# [rrd-users] Re: Is graphing the exact number possible?

BAARDA, Don don.baarda at baesystems.com
Thu Mar 29 02:59:23 MEST 2001

```G'day,

> -----Original Message-----
> From:	Alex van den Bogaerdt [SMTP:alex at slot.hollandcasino.nl]
> Sent:	Thursday, March 29, 2001 7:02 AM
> To:	pwilliamson at mandtbank.com
> Cc:	rrd-users at list.ee.ethz.ch
> Subject:	[rrd-users] Re: Is graphing the exact number possible?
>
>
> Paul C. Williamson wrote:
>
> > in a specified time period?  The reason I ask is that I need to graph
> thei
> >  fOperStatus of a Cisco 2620 ISDN card, and it is either 0 (up) or 1
> (down).
[...]
> If you're (also) interested in the maximum number of lines in
> use, a good way of doing so is to define:
> -  an RRD with step time of one second, and a heartbeat of > 300.
> -  an RRA with averages for 300 PDPs per CDP.
> -  an RRA with maxima for 300 PDPs per CDP.
>
This is the solution I would prefer for accurate graphing of
"events", rather than "intervals". If you extend the heartbeat out to a day
or two, the only time you need to feed data to rrd is when the status
changes (provided the status changes at least every day or two). However,
it's probably a good idea to use a low-ish heartbeat and include periodic
updates as well as "status change events" incase you miss an event. The best
way to do this is use snmp for the periodic samples, and snmp-trap for the
"events".

> Everytime something changes in the line status, remember the number
> of lines.  The *next* time something changes, or the next 5-minute
> boundary, you enter the remembered value (which will be valid from
> the previous update to the current one).
[...]

This is the tricky bit. RRD with assumes a sample refers to the
previous interval between samples, not the next interval. This means at each
change in status, you need to tell rrd what it _was_, not what it now _is_.

ABO

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