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

Yu Watanabe yu.watanabe at jp.fujitsu.com
Thu May 20 06:48:31 CEST 2010

```Hello Karl.

I will confirm your theory and if there're any questions,
would like to get back to you.

Thanks
Yu

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.
>>
>> 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
>
>

```