[rrd-users] Re: Trend Line

[Clifton Royston]

On Thu, Mar 22, 2001 at 09:50:14AM -0500, Dan McGinn-Combs wrote:
> 
> I think this is pretty much what I'm looking for, Paul. I was trying to come
> up with an example for Clifton.
> 
> Your example is right on the money, but let's move it over to hard disk
> space. I have a user drive which began life as 0% utilized. Each week it got
> 5% more utilized, i.e. 0% - 5% - 10% - 15% - 20%. I can pretty much predict
> with some certainty that after 20 weeks it will be completely full. I can
> give that information to management and offer them a choice, either you ask
> individuals to clean up the data they put on the drive, or you buy a new
> drive in 15 more weeks.
> 
> The trend line allows me to make that case.

OK, I got it now.  Yes, this is really important for any kind of
professional.  

One problem with doing this with RRDgraph is that it's not really
designed to graph things out into the future, only to graph what's
already observed.  (Though you might be able to coax it to do that, I
don't know.)

For this kind of thing, I don't try to get it directly out of RRD or a
similar logging/graphing tool.  Instead what I will usually do is try
to get the most relevant data out of the collection tool into some
Ascii format and import it into <shudder> MS Excel.

Once it's in there, with the builtin functions, it's easy to do other
graphing, linear or curve fitting, etc.  Not to mention that if you put
that Excel graph into a Powerpoint slide, put a bold-faced heading on
it, and print it in color, then it *must* be true! ;-)

One advantage about doing it this way is that you can fit the data to
additional factors which may not be available by doing it directly in
RRD which deals mainly with time series data.  Suppose, in your
example, that you think the source of the rapid growth of data on the
hard disk is due to all the staff that's been added to that department
in the last 4 weeks.  You can put that in as your "X" variable, and
curve fit to that, then you can tell the management with even more
accuracy, "We need a new drive before that department gets to 28
people, which looks like it would happen 15 weeks from now at the
present rate."

  -- Clifton

-- 
 Clifton Royston  --  LavaNet Systems Architect --  cliftonr at lava.net
   WWJD?   "JWRTFM!" - Scott Dorsey (kludge)   "JWG" - Eddie Aikau

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