[rrd-users] RRD files not correctly storing the values added using rrdtool update

[Traiano Welcome]

Hi List

I'm seeing what appears to be my rrd files not storing the values I 
added using "rrdtool update", i.e I update the rrd file with one set of 
values (network traffic_in and traffic_out counter values) and rrdtool 
fetch shows completely different values for the corresponding 
time-slots. This causes me to wonder if my rrd update options or rrd 
file structure is wrong. Process illustrated below:

The rrd is created as follows:

---
/usr/bin/rrdtool create \
vlan_interface_traffic.rrd \
--step 300  \
DS:traffic_in:COUNTER:600:0:1.8446744074e+17 \
DS:traffic_out:COUNTER:600:0:1.8446744074e+17 \
RRA:AVERAGE:0.5:1:600 \
RRA:AVERAGE:0.5:6:700 \
RRA:AVERAGE:0.5:24:775 \
RRA:AVERAGE:0.5:288:797 \
RRA:MIN:0.5:1:600 \
RRA:MIN:0.5:6:700 \
RRA:MIN:0.5:24:775 \
RRA:MIN:0.5:288:797 \
RRA:MAX:0.5:1:600 \
RRA:MAX:0.5:6:700 \
RRA:MAX:0.5:24:775 \
RRA:MAX:0.5:288:797 \
RRA:LAST:0.5:1:600 \
RRA:LAST:0.5:6:700 \
RRA:LAST:0.5:24:775 \
RRA:LAST:0.5:288:797 \
---

Values are polled using snmpget and updated every 5 minutes (from cron) 
using this rrdupdate command, for example:

---
rrdtool update vlan_interface_traffic.rrd 1251991500:146522079:2005725
---

However the rrdtool fetch shows this:

---
.
.
--->1251991500: 8.0040000000e+01 1.0666666667e+00
1251991800: 7.5040000000e+01 1.9200000000e+00
1251992100: nan nan
.
---

Correspondingly, the graphs show  traffic several orders of magnitude 
lower than it should.

I've experimented with switching the "max" value for DS (in case it's a 
64-bit problem), as well as making sure the timestamps are normalized. 
Neither option makes any difference. I've also used another rrdtool 
dependent graphing system (cacti) to build the rrd, poll and graph the 
same vlan interface, it seems to manifest the same issue.

Is there possibly something wrong with my rrd create options/rrd 
structure that might be resulting in incorrect values being stored in 
the rrd? Or are there rrd update options that I'm missing from my update 
command?

Thanks in Advance,
Traiano

(TENET, Tertiary Education and Research Network)