableVolumes() {
 	go func() {
 		for {
 			select {
-			case <-t.chanIncomplemteVolumes:
-      case <-t.chanRecoveredVolumes:
-			case fv := <-t.chanFullVolumes:
-				t.SetVolumeReadOnly(fv)
-			case <-t.chanRecoveredDataNodes:
+			case v := <-t.chanIncomplemteVolumes:
+				fmt.Println("Volume", v, "is incomplete!")
+			case v := <-t.chanRecoveredVolumes:
+				fmt.Println("Volume", v, "is recovered!")
+			case v := <-t.chanFullVolumes:
+				t.SetVolumeReadOnly(v)
+				fmt.Println("Volume", v, "is full!")
+			case dn := <-t.chanRecoveredDataNodes:
+				t.RegisterRecoveredDataNode(dn)
+				fmt.Println("DataNode", dn, "is back alive!")
 			case dn := <-t.chanDeadDataNodes:
 				t.UnRegisterDataNode(dn)
+				fmt.Println("DataNode", dn, "is dead!")
 			}
 		}
 	}()
 }
+func (t *Topology) SetVolumeReadOnly(volumeInfo *storage.VolumeInfo) {
+	vl := t.GetVolumeLayout(volumeInfo.RepType)
+	vl.SetVolumeReadOnly(volumeInfo.Id)
+}
+func (t *Topology) SetVolumeWritable(volumeInfo *storage.VolumeInfo) {
+	vl := t.GetVolumeLayout(volumeInfo.RepType)
+	vl.SetVolumeWritable(volumeInfo.Id)
+}
+func (t *Topology) UnRegisterDataNode(dn *DataNode) {
+	for _, v := range dn.volumes {
+		fmt.Println("Removing Volume", v.Id, "from the dead volume server", dn)
+		t.SetVolumeReadOnly(&v)
+	}
+}
+func (t *Topology) RegisterRecoveredDataNode(dn *DataNode) {
+	for _, v := range dn.volumes {
+		if uint64(v.Size) < t.volumeSizeLimit {
+			t.SetVolumeWritable(&v)
+		}
+	}
+}
diff --git a/weed-fs/src/pkg/topology/volume_layout.go b/weed-fs/src/pkg/topology/volume_layout.go
index 031840e88..0c3841c72 100644
--- a/weed-fs/src/pkg/topology/volume_layout.go
+++ b/weed-fs/src/pkg/topology/volume_layout.go
@@ -56,6 +56,26 @@ func (vl *VolumeLayout) GetActiveVolumeCount() int {
 	return len(vl.writables)
 }
 
+func (vl *VolumeLayout) SetVolumeReadOnly(vid storage.VolumeId) bool {
+  for i, v := range vl.writables{
+    if v == vid {
+      vl.writables = append(vl.writables[:i],vl.writables[i+1:]...)
+      return true
+    }
+  }
+  return false
+}
+
+func (vl *VolumeLayout) SetVolumeWritable(vid storage.VolumeId) bool {
+  for _, v := range vl.writables{
+    if v == vid {
+      return false
+    }
+  }
+  vl.writables = append(vl.writables, vid)
+  return true
+}
+
 func (vl *VolumeLayout) ToMap() interface{} {
 	m := make(map[string]interface{})
 	m["replication"] = vl.repType.String()