func (vg *VolumeGrowth) grow(topo *topology.Topology, vid storage.VolumeId, repType storage.ReplicationType, servers ...*topology.DataNode) error {
	for _, server := range servers {
		if err := operation.AllocateVolume(server, vid, repType); err == nil {
			vi := storage.VolumeInfo{Id: vid, Size: 0, RepType: repType, Version: storage.CurrentVersion}
			server.AddOrUpdateVolume(vi)
			topo.RegisterVolumeLayout(&vi, server)
			fmt.Println("Created Volume", vid, "on", server)
		} else {
			fmt.Println("Failed to assign", vid, "to", servers, "error", err)
			return errors.New("Failed to assign " + vid.String())
		}
	}
	return nil
}

func (vg *VolumeGrowth) grow(topo *Topology, vid storage.VolumeId, option *VolumeGrowOption, servers ...*DataNode) error {
	for _, server := range servers {
		if err := AllocateVolume(server, vid, option.Collection, option.ReplicaPlacement); err == nil {
			vi := storage.VolumeInfo{Id: vid, Size: 0, Collection: option.Collection, ReplicaPlacement: option.ReplicaPlacement, Version: storage.CurrentVersion}
			server.AddOrUpdateVolume(vi)
			topo.RegisterVolumeLayout(vi, server)
			glog.V(0).Infoln("Created Volume", vid, "on", server)
		} else {
			glog.V(0).Infoln("Failed to assign", vid, "to", servers, "error", err)
			return fmt.Errorf("Failed to assign %s: %s", vid.String(), err.Error())
		}
	}
	return nil
}

func vacuumVolume_Commit(urlLocation string, vid storage.VolumeId) error {
	values := make(url.Values)
	values.Add("volume", vid.String())
	jsonBlob, err := util.Post("http://"+urlLocation+"/admin/vacuum_volume_commit", values)
	if err != nil {
		return err
	}
	var ret VacuumVolumeResult
	if err := json.Unmarshal(jsonBlob, &ret); err != nil {
		return err
	}
	if ret.Error != "" {
		return errors.New(ret.Error)
	}
	return nil
}

//TODO: Add a caching for vid here
func Lookup(server string, vid storage.VolumeId) (*LookupResult, error) {
	values := make(url.Values)
	values.Add("volumeId", vid.String())
	jsonBlob, err := util.Post("http://"+server+"/dir/lookup", values)
	if err != nil {
		return nil, err
	}
	var ret LookupResult
	err = json.Unmarshal(jsonBlob, &ret)
	if err != nil {
		return nil, err
	}
	if ret.Error != "" {
		return nil, errors.New(ret.Error)
	}
	return &ret, nil
}

func AllocateVolume(dn *topology.DataNode, vid storage.VolumeId, repType storage.ReplicationType) error {
	values := make(url.Values)
	values.Add("volume", vid.String())
	values.Add("replicationType", repType.String())
	jsonBlob, err := util.Post("http://"+dn.Url()+"/admin/assign_volume", values)
	if err != nil {
		return err
	}
	var ret AllocateVolumeResult
	if err := json.Unmarshal(jsonBlob, &ret); err != nil {
		return err
	}
	if ret.Error != "" {
		return errors.New(ret.Error)
	}
	return nil
}

func vacuumVolume_Check(urlLocation string, vid storage.VolumeId, garbageThreshold string) (error, bool) {
	values := make(url.Values)
	values.Add("volume", vid.String())
	values.Add("garbageThreshold", garbageThreshold)
	jsonBlob, err := util.Post("http://"+urlLocation+"/admin/vacuum_volume_check", values)
	if err != nil {
		fmt.Println("parameters:", values)
		return err, false
	}
	var ret VacuumVolumeResult
	if err := json.Unmarshal(jsonBlob, &ret); err != nil {
		return err, false
	}
	if ret.Error != "" {
		return errors.New(ret.Error), false
	}
	return nil, ret.Result
}

func AllocateVolume(dn *DataNode, vid storage.VolumeId, collection string, rp *storage.ReplicaPlacement) error {
	values := make(url.Values)
	values.Add("volume", vid.String())
	values.Add("collection", collection)
	values.Add("replication", rp.String())
	jsonBlob, err := util.Post("http://"+dn.PublicUrl+"/admin/assign_volume", values)
	if err != nil {
		return err
	}
	var ret AllocateVolumeResult
	if err := json.Unmarshal(jsonBlob, &ret); err != nil {
		return err
	}
	if ret.Error != "" {
		return errors.New(ret.Error)
	}
	return nil
}

func distributedOperation(masterNode string, store *storage.Store, volumeId storage.VolumeId, op func(location operation.Location) bool) bool {
	if lookupResult, lookupErr := operation.Lookup(masterNode, volumeId.String()); lookupErr == nil {
		length := 0
		selfUrl := (store.Ip + ":" + strconv.Itoa(store.Port))
		results := make(chan bool)
		for _, location := range lookupResult.Locations {
			if location.Url != selfUrl {
				length++
				go func(location operation.Location, results chan bool) {
					results <- op(location)
				}(location, results)
			}
		}
		ret := true
		for i := 0; i < length; i++ {
			ret = ret && <-results
		}
		return ret
	} else {
		glog.V(0).Infoln("Failed to lookup for", volumeId, lookupErr.Error())
	}
	return false
}

func ReplicatedWrite(masterNode string, s *storage.Store, volumeId storage.VolumeId, needle *storage.Needle, r *http.Request) (size uint32, errorStatus string) {
	ret, err := s.Write(volumeId, needle)
	needToReplicate := !s.HasVolume(volumeId)
	if err != nil {
		errorStatus = "Failed to write to local disk (" + err.Error() + ")"
	} else if ret > 0 {
		needToReplicate = needToReplicate || s.GetVolume(volumeId).NeedToReplicate()
	} else {
		errorStatus = "Failed to write to local disk"
	}
	if !needToReplicate && ret > 0 {
		needToReplicate = s.GetVolume(volumeId).NeedToReplicate()
	}
	if needToReplicate { //send to other replica locations
		if r.FormValue("type") != "standard" {
			if !distributedOperation(masterNode, s, volumeId, func(location operation.Location) bool {
				_, err := operation.Upload("http://"+location.Url+r.URL.Path+"?type=standard", string(needle.Name), bytes.NewReader(needle.Data))
				return err == nil
			}) {
				ret = 0
				errorStatus = "Failed to write to replicas for volume " + volumeId.String()
			}
		}
	}
	if errorStatus != "" {
		if _, err = s.Delete(volumeId, needle); err != nil {
			errorStatus += "\nCannot delete " + strconv.FormatUint(needle.Id, 10) + " from " +
				volumeId.String() + ": " + err.Error()
		} else {
			distributedOperation(masterNode, s, volumeId, func(location operation.Location) bool {
				return nil == operation.Delete("http://"+location.Url+r.URL.Path+"?type=standard")
			})
		}
	}
	size = ret
	return
}