diff --git a/weed/topology/data_center.go b/weed/topology/data_center.go
index bcf2dfd31..5d0471a3a 100644
--- a/weed/topology/data_center.go
+++ b/weed/topology/data_center.go
@@ -7,7 +7,7 @@ type DataCenter struct {
 func NewDataCenter(id string) *DataCenter {
 	dc := &DataCenter{}
 	dc.id = NodeId(id)
-	dc.nodeType = "DataCenter"
+	dc.nodeType = NodeTypeDataCenter
 	dc.children = make(map[NodeId]Node)
 	dc.NodeImpl.value = dc
 	return dc
diff --git a/weed/topology/data_node.go b/weed/topology/data_node.go
index 6ea6d3938..558c63f40 100644
--- a/weed/topology/data_node.go
+++ b/weed/topology/data_node.go
@@ -20,7 +20,7 @@ type DataNode struct {
 func NewDataNode(id string) *DataNode {
 	s := &DataNode{}
 	s.id = NodeId(id)
-	s.nodeType = "DataNode"
+	s.nodeType = NodeTypeDataNode
 	s.volumes = make(map[storage.VolumeId]storage.VolumeInfo)
 	s.NodeImpl.value = s
 	return s
diff --git a/weed/topology/node.go b/weed/topology/node.go
index b7d2f79ec..124d0d9fc 100644
--- a/weed/topology/node.go
+++ b/weed/topology/node.go
@@ -109,13 +109,13 @@ func (n *NodeImpl) RandomlyPickNodes(numberOfNodes int, filterFirstNodeFn func(d
 }
 
 func (n *NodeImpl) IsDataNode() bool {
-	return n.nodeType == "DataNode"
+	return n.nodeType == NodeTypeDataNode
 }
 func (n *NodeImpl) IsRack() bool {
-	return n.nodeType == "Rack"
+	return n.nodeType == NodeTypeRack
 }
 func (n *NodeImpl) IsDataCenter() bool {
-	return n.nodeType == "DataCenter"
+	return n.nodeType == NodeTypeDataCenter
 }
 func (n *NodeImpl) String() string {
 	if n.parent != nil {
diff --git a/weed/topology/node_type.go b/weed/topology/node_type.go
new file mode 100644
index 000000000..580dce517
--- /dev/null
+++ b/weed/topology/node_type.go
@@ -0,0 +1,8 @@
+package topology
+
+const (
+	NodeTypeTopology   = "Topology"
+	NodeTypeDataCenter = "DataCenter"
+	NodeTypeRack       = "Rack"
+	NodeTypeDataNode   = "DataNode"
+)
diff --git a/weed/topology/rack.go b/weed/topology/rack.go
index a48d64323..de283e1a6 100644
--- a/weed/topology/rack.go
+++ b/weed/topology/rack.go
@@ -12,7 +12,7 @@ type Rack struct {
 func NewRack(id string) *Rack {
 	r := &Rack{}
 	r.id = NodeId(id)
-	r.nodeType = "Rack"
+	r.nodeType = NodeTypeRack
 	r.children = make(map[NodeId]Node)
 	r.NodeImpl.value = r
 	return r
diff --git a/weed/topology/topology.go b/weed/topology/topology.go
index 0eb2eb32c..95e932f23 100644
--- a/weed/topology/topology.go
+++ b/weed/topology/topology.go
@@ -33,7 +33,7 @@ type Topology struct {
 func NewTopology(id string, seq sequence.Sequencer, volumeSizeLimit uint64, pulse int) *Topology {
 	t := &Topology{}
 	t.id = NodeId(id)
-	t.nodeType = "Topology"
+	t.nodeType = NodeTypeTopology
 	t.NodeImpl.value = t
 	t.children = make(map[NodeId]Node)
 	t.collectionMap = util.NewConcurrentReadMap()