I've been using diskio087d plugin for some time but noticed today that it was not showing the full extent of i/o done to my disk. I had reinstalled the system and wanted to check that everything was graphing correctly so I kicked off a `dd if=/dev/sda of=/dev/null` and left it running and the resulting cacti graph peaked at around 10MB/s yet dd is telling me that it's doing nearer 200MB/s. I checked the plugin diskio.xml and it is using snmp OIDs that are 32 bit counters and this wraps around in a single 5 minute cycle and gives misleading numbers. There are 64 bit counters in the same oid range so I changed the xml as per
--- /usr/share/cacti/resource/snmp_queries/disk_io.xml 2017-03-11 13:55:25.472386465 +0000
+++ /tmp/puppet-file20170311-18930-w11cy2 2017-03-11 17:46:32.367725798 +0000
@@ -23,14 +23,14 @@
<name>Number of Bytes Written</name>
<name>Number of Read accesses</name>
then deleted and recreated the graph (easier than fixing up the rrd) and now it shows me more realistic numbers in the 150+MB/s range.
Oh, that patch is doing the exact opposite as it's puppet trying to back out my change... oops.