[Beowulf] Computation on the head node

[Perry E. Metzger]

Vlad Manea <vlad at geociencias.unam.mx> writes:
> 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...

As is always the case, "it depends". Your computational load might be
such that doing computation on the head speeds up the overall
computation by adding a needed CPU, or might be such that it slows it
down by robbing the whole cluster of needed file i/o performance. That
depends enormously on the particular task you're doing. The only real
way to know is to test it and see what happens.

In general, if you have enough machines, I don't think there is much
point in doing computation on the head -- it complicates matters and
if you have enough machines you're only adding a tiny percentage of
extra CPU -- but if you have a very small cluster and you need the
extra CPU and your tests say it is fine, then go for it. You'll have
to test to be sure.

Perry