High performance computing (HPC) has crossed the Petaflop mark and is reaching the Exaflop range quickly. The exascale system is projected to have millions of nodes, with thousands of cores for each node. At such an extreme scale, the substantial amount of concurrency can cause a critical contention issue for I/O system. The contention can destroy the request locality, increase the access latency, and waste the precious I/O interconnection bandwidth. This study proposes a dynamically coordinated I/O architecture for exascale systems. The fundamental idea is to coordinate I/O accesses according to access pattern, network topology, interconnection condition, and data distribution on storage devices to reduce the contention and regain the locality. The preliminary results have shown the promise of a dynamically coordinated I/O architecture. It has a potential to manage the substantial amount of I/O concurrency and provides a scalable I/O architecture for exascale systems.