=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".
get used to that right away. Assume a byte is eight bits and start to
think in bits not bytes. The counter, however, still counts bytes!
In the SNMP world most of the counters are 32 bits. That means they are
-counting from 0 to 4294967295. We will use these values in the examples.
+counting from 0 to 4'294'967'295. We will use these values in the examples.
The device, when asked, returns the current value of the counter. We
know the time that has passes since we last asked so we now know how
many bytes have been transfered ***on average*** per second. This is
I will use the following abbreviations:
M: meter
- KM: kilometer (= 1000 meters).
+ KM: kilometer (= 1'000 meters).
H: hour
S: second
KM/H: kilometers per hour
M/S: meters per second
You are driving a car. At 12:05 you read the counter in the dashboard
-and it tells you that the car has moved 12345 KM until that moment.
-At 12:10 you look again, it reads 12357 KM. This means you have
+and it tells you that the car has moved 12'345 KM until that moment.
+At 12:10 you look again, it reads 12'357 KM. This means you have
traveled 12 KM in five minutes. A scientist would translate that
into meters per second and this makes a nice comparison toward the
problem of (bytes per five minutes) versus (bits per second).
-We traveled 12 kilometers which is 12000 meters. We did that in five
-minutes or 300 seconds. Our speed is 12000M / 300S or 40 M/S.
+We traveled 12 kilometers which is 12'000 meters. We did that in five
+minutes or 300 seconds. Our speed is 12'000M / 300S or 40 M/S.
We could also calculate the speed in KM/H: 12 times 5 minutes
is an hour, so we have to multiply 12 KM by 12 to get 144 KM/H.
I hope you understand that there is no difference in calculating M/S or
bps; only the way we collect the data is different. Even the K from kilo
-is the same as in networking terms k also means 1000.
+is the same as in networking terms k also means 1'000.
We will now create a database where we can keep all these interesting
numbers. The method used to start the program may differ slightly from
=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 920804400 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
The vertical axis displays the range we entered. We provided
kilometers and when divided by 300 seconds, we get very small
-numbers. To be exact, the first value was 12 (12357-12345) and divided
+numbers. To be exact, the first value was 12 (12'357-12'345) and divided
by 300 this makes 0.04, which is displayed by RRDtool as "40 m"
-meaning "40/1000". The "m" (milli) has nothing to do with meters,
+meaning "40/1'000". The "m" (milli) has nothing to do with meters,
kilometers or millimeters! RRDtool doesn't know about the physical
units of our data, it just works with dimensionless numbers.
If we had measured our distances in meters, this would have been
-(12357000-12345000)/300 = 12000/300 = 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
more detail. Also, you may want to read my tutorial on CDEFs and Steve
Rader's tutorial on RPN. But first finish this tutorial.
-Hang on! If we can multiply values with 1000, it should also be possible
+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 * 3600
- -*- Calculate kilometers per hour: value / 1000
- -*- Together this makes: value * (3600/1000) 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 1000. Applying that correction:
- -*- value * 3.6 *1000 == value * 3600
+this by multiplying with 1'000. Applying that correction:
+
+ 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
LINE1:outoctets#0000FF:"Out traffic"
This should produce a picture with one day worth of traffic.
-One day is 24 hours of 60 minutes of 60 seconds: 24*60*60=86400, we
-start at now minus 86400 seconds. We define (with DEFs) inoctets and
+One day is 24 hours of 60 minutes of 60 seconds: 24*60*60=86'400, we
+start at now minus 86'400 seconds. We define (with DEFs) inoctets and
outoctets as the average values from the database myrouter.rrd and draw
an area for the "in" traffic and a line for the "out" traffic.
counter with one difference: RRDtool assumes the counter is reset when
it's read. That is: its delta is known without calculation by RRDtool
whereas RRDtool needs to calculate it for the counter type.
-Example: our first example (12345, 12357, 12363, 12363) would read:
+Example: our first example (12'345, 12'357, 12'363, 12'363) would read:
unknown, 12, 6, 0. The rest of the calculations stay the same.
The other one, derive, is like counter. Unlike counter, it can also
decrease so it can have a negative delta. Again, the rest of the
=item *
Line C is of type DERIVE. It should be a counter that can decrease. It does
-so between 2400 and 0, with 1800 in-between.
+so between 2'400 and 0, with 1'800 in-between.
=item *
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