Actual storage systems are very large, with complex and distributed architectural configurations, composed of various technologies devices. However, simulation, analysis and evaluation tools in the literature do not handle this complex design and these heterogeneous components. This paper presents OGSSim (Open and Generic Storage systems Simulation tool): a new simulation tool for such systems. Being generic to all devices technologies and open to diverse management strategies and architecture layouts, it fulfills all the storage systems needs in term of representativeness. Also, it has been validated against real systems, thus its accuracy makes it a useful tool for the conception of future storage systems, the choice of hardware components and the analysis of the adequacy between the applications needs and the management strategies combined with the configuration layout. This validation confirmed only a maximum of 15% of difference between real and simulated execution time. Also, OGSSim execution in a competitive time, just 3.5 sec for common workloads on a large system of 500 disks, makes it a challenging simulation and evaluation tool. Thus, it is the appropriate and accurate tool for modern storage systems conception, evaluation and maintenance.