# [rrd-users] Transfer rate for rrd graph command

Yu Watanabe yu.watanabe at jp.fujitsu.com
Tue May 25 10:18:44 CEST 2010

```Hello Karl.

Thank you for the explanation you have given to me in the previous email.

It would be greatful, if you could once again help us out.

In fact, I am now trying to make a traffic bit/sec graph using the rrdtool.
And, I would like to know how does the rrdtool calculate the y-axis value that
corresponds to the x-axis , which is time value.

We have understood most of your theory.
And, the following is the additional item which we would like to know.

>Now assume you 'zoom out' to 1 hour (3600s) on the same graph
>width of 600px - so 1px represents (the average of) 6s now.
>=> for the 1px that includes the 3s 20 MB/s and 3s 10 MB/s
>   the average is (3x10 + 3x20) / 6 => 15MB/s
>   => so now your peak dropped from 20 to 15 MB/s (avg)
>
>The above get's more complicated if the 3s period mentioned
>doesn't fit into a 6s period, but spans two instead ...

How would the rrd calculate y-axis if each pixel represents
a decimal , not an integer?

I have created an graph in following condition but not sure about
above question.

1. width of x-axis : 500px
2. height of y-axis : 120px
3. data recorded : 1 value per hour
4. time range of start and end : 2010/4/1 00:00:00 〜2010/4/30 23:59:00

Assuming from the above condition, the number of records to be used from rrd
are 720. rrdtool would try to plot 500px of data using 720 records. So,
per pixel would be 1.44 record/pixel (720 record / 500 pixl = 1.44)

If this calculation is valid , how does each record fit into this
decimal?

Thank you
Yu Watanabe

Karl Fischer さんは書きました:
>> Hello all.
>>
>> I would like to ask a question regarding to the transfer rate for rrd graph command.
>> I was checking the following page to find out why the y-axis value seems to decrease
>> when the range of date changes.
>> Y-axis
>> http://oss.oetiker.ch/rrdtool-trac/wiki/RrdFaq
>>
>> However, I couldn't quite understand the "transfer rate 120" meant in the paragraph.
>> Could someone explain following items?
>>
>> 1. What does value 120 means?
>> 2. What does transfer rate 120 means?
>
>Hello Yu,
>
>let's phrase it differently:
>
>Assume the following:
>
>* you have recorded data with 1 value per second
>* you are displaying a graph for 10 minutes (600s)
>* the graph width is 600px
>=> that means 1px (horizontal) equals 1s
>=> that will give you the exact values that were measured.
>
>Now assume:
>* you have recorded an average transfer rate of 10 MB/s
>* for 3 seconds (peak) the recording is 20 MB/s
>=> the above graph will show you exactly that.
>
>Now assume you 'zoom out' to 1 hour (3600s) on the same graph
>width of 600px - so 1px represents (the average of) 6s now.
>=> for the 1px that includes the 3s 20 MB/s and 3s 10 MB/s
>   the average is (3x10 + 3x20) / 6 => 15MB/s
>   => so now your peak dropped from 20 to 15 MB/s (avg)
>
>The above get's more complicated if the 3s period mentioned
>doesn't fit into a 6s period, but spans two instead ...
>
>Similar things happen with aggregation in larger scales ...
>
>does that help?
>
>- Karl
>
>_______________________________________________
>rrd-users mailing list
>rrd-users at lists.oetiker.ch
>https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
>

```