Offline mass data processing using online computing resources at HERA-B

Traditionally in High Energy Physics experiments, online and offline computing and software are sharply separated. At the HERA-B experiment the introduction in the online environment of commodity hardware and the Linux operating system allows to blur such a sharp border online/offline. This paper describes how at HERA-B the online computing resources are employed offline for performing mass data processing like Monte Carlo production and data reprocessing.