#!/bin/bash
ini=/var/local/emhttp/diskload.ini
tmp=/var/local/emhttp/diskload.tmp
declare -a reads writes

# t = poll interval in seconds
t=2

# initialize array values upon first start
stats=($(awk '/(sd[a-z]*|nvme[0-9]*n1|vd[a-z]*) /{print $3,$6,$10,$4,$8}' /proc/diskstats))
c=0; s=${#stats[@]}
for ((i=0;i<s;i+=5)); do
  reads[c]=${stats[i+1]}
  writes[c]=${stats[i+2]}
  ((c++))
done
sleep $t

while :; do
  stats=($(awk '/(sd[a-z]*|nvme[0-9]*n1|vd[a-z]*) /{print $3,$6,$10,$4,$8}' /proc/diskstats))
  c=0; s=${#stats[@]}
  for ((i=0;i<s;i+=5)); do
    reads[c]=$((stats[i+1]-reads[c]))
    writes[c]=$((stats[i+2]-writes[c]))
    echo ${stats[i]}=$((reads[c]*512/t)) $((writes[c]*512/t)) ${stats[i+3]} ${stats[i+4]} >>$tmp
    reads[c]=${stats[i+1]}
    writes[c]=${stats[i+2]}
    ((c++))
  done
  mv -f $tmp $ini
  sleep $t
done