A method is performed by a solid state device (SSD) controller to generate a parity. The method includes receiving input data to be stored to pages of a storage device, wherein each page is capable of being allocated with multiple codewords; configuring codewords of the pages into multiple groups, wherein each group has an integer number of codewords, at least one of the pages is allocated with a non-integer number of codewords, and wherein the integer number is larger than the non-integer number; obtaining parities for the multiple groups, and storing the parities to reserved spaces of the storage device. With the calculation of a parity decoupled from physical pages, the selection of a rate of code used is unconstrained by an integer number of codewords per page.