public String createVolume(String volumeName,long capacity,String volumeTypeId) throws Exception {
  return createVolume(volumeName,capacity,volumeTypeId,null,null);
}

public String createVolume ( String volumeName , long capacity , String volumeTypeId ) throws Exception { return createVolume ( volumeName , capacity , volumeTypeId , null , null ) ; }
create volume operation ( it is asynchronous operation )
