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Abstract

A method for assuring consistency between data and parity in a disk array system following a reset or a power failure condition which interrupts the execution of write I/O operations. The method includes the steps of: examining drive activities to identify unfinished write I/O operations due to an interrupt condition; logging information necessary to identify the unfinished operations and the array redundancy groups associated with the unfinished operations into a non-volatile memory; and checking for log entries in the non-volatile memory during a disk array subsystem initialization or the restoration of power. For each unfinished operation identified in the log, the method further includes the steps of: performing a bit-wise exclusive-OR of corresponding portions of the data stored within the associated redundancy group to calculate parity consistent therewith; and writing the calculated parity to the parity storage areas within the associated redundancy group. For an array operating with a failed disk drive member (i.e., in degraded mode), the method also logs information necessary to identify the storage areas to which the unfinished write I/O operations map new data and parity, and some form of the old data and parity information saved to that storage areas to which the unfinished write I/O operations map new data and parity. Following the system reset, or restoration of power, consistent parity is determined for each associated redundancy group.

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