[mrtg] Re: Availability of specific devices

[Alex van den Bogaerdt]

Stefan.Heins at seb.de wrote:

> For the management i have to proof the availability of specific devices.
> Our contract says that the devices has to be availaby for 98,5%.
> How can i do this with mrtg? Does somebody out there has the same problem
> already solved?

Availability can't be monitored.  You can make a close approximation.

If you poll the device every five minutes, there is a chance that
you don't get to see an outage of upto five minutes.

If you lower the interval: for every number of seconds you choose,
there is a lower number of seconds (non-integer).  You will reach
the point where you can't monitor quickly enough far sooner than
the moment where you don't care about "outages".

If you only look at the uptime of the device you don't really know
if it was available or just up and not accepting any requests
apart from SNMP (or whatever other method).


That being said:  You probably need to create some scripts that
return the data to MRTG (use the external program interface).

You will probably have some issues with timing and thus rounding.

The script could, for instance, return 100 when the device is up
and 0 when it's not up.  Use a GAUGE counter and MRTG will not
divide the counter value by the amount of seconds between two
updates. This will result in a rate of 100 (more or less) or 0.
The result: for each interval you have 100% up or 0% up.  This
will also reflect upto the weekly, monthly and yearly graph after
the data is consolidated.  Again: there will probably be some
rounding issues so the rate could become 101% and then 99% or so.
This cannot be helped, unless you really know what you're doing
and you really know how MRTG works. If so, you don't need to ask.

Another path to follow:  Use a normal counter, and monitor sysUptime.
The same problems with timing apply.

The most important thing to do is to get a suitable number for
MRTG to process.  The 100 vs. 0 trick can be implemented in many
ways.

HTH
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