We use Cacti at work to graph the usage of our clients links. It is a pretty popular feature with our customers. A problem (well not really. More like a gotcha) with rrdtool is the way it stores data. Here’ a quote from the rrd tutorial
“Round robin is a technique that works with a fixed amount of data, and a pointer to the current element. Think of a circle with some dots plotted on the edge, these dots are the places where data can be stored. Draw an arrow from the center of the circle to one of the dots, this is the pointer. When the current data is read or written, the pointer moves to the next element. As we are on a circle there is no beginning nor an end, you can go on and on. After a while, all the available places will be used and the process automatically reuses old locations. This way, the database will not grow in size and therefore requires no maintenance. RRDTool works with with Round Robin Databases (RRDs).”
So rrd stores the difference in values (between the last value and current) in the database, rather than the value itself. This creates a problem when routers are rebooted. The counters on the interfaces get cleared and rrd is fooled into thinking that there is a spike in usage. This results to “spikes” in the graphs. Sometimes you see that a 128kbps link has maxed out at 98mbps!!! :). The best way to stop this from happening is to set the correct min and max values for the ds names. Coming back to cacti again. When cacti creates a new rrd database, it does not really give one the option to setup the maximum and minimum speeds of a interface. It defaults to a max of 100000000 (i.e. 100mbps). Occasionally when we have to reboot our routers, I do the following to remove the spikes
cp filename.rrd filename.rrd.backup
Any good admin knows that before you mess with a file, you make a backup :).
rrdtool info filename.rrd | more
This gives us the chance to get the ds (data sources) names
rrdtool tune filename.rrd -a ds_name:MAXIMUM_VALUE
Set the maximum of the ds to the required
rrdtool dump filename.rrd > filename.xml
Export all data in the rrd to a xml file
mv filename.rrd filename.rrd.old
Rename the rrd to make way for the new one.
rrdtool restore filename.xml filename.rrd -r
Restore the rrd from the xml file with the -r (range check) option. So any values that are higher than the new maximum value are ignored.
And the spikes are gone..
The Kona Airport is such a big difference from the huge hectic airports that we see in many cities nowadays. Actually this was the first airport that I saw in the US that was completely “open”. As you can see from the picture, you can literally see the plane from the baggage checking area. In fact there is only one terminal. I instantly felt at home on the Big Island. The whole atmosphere was so laid back. No hurry to get anywhere. No hustling..No jostling. Not to mention that the weather was just great.
So off we go and collect our luggage. I took out my new 
So we were supposed to go South from the airport to get to our hotel, but as it happens with such things :), we went North. It was interesting to observe the landscape. I wish I had a picture to show for it. The ground was made up of cooled down lava. It was like a chocolate brownie, but just black in color :). As we drove along the highway, wondering why we don’t see the exit to the town yet, we noticed that there were white stones placed in funny ways on the ground (cooled lava). There were sentences from “I love you Jim” to “Katsumoto was here on 1/1/2001” [Alright.. I made that up] and the usual graffiti symbols. It was great to see them scattered all along the road. Now when one see such stuff, one has to dutifully pull over and take some pictures :). Michelle immediately went into “artist” mode and made up the following…
Why 2..? well that is something that Michelle has to explain. Just make sure that you have a couple of hours to spare when you ask her that question :). After taking some pictures, we hop back into the SUV and start driving. Somewhere around this time, we realize that something is wrong with our sense of direction 🙂 and decide to turn around. An advice for anyone having to drive through Kailua. Don’t ever drive through the town during rush hour. It was a nightmare. Took us ~30 minutes to get across a 2 mile strip. It was faster to walk :). Finally we get to our hotel. It was a great place. I would recommend it to anyone. The condo was pretty spacious and had all required amenities. I took a picture of the condo as soon as we arrived.
It was a long day and when it came time to hit the town for dinner, the girls passed on the offer. Mark and Me went into town and after strolling along for sometime and looking at umpteen restaurents, decided to dine at 
Official Result Postcard