I don't know if this is simplifying things too much, or just a dumb
reply, but the problem I've seen with ganglia is that every host in the
cluster is listening to every other host in the cluster and broadcasting
all the information, causing a lot of traffic (160 nodes in my cluster).
So what I've done is make 158 nodes "deaf" by editing the gmond.conf
file and setting "deaf on", then restarting the gmond on each. Now only
two nodes are listening to traffic and broadcasting all data, and the
other 158 nodes are just sending out their own data. This reduced the
traffic considerably. My network folks are happier.
James Casbon wrote:
Hi,
So I have been using ganglia without problems for a while, and it seems
excellent. The other day the network administrator calls up and asks why we
are using so much (15%) of his bandwidth stating that he noticed some weird
traffic that was flatlining and therefore didn't look like normal network
usage.
Now, I traced this to ganglia's multicast, which I have had to disable. But I
have a few questions:
* Is is normal to produce this much traffic? Can I set the interval on
broadcasts to be much higher or something?
* Now, I'm pretty sure most of the traffic is coming from the workstations, as
most of the cluster is behind another NIC connected to our server and not
able to even see the internet. Multicast traffic wont be copied over the NIC
since there is no NAT for the cluster, right?
* So that leaves the workstations. A firewall box does NAT for the
workstations, but both NICs of the firewall are connected to the same switch
(run by the network administrator), with one connecting a true internet IP
and the other on our local subnet. Now, I tried dropping the multicast
packets using iptables, but no log messages show up with dropped packets. So
I started thinking, maybe the switch is routing the multicast packets before
they even get to the firewall, so its not even possible to drop them there.
Is that the case? Or can I filter them using iptables, and if so what is the
correct line to include in the NAT script (I use the iptables script found at
http://en.tldp.org/HOWTO/IP-Masquerade-HOWTO/stronger-firewall-examples.html#RC.FIREWALL-2.4.X-STRONGER)?
I'm still getting my head round this multicast thing, so apologies if this is
obvious.
Many thanks,
James
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Paul Henderson
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Princeton Plasma Physics Laboratory
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