Device and method for fault tolerant dual fetch and store

Abstract

Fault tolerant systems allow continuous service during the occurrence of a hardware failure. To provide such service, usually dual copies of data are stored in case of a hardware failure affecting the original copy. This dual copying causes the system an overall performance degradation. The present invention discloses a device and method for performing parallel fetch and store commands, allowing multiple copying of data into storage without affecting the performance of the system. In one embodiment of the invention, a method is described utilizing a multiprocessor system having two system controllers (SCs) and a plurality of requestors defined as a plurality of central processors (CPs) and input-output (I/O) processors. Asymmetric structure is accomodated. Single and dual requests can be intermixed. Each requestor has access to both system controllers, allowing either controller to process a requestor issued command. An interlocking data protection mechanism is also provided to protect data integrity by allowing requestors data access to a given unit of data only on a one at a time basis. Data exclusivity ownership access to a given unit of data is being provided by and removed by the system controllers. When a command is issued by one of the requestors, the system controllers process the command and provide the requestor with a response upon processing completion. In the mean time, the requestor can perform any required data updates. This concurrent processing improves the performance of the system but also protects its integrity.