[mrtg] Storing more data with RRD

[Steve Shipway]

> MRTG and RRD automatically scale data to keep the file size on disk
> small. How can I increase the size of the RRD file on creation so that
> it stores six (6) months of 5 minute data vs the standard one month
> resolution?

Actually, the default .rrd file generated by MRTG will store
approximately
2 days of 5-min resolution,
2 weeks of 30-min resolution,
2 months of 2-hour resolution, and
2 years of 1-day resolution
(under older versions of MRTG, the default used to be closer to
1d/1w/1m/1y.  I'm sure someone can give the precise numbers)

You can change the default by using the RRDRowCount: option in the .cfg
file, but you must do this BEFORE the .rrd files are generated; IE,
before the first run of MRTG on the file.

The default is about 800 for 2 days (if your interval is 5min - multiply
by 5 if it is 1min).  If you want to extend this to 6 months, then you
will need to multiply by 90 - 72000 or so.  You will get some rather
large .rrd files.  You will also need to have a way to display this
extra data as the default tools will not do so because they do not
expect it to be there.

The routers2 frontend will go back 2 days if possible (as in the default
configuration) but not further.  However, an alternative with routers2
is RRD Archiving.  This stores a copy of the .rrd files into a separate
location daily, and routers2 can then explore this archive.  This will
give you similar functionality to what you want - we use it here to
preserve 5-min resolution for a months and 30-min resolution for a year.

Steve