[rrd-users] Missing data overnight from daylight saving changes

[Richard Curtis]

Hi,
  I have a simple rrd to store filesystem utilisation on an hourly basis.
The data is gathered on other hosts, then processed into rrd via a
script run at 4am.

The rrd was created as:
rrdtool create myrouter.rrd    DS:used:GAUGE:3600:0:100
RRA:LAST:0.5:1:8760   --start 1256403600 --step 3600

And the following values entered:
rrdtool update myrouter.rrd 1256410800:39
rrdtool update myrouter.rrd 1256414400:39
rrdtool update myrouter.rrd 1256418000:39
rrdtool update myrouter.rrd 1256421600:39
rrdtool update myrouter.rrd 1256425200:39
rrdtool update myrouter.rrd 1256432400:39
rrdtool update myrouter.rrd 1256436000:39
rrdtool update myrouter.rrd 1256439600:39
rrdtool update myrouter.rrd 1256443200:39

but I have a gap in data between midnight of the 25-Oct (BST) and 2am
(GMT) on 26-Oct.
An rrdtool dump shows:
    <!-- 2009-10-24 20:00:00 BST / 1256410800 --> <row><v>
3.9000000000e+01 </v></row>
                        <!-- 2009-10-24 21:00:00 BST / 1256414400 -->
<row><v> 3.9000000000e+01 </v></row>
                        <!-- 2009-10-24 22:00:00 BST / 1256418000 -->
<row><v> 3.9000000000e+01 </v></row>
                        <!-- 2009-10-24 23:00:00 BST / 1256421600 -->
<row><v> 3.9000000000e+01 </v></row>
                        <!-- 2009-10-25 00:00:00 BST / 1256425200 -->
<row><v> 3.9000000000e+01 </v></row>
                        <!-- 2009-10-25 01:00:00 BST / 1256428800 -->
<row><v> NaN </v></row>
                        <!-- 2009-10-25 01:00:00 GMT / 1256432400 -->
<row><v> NaN </v></row>
                        <!-- 2009-10-25 02:00:00 GMT / 1256436000 -->
<row><v> 3.9000000000e+01 </v></row>
                        <!-- 2009-10-25 03:00:00 GMT / 1256439600 -->
<row><v> 3.9000000000e+01 </v></row>
                        <!-- 2009-10-25 04:00:00 GMT / 1256443200 -->
<row><v> 3.9000000000e+01 </v></row>

Am I missing something here?  I did insert a value for 256432400, but
it looks like rrdtool is expecting a value for both 01:00 BST and
01:00 GMT.
Do I need to do some magic when I insert the values and double input
when the clocks go back?

Richard