Storing data redundantly

A method for storing data blocks, including forming the data blocks into groups comprising N·M data blocks, where N and M are different positive integers. For every group, the N·M data blocks are assigned to correspond to elements of an array comprising N rows and M columns. A respective parity block is calculated for each of the N rows and M columns, to form (N+M) parity blocks. The resulting (N+M) parity blocks and N·M data blocks are stored in respective storage devices.