Design 4 — Bare Metal + MPI + RoCE

The simplest possible setup. No scheduler, no orchestrator — mpirun directly across a known list of hosts. RoCE handles RDMA. Closer to a lab cluster than a production system, but useful as a baseline.

Best for: Small dedicated clusters, benchmark rigs, anywhere the workload is one job at a time and you control the host list manually. Trade-offs: No queueing, no fairness, no automated fault recovery. Falls over the moment you have more than one user.