add dataCenter option when assign file keys

add dataCenter option when starting volume servers
some work related to freeze a volume. Not tested yet.

16 files changed, 287 insertions, 115 deletions

diff --git a/go/replication/store_replicate.go b/go/replication/store_replicate.go
index cc5d806d2..8306a31b4 100644
--- a/go/replication/store_replicate.go
+++ b/go/replication/store_replicate.go
@@ -3,7 +3,7 @@ package replication
 import (
 	"bytes"
 	"code.google.com/p/weed-fs/go/operation"
-  "code.google.com/p/weed-fs/go/storage"
+	"code.google.com/p/weed-fs/go/storage"
 	"log"
 	"net/http"
 	"strconv"
diff --git a/go/replication/volume_growth.go b/go/replication/volume_growth.go
index 1f266f73f..ce54b1fd4 100644
--- a/go/replication/volume_growth.go
+++ b/go/replication/volume_growth.go
@@ -31,24 +31,24 @@ func NewDefaultVolumeGrowth() *VolumeGrowth {
 	return &VolumeGrowth{copy1factor: 7, copy2factor: 6, copy3factor: 3}
 }
 
-func (vg *VolumeGrowth) GrowByType(repType storage.ReplicationType, topo *topology.Topology) (int, error) {
+func (vg *VolumeGrowth) GrowByType(repType storage.ReplicationType, dataCenter string, topo *topology.Topology) (int, error) {
 	switch repType {
 	case storage.Copy000:
-		return vg.GrowByCountAndType(vg.copy1factor, repType, topo)
+		return vg.GrowByCountAndType(vg.copy1factor, repType, dataCenter, topo)
 	case storage.Copy001:
-		return vg.GrowByCountAndType(vg.copy2factor, repType, topo)
+		return vg.GrowByCountAndType(vg.copy2factor, repType, dataCenter, topo)
 	case storage.Copy010:
-		return vg.GrowByCountAndType(vg.copy2factor, repType, topo)
+		return vg.GrowByCountAndType(vg.copy2factor, repType, dataCenter, topo)
 	case storage.Copy100:
-		return vg.GrowByCountAndType(vg.copy2factor, repType, topo)
+		return vg.GrowByCountAndType(vg.copy2factor, repType, dataCenter, topo)
 	case storage.Copy110:
-		return vg.GrowByCountAndType(vg.copy3factor, repType, topo)
+		return vg.GrowByCountAndType(vg.copy3factor, repType, dataCenter, topo)
 	case storage.Copy200:
-		return vg.GrowByCountAndType(vg.copy3factor, repType, topo)
+		return vg.GrowByCountAndType(vg.copy3factor, repType, dataCenter, topo)
 	}
 	return 0, errors.New("Unknown Replication Type!")
 }
-func (vg *VolumeGrowth) GrowByCountAndType(count int, repType storage.ReplicationType, topo *topology.Topology) (counter int, err error) {
+func (vg *VolumeGrowth) GrowByCountAndType(count int, repType storage.ReplicationType, dataCenter string, topo *topology.Topology) (counter int, err error) {
 	vg.accessLock.Lock()
 	defer vg.accessLock.Unlock()
 
@@ -56,16 +56,20 @@ func (vg *VolumeGrowth) GrowByCountAndType(count int, repType storage.Replicatio
 	switch repType {
 	case storage.Copy000:
 		for i := 0; i < count; i++ {
-			if ok, server, vid := topo.RandomlyReserveOneVolume(); ok {
+			if ok, server, vid := topo.RandomlyReserveOneVolume(dataCenter); ok {
 				if err = vg.grow(topo, *vid, repType, server); err == nil {
 					counter++
+				} else {
+					return counter, err
 				}
+			} else {
+				return counter, fmt.Errorf("Failed to grown volume for data center %s", dataCenter)
 			}
 		}
 	case storage.Copy001:
 		for i := 0; i < count; i++ {
-			//randomly pick one server, and then choose from the same rack
-			if ok, server1, vid := topo.RandomlyReserveOneVolume(); ok {
+			//randomly pick one server from the datacenter, and then choose from the same rack
+			if ok, server1, vid := topo.RandomlyReserveOneVolume(dataCenter); ok {
 				rack := server1.Parent()
 				exclusion := make(map[string]topology.Node)
 				exclusion[server1.String()] = server1
@@ -81,8 +85,8 @@ func (vg *VolumeGrowth) GrowByCountAndType(count int, repType storage.Replicatio
 		}
 	case storage.Copy010:
 		for i := 0; i < count; i++ {
-			//randomly pick one server, and then choose from the same rack
-			if ok, server1, vid := topo.RandomlyReserveOneVolume(); ok {
+			//randomly pick one server from the datacenter, and then choose from the a different rack
+			if ok, server1, vid := topo.RandomlyReserveOneVolume(dataCenter); ok {
 				rack := server1.Parent()
 				dc := rack.Parent()
 				exclusion := make(map[string]topology.Node)
@@ -100,28 +104,32 @@ func (vg *VolumeGrowth) GrowByCountAndType(count int, repType storage.Replicatio
 	case storage.Copy100:
 		for i := 0; i < count; i++ {
 			nl := topology.NewNodeList(topo.Children(), nil)
-			picked, ret := nl.RandomlyPickN(2, 1)
+			picked, ret := nl.RandomlyPickN(2, 1, dataCenter)
 			vid := topo.NextVolumeId()
+			println("growing on picked servers", picked)
 			if ret {
 				var servers []*topology.DataNode
 				for _, n := range picked {
 					if n.FreeSpace() > 0 {
-						if ok, server := n.ReserveOneVolume(rand.Intn(n.FreeSpace()), vid); ok {
+						if ok, server := n.ReserveOneVolume(rand.Intn(n.FreeSpace()), vid, ""); ok {
 							servers = append(servers, server)
 						}
 					}
 				}
+				println("growing on servers", servers)
 				if len(servers) == 2 {
 					if err = vg.grow(topo, vid, repType, servers...); err == nil {
 						counter++
 					}
 				}
+			} else {
+				return counter, fmt.Errorf("Failed to grown volume on data center %s and another data center", dataCenter)
 			}
 		}
 	case storage.Copy110:
 		for i := 0; i < count; i++ {
 			nl := topology.NewNodeList(topo.Children(), nil)
-			picked, ret := nl.RandomlyPickN(2, 2)
+			picked, ret := nl.RandomlyPickN(2, 2, dataCenter)
 			vid := topo.NextVolumeId()
 			if ret {
 				var servers []*topology.DataNode
@@ -130,7 +138,7 @@ func (vg *VolumeGrowth) GrowByCountAndType(count int, repType storage.Replicatio
 					dc1, dc2 = dc2, dc1
 				}
 				if dc1.FreeSpace() > 0 {
-					if ok, server1 := dc1.ReserveOneVolume(rand.Intn(dc1.FreeSpace()), vid); ok {
+					if ok, server1 := dc1.ReserveOneVolume(rand.Intn(dc1.FreeSpace()), vid, ""); ok {
 						servers = append(servers, server1)
 						rack := server1.Parent()
 						exclusion := make(map[string]topology.Node)
@@ -144,7 +152,7 @@ func (vg *VolumeGrowth) GrowByCountAndType(count int, repType storage.Replicatio
 					}
 				}
 				if dc2.FreeSpace() > 0 {
-					if ok, server := dc2.ReserveOneVolume(rand.Intn(dc2.FreeSpace()), vid); ok {
+					if ok, server := dc2.ReserveOneVolume(rand.Intn(dc2.FreeSpace()), vid, ""); ok {
 						servers = append(servers, server)
 					}
 				}
@@ -158,13 +166,13 @@ func (vg *VolumeGrowth) GrowByCountAndType(count int, repType storage.Replicatio
 	case storage.Copy200:
 		for i := 0; i < count; i++ {
 			nl := topology.NewNodeList(topo.Children(), nil)
-			picked, ret := nl.RandomlyPickN(3, 1)
+			picked, ret := nl.RandomlyPickN(3, 1, dataCenter)
 			vid := topo.NextVolumeId()
 			if ret {
 				var servers []*topology.DataNode
 				for _, n := range picked {
 					if n.FreeSpace() > 0 {
-						if ok, server := n.ReserveOneVolume(rand.Intn(n.FreeSpace()), vid); ok {
+						if ok, server := n.ReserveOneVolume(rand.Intn(n.FreeSpace()), vid, ""); ok {
 							servers = append(servers, server)
 						}
 					}
diff --git a/go/replication/volume_growth_test.go b/go/replication/volume_growth_test.go
index a4104716e..031972bee 100644
--- a/go/replication/volume_growth_test.go
+++ b/go/replication/volume_growth_test.go
@@ -5,9 +5,7 @@ import (
 	"code.google.com/p/weed-fs/go/topology"
 	"encoding/json"
 	"fmt"
-	"math/rand"
 	"testing"
-	"time"
 )
 
 var topologyLayout = `
@@ -80,7 +78,7 @@ func setup(topologyLayout string) *topology.Topology {
 	fmt.Println("data:", data)
 
 	//need to connect all nodes first before server adding volumes
-	topo, err := topology.NewTopology("mynetwork", "/etc/weedfs/weedfs.conf",
+	topo, err := topology.NewTopology("weedfs", "/etc/weedfs/weedfs.conf",
 		"/tmp", "testing", 32*1024, 5)
 	if err != nil {
 		panic("error: " + err.Error())
@@ -125,12 +123,3 @@ func TestRemoveDataCenter(t *testing.T) {
 		t.Fail()
 	}
 }
-
-func TestReserveOneVolume(t *testing.T) {
-	topo := setup(topologyLayout)
-	rand.Seed(time.Now().UnixNano())
-	vg := &VolumeGrowth{copy1factor: 3, copy2factor: 2, copy3factor: 1, copyAll: 4}
-	if c, e := vg.GrowByCountAndType(1, storage.Copy000, topo); e == nil {
-		t.Log("reserved", c)
-	}
-}
diff --git a/go/storage/needle_map.go b/go/storage/needle_map.go
index c836a87fb..89773b341 100644
--- a/go/storage/needle_map.go
+++ b/go/storage/needle_map.go
@@ -52,37 +52,61 @@ const (
 
 func LoadNeedleMap(file *os.File) (*NeedleMap, error) {
 	nm := NewNeedleMap(file)
-  bufferReader := bufio.NewReaderSize(nm.indexFile, 1024*1024)
-	bytes := make([]byte, 16*RowsToRead)
-	count, e := bufferReader.Read(bytes)
-	for count > 0 && e == nil {
-		for i := 0; i < count; i += 16 {
-			key := util.BytesToUint64(bytes[i : i+8])
-			offset := util.BytesToUint32(bytes[i+8 : i+12])
-			size := util.BytesToUint32(bytes[i+12 : i+16])
-			nm.FileCounter++
-			nm.FileByteCounter = nm.FileByteCounter + uint64(size)
-			if offset > 0 {
-				oldSize := nm.m.Set(Key(key), offset, size)
-				//log.Println("reading key", key, "offset", offset, "size", size, "oldSize", oldSize)
-				if oldSize > 0 {
-					nm.DeletionCounter++
-					nm.DeletionByteCounter = nm.DeletionByteCounter + uint64(oldSize)
-				}
-			} else {
-				oldSize := nm.m.Delete(Key(key))
-				//log.Println("removing key", key, "offset", offset, "size", size, "oldSize", oldSize)
+	e := walkIndexFile(file, func(key uint64, offset, size uint32) error {
+		nm.FileCounter++
+		nm.FileByteCounter = nm.FileByteCounter + uint64(size)
+		if offset > 0 {
+			oldSize := nm.m.Set(Key(key), offset, size)
+			//log.Println("reading key", key, "offset", offset, "size", size, "oldSize", oldSize)
+			if oldSize > 0 {
 				nm.DeletionCounter++
 				nm.DeletionByteCounter = nm.DeletionByteCounter + uint64(oldSize)
 			}
+		} else {
+			oldSize := nm.m.Delete(Key(key))
+			//log.Println("removing key", key, "offset", offset, "size", size, "oldSize", oldSize)
+			nm.DeletionCounter++
+			nm.DeletionByteCounter = nm.DeletionByteCounter + uint64(oldSize)
 		}
+		return nil
+	})
+	return nm, e
+}
+
+// walks through the index file, calls fn function with each key, offset, size
+// stops with the error returned by the fn function
+func walkIndexFile(r io.Reader, fn func(key uint64, offset, size uint32) error) error {
+	br := bufio.NewReaderSize(r, 1024*1024)
+	bytes := make([]byte, 16*RowsToRead)
+	count, e := br.Read(bytes)
+	var (
+		key          uint64
+		offset, size uint32
+		i            int
+	)
 
-		count, e = bufferReader.Read(bytes)
+	for count > 0 && e == nil {
+		for i = 0; i+16 <= count; i += 16 {
+			key = util.BytesToUint64(bytes[i : i+8])
+			offset = util.BytesToUint32(bytes[i+8 : i+12])
+			size = util.BytesToUint32(bytes[i+12 : i+16])
+			if e = fn(key, offset, size); e != nil {
+				return e
+			}
+		}
+		if count%16 != 0 {
+			copy(bytes[:count-i], bytes[i:count])
+			i = count - i
+			count, e = br.Read(bytes[i:])
+			count += i
+		} else {
+			count, e = br.Read(bytes)
+		}
 	}
 	if e == io.EOF {
-		e = nil
+		return nil
 	}
-	return nm, e
+	return e
 }
 
 func (nm *NeedleMap) Put(key uint64, offset uint32, size uint32) (int, error) {
diff --git a/go/storage/store.go b/go/storage/store.go
index 954bae0ae..0889c9330 100644
--- a/go/storage/store.go
+++ b/go/storage/store.go
@@ -20,6 +20,8 @@ type Store struct {
 	MaxVolumeCount int
 
 	masterNode      string
+	dataCenter      string //optional informaton, overwriting master setting if exists
+	rack            string //optional information, overwriting master setting if exists
 	connected       bool
 	volumeSizeLimit uint64 //read from the master
 
@@ -99,6 +101,16 @@ func (s *Store) CommitCompactVolume(volumeIdString string) error {
 	}
 	return s.volumes[vid].commitCompact()
 }
+func (s *Store) FreezeVolume(volumeIdString string) error {
+	vid, err := NewVolumeId(volumeIdString)
+	if err != nil {
+		return errors.New("Volume Id " + volumeIdString + " is not a valid unsigned integer!")
+	}
+	if s.volumes[vid].readOnly {
+		return errors.New("Volume " + volumeIdString + " is already read-only")
+	}
+	return s.volumes[vid].freeze()
+}
 func (s *Store) loadExistingVolumes() {
 	if dirs, err := ioutil.ReadDir(s.dir); err == nil {
 		for _, dir := range dirs {
@@ -138,6 +150,12 @@ type JoinResult struct {
 func (s *Store) SetMaster(mserver string) {
 	s.masterNode = mserver
 }
+func (s *Store) SetDataCenter(dataCenter string) {
+	s.dataCenter = dataCenter
+}
+func (s *Store) SetRack(rack string) {
+	s.rack = rack
+}
 func (s *Store) Join() error {
 	stats := new([]*VolumeInfo)
 	for k, v := range s.volumes {
@@ -159,6 +177,8 @@ func (s *Store) Join() error {
 	values.Add("publicUrl", s.PublicUrl)
 	values.Add("volumes", string(bytes))
 	values.Add("maxVolumeCount", strconv.Itoa(s.MaxVolumeCount))
+	values.Add("dataCenter", s.dataCenter)
+	values.Add("rack", s.rack)
 	jsonBlob, err := util.Post("http://"+s.masterNode+"/dir/join", values)
 	if err != nil {
 		return err
diff --git a/go/storage/volume.go b/go/storage/volume.go
index 98f712433..4e6db3634 100644
--- a/go/storage/volume.go
+++ b/go/storage/volume.go
@@ -70,10 +70,29 @@ func (v *Volume) load(alsoLoadIndex bool) error {
 		e = v.maybeWriteSuperBlock()
 	}
 	if e == nil && alsoLoadIndex {
-    indexFile, ie := os.OpenFile(fileName+".idx", os.O_RDWR|os.O_CREATE, 0644)
-    if ie != nil {
-      return fmt.Errorf("cannot create Volume Data %s.dat: %s", fileName, e)
-    }
+		var indexFile *os.File
+		if v.readOnly {
+			if indexFile, e = os.Open(fileName + ".idx"); e != nil && !os.IsNotExist(e) {
+				return fmt.Errorf("cannot open index file %s.idx: %s", fileName, e)
+			}
+			if indexFile != nil {
+				log.Printf("converting %s.idx to %s.cdb", fileName, fileName)
+				if e = ConvertIndexToCdb(fileName+".cdb", indexFile); e != nil {
+					log.Printf("error converting %s.idx to %s.cdb: %s", fileName, fileName)
+				} else {
+					indexFile.Close()
+					os.Remove(indexFile.Name())
+					indexFile = nil
+				}
+			}
+			v.nm, e = OpenCdbMap(fileName + ".cdb")
+			return e
+		} else {
+			indexFile, e = os.OpenFile(fileName+".idx", os.O_RDWR|os.O_CREATE, 0644)
+			if e != nil {
+				return fmt.Errorf("cannot create Volume Data %s.dat: %s", fileName, e)
+			}
+		}
 		v.nm, e = LoadNeedleMap(indexFile)
 	}
 	return e
@@ -224,6 +243,31 @@ func (v *Volume) commitCompact() error {
 	}
 	return nil
 }
+func (v *Volume) freeze() error {
+	if v.readOnly {
+		return nil
+	}
+	nm, ok := v.nm.(*NeedleMap)
+	if !ok {
+		return nil
+	}
+	v.accessLock.Lock()
+	defer v.accessLock.Unlock()
+	bn, _ := nakeFilename(v.dataFile.Name())
+	cdbFn := bn + ".cdb"
+	log.Printf("converting %s to %s", nm.indexFile.Name(), cdbFn)
+	err := DumpNeedleMapToCdb(cdbFn, nm)
+	if err != nil {
+		return err
+	}
+	if v.nm, err = OpenCdbMap(cdbFn); err != nil {
+		return err
+	}
+	nm.indexFile.Close()
+	os.Remove(nm.indexFile.Name())
+	v.readOnly = true
+	return nil
+}
 
 func ScanVolumeFile(dirname string, id VolumeId,
 	visitSuperBlock func(SuperBlock) error,
diff --git a/go/topology/configuration.go b/go/topology/configuration.go
index 4c8424214..058600a7c 100644
--- a/go/topology/configuration.go
+++ b/go/topology/configuration.go
@@ -46,11 +46,20 @@ func (c *Configuration) String() string {
 	return ""
 }
 
-func (c *Configuration) Locate(ip string) (dc string, rack string) {
-	if c != nil && c.ip2location != nil {
-		if loc, ok := c.ip2location[ip]; ok {
-			return loc.dcName, loc.rackName
+func (c *Configuration) Locate(ip string, dcName string, rackName string) (dc string, rack string) {
+	if dcName == "" {
+		if c != nil && c.ip2location != nil {
+			if loc, ok := c.ip2location[ip]; ok {
+				return loc.dcName, loc.rackName
+			}
+		}
+	} else {
+		if rackName == "" {
+			return dcName, "DefaultRack"
+		} else {
+			return dcName, rackName
 		}
 	}
+
 	return "DefaultDataCenter", "DefaultRack"
 }
diff --git a/go/topology/data_node.go b/go/topology/data_node.go
index ea4ea5d39..3a6edb447 100644
--- a/go/topology/data_node.go
+++ b/go/topology/data_node.go
@@ -34,8 +34,11 @@ func (dn *DataNode) AddOrUpdateVolume(v storage.VolumeInfo) {
 		dn.volumes[v.Id] = v
 	}
 }
+func (dn *DataNode) GetDataCenter() *DataCenter {
+	return dn.Parent().Parent().(*NodeImpl).value.(*DataCenter)
+}
 func (dn *DataNode) GetTopology() *Topology {
-	p := dn.parent
+	p := dn.Parent()
 	for p.Parent() != nil {
 		p = p.Parent()
 	}
diff --git a/go/topology/node.go b/go/topology/node.go
index 786f76702..d61f01244 100644
--- a/go/topology/node.go
+++ b/go/topology/node.go
@@ -10,7 +10,7 @@ type Node interface {
 	Id() NodeId
 	String() string
 	FreeSpace() int
-	ReserveOneVolume(r int, vid storage.VolumeId) (bool, *DataNode)
+	ReserveOneVolume(r int, vid storage.VolumeId, dataCenter string) (bool, *DataNode)
 	UpAdjustMaxVolumeCountDelta(maxVolumeCountDelta int)
 	UpAdjustVolumeCountDelta(volumeCountDelta int)
 	UpAdjustActiveVolumeCountDelta(activeVolumeCountDelta int)
@@ -26,6 +26,8 @@ type Node interface {
 	CollectDeadNodeAndFullVolumes(freshThreshHold int64, volumeSizeLimit uint64)
 
 	IsDataNode() bool
+	IsRack() bool
+	IsDataCenter() bool
 	Children() map[NodeId]Node
 	Parent() Node
 
@@ -78,23 +80,26 @@ func (n *NodeImpl) Parent() Node {
 func (n *NodeImpl) GetValue() interface{} {
 	return n.value
 }
-func (n *NodeImpl) ReserveOneVolume(r int, vid storage.VolumeId) (bool, *DataNode) {
+func (n *NodeImpl) ReserveOneVolume(r int, vid storage.VolumeId, dataCenter string) (bool, *DataNode) {
 	ret := false
 	var assignedNode *DataNode
 	for _, node := range n.children {
 		freeSpace := node.FreeSpace()
-		//fmt.Println("r =", r, ", node =", node, ", freeSpace =", freeSpace)
+		// fmt.Println("r =", r, ", node =", node, ", freeSpace =", freeSpace)
 		if freeSpace <= 0 {
 			continue
 		}
+		if dataCenter != "" && node.IsDataCenter() && node.Id() != NodeId(dataCenter) {
+			continue
+		}
 		if r >= freeSpace {
 			r -= freeSpace
 		} else {
 			if node.IsDataNode() && node.FreeSpace() > 0 {
-				//fmt.Println("vid =", vid, " assigned to node =", node, ", freeSpace =", node.FreeSpace())
+				// fmt.Println("vid =", vid, " assigned to node =", node, ", freeSpace =", node.FreeSpace())
 				return true, node.(*DataNode)
 			}
-			ret, assignedNode = node.ReserveOneVolume(r, vid)
+			ret, assignedNode = node.ReserveOneVolume(r, vid, dataCenter)
 			if ret {
 				break
 			}
diff --git a/go/topology/node_list.go b/go/topology/node_list.go
index db7723714..2be90b123 100644
--- a/go/topology/node_list.go
+++ b/go/topology/node_list.go
@@ -30,23 +30,37 @@ func (nl *NodeList) FreeSpace() int {
 	return freeSpace
 }
 
-func (nl *NodeList) RandomlyPickN(n int, min int) ([]Node, bool) {
+func (nl *NodeList) RandomlyPickN(count int, minSpace int, firstNodeName string) ([]Node, bool) {
 	var list []Node
+	var preferredNode *Node
+	if firstNodeName != "" {
+		for _, n := range nl.nodes {
+			if n.Id() == NodeId(firstNodeName) && n.FreeSpace() >= minSpace {
+				preferredNode = &n
+				break
+			}
+		}
+		if preferredNode == nil {
+			return list, false
+		}
+	}
+
 	for _, n := range nl.nodes {
-		if n.FreeSpace() >= min {
+		if n.FreeSpace() >= minSpace && n.Id() != NodeId(firstNodeName) {
 			list = append(list, n)
 		}
 	}
-	if n > len(list) {
+	if count > len(list) || count == len(list) && firstNodeName != "" {
 		return nil, false
 	}
-	for i := n; i > 0; i-- {
+	for i := len(list); i > 0; i-- {
 		r := rand.Intn(i)
-		t := list[r]
-		list[r] = list[i-1]
-		list[i-1] = t
+		list[r], list[i-1] = list[i-1], list[r]
+	}
+	if firstNodeName != "" {
+	  list[0] = *preferredNode
 	}
-	return list[len(list)-n:], true
+	return list[:count], true
 }
 
 func (nl *NodeList) ReserveOneVolume(randomVolumeIndex int, vid storage.VolumeId) (bool, *DataNode) {
diff --git a/go/topology/node_list_test.go b/go/topology/node_list_test.go
index c6e530724..0037cbaa9 100644
--- a/go/topology/node_list_test.go
+++ b/go/topology/node_list_test.go
@@ -20,22 +20,38 @@ func TestXYZ(t *testing.T) {
 	}
 	nl := NewNodeList(topo.Children(), nil)
 
-	picked, ret := nl.RandomlyPickN(1, 0)
+	picked, ret := nl.RandomlyPickN(1, 0, "")
 	if !ret || len(picked) != 1 {
 		t.Error("need to randomly pick 1 node")
 	}
 
-	picked, ret = nl.RandomlyPickN(4, 0)
+  picked, ret = nl.RandomlyPickN(1, 0, "dc1")
+  if !ret || len(picked) != 1 {
+    t.Error("need to randomly pick 1 node")
+  }
+  if picked[0].Id() != "dc1" {
+    t.Error("need to randomly pick 1 dc1 node")
+  }
+
+  picked, ret = nl.RandomlyPickN(2, 0, "dc1")
+  if !ret || len(picked) != 2 {
+    t.Error("need to randomly pick 1 node")
+  }
+  if picked[0].Id() != "dc1" {
+    t.Error("need to randomly pick 2 with one dc1 node")
+  }
+
+	picked, ret = nl.RandomlyPickN(4, 0, "")
 	if !ret || len(picked) != 4 {
 		t.Error("need to randomly pick 4 nodes")
 	}
 
-	picked, ret = nl.RandomlyPickN(5, 0)
+	picked, ret = nl.RandomlyPickN(5, 0, "")
 	if !ret || len(picked) != 5 {
 		t.Error("need to randomly pick 5 nodes")
 	}
 
-	picked, ret = nl.RandomlyPickN(6, 0)
+	picked, ret = nl.RandomlyPickN(6, 0, "")
 	if ret || len(picked) != 0 {
 		t.Error("can not randomly pick 6 nodes:", ret, picked)
 	}
diff --git a/go/topology/topo_test.go b/go/topology/topo_test.go
index 99e570821..d5ea08086 100644
--- a/go/topology/topo_test.go
+++ b/go/topology/topo_test.go
@@ -127,7 +127,10 @@ func TestReserveOneVolume(t *testing.T) {
 	topo := setup(topologyLayout)
 	rand.Seed(time.Now().UnixNano())
 	rand.Seed(1)
-	ret, node, vid := topo.RandomlyReserveOneVolume()
+	ret, node, vid := topo.RandomlyReserveOneVolume("dc1")
+	if node.Parent().Parent().Id() != NodeId("dc1") {
+		t.Fail()
+	}
 	fmt.Println("assigned :", ret, ", node :", node, ", volume id:", vid)
 
 }
diff --git a/go/topology/topology.go b/go/topology/topology.go
index 5dcc56204..e488319d1 100644
--- a/go/topology/topology.go
+++ b/go/topology/topology.go
@@ -4,6 +4,7 @@ import (
 	"code.google.com/p/weed-fs/go/sequence"
 	"code.google.com/p/weed-fs/go/storage"
 	"errors"
+	"fmt"
 	"io/ioutil"
 	"log"
 	"math/rand"
@@ -71,25 +72,13 @@ func (t *Topology) Lookup(vid storage.VolumeId) []*DataNode {
 	return nil
 }
 
-func (t *Topology) RandomlyReserveOneVolume() (bool, *DataNode, *storage.VolumeId) {
+func (t *Topology) RandomlyReserveOneVolume(dataCenter string) (bool, *DataNode, *storage.VolumeId) {
 	if t.FreeSpace() <= 0 {
+		fmt.Println("Topology does not have free space left!")
 		return false, nil, nil
 	}
 	vid := t.NextVolumeId()
-	ret, node := t.ReserveOneVolume(rand.Intn(t.FreeSpace()), vid)
-	return ret, node, &vid
-}
-
-func (t *Topology) RandomlyReserveOneVolumeExcept(except []Node) (bool, *DataNode, *storage.VolumeId) {
-	freeSpace := t.FreeSpace()
-	for _, node := range except {
-		freeSpace -= node.FreeSpace()
-	}
-	if freeSpace <= 0 {
-		return false, nil, nil
-	}
-	vid := t.NextVolumeId()
-	ret, node := t.ReserveOneVolume(rand.Intn(freeSpace), vid)
+	ret, node := t.ReserveOneVolume(rand.Intn(t.FreeSpace()), vid, dataCenter)
 	return ret, node, &vid
 }
 
@@ -98,12 +87,12 @@ func (t *Topology) NextVolumeId() storage.VolumeId {
 	return vid.Next()
 }
 
-func (t *Topology) PickForWrite(repType storage.ReplicationType, count int) (string, int, *DataNode, error) {
+func (t *Topology) PickForWrite(repType storage.ReplicationType, count int, dataCenter string) (string, int, *DataNode, error) {
 	replicationTypeIndex := repType.GetReplicationLevelIndex()
 	if t.replicaType2VolumeLayout[replicationTypeIndex] == nil {
 		t.replicaType2VolumeLayout[replicationTypeIndex] = NewVolumeLayout(repType, t.volumeSizeLimit, t.pulse)
 	}
-	vid, count, datanodes, err := t.replicaType2VolumeLayout[replicationTypeIndex].PickForWrite(count)
+	vid, count, datanodes, err := t.replicaType2VolumeLayout[replicationTypeIndex].PickForWrite(count, dataCenter)
 	if err != nil || datanodes.Length() == 0 {
 		return "", 0, nil, errors.New("No writable volumes avalable!")
 	}
@@ -114,6 +103,7 @@ func (t *Topology) PickForWrite(repType storage.ReplicationType, count int) (str
 func (t *Topology) GetVolumeLayout(repType storage.ReplicationType) *VolumeLayout {
 	replicationTypeIndex := repType.GetReplicationLevelIndex()
 	if t.replicaType2VolumeLayout[replicationTypeIndex] == nil {
+		fmt.Println("adding replication type", repType)
 		t.replicaType2VolumeLayout[replicationTypeIndex] = NewVolumeLayout(repType, t.volumeSizeLimit, t.pulse)
 	}
 	return t.replicaType2VolumeLayout[replicationTypeIndex]
@@ -123,8 +113,8 @@ func (t *Topology) RegisterVolumeLayout(v *storage.VolumeInfo, dn *DataNode) {
 	t.GetVolumeLayout(v.RepType).RegisterVolume(v, dn)
 }
 
-func (t *Topology) RegisterVolumes(init bool, volumeInfos []storage.VolumeInfo, ip string, port int, publicUrl string, maxVolumeCount int) {
-	dcName, rackName := t.configuration.Locate(ip)
+func (t *Topology) RegisterVolumes(init bool, volumeInfos []storage.VolumeInfo, ip string, port int, publicUrl string, maxVolumeCount int, dcName string, rackName string) {
+	dcName, rackName = t.configuration.Locate(ip, dcName, rackName)
 	dc := t.GetOrCreateDataCenter(dcName)
 	rack := dc.GetOrCreateRack(rackName)
 	dn := rack.FindDataNode(ip, port)
diff --git a/go/topology/volume_layout.go b/go/topology/volume_layout.go
index cd725c132..d8ed49b0b 100644
--- a/go/topology/volume_layout.go
+++ b/go/topology/volume_layout.go
@@ -51,22 +51,52 @@ func (vl *VolumeLayout) Lookup(vid storage.VolumeId) []*DataNode {
 	return nil
 }
 
-func (vl *VolumeLayout) PickForWrite(count int) (*storage.VolumeId, int, *VolumeLocationList, error) {
+func (vl *VolumeLayout) PickForWrite(count int, dataCenter string) (*storage.VolumeId, int, *VolumeLocationList, error) {
 	len_writers := len(vl.writables)
 	if len_writers <= 0 {
 		fmt.Println("No more writable volumes!")
 		return nil, 0, nil, errors.New("No more writable volumes!")
 	}
-	vid := vl.writables[rand.Intn(len_writers)]
-	locationList := vl.vid2location[vid]
-	if locationList != nil {
+	if dataCenter == "" {
+		vid := vl.writables[rand.Intn(len_writers)]
+		locationList := vl.vid2location[vid]
+		if locationList != nil {
+			return &vid, count, locationList, nil
+		}
+		return nil, 0, nil, errors.New("Strangely vid " + vid.String() + " is on no machine!")
+	} else {
+		var vid storage.VolumeId
+		var locationList *VolumeLocationList
+		counter := 0
+		for _, v := range vl.writables {
+			volumeLocationList := vl.vid2location[v]
+			for _, dn := range volumeLocationList.list {
+				if dn.GetDataCenter().Id() == NodeId(dataCenter) {
+					counter++
+					if rand.Intn(counter) < 1 {
+						vid, locationList = v, volumeLocationList
+					}
+				}
+			}
+		}
 		return &vid, count, locationList, nil
 	}
-	return nil, 0, nil, errors.New("Strangely vid " + vid.String() + " is on no machine!")
+	return nil, 0, nil, errors.New("Strangely This Should Never Have Happened!")
 }
 
-func (vl *VolumeLayout) GetActiveVolumeCount() int {
-	return len(vl.writables)
+func (vl *VolumeLayout) GetActiveVolumeCount(dataCenter string) int {
+	if dataCenter == "" {
+		return len(vl.writables)
+	}
+	counter := 0
+	for _, v := range vl.writables {
+		for _, dn := range vl.vid2location[v].list {
+			if dn.GetDataCenter().Id() == NodeId(dataCenter) {
+				counter++
+			}
+		}
+	}
+	return counter
 }
 
 func (vl *VolumeLayout) removeFromWritable(vid storage.VolumeId) bool {
diff --git a/go/weed/master.go b/go/weed/master.go
index f6cc88df0..7da7831bf 100644
--- a/go/weed/master.go
+++ b/go/weed/master.go
@@ -77,25 +77,27 @@ func dirAssignHandler(w http.ResponseWriter, r *http.Request) {
 	if repType == "" {
 		repType = *defaultRepType
 	}
+	dataCenter := r.FormValue("dataCenter")
 	rt, err := storage.NewReplicationTypeFromString(repType)
 	if err != nil {
 		w.WriteHeader(http.StatusNotAcceptable)
 		writeJsonQuiet(w, r, map[string]string{"error": err.Error()})
 		return
 	}
-	if topo.GetVolumeLayout(rt).GetActiveVolumeCount() <= 0 {
+
+	if topo.GetVolumeLayout(rt).GetActiveVolumeCount(dataCenter) <= 0 {
 		if topo.FreeSpace() <= 0 {
 			w.WriteHeader(http.StatusNotFound)
 			writeJsonQuiet(w, r, map[string]string{"error": "No free volumes left!"})
 			return
 		} else {
-			if _, err = vg.GrowByType(rt, topo); err != nil {
+			if _, err = vg.GrowByType(rt, dataCenter, topo); err != nil {
 				writeJsonQuiet(w, r, map[string]string{"error": "Cannot grow volume group! " + err.Error()})
 				return
 			}
 		}
 	}
-	fid, count, dn, err := topo.PickForWrite(rt, c)
+	fid, count, dn, err := topo.PickForWrite(rt, c, dataCenter)
 	if err == nil {
 		writeJsonQuiet(w, r, map[string]interface{}{"fid": fid, "url": dn.Url(), "publicUrl": dn.PublicUrl, "count": count})
 	} else {
@@ -120,7 +122,7 @@ func dirJoinHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	debug(s, "volumes", r.FormValue("volumes"))
-	topo.RegisterVolumes(init, *volumes, ip, port, publicUrl, maxVolumeCount)
+	topo.RegisterVolumes(init, *volumes, ip, port, publicUrl, maxVolumeCount, r.FormValue("dataCenter"), r.FormValue("rack"))
 	m := make(map[string]interface{})
 	m["VolumeSizeLimit"] = uint64(*volumeSizeLimitMB) * 1024 * 1024
 	writeJsonQuiet(w, r, m)
@@ -151,7 +153,7 @@ func volumeGrowHandler(w http.ResponseWriter, r *http.Request) {
 			if topo.FreeSpace() < count*rt.GetCopyCount() {
 				err = errors.New("Only " + strconv.Itoa(topo.FreeSpace()) + " volumes left! Not enough for " + strconv.Itoa(count*rt.GetCopyCount()))
 			} else {
-				count, err = vg.GrowByCountAndType(count, rt, topo)
+				count, err = vg.GrowByCountAndType(count, rt, r.FormValue("dataCneter"), topo)
 			}
 		} else {
 			err = errors.New("parameter count is not found")
diff --git a/go/weed/volume.go b/go/weed/volume.go
index 33121388e..6cbbceaef 100644
--- a/go/weed/volume.go
+++ b/go/weed/volume.go
@@ -2,7 +2,7 @@ package main
 
 import (
 	"code.google.com/p/weed-fs/go/operation"
-  "code.google.com/p/weed-fs/go/replication"
+	"code.google.com/p/weed-fs/go/replication"
 	"code.google.com/p/weed-fs/go/storage"
 	"log"
 	"math/rand"
@@ -38,6 +38,8 @@ var (
 	maxVolumeCount = cmdVolume.Flag.Int("max", 5, "maximum number of volumes")
 	vReadTimeout   = cmdVolume.Flag.Int("readTimeout", 3, "connection read timeout in seconds")
 	vMaxCpu        = cmdVolume.Flag.Int("maxCpu", 0, "maximum number of CPUs. 0 means all available CPUs")
+	dataCenter     = cmdVolume.Flag.String("dataCenter", "", "current volume server's data center name")
+	rack           = cmdVolume.Flag.String("rack", "", "current volume server's rack name")
 
 	store *storage.Store
 )
@@ -86,6 +88,16 @@ func vacuumVolumeCommitHandler(w http.ResponseWriter, r *http.Request) {
 	}
 	debug("commit compact volume =", r.FormValue("volume"), ", error =", err)
 }
+func freezeVolumeHandler(w http.ResponseWriter, r *http.Request) {
+	//TODO: notify master that this volume will be read-only
+	err := store.FreezeVolume(r.FormValue("volume"))
+	if err == nil {
+		writeJsonQuiet(w, r, map[string]interface{}{"error": ""})
+	} else {
+		writeJsonQuiet(w, r, map[string]string{"error": err.Error()})
+	}
+	debug("freeze volume =", r.FormValue("volume"), ", error =", err)
+}
 func storeHandler(w http.ResponseWriter, r *http.Request) {
 	switch r.Method {
 	case "GET":
@@ -289,10 +301,13 @@ func runVolume(cmd *Command, args []string) bool {
 	http.HandleFunc("/admin/vacuum_volume_check", vacuumVolumeCheckHandler)
 	http.HandleFunc("/admin/vacuum_volume_compact", vacuumVolumeCompactHandler)
 	http.HandleFunc("/admin/vacuum_volume_commit", vacuumVolumeCommitHandler)
+	http.HandleFunc("/admin/freeze_volume", freezeVolumeHandler)
 
 	go func() {
 		connected := true
 		store.SetMaster(*masterNode)
+		store.SetDataCenter(*dataCenter)
+		store.SetRack(*rack)
 		for {
 			err := store.Join()
 			if err == nil {