(I just noticed that Simon Hobson has already said pretty much the same thing (including an example!) already in a separate post. However I'll leave this response on the list just in case it can help give any additional clarification)
> I have an inconsistency when I graph the same event over 10days versus > 48hrs. I would expect because I am using MAX that the peak on the 48hr > graph and the 10day graph for the *same* event would still read the same > number. However, the peak for Sunday noon on the 48hr graph is at 600, > and the peak for that same period on the 10day graph is *higher* at 1.1k. I > believe I have included all the necessary files below. I didn't want to paste > the raw info here as it would be very large. Any insight would be appreciated. This is because the max of the sum is not the same as the sum of the max for two series. max( a + b ) != max( a ) + max( b ) Your problem is that, in the two graphs, you are likely using different RRAs which have been consolidated BEFORE you do your addition-and-max calculations, resulting in different outcomes. Here is an example. Series 1 (highest-granularity RRA): 1 2 3 4 5 6 Series 2 (highest-granularity RRA): 12 11 10 9 8 7 Now, working on the highest granularity, we add the series and get: 13 13 13 13 13 13 Take the max of this == 13. However, if we have a lower-granularity RRA that consolidates 2 data points using MAX, the series will become: Series 1 (low-granularity RRA): 2 4 6 Series 2 (low-granularity RRA): 12 10 8 Then, adding the value together gives: 14 14 14 Take the max of this series and you get 14 -- the higher-granularity RRA results in a lower value. How to avoid this -- The only ways are to do the calculation before there is any consolidation at all in every case. Try one of these options: 1. Create a separate RRD file that stores the sum of the values, and write to this every interval as you update the other RRD files. Then report on this for the total line. This is the easiest for rrdgraph, but it may be difficult if your updates for the components come in at different times. 2. Extend the highest-granularity RRA to cover all 10 days (or more). Then, in your rrdgraph command, force the use of this higher-granularity RRA, even though it would default to the lower-granularity one. This means a lot more consolidation done on the fly, but it gets done after the calculation. This is probably OK for a 10dy graph, but I wouldn't want to do it on a 10yr graph. Steve Steve Shipway [email protected]
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