RRDB Contains Only NaN - rrdtool

Question

I'm getting all NaN's in my rrdb. Why?
rrdtool create temps.rrd --step 120 \
DS:temp:GAUGE:250:-10:212 \
DS:rate:DERIVE:250:-10:212 \
DS:setpoint:GAUGE:250:-10:212 \
RRA:AVERAGE:0.3:1:43200
After a night of collecting data & updating every 2 minutes something like this:
/usr/bin/rrdupdate temps.rrd N:30.8:30.8:9.6
The DS is changing, but the RRA doesn't have any entries.
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE rrd SYSTEM "http://oss.oetiker.ch/rrdtool/rrdtool.dtd">
<!-- Round Robin Database Dump -->
<rrd>
<version>0003</version>
<step>120</step> <!-- Seconds -->
<lastupdate>1375360140</lastupdate> <!-- 2013-08-01 07:29:00 CDT -->
<ds>
<name> temp </name>
<type> GAUGE </type>
<minimal_heartbeat>250</minimal_heartbeat>
<min>-1.0000000000e+01</min>
<max>2.1200000000e+02</max>
<!-- PDP Status -->
<last_ds>60.1</last_ds>
<value>NaN</value>
<unknown_sec> 60 </unknown_sec>
</ds>
<ds>
<name> rate </name>
<type> DERIVE </type>
<minimal_heartbeat>250</minimal_heartbeat>
<min>-1.0000000000e+01</min>
<max>2.1200000000e+02</max>
<!-- PDP Status -->
<last_ds>59.9</last_ds>
<value>NaN</value>
<unknown_sec> 60 </unknown_sec>
</ds>
<ds>
<name> setpoint </name>
<type> GAUGE </type>
<minimal_heartbeat>250</minimal_heartbeat>
<min>-1.0000000000e+01</min>
<max>2.1200000000e+02</max>
<!-- PDP Status -->
<last_ds>60.0</last_ds>
<value>NaN</value>
<unknown_sec> 60 </unknown_sec>
</ds>
<!-- Round Robin Archives -->
<rra>
<cf>AVERAGE</cf>
<pdp_per_row>1</pdp_per_row> <!-- 120 seconds -->
<params>
<xff>3.0000000000e-01</xff>
</params>
<cdp_prep>
<ds>
<primary_value>NaN</primary_value>
<secondary_value>NaN</secondary_value>
<value>NaN</value>
<unknown_datapoints>0</unknown_datapoints>
</ds>
<ds>
<primary_value>NaN</primary_value>
<secondary_value>NaN</secondary_value>
<value>NaN</value>
<unknown_datapoints>0</unknown_datapoints>
</ds>
<ds>
<primary_value>NaN</primary_value>
<secondary_value>NaN</secondary_value>
<value>NaN</value>
<unknown_datapoints>0</unknown_datapoints>
</ds>
</cdp_prep>
<database>
<!-- 2013-06-02 07:30:00 CDT / 1370176200 --> <row><v>NaN</v><v>NaN</v><v>NaN</v></row>
<!-- 2013-06-02 07:32:00 CDT / 1370176320 --> <row><v>NaN</v><v>NaN</v><v>NaN</v></row>
<!-- 2013-06-02 07:34:00 CDT / 1370176440 --> <row><v>NaN</v><v>NaN</v><v>NaN</v></row>
many lines, all NaN
<!-- 2013-08-01 07:26:00 CDT / 1375359960 --> <row><v>NaN</v><v>NaN</v><v>NaN</v></row>
<!-- 2013-08-01 07:28:00 CDT / 1375360080 --> <row><v>NaN</v><v>NaN</v><v>NaN</v></row>
</database>
</rra>
</rrd>

Answer 1

Your problem is that you are not actually storing any data; your rrdupdate calls are failing.
If you run the rrdupdate command from the commandline, you will immediately see the error:
$ rrdtool update temps.rrd N:30.8:31.2:9.1
ERROR: temps.rrd: not a simple signed integer: '31.2'
The reason for this is that, while the first and third DS are of type GAUGE, the second is of type DERIVE. It is a (poorly documented) fact that you can only use a non-integer value when the data type is GAUGE.
So, you have four options -
Make sure your second value (for 'rate') is always an integer
Change it to type GAUGE and pass the rate rather than the value
Remove the second DS entirely, and calculate this on the fly when displaying the data
Replace the rate DS with a COMPUTE DS type to calculate at storage time
The last may be the best option but would need some work.