Abstract: The present invention provides a method and system for assigning data chunks to column parity sets in a dual-drive fault tolerant storage disk drive system having N disk drives, where N is a prime number. Each of the N disk drives are organized into N chunks such that the N disk drives are configured as one or more N×N array of chunks. The array has chunks arranged in N rows from row 1 to row N and in N columns from column 1 to column N. Each row includes a plurality of data chunks for storing data, a column parity chunk for storing a column parity set, and a row parity chunk for storing a row parity set. These data chunks are assigned in a predetermined order. The data chunks in each row are assigned to the row parity set. Each column parity set is associated with a set of data chunks in the array, wherein row m is associated with column parity set Qm where m is an integer that ranges from 1 to N.

Abstract: A two-dimensional parity arrangement that provides two-drive fault tolerance in a RAID system is presented. The parity arrangement uses simple exclusive-or (XOR) parity codes rather than the more complex Reed-Solomon codes used in a conventional RAID 6 implementation. User data on the physical disk drives in the RAID system is arranged into XOR row parity sets and XOR column parity sets. The XOR parity sets are distributed across the physical disk drives by arranging the parity sets such that the data on each physical drive exists in two separate parity sets, with no stripe unit in the same two sets. The storage lost due to parity is equal to the capacity of two drives, or 2/N the total capacity of an N-drive array. Accordingly, this parity arrangement uses less storage than mirroring when the number of total drives is greater than four.