At&t Bell Laboratories

Calvin J Richardson

David A Schmitt

Robert C Hansen

In a processing system (100) that swaps processes between a main memory (114 or 124) and a pair of duplicated disks (132, 142), system processing capability is protected against loss of access to both system-essential duplicated disks. Upon loss of access to one duplicated disk, processes designed as essential to the system's operation and not resident in the main memory are swapped into the main memory from the other duplicated disk. All essential processes are then locked into the main memory to prevent their removal therefrom. Thus the essential processes remain accessible to the processing system even upon loss of access to both of the disks. Upon loss of access to both of the disks, the system may undergo reconfiguration in an attempt to regain access to at least one of the disks. If reconfiguration fails, non-essential processes are killed and the system continues processing using only the essential processes. Upon restoration of access to one of the disks, the restored disk is initialized from tape and the system is then bootstrapped from the restored disk, and normal processing is resumed. Upon restoration of access to the second disk, the second disk is repopulated from the first disk and the essential processes are unlocked from the main memory.

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Calvin J Richardson