The common third level trigger and forth level reconstruction farm for the future HERA-B experiment will have to perform full on-line event reconstruction and calibration for an expected input rate of 2000 events/s. More than hundred powerful RISC processors connected in a network able to distribute several hundreds of MB/s with low latency are likely to be necessary for this task. Proper simulation of the real time multi-processor systems is central for an optimal design of a scalable and flexible parallel data processing architecture. A discrete event, process oriented simulation developed in concurrentμC++ is used as a framework for modelling and evaluating different farm architectures.