=for changes please consult me first. Thanks, Alex
+
=head1 NAME
rrdtutorial - Alex van den Bogaerdt's RRDtool tutorial
go on and on and on. After a while, all the available places will be used and
the process automatically reuses old locations. This way, the dataset
will not grow in size and therefore requires no maintenance.
-RRDtool works with with Round Robin Databases (RRDs). It stores and retrieves
+RRDtool works with Round Robin Databases (RRDs). It stores and retrieves
data from them.
=head2 What data can be put into an RRD?
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)
-transfered from and to a network or a computer. But it can also be
+transferred from and to a network or a computer. But it can also be
used to display tidal waves, solar radiation, power consumption,
number of visitors at an exhibition, noise levels near an airport,
temperature on your favorite holiday location, temperature in the
-fridge and whatever you imagination can come up with.
+fridge and whatever your imagination can come up with.
You only need a sensor to measure the data and be able to feed the
numbers into RRDtool. RRDtool then lets you create a database, store
Assume we have a device that transfers bytes to and from the Internet.
This device keeps a counter that starts at zero when it is turned on,
-increasing with every byte that is transfered. This counter will probably have
+increasing with every byte that is transferred. This counter will probably have
a maximum value. If this value is reached and an extra byte is counted,
the counter starts over at zero. This is the same as many counters
in the world such as the mileage counter in a car.
counting from 0 to 4294967295. 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
+many bytes have been transferred ***on average*** per second. This is
not very hard to calculate. First in words, then in calculations:
=over 3
920808600: 6.6666666667e-03
920808900: 3.3333333333e-03
920809200: nan
+ 920809500: nan
-If it doesn't, something may be wrong. Perhaps your OS will print
-"NaN" in a different form. "NaN" stands for "Not A Number". If your OS
-writes "U" or "UNKN" or something similar that's okay. If something
-else is wrong, it will probably be due to an error you made (assuming
-that my tutorial is correct of course :-). In that case: delete the
-database and try again.
+Note that you might get more rows than you expect. The reason for this is
+that you ask for a time range that ends on 920809200. The number that is
+written behind 920809200: in the list above covers the time range from
+920808900 to 920809200, EXCLUDING 920809200. Hence to be on the sure side,
+you receive the entry from 920809200 to 920809500 as well since it INCLUDES
+920809200. You may also see "NaN" instead of "nan" this is OS dependent.
+"NaN" stands for "Not A Number". If your OS writes "U" or "UNKN" or
+something similar that's okay. If something else is wrong, it will probably
+be due to an error you made (assuming that my tutorial is correct of course
+:-). In that case: delete the database and try again.
The meaning of the above output will become clear below.
other types of values like temperature.
Many people interested in RRDtool will use the counter that keeps track
-of octets (bytes) transfered by a network device. So let's do just
+of octets (bytes) transferred by a network device. So let's do just
that next. We will start with a description of how to collect data.
Some people will make a remark that there are tools which can do this data
projects / rrdtool.git / blobdiff