[rrd-users] Re: Cisco NAM + Perl + SNMP + RMON2 + RRDtool

Alex van den Bogaerdt alex at ergens.op.het.net
Wed Dec 8 23:34:53 MET 2004

On Wed, Dec 08, 2004 at 11:11:07PM +0100, Serge Maandag wrote:

> > RRA:LAST:0.5:30:800
> > RRA:LAST:0.5:120:800
> That is two times the same resolution, but with different sizes.
> The first one is redundant.


* create - create a new RRD

	rrdtool create filename [--start|-b start time]
		[--step|-s step]
		[DS:ds-name:DST:heartbeat:min:max] [RRA:CF:xff:steps:rows]

I think these two RRAs are quite different.

One will store CDPs of (30*60=)1800 seconds (800 of them),
the other has CDPs of (120*60=)7200 seconds (800 of them).

When creating a graph with width 600 pixels and time 50days, 
the first RRA will serve one CDP per pixel column, the 2nd
RRA will serve one CDP per 4 pixel columns.

> I just realized that the LAST function isn't all too clear to me.
> It doesn't seem to be explained on the rrdtool site, but I may have
> Overlooked it.

It should be the last seen rate. Never used it so can't say for sure.
I _think_ it is to sort of override an earlier found rate, to make
sure you have the most current rate when updating more than once per
interval.  Never understood why one would want to do this, as is seems
to be a waste of resources :)

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