[rrd-users] Differences between log and rrd values

[William Cassis]

Hello,

I've been running MRTG and storing values in log files for the past few
years and have recently decided to transition the logs to RRD databases.


With this in mind, I set up another copy of MRTG with the same config
but have it writing to RRDs rather than log files.  I ran both the log
and RRD versions of MRTG side-by-side for the last two months and have
noticed something strange- the RRD values are *always* lower than the
log values for the same interface.  This is happening across multiple
devices and all types of interfaces (10mb, 100mb, and 1000mb ethernet,
serial interfaces, ds3s, etc).

After dumping out the RRD database with 'rrdtool fetch' and comparing
the data points with the log file, the timestamps on entries are very
close (within 10 seconds) but the RRD's recorded value is always lower.
I would understand if this happened occasionally due to the wave nature
of bandwidth graphs but to have every value be lower in the RRD seems
off.

Has anyone else seen this happen?

Regards,

William Cassis
will at nextlevelinternet.com