# [rrd-users] Re: RRD general info about length of storage

Alex van den Bogaerdt alex at slot.hollandcasino.nl
Wed Feb 13 23:46:45 MET 2002

```Clay Jones wrote:

> Your explanation states that a larger (yearly for example) RRA obtains its
> points from a smaller (daily) RRA.  Tobi states that the points from every
> RRA would come from an RRD.

Wrong twice.

You need to read better.  Tobi didn't say that points from every RRA
come from an RRD and I didn't say that larger RRAs obtain values from
smaller RRAs.

It is your own interpretation that is wrong.

> Clay Jones wrote:
> >
> >
> > Is it correct that the RRD would contain 1 year's worth of data points if I
> > specify an RRA with a yearly average?  Is keeping 1 year's work of 5 minute
> > data points the only way to generate a yearly average graph?
>
> No.

As in: no it is not correct.

> It works like this:
>  - The database is working on intervals of "x" seconds.  The default is 300.
>  - Each RRA works on a certain amount of intervals per slot
>  - Each RRA has a certain amount of slots

The database is the complete database is all of the data in the database.
This is *not* just one RRA, it is the complete RRD.  The whole database
works with units of one interval, the default being intervals of 300 seconds.

Every quantity (well, almost every quantity) works in multiples of such
intervals.  Each and every RRA has a certain amount of rows, each row is
a certain amount of intervals.  The rows are sometimes called slots.

> Suppose the database works with intervals of 300 seconds, the RRA works
> with slots of 12 intervals, this would mean that each slot is worth
> 3600 (12*300) seconds of data (this is an hour).  If you store enough
> of those slots (366*24), you can display one year of data.

One of the RRAs in the RRD has 366*24 rows, each row being built from
12 intervals, each interval was 300 seconds.
366*24*12*300 is 366 * {one day} is one year.  This is what you asked.

> You could also work with an RRA of 288 intervals.  This stores 86400
> seconds per slot (one day) and you'd need 366 of such intervals.

Another possible RRA, perhaps in the same RRD, has rows of 288 intervals
at a time.  This RRA has 366 rows.  Each row is thus one day, the RRA
is storing a year again.

I never said this second RRA is built from the first RRA.  I think you
are confused by what an interval means.

Alex

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