[rrd-users] Re: A doubt on RRD database

[Serge Maandag]

> I'm interested in installing RRDTool on my FreeBSD box.
> I searched the web and found a nice tutorial:
> 
> What type of database does RRD create? If the database is 
> filled with new data and the oldest is overwritten then how 
> can RRD generate a timeline graph? What's this "loop" thing?

An RRD database is a FIFO.
You create multiple RRAs in your RRD database, they will hold 
your historical data.

Every RRA has a type (MAX, AVERAGE, ..), a size and a granularity.
For instance 
- RRA 1: one sample per 5 minutes for 24 hours
- RRA 2: one sample per hour for 1 week

Say you configured the above and you update your database every 5
minutes.
Then after the 12th update, one hour will have passed and 12 values of
the
First RRA will be consolidated into the second. If the type of your RRAs
is
AVERAGE, the average of the 12 samples will be added to RRA 2. 
The oldest 5 minutes sample will be shifted out of the first RRA and the

oldest hourly sample will be shifted out of the second RRA.

Serge.

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