diff --git a/weed-fs/src/cmd/weed/weed.go b/weed-fs/src/cmd/weed/weed.go
index 52361dc60..97d644da8 100644
--- a/weed-fs/src/cmd/weed/weed.go
+++ b/weed-fs/src/cmd/weed/weed.go
@@ -9,7 +9,9 @@ import (
 	"os"
 	"strings"
 	"sync"
+  "math/rand"
 	"text/template"
+  "time"
 	"unicode"
 	"unicode/utf8"
 )
@@ -39,6 +41,7 @@ func setExitStatus(n int) {
 }
 
 func main() {
+  rand.Seed(time.Now().UnixNano())
 	flag.Usage = usage
 	flag.Parse()
 
diff --git a/weed-fs/src/pkg/topology/node.go b/weed-fs/src/pkg/topology/node.go
index b3bbcbc95..ceea7731e 100644
--- a/weed-fs/src/pkg/topology/node.go
+++ b/weed-fs/src/pkg/topology/node.go
@@ -8,7 +8,7 @@ import (
 type NodeId string
 type Node struct {
 	Id                  NodeId
-	countVolumeCount    int
+	activeVolumeCount   int
 	reservedVolumeCount int
 	maxVolumeCount      int
 	parent              *Node
@@ -21,30 +21,45 @@ func NewNode() *Node {
 	n.children = make(map[NodeId]*Node)
 	return n
 }
+func (n *Node) String() string {
+  if n.parent!=nil {
+    return n.parent.String()+":"+string(n.Id)
+  }
+  return string(n.Id)
+}
 
 func (n *Node) ReserveOneVolume(r int, vid storage.VolumeId) bool {
+  ret := false
+  if n.children == nil {
+    return true
+  }
 	for _, node := range n.children {
-		freeSpace := node.maxVolumeCount - node.countVolumeCount - node.reservedVolumeCount
-		if r > freeSpace {
+		freeSpace := node.maxVolumeCount - node.activeVolumeCount - node.reservedVolumeCount
+    fmt.Println("r =", r, ", node =", node, ", freeSpace =", freeSpace)
+    if freeSpace <= 0 {
+      continue
+    }
+		if r >= freeSpace {
 			r -= freeSpace
 		} else {
-			if node.ReserveOneVolume(r, vid) {
-				node.reservedVolumeCount++
-				return true
-			} else {
-				return false
-			}
+		  ret = node.ReserveOneVolume(r, vid)
+		  if ret {
+		    break
+		  }
 		}
 	}
-	return false
+	if ret {
+	  n.reservedVolumeCount++
+	}
+	return ret
 }
 
 func (n *Node) AddVolume(v *storage.VolumeInfo) {
 	if n.maxVolumeId < v.Id {
 		n.maxVolumeId = v.Id
 	}
-	n.countVolumeCount++
-	fmt.Println(n.Id, "adds 1, volumeCount =", n.countVolumeCount)
+	n.activeVolumeCount++
+	fmt.Println(n.Id, "adds 1, volumeCount =", n.activeVolumeCount)
 	if n.reservedVolumeCount > 0 { //if reserved
 		n.reservedVolumeCount--
 	}
@@ -52,6 +67,12 @@ func (n *Node) AddVolume(v *storage.VolumeInfo) {
 		n.parent.AddVolume(v)
 	}
 }
+func (n *Node) AddMaxVolumeCount(maxVolumeCount int) {//can be negative
+  n.maxVolumeCount += maxVolumeCount
+  if n.parent != nil {
+    n.parent.AddMaxVolumeCount(maxVolumeCount)
+  }
+}
 
 func (n *Node) GetMaxVolumeId() storage.VolumeId {
 	return n.maxVolumeId
@@ -60,17 +81,27 @@ func (n *Node) GetMaxVolumeId() storage.VolumeId {
 func (n *Node) AddNode(node *Node) {
 	if n.children[node.Id] == nil {
 		n.children[node.Id] = node
-		n.countVolumeCount += node.countVolumeCount
+		n.activeVolumeCount += node.activeVolumeCount
+		n.reservedVolumeCount += node.reservedVolumeCount
 		n.maxVolumeCount += node.maxVolumeCount
-		fmt.Println(n.Id, "adds", node.Id, "volumeCount =", n.countVolumeCount)
+		fmt.Println(n.Id, "adds", node.Id, "volumeCount =", n.activeVolumeCount)
 	}
 }
 
-func (n *Node) RemoveNode(node *Node) {
-	if n.children[node.Id] != nil {
+func (n *Node) RemoveNode(nodeId NodeId) {
+	node := n.children[nodeId]
+	if node != nil {
 		delete(n.children, node.Id)
-		n.countVolumeCount -= node.countVolumeCount
+		n.activeVolumeCount -= node.activeVolumeCount
 		n.maxVolumeCount -= node.maxVolumeCount
-		fmt.Println(n.Id, "removes", node.Id, "volumeCount =", n.countVolumeCount)
+		n.reservedVolumeCount -= node.reservedVolumeCount
+		p := n.parent
+		for p != nil {
+			p.activeVolumeCount -= node.activeVolumeCount
+			p.maxVolumeCount -= node.maxVolumeCount
+			p.reservedVolumeCount -= node.reservedVolumeCount
+			p = p.parent
+		}
+		fmt.Println(n.Id, "removes", node.Id, "volumeCount =", n.activeVolumeCount)
 	}
 }
diff --git a/weed-fs/src/pkg/topology/topo_test.go b/weed-fs/src/pkg/topology/topo_test.go
index 0458c699e..928454791 100644
--- a/weed-fs/src/pkg/topology/topo_test.go
+++ b/weed-fs/src/pkg/topology/topo_test.go
@@ -3,8 +3,10 @@ package topology
 import (
 	"encoding/json"
 	"fmt"
+	"math/rand"
 	"pkg/storage"
 	"testing"
+	"time"
 )
 
 var topologyLayout = `
@@ -77,40 +79,41 @@ func setup() *Topology {
 	fmt.Println("data:", data)
 	printMap(data)
 
-  //need to connect all nodes first before server adding volumes
+	//need to connect all nodes first before server adding volumes
 	topo := NewTopology(NodeId("mynetwork"))
 	mTopology := data.(map[string]interface{})
 	for dcKey, dcValue := range mTopology {
 		dc := NewDataCenter(NodeId(dcKey))
 		dc.Node.parent = &topo.Node
 		dcMap := dcValue.(map[string]interface{})
-    topo.Node.AddNode(&dc.Node)
+		topo.Node.AddNode(&dc.Node)
 		for rackKey, rackValue := range dcMap {
 			rack := NewRack(NodeId(rackKey))
-      rack.Node.parent = &dc.Node
+			rack.Node.parent = &dc.Node
 			rackMap := rackValue.(map[string]interface{})
-      dc.Node.AddNode(&rack.Node)
+			dc.Node.AddNode(&rack.Node)
 			for serverKey, serverValue := range rackMap {
 				server := NewServer(NodeId(serverKey))
-        server.Node.parent = &rack.Node
+				server.Node.parent = &rack.Node
 				serverMap := serverValue.(map[string]interface{})
-        rack.Node.AddNode(&server.Node)
+				rack.Node.AddNode(&server.Node)
 				for _, v := range serverMap["volumes"].([]interface{}) {
-				  m := v.(map[string]interface{})
+					m := v.(map[string]interface{})
 					vi := &storage.VolumeInfo{Id: storage.VolumeId(int64(m["id"].(float64))), Size: int64(m["size"].(float64))}
 					server.AddVolume(vi)
 				}
+				server.Node.AddMaxVolumeCount(int(serverMap["limit"].(float64)))
 			}
 		}
 	}
 
 	fmt.Println("topology:", *topo)
 
-  bytes, err := json.Marshal(topo.Node.children)
-  if err!=nil{
-    fmt.Println("json error:", err)
-  }
-  fmt.Println("json topo:", string(bytes))
+	bytes, err := json.Marshal(topo.Node.children)
+	if err != nil {
+		fmt.Println("json error:", err)
+	}
+	fmt.Println("json topo:", string(bytes))
 
 	return topo
 }
@@ -143,34 +146,26 @@ func TestAddVolume(t *testing.T) {
 	topo.AddVolume(v)
 }
 
-func TestAddServer(t *testing.T) {
-
-}
-
-func TestAddRack(t *testing.T) {
-
-}
-
-func TestAddDataCenter(t *testing.T) {
-
-}
-
-func TestReserveVolume(t *testing.T) {
-
-}
-
-func TestRemoveVolume(t *testing.T) {
-
-}
-
-func TestRemoveServer(t *testing.T) {
-
-}
-
-func TestRemoveRack(t *testing.T) {
-
-}
-
 func TestRemoveDataCenter(t *testing.T) {
+	topo := setup()
+	topo.RemoveNode(NodeId("dc2"))
+	if topo.activeVolumeCount != 15 {
+		t.Fail()
+	}
+	topo.RemoveNode(NodeId("dc3"))
+	if topo.activeVolumeCount != 12 {
+		t.Fail()
+	}
+}
 
+func TestReserveOneVolume(t *testing.T) {
+	topo := setup()
+  rand.Seed(time.Now().UnixNano())
+	ret, vid := topo.RandomlyReserveOneVolume()
+	fmt.Println("topology:", topo.Node)
+  fmt.Println("assigned :", ret)
+	fmt.Println("assigned volume id:", vid)
+	if topo.reservedVolumeCount != 1 {
+		t.Fail()
+	}
 }
diff --git a/weed-fs/src/pkg/topology/topology.go b/weed-fs/src/pkg/topology/topology.go
index 3dd08a1fe..49ec944ad 100644
--- a/weed-fs/src/pkg/topology/topology.go
+++ b/weed-fs/src/pkg/topology/topology.go
@@ -3,6 +3,7 @@ package topology
 import (
   "math/rand"
 	"pkg/storage"
+	"fmt"
 )
 
 type Topology struct {
@@ -16,7 +17,10 @@ func NewTopology(id NodeId) *Topology{
 }
 
 func (t *Topology) RandomlyReserveOneVolume() (bool,storage.VolumeId) {
-  r := rand.Intn(t.Node.maxVolumeCount-t.Node.countVolumeCount-t.Node.reservedVolumeCount)
+  slots := t.Node.maxVolumeCount-t.Node.activeVolumeCount-t.Node.reservedVolumeCount
+  r := rand.Intn(slots)
+  r = rand.Intn(slots)
+  fmt.Println("slots:", slots, "random :", r)
   vid := t.nextVolumeId()
   return t.Node.ReserveOneVolume(r,vid), vid
 }