Ganglia

unicast vs multicast

• As of version 3.0.0, released 2005-02-07, status messages can be sent over unicast.

components

gmetad

This daemon collect data from the other hosts and write them to RRD databases.

It is installed on zwinger using ganglia-monitor-core-gmetad-2.5.6-1.i386.rpm

gmond

It is a daemon installed on each machine that locally collect usefull informations. It is queried from time to time by the gmetad hosts.

gmond is nstalled on each machine using ganglia-monitor-core-gmond-2.5.6-1.i386.rpm

/etc/gmond.conf on each machine MUST be a symlink to /home/wikipedia/gmond.conf. If the default gmond.conf is used, ganglia stats for the entire cluster will not be recorded in the right place and will be effectively lost. (But see merging RRDs below.)

version mismatches

• things go wrong when gmond and gmetad have different versions. or is it when peer gmonds have different versions? something like that anyway

zwinger

RRDs (ganglia statistics, in this case) are in /home/wikipedia/rrds there is some old data in the default location, /var/lib/ganglia/rrds

cluster-wide ganglia restart

If something is amiss with the state of ganglia, and reconfiguring and restarting gmetad isn't enough, do this on zwinger as root:

#!/bin/bash
/etc/init.d/gmetad stop
dsh -f -a /etc/init.d/gmond stop
sleep 5
dsh -f -a /etc/init.d/gmond start
/etc/init.d/gmetad start

or you can just run /home/wikipedia/bin/ganglia-restart-all.

merging RRDs

It is possible, in principle, to merge RRDs using a perl script which can be found on the net somewhere. Looks like a royal pain though.

The script location is available through on RRDTool official website. You might want to look at the README file.