Where did the traffic spikes go?
Take caution when using long term graphs for network capacity planning. In order to visualize historical interface trending information on a reasonably sized graph, the data needs to be averaged. This may smooth out important spikes that would otherwise indicate interface congestion.
Looking at a 24 hour graph with 1 minute resolution, it is easy to spot 9Gb/s spikes throughout the day. The graph is a reasonable size and the data paints a good picture of an interface nearing a congestion problem:
When looking at 7 day historical information, many graphing systems automatically change the resolution to the appropriate average for the time period. In this example the average is 15 minutes. Compare the difference between 1 minute and 15 minute resolution. The 9Gb/s spikes dropped to less then 5Gb/s. When trying to determine link capacity issues, this is a large discrepancy:
The accuracy problem is resolved by changing the averaging back to 1 minute resolution. But, look what happens to the graph. The width changes from a few inches to over 140 inches. That is a lot of scrolling to the right:
It is possible to “display” the data on a single screen, but good luck reading it:
Understanding how these tools present data will help drive accurate capacity planning.