diff --git a/weed-fs/src/pkg/replication/volume_growth.go b/weed-fs/src/pkg/replication/volume_growth.go
new file mode 100644
index 000000000..49afc741c
--- /dev/null
+++ b/weed-fs/src/pkg/replication/volume_growth.go
@@ -0,0 +1,29 @@
+package replication
+
+import (
+	"pkg/topology"
+)
+
+/*
+This package is created to resolve these replica placement issues:
+1. growth factor for each replica level, e.g., add 10 volumes for 1 copy, 20 volumes for 2 copies, 30 volumes for 3 copies
+2. in time of tight storage, how to reduce replica level
+3. optimizing for hot data on faster disk, cold data on cheaper storage,
+4. volume allocation for each bucket
+*/
+
+type VolumeGrowth struct {
+	copy1factor int
+	copy2factor int
+	copy3factor int
+	copyAll     int
+}
+
+func (vg *VolumeGrowth) GrowVolumeCopy(copyLevel int, topo topology.Topology) {
+	if copyLevel == 1 {
+		for i := 0; i <vg.copy1factor; i++ {
+			topo.RandomlyCreateOneVolume()
+		}
+	}
+
+}
diff --git a/weed-fs/src/pkg/storage/storage_limit.go b/weed-fs/src/pkg/storage/storage_limit.go
index 915ec48a3..b40618046 100644
--- a/weed-fs/src/pkg/storage/storage_limit.go
+++ b/weed-fs/src/pkg/storage/storage_limit.go
@@ -1,21 +1,13 @@
 package storage
 
 import (
-	"syscall"
 )
 
 type StorageLimit struct {
 	sizeLimit     uint64
-	detectedLimit uint64
 }
 
 func NewStorageLimit(desiredLimit uint64) *StorageLimit {
-	s := syscall.Statfs_t{}
-	errNo := syscall.Statfs(".", &s)
-	detected := uint64(0)
-	if errNo==nil {
-    detected = s.Bavail*uint64(s.Bsize)
-	}
-	sl := &StorageLimit{sizeLimit: desiredLimit, detectedLimit: detected}
+	sl := &StorageLimit{sizeLimit: desiredLimit}
 	return sl
 }
diff --git a/weed-fs/src/pkg/storage/storage_limit_test.go b/weed-fs/src/pkg/storage/storage_limit_test.go
deleted file mode 100644
index c818356f9..000000000
--- a/weed-fs/src/pkg/storage/storage_limit_test.go
+++ /dev/null
@@ -1,11 +0,0 @@
-package storage
-
-import (
-    "testing"
-)
-
-func TestReadStorageLimit(t *testing.T) {
-  sl := NewStorageLimit(1000)
-  println("detected:",sl.detectedLimit)
-}
-
diff --git a/weed-fs/src/pkg/storage/store.go b/weed-fs/src/pkg/storage/store.go
index 1c3ba4a51..1dbb89c06 100644
--- a/weed-fs/src/pkg/storage/store.go
+++ b/weed-fs/src/pkg/storage/store.go
@@ -89,11 +89,23 @@ func (s *Store) Close() {
 	}
 }
 func (s *Store) Write(i VolumeId, n *Needle) uint32 {
-	return s.volumes[i].write(n)
+  v := s.volumes[i]
+  if v!=nil{
+    return v.write(n)
+  }
+  return 0
 }
 func (s *Store) Delete(i VolumeId, n *Needle) uint32 {
-	return s.volumes[i].delete(n)
+  v := s.volumes[i]
+  if v!=nil{
+    return v.delete(n)
+  }
+  return 0
 }
 func (s *Store) Read(i VolumeId, n *Needle) (int, error) {
-	return s.volumes[i].read(n)
+  v := s.volumes[i]
+  if v!=nil{
+    return v.read(n)
+  }
+  return 0, errors.New("Not Found")
 }
diff --git a/weed-fs/src/pkg/topology/node.go b/weed-fs/src/pkg/topology/node.go
index 4eccdbf65..9c1a87f89 100644
--- a/weed-fs/src/pkg/topology/node.go
+++ b/weed-fs/src/pkg/topology/node.go
@@ -11,4 +11,19 @@ type Node struct {
 	Ip          string
 	Port        int
 	PublicUrl   string
+	
+	//transient
+	allocation *Allocation
 }
+type Allocation struct {
+  count int
+  limit int
+}
+
+func (n *Node) GetAllocation() *Allocation{
+  if n.allocation == nil {
+    n.allocation = &Allocation{count:len(n.volumes), limit : n.volumeLimit}
+  }
+  return n.allocation
+}
+
diff --git a/weed-fs/src/pkg/topology/topology.go b/weed-fs/src/pkg/topology/topology.go
index 7db3d0e32..7d903b961 100644
--- a/weed-fs/src/pkg/topology/topology.go
+++ b/weed-fs/src/pkg/topology/topology.go
@@ -1,9 +1,16 @@
 package topology
 
 import (
-
+  "pkg/storage"
 )
 
 type Topology struct {
   datacenters     map[DataCenterId]*DataCenter
 }
+//FIXME
+func (t *Topology) RandomlyCreateOneVolume() storage.VolumeId{
+  return t.findMaxVolumeId()
+}
+func (t *Topology) findMaxVolumeId() storage.VolumeId{
+  return storage.VolumeId(0);
+}