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

Alex van den Bogaerdt alex at slot.hollandcasino.nl
Thu Feb 14 01:06:46 MET 2002

```Clay Jones wrote:

> >Alex wrote:
> >Suppose the database works with intervals of 300 seconds, the RRA works
> >with slots of 12 intervals
>
> Why does the RRA work with slots of 12 intervals?  What if you don't specify
> an hourly RRA (i.e. 12 intervals)?  Is this behavior the default?

There is no default rra.  The properties of an RRA are something you
have to carefully select, based on your needs.

> >Alex wrote:
> >Each and every RRA has a certain amount of rows, each row is
> >a certain amount of intervals.
>
> What if you ONLY specified a yearly average RRA.  Would the database keep 1
> year's worth of data to fill row #1 in this yearly RRA?

What do you mean by "yearly RRA".  It *looks* like you try to describe
an RRA that is compatible with MRTG, in that case each row of the RRA
should contain one days worth of data and you'd need 366 of such rows
to describe a full year.

On the other hand, it looks as if you want to define rows that contain
one year EACH.  First of all, a year is not a fixed amount of data.
You can define rows that contain 365 days each, not one year.
To gather 365 days (assuming the default of 300 seconds per interval)
of data you'd need to collect 105120 intervals which will be combined
to form one row in your RRA.  (There are 288 intervals per day, and
365 days; 288 * 365 is 105120).

The start and end time of each and every row in an RRA are fixed.
They will be at a whole multiple of the row size.  If you store
31536000 seconds per row (365 days * 24 hours * 60 minutes * 60 seconds
which not accidentally equals 105120*300) each row will describe the
interval in time n*31536000 upto and including (n+1)*31536000.  Today
is 1013644858, you'd thus be filling the row where n is 32.
(calculated by subtracting (1013644858 % 31536000) from 1013644858)

This row describes 32*31536000 to 33*31536000 which is (in UTC time)
Mon Dec 24 00:00:00 2001 to Tue Dec 24 00:00:00 2002

Hardly useful I'd say.

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