Trouble updating an RRDtool database

I created a database with the following syntax.

rrdtool create mydatabase.rrd -s 60 \
DS:users:COUNTER:600:0:U \
DS:activeusers:GAUGE:600:0:U \
RRA:AVERAGE:0.5:360:576 \
RRA:AVERAGE:0.5:8640:672 \
RRA:AVERAGE:0.5:259200:732 \
RRA:AVERAGE:0.5:3153600:732

And I have a crontab entry that runs the follo开发者_高级运维wing.

* * * * * rrdtool update mydatabase.rrd N:$users:$active` 

$users and $active are pulled from an external source, this is just representative.

I waited about 24 hours, and the RRDtool fetch gave me a pile of NaN results. Am I missing something really basic here, or should that work as described?

Make sure that you are actually inputting valid data. Send N:$users:$active a logfile.

Also, have an RRA file with a little bit of a higher resolution. At the moment you are storing one entry every 360 minutes = 6 hours in the first RRA file. In the last RRA file you store one update every six years for 732 years.