This work evaluates the I/O performance in a multicorecluster environment for an atmosphere model for weather and climate simulations. It contains large data sets for I/Oin scientific applications. The analysis demonstrates that the scalability of the system gets worse as we increase the number of cores per machine, with greater impact on output operations. We also demonstrate poor capacity of the multicore system for providing high aggregate I/O bandwidth and that the scalability is not improved when I/O operations are running trough a parallel file system neither running on local disk.