[rrd-users] Re: RRA - Newbie Question

Alex van den Bogaerdt alex at ergens.op.het.net
Fri Oct 24 17:58:30 MEST 2003

On Thu, Oct 23, 2003 at 06:22:24PM +0530, Jayanth Vasisht (RBIN/MDS) wrote:

Please don't top-post.  This makes it hard to comment, especially
on the part below.  What is written by Serge, and what is written
by you ...

> I plan to update 3 times a day, so I guess the step value would be "28880" secs.

Can be.  However, this means rrdtool will store your updates at n*28880
which may not be what you expect.  You may want to consider using a step
of 3600.

> There's no way to tell if we don't know your step value.


> I want to monitor the Free Disk Space on a server and would like to keep
> the weekly free space data for 6 months and the monthly data for 1 year.
> I would update the rrd with 3 updates a day(one update every 8 hours),
> for 7 days a week. Are these RRA's correct for what I want to achieve
> RRA:MAX:0.5:21:26 (Weekly Max for 6 months)
> RRA:MAX:0.5:84:12 (Monthly MAX for 12 months)

21 periods of 8 hours equals exactly 1 week.
84 periods of 8 hours equals exactly 4 weeks.

4 weeks is not a month.
26 weeks is not three months
12 times 4 weeks is not a year.

You *do* seem to understand the numbers, I just disagree with your

What happens when daylight saving changes.

What happens when you want to view november 1st, 2002 (not much as your
database will be empty anyway but you know what I mean).


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