The introduction of multiprocessor architectures into computer systems has further increased the gap between processing times and access times to mass memories, thus making the processes more and more I/O-bound. To provide higher performance levels (both transfer rate and I/O rate), disk array technology is based on the use of a number of logically interconnected disks of a small size, in order to replace disks which have a large capacity but are very expensive. With a view to improving the performance and fault tolerance of the mass storage units, this paper concentrates on the architectural issues of parallelizing I/O access in a disk array system by means of definition of a new, particularly flexible architecture, called Partial Dynamic Declustering, which is fault-tolerant and offers higher levels of performance and reliability than the solutions normally used. A fast distributed algorithm based on a dynamic structure and usable for the implementation of an efficient I/O subsystem manager is proposed and evaluated by a simulative analysis. A specific study also characterizes the system's performance with varying degrees of declustering and workload types (from the transactional to the scientific type). The results obtained allow us to obtain the optimal configuration of the system (number of disks per group) which will ensure the desired response time values for varying workloads.