[rrd-users] changing step time?

[Tobias Oetiker]

Hi Gregory,

Yesterday Gregory Guthrie wrote:

> I started a new database a few weeks ago, and have a few questions;
>   
> 1) What is the actual meaning of "step" - specifically what
>    happens if values are fed in more often? The documentation
>    says that if updates are less frequent, they are interpolated
>    (up to heartbeat), but I didn't see this converse case.

the step is the 'base' interval at which an rrd handles data. This
means that if you feed data more often, rrdtool will average the
data into a 1 step interval (Primary Data Point) before handing it
to the different RRAs
>
> 2) Can I change step after the database is created?
>   - I setup one value for daily step size, but now want to do twice-daily updates.
>   - Can I change step size, and just start inserting updates more often?

you can not chnage the step size of an existing rrd file, but you
can feed updates as often as you have them.

> 3) If I were to re-create the database, is there any (easy) way
>    to preserve the data already collected?

I have recently written a tool called rrdjig
https://svn.oetiker.ch/rrdtool/trunk/contrib/rrdjig/
which might be interesting for you. It lets you 'replay' updates
from an existing rrd into a new one. rrdjig will try to recreate
the update instructions that were fed into the original rrd file.
In your case, this means it would generate 1 update instruction per
day. If you setup a new rrd to store two updates per day you must
make sure the mrhb of the new rrd is sufficient large.

cheers
tobi


-- 
Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 9902 / sb: -9900