NMIS8 is a Network Management System which performs performance management.  NMIS8 collects SNMP data from routers, switches, firewalls, servers, and many more types of IT devices.  It stores the collected data in a performance database, which is an RRD file using RRDTool.  

This article will describe how much data NMIS8 stores and how to modify NMIS8 to store more data.

How much data does NMIS8 Store?

RRDTool is a round robin database, which stores data in a binary file which is effectively circular, you define how many elements of data you want to keep and keep feeding data and it will keep adding elements up to that many of entries, when it is full, the oldest entries are overwritten.  To keep summarised data you define a summarisation scheme, so the data is rolled up into the next level.  In NMIS8 we define how much data RRDTool keeps by using the NMIS8 modelling system.  The files for the NMIS8 models are stored in /path/to/nmis8/models and specifically the default database definitions are kept in /path/to/nmis8/models/Common-database.nmis

By default NMIS8 polls for performance data every 5 minutes and data in the following scheme:

This summarisation scheme was chosen to get a good balance of data stored and disk space used.  The file sizes created using this scheme are as follows:

What about statistical summarisation?

NMIS8 does not just keep the AVERAGES, it also keeps the MAXIMUM and MINIMUM for each data point, so in effect you have the range of data seen for a given summarisation, this is very important statistically, and many systems do not maintain this information.  When doing analysis of performance data, it is important to use the averages (MEAN) as well as the MAXIMUM and MINIMUM (RANGE).

Can NMIS8 Store More Performance Data?

Yes, NMIS8 can be configured to store as much performance data as you have disk for.  This is very easy to do when you first install an NMIS system.  To store more data, first you need to determine how much more data you would like to store, then plug those numbers into the RRD Calculator Spreadsheet rrd_calc.xls, attached for your convenience, this will tell you what you need to change in the NMIS8 model file  /path/to/nmis8/models/Common-database.nmis

The default Common-database.nmis file contains this:

 'db' => {
   'hbeat' => '900',
   'poll' => '300',
   'size' => {
 'reachability' => {
 'step_year' => '288',
 'rows_month' => '2268',
 'rows_year' => '1890',
 'step_day' => '1',
 'step_month' => '24',
 'step_week' => '6',
 'rows_day' => '2304',
 'rows_week' => '1536'
 },
 'interface' => {
 'step_year' => '288',
 'rows_month' => '2268',
 'rows_year' => '1890',
 'step_day' => '1',
 'step_month' => '24',
 'step_week' => '6',
 'rows_day' => '2304',
 'rows_week' => '1536'
 },
 'default' => {
 'step_year' => '288',
 'rows_month' => '2268',
 'rows_year' => '1890',
 'step_day' => '1',
 'step_month' => '24',
 'step_week' => '6',
 'rows_day' => '2304',
 'rows_week' => '1536'
 },
 'metrics' => {
 'step_year' => '288',
 'rows_month' => '2268',
 'rows_year' => '1890',
 'step_day' => '1',
 'step_month' => '24',
 'step_week' => '6',
 'rows_day' => '2304',
 'rows_week' => '1536'
 }
 }
 },