1. A method comprising: programming and erasing blocks of a non-volatile storage medium such that variation of a program/erase cycle count for the blocks remains within a predetermined range; grouping the blocks of the non-volatile storage medium based on retention times for the blocks, wherein the blocks are grouped using larger ranges of retention times for groups associated with larger retention times; determining a new configuration parameter for at least one of the groups of blocks in response to a change in the program/erase cycle count, the new configuration parameter comprising a voltage parameter; and accessing the at least one group of blocks using the new configuration parameter.