Using entanglements to increase the reliability of two-dimensional square RAID arrays

Two-dimensional square RAID arrays organize their data disks in such a way that each of them belongs to exactly one row parity stripe and one column parity stripe. Even so, they remain vulnerable to the loss of any given data disk and the parity disks of its two stripes. We show how to eliminate all but one of these fatal triple failures by entangling the parity disks of the array, that is, XORing the contents of each parity disk with that of its predecessors. As a result, our new organization reduces the number of fatal triple failures by 96 to 99 percent and the number of fatal quadruple failures by around 85 percent without the need for any additional hardware.