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
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
+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
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 ...
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 *
projects / rrdtool.git / blobdiff