[rrd-users] Graph scaling issue

Hilman, Harlan - CIDM-2 hlhilman at bpa.gov
Wed Oct 16 16:39:55 MEST 2002

I'm trying to use a Perl script to collect inoctets and outoctets from an
OC3 interface via SNMP, then save the average and max in rrd via "rrdtool
update".  Because of a 32-bit counter limitation, the collection interval
(and rrd averaging) is set to 1 minute to avoid rollover. The entire process
uses raw numbers with the exception of one CDEF that changes octets to bits.
All seems to work as expected, but it looks like the graphs (generated by
"rrdtool graph") seem to be running higher than what I'd expect.  From what
I can determine, the maximum bit rate on an OC3 should be 155.52Mb/s, but
during nightly backups the graphs show a 1-minute max consistently exceeding
160Mb/s.   The only reference available for this OC3 is the current MRTG
graphs which are inaccurate above ~114Mb/s due to a minimum 5 minute
interval (which is why we're trying to implement rrd).  I'm sure I'm missing
something obvious, but can't figure out what it is, so I'd greatly
appreciate any suggestions that could "set me straight" :-)

- Harlan

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