MDS (maximum distance separable) array codes are widely used in storage systems to protect data against erasures. The rebuilding ratio problem is addressed and efficient parity codes are proposed. A controller as disclosed is configured for receiving configuration data at the controller that indicates operating features of the array and determining a parity code for operation of the array according to a permutation, wherein the configuration data specifies the array as comprising nodes defined by A=(ai,j) with size rm×k for some integers k,m, and wherein for T={v0 , . . . , Vk-1} ⊂Zrm a subset of vectors of size k, where for each v=(v1, . . . , vm)∈T, gcd (v1, . . . , vm, r), where gcd is the greatest common divisor, such that for any l, 0≦l≦r−1, and v ∈T, the code values are determined by the permutation fvl:[0,rm−1]→[0,rm−1]by fvl(x)=x+lv.