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The 9021-type processors offer the highest performance of the IBM Enterprise System/9000™ (ES/9000™) series. They also have the highest levels of concurrent error detection, fault isolation, recovery, and availability of any IBM general-purpose processor. High availability is achieved by minimizing component failure rates through improvements of the base technology, and design techniques that permit hard and soft failure detection, recovery and isolation, and component replacement concurrent with system operation. In this paper, we discuss fault-tolerant design techniques for array, logic, and storage subsystems. We also present diagnostic strategy, fault isolation, and recovery techniques. New features such as the redundant power system and Processor Availability Facility are described. The overall recovery design is described, as well as specific implementation schemes. The design process to verify the error detection, fault isolation, and recovery is also described.
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