diff --git a/weed/topology/volume_layout.go b/weed/topology/volume_layout.go
index 6ab90e9e2..799cbca62 100644
--- a/weed/topology/volume_layout.go
+++ b/weed/topology/volume_layout.go
@@ -50,7 +50,7 @@ func (vl *VolumeLayout) RegisterVolume(v *storage.VolumeInfo, dn *DataNode) {
 	vl.accessLock.Lock()
 	defer vl.accessLock.Unlock()
 
-	if _, ok := vl.vid2location[v.Id]; !ok || vl.vid2location[v.Id] == nil {
+	if _, ok := vl.vid2location[v.Id]; !ok {
 		vl.vid2location[v.Id] = NewVolumeLocationList()
 	}
 	vl.vid2location[v.Id].Set(dn)
@@ -72,17 +72,13 @@ func (vl *VolumeLayout) RegisterVolume(v *storage.VolumeInfo, dn *DataNode) {
 			return
 		}
 	}
-	if vl.vid2location[v.Id].Length() == vl.rp.GetCopyCount() && vl.isWritable(v) {
-		if _, ok := vl.oversizedVolumes[v.Id]; !ok {
-			vl.addToWritable(v.Id)
-		}
-	} else {
-		vl.rememberOversizedVolumne(v)
-		vl.removeFromWritable(v.Id)
-	}
+
+	vl.rememberOversizedVolume(v)
+	vl.ensureCorrectWritables(v)
+
 }
 
-func (vl *VolumeLayout) rememberOversizedVolumne(v *storage.VolumeInfo) {
+func (vl *VolumeLayout) rememberOversizedVolume(v *storage.VolumeInfo) {
 	if vl.isOversized(v) {
 		vl.oversizedVolumes[v.Id] = true
 	}
@@ -92,9 +88,31 @@ func (vl *VolumeLayout) UnRegisterVolume(v *storage.VolumeInfo, dn *DataNode) {
 	vl.accessLock.Lock()
 	defer vl.accessLock.Unlock()
 
-	vl.removeFromWritable(v.Id)
-	delete(vl.vid2location, v.Id) // somehow this line does not work as expected
-	// vl.vid2location[v.Id] = nil
+	// remove from vid2location map
+	location, ok := vl.vid2location[v.Id]
+	if !ok {
+		return
+	}
+
+	if location.Remove(dn) {
+
+		vl.ensureCorrectWritables(v)
+
+		if location.Length() == 0 {
+			delete(vl.vid2location, v.Id)
+		}
+
+	}
+}
+
+func (vl *VolumeLayout) ensureCorrectWritables(v *storage.VolumeInfo) {
+	if vl.vid2location[v.Id].Length() == vl.rp.GetCopyCount() && vl.isWritable(v) {
+		if _, ok := vl.oversizedVolumes[v.Id]; !ok {
+			vl.addToWritable(v.Id)
+		}
+	} else {
+		vl.removeFromWritable(v.Id)
+	}
 }
 
 func (vl *VolumeLayout) addToWritable(vid needle.VolumeId) {
@@ -252,7 +270,7 @@ func (vl *VolumeLayout) SetVolumeAvailable(dn *DataNode, vid needle.VolumeId) bo
 	defer vl.accessLock.Unlock()
 
 	vl.vid2location[vid].Set(dn)
-	if vl.vid2location[vid].Length() >= vl.rp.GetCopyCount() {
+	if vl.vid2location[vid].Length() == vl.rp.GetCopyCount() {
 		return vl.setVolumeWritable(vid)
 	}
 	return false