Cacti 0.8.8a and built in Poller Intervals

[Nicarlo]

Good day all,

Im recently installed the newest version of cacti and noticed that in the Poller tab under the Utilities area we have a choice for 10,15,20,30 sec intervals.

I've attempted to search the forums for anything under 1 min poller intervals however the thread that come up seems to be very old. Are these intervals now supported under the newest version of cacti and does it require any special configurations to get going?

If someone would be able to point me to the proper documentation for this, you'd be saving me a lot of trouble.

Thank you!

[mikygee]

Hello,
Have you considered the plugin realtime ?
It won't help you to have a low poller interval for all hosts but during network operations and migration you'll be able to lower the polling for one graph.
I poll a low number of hosts, however it takes 14 seconds with 1 thread and 1 php script per thread. But if you have much more hosts you won't be able to lower the polling that much. Moreover you'll add an overhead on your network devices and bandwidth.
And last, the rrd files will average your values after some time. By default, Cacti is configured to average the values of 30 minutes into one value when you look at a one year graph. That means that if you lower your poller less than a minute you'll need to configure your rra to keep these values, and these values are set at the rrd creation, so you'll need to recreate your rrd and of course take the disk space consideration.
I hope this helps a little

[Nicarlo]

Hi Mikygee,

First i'd like to thank you very much for the quick reply.

Thank you for pointing me to the realtime plugin. I still have about 30 devices where I'd like to pull at least every minute. If I were to set the poll interval to 1 minute and reduced the cron interval every minute as well would there be any additional configurations that would be required.

Thank you very much!

[mikygee]

Hello,

Yes, it's what I was wrinting in my previous message. If you have a low poller interval time, it's because you want your graphs to be accurate, so you need to change the rra settings Management > Data sources RRAs
For example, you'll want to keep one point every minute for one week, then one point every two minutes (the average of two points) for one month.
Because you'll keep more records, your rrd will be much bigger. And after you'll change these settings you'll need to recreate your rras/rrds because these settings are set up at the rrd creation.

The default settings for Cacti are not good at all to me, they tend to average values a lot. So if you look at the peak bandwidth you look 2 months ago, the value will be very low because Cacti will make the average of 30 minutes (or one day) and make one point out of it. You'll think that today's traffic is much higher but it's an illusion.

I would recommend anyone to get enough disk space and modify these settings after Cacti's installation and keep one point per minute or per five minute for one week, then one point per 10 minutes for one month, one point for 30 minutes for one year. And also make sure Cacti will keep values for 25 months or 36 months.
This is because you often want to compare the evolution of your bandwidth or firewalls sessions between christmas 2010, 2011 and 2012 for example, and see the evolution. There's no point comparing december 24th with january 13th for example because depending on the business your network carries, the 24th can be a very quiet day or a very busy day.

I've use Cacti for a mobile phone ISP and new years eve is a very busy day, you can compare the traffic only with the new years eve from the year before. But in summer, people go on holiday and use their phone less, so you need to compare august 2012 with august 2011. If you compare august 2012 with september 2012, well it won't help.
Also for another company that have devices in the cars, every friday night they have a high load on the network, and every summer before some public holiday they have a high load. So you definately want to keep your data for more that one year, and as far as I remember Cacti keeps the data for 380 days only or something like that. I don't agree with the default settings at all. They are too conservative.

[Nicarlo]

Mikygee,

Thank you very much for your help. Got this working.

Cheers mate