Should the number of compute nodes in cluster be power of 2 ?

Hi everyone,

I'm in the process of building a small high-performance Linux cluster
from PCs. The cluster will have 7 or 8 Pentium 4 compute nodes and will
run Rocks. The cluster will have to run PVM and/or MPI parallel
programs + some job scheduling for non-paralellized code.

Is there any reason to prefer a number of compute nodes which is a
power of 2 (8, 16, ...), e.g. some parallel programs that might run
much more efficiently on 8 nodes rather than 7 ? Obviously, you can
stack 2^n boxes more nicely, and the nodes will fit well on the screen
in the cluster-monitoring application. But are there more fundamental
implications ?

Thanks,

alex