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
}
func ReplicatedDelete(masterNode string, store *storage.Store, volumeId storage.VolumeId, n *storage.Needle, r *http.Request) (ret uint32) {
	ret, err := store.Delete(volumeId, n)
	if err != nil {
		log.Println("delete error:", err)
		return
	}

	needToReplicate := !store.HasVolume(volumeId)
	if !needToReplicate && ret > 0 {
		needToReplicate = store.GetVolume(volumeId).NeedToReplicate()
	}
	if needToReplicate { //send to other replica locations
		if r.FormValue("type") != "standard" {
			if !distributedOperation(masterNode, store, volumeId, func(location operation.Location) bool {
				return nil == operation.Delete("http://"+location.Url+r.URL.Path+"?type=standard")
			}) {
				ret = 0
			}
		}
	}
	return
}