=head1 DESCRIPTION
-RRDtool is written by Tobias Oetiker <oetiker@ee.ethz.ch> with
+RRDtool is written by Tobias Oetiker E<lt>tobi@oetiker.chE<gt> with
contributions from many people all around the world. This document is
-written by Alex van den Bogaerdt <alex@ergens.op.het.net> to help you
+written by Alex van den Bogaerdt E<lt>alex@ergens.op.het.netE<gt> to help you
understand what RRDtool is and what it can do for you.
The documentation provided with RRDtool can be too technical for some
=head2 What data can be put into an RRD?
-XXX time series ??? XXX You name it, it will probably fit. You should
-be able to measure some value at several points in time and provide
-this information to RRDtool. If you can do this, RRDtool will be able
-to store it. The values must be numerical but don't have to be
-integers, as is the case with MRTG (the next section will give more
-details on this more specialized application).
+You name it, it will probably fit as long as it is some sort of time-series
+data. This means you have to be able to measure some value at several points in time and
+provide this information to RRDtool. If you can do this, RRDtool will be
+able to store it. The values must be numerical but don't have to be
+integers, as is the case with MRTG (the next section will give more details
+on this more specialized application).
Many examples below talk about SNMP which is an acronym for Simple Network
Management Protocol. "Simple" refers to the protocol -- it does not
started as a tiny little script for graphing the use of a university's
connection to the Internet. MRTG was later (ab-)used as a tool for
graphing other data sources including temperature, speed, voltage,
-number of printouts and the like.
+number of printouts and the like.
Most likely you will start to use RRDtool to store and process data
collected via SNMP. The data will most likely be bytes (or bits)
came with RRDtool for the location and usage of the list.
I suggest you take a moment to subscribe to the mailing list right now
-by sending an email to E<lt>rrd-users-request@list.ee.ethz.chE<gt> with a
+by sending an email to E<lt>rrd-users-request@lists.oetiker.chE<gt> with a
subject of "subscribe". If you ever want to leave this list, just write
an email to the same address but now with a subject of "unsubscribe".
=head2 What has been created?
-We created the round robin database called test (test.rrd) which
-starts at noon the day I started writing this document, 7th of March,
-1999 (this date translates to 920'804'400 seconds as explained
-below). Our database holds one data source (DS) named "speed" that
-represents a counter. This counter is read every five minutes
-(default). In the same database two round robin archives (RRAs) are
-kept, one averages the data every time it is read (e.g., there's
-nothing to average) and keeps 24 samples (24 times 5 minutes is 2
-hours). The other averages 6 values (half hour) and contains 10 of
-such averages (e.g., 5 hours).
-
-=for comment
- XXX The remaining options will be discussed later on. (there aren't any
- XXX in the example above, Fritz)
+We created the round robin database called test (test.rrd) which starts at
+noon the day I started writing this document, 7th of March, 1999 (this date
+translates to 920'804'400 seconds as explained below). Our database holds
+one data source (DS) named "speed" that represents a counter. This counter
+is read every five minutes (this is the default therefore you don't have to
+put C<--step=300>). In the same database two round robin archives (RRAs)
+are kept, one averages the data every time it is read (e.g., there's nothing
+to average) and keeps 24 samples (24 times 5 minutes is 2 hours). The other
+averages 6 values (half hour) and contains 10 such averages (e.g. 5 hours).
RRDtool works with special time stamps coming from the UNIX world.
This time stamp is the number of seconds that passed since January
units of our data, it just works with dimensionless numbers.
If we had measured our distances in meters, this would have been
-(12'357'000-12'345'000)/300 = 12'000/300 = 40.
+(12'357'000-12'345'000)/300 = 12'000/300 = 40.
As most people have a better feel for numbers in this range, we'll
correct that. We could recreate our database and store the correct
Hang on! If we can multiply values with 1'000, it should also be possible
to display kilometers per hour from the same data!
-=for comment
-XXX strange format below: -*- ; Fritz
-
To change a value that is measured in meters per second:
- -*- Calculate meters per hour: value * 3'600
- -*- Calculate kilometers per hour: value / 1'000
- -*- Together this makes: value * (3'600/1'000) or value * 3.6
+
+ Calculate meters per hour: value * 3'600
+ Calculate kilometers per hour: value / 1'000
+ Together this makes: value * (3'600/1'000) or value * 3.6
In our example database we made a mistake and we need to compensate for
this by multiplying with 1'000. Applying that correction:
- -*- value * 3.6 * 1'000 == value * 3'600
+
+ value * 3.6 * 1'000 == value * 3'600
Now let's create this PNG, and add some more magic ...
- rrdtool graph speed3.png \
+ rrdtool graph speed3.png \
--start 920804400 --end 920808000 \
--vertical-label km/h \
DEF:myspeed=test.rrd:speed:AVERAGE \
=head2 Updates in Reality
-We've already used the "update" command: it took one or more
+We've already used the C<update> command: it took one or more
parameters in the form of "<time>:<value>". You'll be glad to know
that you can specify the current time by filling in a "N" as the time.
Or you could use the "time" function in Perl (the shortest example in
Should become: 18'446'744'073'709'551'800
But really is: 184
Delta: -18'446'744'073'709'550'816
- Correction1: -18'446'744'073'709'550'816
+ Correction1: -18'446'744'073'709'550'816
+ 4'294'967'296 = -18'446'744'069'414'583'520
- Correction2: -18'446'744'069'414'583'520
+ Correction2: -18'446'744'069'414'583'520
+ 18'446'744'069'414'584'320 = 800
Before: 18'446'744'073'709'551'615 ( maximum value )
View both images together (add them to your index.html file)
and compare. Both graphs should show the same, despite the
-input being different.
+input being different.
=head1 WRAPUP
projects / rrdtool.git / blobdiff