Soft errors due to cosmic particles are a growing reliability threat for VLSI systems. In this paper we analyze the soft error vulnerability of FPGAs used in storage systems. Since the reliability requirements of these high performance storage subsystems are very stringent, the reliability of the FPGA chips used in the design of such systems plays a critical role in the overall system reliability. We validate the projections produced by our analytical model by using field error rates obtained from actual field failure data of a large FPGA-based design used in the Logical Unit Module board of a commercial storage system. This comparison confirms that the projections obtained from our analytical tool are accurate (there is an 81% overlap in FIT rate range obtained with our analytical modeling framework and the field failure data studied).