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Re: How do you (not how do I) calculate 95th percentile?
From: Tom Sands <tsands () rackspace com>
Date: Wed, 22 Feb 2006 12:50:34 -0600

Jo Rhett wrote:

I am wondering what other people are doing for 95th percentile calculations
these days.  Not how you gather the data, but how often you check the
counter? Do you use averages or maximums over time periods to create the buckets used for the 95th percentile calculation?

We use maximums, every 5 minutes.

A lot of smaller folks check the counter every 5 min and use that same
value for the 95th percentile. Most of us larger folks need to check more often to prevent 32bit counters from rolling over too often.

Actually, a lot of people do 5 minutes... and I would say that larger companies don't check them more often because they are using 64 bit counters, as should anyone with over about 100Mbps of traffic.

 Are you larger
folks averaging the retrieved values over a larger period?  Using the
maximum within a larger period?  Or just using your saved values?

In our setup, as with a lot of people likely, any data that is older than 30 days is averaged. However, we store the exact maximums for the most current 30 days.

This is curiosity only.  A few years ago we compared the same data and the
answers varied wildly.  It would appear from my latest check that it is
becoming more standardized on 5-minute averages, so I'm asking here on Nanog as a reality check.

Note: I have AboveNet, Savvis, Verio, etc calculations.  I'm wondering
if there are any other odd combinations out there.

Reply to me offlist.  If there is interest I'll summarize the results
without identifying the source.

Tom Sands                                                       
Chief Network Engineer                          
Rackspace Managed Hosting               

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