A method for maintaining a data set includes storing a base copy of the data set in a first non-volatile memory having a first writing speed, storing changes to the data set in a first change data set in a second non-volatile memory having a second writing speed, and generating a current copy of the data set by reading the base copy and the changes. If a threshold number of entries in the first change data set is reached, then part or all of the first change data set is moved into a second change data set in the first non-volatile memory, where the generating step includes reading the second change data set. If a threshold number of entries in the second change data set is reached, then the current copy is generated by reading the base copy and the changes in the first and the second non-volatile memory.