# lua -v
Lua 5.1.5  Copyright (C) 1994-2012 Lua.org, PUC-Rio

i A liblua5.1-0                     - Shared library for the Lua interpreter ver

# cat /proc/diskstats | grep "sda " | awk '{print$12}'

iostat -d | grep sda | awk '{print$2}' | cut -c1-2

# iostat -x -d sda
Linux 3.11.4-gentoo (localhost)     05.12.2013     _x86_64_    (8 CPU)

Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
sda               0,04   182,35    4,19   20,52   109,84   814,18    74,78     1,99   80,61    4,05   96,25   1,75   4,33

r/s and w/s— respectively, the number of read and write requests issued by processes to the OS for a device.
rsec/s and wsec/s — sectors read/written (each sector 512 bytes).
rkB/s and wkB/s — kilobytes read/written.
avgrq-sz — average sectors per request (for both reads and writes). Do the math — (rsec + wsec) / (r + w) = (134.13+178.84)/(10.18+9.78)=15.6798597
If you want it in kilobytes, divide by 2.
If you want it separate for reads and writes — do you own math using rkB/s and wkB/s.
avgqu-sz — average queue length for this device.
await — average response time (ms) of IO requests to a device. The name is a bit confusing as this is the total response time including wait time in the requests queue (let call it qutim), and service time that device was working servicing the requests (see next column — svctim).So the formula is await = qutim + svctim.
svctim — average time (ms) a device was servicing requests. This is a component of total response time of IO requests.
%util — this is a pretty confusing value. The man page defines it as, Percentage of CPU time during which I/O requests were issued to the device (bandwidth utilization for the device). Device saturation occurs when this value is close to 100%. A bit difficult to digest. Perhaps it’s better to think of it as percentage of time the device was servicing requests as opposed to being idle. To understand it better here is the formula:utilization = ( (read requests + write requests) * service time in ms / 1000 ms ) * 100%
    or
%util = ( r + w ) * svctim /10 = ( 10.18 + 9.78 ) * 8.88 = 17.72448

# snmpwalk -v 2c -c rouser 192.168.0.1 1.3.6.1.4.1.2021.9.1.9.1
UCD-SNMP-MIB::dskPercent.1 = INTEGER: 37

# snmpwalk -v 2c -c rouser 192.168.0.1 1.3.6.1.4.1.2021.9.1.9.1 | awk '{print$4}'

# which dfsda2
/usr/local/sbin/dfsda2
# dfsda2
54
# cat /usr/local/sbin/dfsda2
df -h /dev/sda2 | awk 'NR==2{print$5}' | cut -c1-2   

# nano bargraph.lua
...
        {
            name="exec",
            arg="dfsda2",
            max=100,
            cap="s",
            angle=90,
            blocks=40,
            width=5,
            height=7,
            space=1,
            bg_colour={0xff0000,0.15},
            fg_colour={0xff0000,1},
            x=0,y=293
        },
...