how to find vertica write per sec

how to find vertica write per sec i am using this query to find
SELECT  node_name,
  round(min(start_time), 'MI') as start_time,
  round(max(end_time), 'MI') as end_time,
  round( ( (sum(total_read_bytes_end_value - total_read_bytes_start_value) / 1024) / 
           (datediff('millisecond', min(start_time), max(end_time)) / 1000.0) )::float, 2) as read_kbytes_per_sec,
  round( ( (sum(total_written_bytes_end_value - total_written_bytes_start_value) / 1024) / 
           (datediff('millisecond', min(start_time), max(end_time)) / 1000.0) )::float, 2) as written_kbytes_per_sec FROM v_internal.dc_io_info_by_minute GROUP BY node_name, round(start_time, 'MI') ORDER BY 2 desc ;