I can see one problem in the file /usr/share/munin/plugins/iostat_ios as
follows:
LINE 202: print("${dev}_rtime.value ", ($rtime_diff != 0) ?
($rio_diff / $rtime_diff) : 0, "\n",
LINE 203: "${dev}_wtime.value ", ($wtime_diff != 0) ?
($wio_diff / $wtime_diff) : 0, "\n",
LINE 204: );
Here we see it divides number of IO operations by time in milliseconds. However
the graph has the vertical axis in seconds. Dividing by time gives Hz never
back to seconds again. So the graph results are really in Hz (not a useful unit
given the context we are working with here). I suggest that the calculation
should be:
LINE 202: print("${dev}_rtime.value ", ($rio_diff != 0) ?
($rtime_diff / $rio_diff) : 0, "\n",
LINE 203: "${dev}_wtime.value ", ($wio_diff != 0) ?
($wtime_diff / $wio_diff) : 0, "\n",
LINE 204: );
There's another (minor) problem which is to say that returning 0 in a situation
where no IO has occurred is a lie, should return NaN or NA but if you read the
Munin protocol specification (see link below) it claims "Output must be integer
or decimal number," so the have no provision for a plugin saying "hey, this
value does not exist right now" and that's strange because the RRD system does
support NaN for missing values -- but that's a bigger problem for another day.
http://munin-monitoring.org/wiki/protocol-config
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https://bugs.launchpad.net/bugs/919429
Title:
Munin "IO Service Time" graph gives completely implausible numbers
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