[rrd-users] trying to understand the relationship between source data, what's in rrd and what gets plotted

[Mark Seger]

Simon Hobson wrote:
> Mark Seger wrote:
>   
>> The thing that's interesting about this whole situation is that on one
>> level rrd appears to draw a cleaner graph and the gnuplot one looks a
>> little fuzzier, but I also think the gnuplot provides valuable
>> information that gets lost, and probably missed with rrd.  If my
>> examples were disk performance numbers rrd could have led someone to the
>> conclusion that everything was running just fine at a load of 20 while
>> gnuplot shows there's really a range from 0 to 20 and things are not
>> fine.  If you zoom into the rrd data you definitely can see see the
>> details of the drop off, but my fear is how many people would bother. 
>> They would see the day long data and think everything is fine.
>>     
>
> On the other hand, I can't remember when it was, but I certainly 
> learned about the basic arithmetic functions of min, max, and average 
> at school. RRD is simply a tool, as is GNUplot.
>
> What I would say is that if you want to plot every datapoint, as 
> collected, with no normalisation or consolidation then rrd is 
> probably not the right tool - you should plot with GNUplot.
>
> What rrd does do (very well) is allow you to collect detailed numbers 
> and balance the storage and processing requirements vs the need to 
> keep detailed numbers for a long time - eg collecting every 5 seconds 
> for a few hours, but dropping the resolution to make it practical to 
> store data for a whole year.
>   
yes, I agree completely about the ability about rrd's strength being to 
be able to store data long term.  but if take a sample every 5 seconds 
but then can't look at it at that granularity what's the point?  I did 
see the suggestions about using multiple lines/averages for each 
variable, and if you only have a few I suppose that could work too, but 
I'm trying to deal with hundreds.  perhaps the best compromise is to use 
gnuplot for fine grained plotting and using rrd for archiving.
-mark
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