[mrtg] Re: rrd file size to store 5-min data for 1 yr

Alex van den Bogaerdt alex at ergens.op.het.net
Fri May 9 13:10:01 MEST 2003

On Fri, May 09, 2003 at 06:54:42PM +0800, Francis Borman wrote:

> I knwo that we can tune up the RRD, so that we can store as much data as we
> like. However, the rrd size for just storing 5-min data for two days is
> about 170kb!!! It seems that to store 1 yr 5-min data, the file size must be
> 31 MB!!

Sounds right; multiply 170kb by (365/2) for approximate values.

> Let say, if I have one rrd per router interface, and if I got 1000
> interfaces to monitor, I must prepare 31GB for just data storage?!!!!!

Now you know why data consolidation is taking place...

Do you want to keep the data or not?

> It seems a huge capacity for a PC/Server!!!! It also takes a very long time
> to retrieve data for one particular date!!!!! (That's why we need to store
> 5-min data for a yr)

No, it doesn't take a long time (or at least it shouldn't).  The offset
in the file is calculated (very fast) and the data necessary to RRDtool
is fetched from it (also reasonably fast).

*If* you are going to display the 5-minute averages, no consolidation is
necessary so everything should be fast.

> We are now doing sth that archive all rrd every midnite and write a script
> for data retrieval. When we comes up a situation that need to reference the
> past data, we use that script to retrieve the archived rrd of that date. It
> seems to work for somehow, but what if I need to retrieved data for a
> particular week??? It seems that we need another way to handle it......

If you almost never need to use the historic data, just process the request
by hand.  Don't automate.  Work from backed up data.

If you *do* need the data on a frequent basis you know it and you can prepare
a suitable RRA in your RRD that has just the right resolution (for the image)
and enough rows of data (again for the image).

I don't see the problem here, except maybe that you didn't define to yourself
what your needs are.

Much of what looks like rudeness in hacker circles is not intended to give
offence. Rather, it's the product of the direct, cut-through-the-bullshit
communications style that is natural to people who are more concerned about
solving problems than making others feel warm and fuzzy.


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