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-<meta http-equiv="content-type" content="text/html; charset=utf-8" />
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+ <li><a href="#name">NAME</a></li>
<li><a href="#description">DESCRIPTION</a></li>
<li><a href="#tutorial">TUTORIAL</a></li>
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+<p>
+</p>
+<hr />
+<h1><a name="name">NAME</a></h1>
<p>rrdtutorial - Alex van den Bogaerdt's RRDtool tutorial</p>
<p>
</p>
many bytes have been transfered ***on average*** per second. This is
not very hard to calculate. First in words, then in calculations:</p>
<ol>
-<li>
-<p>Take the current counter, subtract the previous value from it.</p>
-</li>
-<li>
-<p>Do the same with the current time and the previous time (in seconds).</p>
-</li>
-<li>
-<p>Divide the outcome of (1) by the outcome of (2), the result is
+<li></li>
+Take the current counter, subtract the previous value from it.
+<p></p>
+<li></li>
+Do the same with the current time and the previous time (in seconds).
+<p></p>
+<li></li>
+Divide the outcome of (1) by the outcome of (2), the result is
the amount of bytes per second. Multiply by eight to get the
-number of bits per second (bps).</p>
-</li>
-</ol>
+number of bits per second (bps).
+<p></p></ol>
<pre>
bps = (counter_now - counter_before) / (time_now - time_before) * 8</pre>
<p>For some people it may help to translate this to an automobile example.
</p>
<h2><a name="rrdtool_under_the_microscope">RRDtool under the Microscope</a></h2>
<ul>
-<li>
-<p>Line A is a COUNTER type, so it should continuously increment and RRDtool
+<li></li>
+Line A is a COUNTER type, so it should continuously increment and RRDtool
must calculate the differences. Also, RRDtool needs to divide the
difference by the amount of time lapsed. This should end up as a
-straight line at 1 (the deltas are 300, the time is 300).</p>
-</li>
-<li>
-<p>Line B is of type GAUGE. These are ``real'' values so they should match
-what we put in: a sort of a wave.</p>
-</li>
-<li>
-<p>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.</p>
-</li>
-<li>
-<p>Line D is of type ABSOLUTE. This is like counter but it works on
+straight line at 1 (the deltas are 300, the time is 300).
+<p></p>
+<li></li>
+Line B is of type GAUGE. These are ``real'' values so they should match
+what we put in: a sort of a wave.
+<p></p>
+<li></li>
+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.
+<p></p>
+<li></li>
+Line D is of type ABSOLUTE. This is like counter but it works on
values without calculating the difference. The numbers are the same
-and as you can see (hopefully) this has a different result.</p>
-</li>
-</ul>
+and as you can see (hopefully) this has a different result.
+<p></p></ul>
<p>This translates in the following values, starting at 23:10 and ending
at 00:10 the next day (where ``u'' means unknown/unplotted):</p>
<pre>
the lines.</p>
<p>Let's go over the data again:</p>
<ul>
-<li>
-<p>Line A: 300,600,900 and so on. The counter delta is a constant 300 and
+<li></li>
+Line A: 300,600,900 and so on. The counter delta is a constant 300 and
so is the time delta. A number divided by itself is always 1 (except
-when dividing by zero which is undefined/illegal).</p>
+when dividing by zero which is undefined/illegal).
<p>Why is it that the first point is unknown? We do know what we put into
the database, right? True, But we didn't have a value to calculate the delta
from, so we don't know where we started. It would be wrong to assume we
started at zero so we don't!</p>
-</li>
-<li>
-<p>Line B: There is nothing to calculate. The numbers are as they are.</p>
-</li>
-<li>
-<p>Line C: Again, the start-out value is unknown. The same story is holds
+<p></p>
+<li></li>
+Line B: There is nothing to calculate. The numbers are as they are.
+<p></p>
+<li></li>
+Line C: Again, the start-out value is unknown. The same story is holds
as for line A. In this case the deltas are not constant, therefore the line
is not either. If we would put the same numbers in the database as we did for
line A, we would have gotten the same line. Unlike type counter,
this type can decrease and I hope to show you later on why
-this makes a difference.</p>
-</li>
-<li>
-<p>Line D: Here the device calculates the deltas. Therefore we DO know the
+this makes a difference.
+<p></p>
+<li></li>
+Line D: Here the device calculates the deltas. Therefore we DO know the
first delta and it is plotted. We had the same input as with line A, but
the meaning of this input is different and thus the line is different.
In this case the deltas increase each time with 300. The time delta
stays at a constant 300 and therefore the division of the two gives
-increasing values.</p>
-</li>
-</ul>
+increasing values.
+<p></p></ul>
<p>
</p>
<h2><a name="counter_wraps">Counter Wraps</a></h2>