A method and apparatus for reconstructing lost data from a failed disk drive in a disk array. The disk drive array formed into at least one parity group including data extents divided into data segments and parity segments that are generated from the data segments. The method includes providing access to the array, identifying a failed drive and failed parity group associated with the failed drive, and retrieving the parity segments from operative drives in a parity group containing the failed drive in an instance data is being read from the failed parity group. Parity information is reconstructed for the failed disk drive from the parity segments on the operative disk drives, and data segments of the extent associated with the failed disk drive is reconstructed from the reconstructed parity information, and the parity segments and data segments on the operative disk drives of the failed parity group.