[rrd-users] time as a counter?

[Grant Kelly]

Hi,

I'm new to rrdtool so I've been reading all the documentation and tutorials
I can find. However, I have been unsuccessful with creating a database.
There are a bunch of weather stations I would like to watch and record the
last time their data is updated. I have a python script which looks at the
data and determines the time of the most recent data. This time is typically
10-30 minutes behind the actual time. I run the script every 10 minutes to
update a web page that displays the time of the most recent data for each
station.

What I would like to do is add to this script a call to rrdtool.update()
which will send a unix timestamp to be saved in now's slot.
Is this the correct way to create the rrd?

rrdtool create test.rrd -b 1177916700 --step 600
DS:updated:COUNTER:720:1177900000:U RRA:LAST:0.5:1:105120

That is, start at Apr 30 12:05AM. Create PDP 'updated' every 10 minutes.
Allow 12 minutes between database updates. Keep the last 1 values and keep
105120 of them.

Does this make sense? The RRA is still a bit confusing to me. I will only
have one sample every 10 minutes and I would like to keep that one sample as
the PDP for that 10-minute slot. rrdtool can handle much more complicated
situations than this, but it seems like this very simple situation is not so
easy to configure.

The goal is to make graphs that show when the stations stopped updating at
expected times, i.e. there would be a flat line since the 'updated' time
didn't increase from PDP to PDP. Eventually, I want to color the area under
the line according to some threshold, such as "red if the station hasn't
updated for 6 hours."

Any suggestions are welcome.

Thanks,
Grant
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