Encoding and rebuilding the data content of up to two unavailable DASDs in a DASD array

摘要

The data contents of up to two concurrently failed or erased DASDs can be reconstituted where the data is distributed across M DASDs as an (M-1)*M block array and where (1) the (M-1)st DASD contains the simple parity taken over each of the array diagonals in diagonal major order in the same mode (odd/even) as that exhibited by the major diagonal of the array and (2) where the M-th DASD contains the simple even parity over each of the rows in row major order. Relatedly, short write updates require fewer operations for data blocks located off the major data array diagonal.