Hi Vlad:

Vlad Manea wrote:
Hi guys,

I have a question regarding the head node for a small cluster that I would like
to build:

which are the disadvantages of using the head node as a computation node?
Since I plan to have NFS on it, I guess there will be problems with comunication which probably will slow down the whole cluster, but I am not sure since this
is my first attempt to built one...

Ignoring some of the other noise on this, I would recommend you follow something like what Mark Hahn had suggested.

A simple "quick and dirty" guide to this can be had at http://www.linux-mag.com/id/3535 . This assumes you use Rocks for setting the cluster up. Others work just as well, Perceus is good kit.

As for using the head node for computation, as Mark noted, it really isn't a great idea, as you will be having your compute processes compete for resources (CPU, network, IO) with the management/file server processes.

Generally as your cluster grows, you start running into scaling issues with various elements. My comments on RAID before were a caution that you shouldn't ignore IO (which many people do in fact ignore) when designing/building this system. Likewise, if your codes are bound by latency (CFD/structural codes), you may wish to explore lower latency network fabrics for your communication layer.

Before we go down any directions, could you describe your codes, and what will generally be running on the cluster? This would help steer some of the larger design issues (Monte Carlo clusters look very different from CFD clusters from ...). Many groups we have spoken to in the Geoscience computing arena are I/O bound (as well as FFT bound).

Joe


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