code: def io_size_kb(prev, curr, counters):
      
      bw_stats, io_stats = counters
      size_mb = div(getattr(curr, bw_stats), getattr(curr, io_stats))
      return mul(size_mb, 1024)
docs: calculate the io size based on bandwidth and throughput
  
      formula: average_io_size = bandwidth / throughput
      :param prev: prev resource, not used
      :param curr: current resource
      :param counters: two stats, bandwidth in MB and throughput count
      :return: value, NaN if invalid