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Horst F. Wedde, Carsten Stange und Jon A. Lind
Integration of Adaptive File Assignment inot Distributed Safety Critical Systems
21st IFAC/IFIP Workshop on Real Time Programming, Gramado, RS,Brazil, 1996-11


Safety-critical systems typically operate in unpredictable environments. Requirements for safety and reliability are in conflict with those for real-time responsiveness. Due to unpredictable environmental needs there is no static trade-off between measures to accommodate the conflicting objectives. Instead every feature or operating system service has to be adaptive. - The distributed operating system MELODY was developed for supporting safety-critical applications under such constraints. An essential adaptive feature in MELODY is its handling of distributed information resulting in strongly consistent (public) and weakly consistent (private) file copies, distributed over different system sites for both better availability and better reliability. Their number, location, and quality are adaptively rearranged to ensure system survivability under hard real-time constraints. The corresponding local managers are called File Assigners (FA) . The paper describes their functionality. It focuses on their adaptive real-time integration into the task scheduler and file server operations. The quality of two different integration strategies (Task Scheduler and File Server oriented) has been evaluated through distributed experiments. Some experimental results are reported.