[rrd-users] Re: Resizing RRDs

[Alex van den Bogaerdt]

On Thu, Aug 31, 2006 at 10:12:19AM -0700, Kelby Cody wrote:
> I'm having trouble resizing my existing RRDs for 5 minute intervals
> from 2 days to 6 months.  I'm running cacti 0.8.6h on a Windows XP box
> with rrdtool 1.2.15.  When I use the 'rrdtool resize' command it
> resizes properly but when I use the zoom-in function of Cacti to see
> the historical data it shows a blank graph.  The only data that will 
> show when I zoom in is the past 48 hours of 5 minute data.  The yearly
> and monthly graphs show the correct historical data when zoomed out but
> if I try to zoom in on them it is blank.  Does anyone know what I'm
> doing wrong? 

Normally when you look at the past, rrdtool has no choice but
to look at RRAs covering a large amount of time per row.  These
contain the historic data and all is fine.

Resize just adds extra rows, but does not fill them with data.
Now, when you look into the past, rrdtool has a choice which
RRA to use.  In your case it selects the one matching your request
as close as possible.  That will be the one you just expanded.
Rrdtool is now looking at those freshly added rows, containing
no information (yet).

Eventually this problem will resolve itself, after all rows have
been filled with known data.

Ways to work around this:

1)
Carefully set start and end times so that they match another RRA
exactly.  For instance, if one RRA contains 30 minute averages,
set both start and end to a multiple of 30 minutes and make sure
the amount of pixels times 30 minutes equals the time from start
to end. ex: --width 400 start=end-200h end=1157056200

2)
Don't add all those new rows in one run.  Each day add a couple
rows (288 rows a day for 5 minute intervals)

HTH
-- 
Alex van den Bogaerdt
http://www.vandenbogaerdt.nl/rrdtool/

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