95th Percentile

The 95th percentile is the number that is greater that 95% of the numbers in a given set. The reason this statistic is so useful in measuring data throughput is that it gives a very accurate picture of the maximum traffic generated on an interface. This is a standard measure that is used for interpreting the performance data.

The 95th Percentile is the highest value left when the top 5% of a numerically sorted set of collected data is discarded. It is used as a measure of the peak value used when one discounts a fair amount for transitory spikes. This makes it markedly different from the average. The following example would help you understand it better.

Consider if the data collected for CPU Utilization is 60,45,43,21,56,89,76,32,22,10. The sorted order of this set of values is 89,76,60,56,45,43,32,22,21,10. Top 2 values, viz., 89 and 76 ( i.e.,5% of the total set ) are discarded. The next highest value,60, is the 95th percentile value. The average of the remaining set is 36.13 which is much lesser than the average of all the values 41.4. The value 36.13 is the 95th Percentile Average.

The unit for threshold is based on the unit of the monitor ie., for all utilization monitors like CPU, Memory, Disk, Interface Rx/Tx etc., the threshold will be in percentage. For Rx/Tx Traffic, the threshold will be in bps (bits per second). For any other monitor like Free Disk Space in MB, the threshold unit will be in MB.