Data storage control circuitry for controlling storage and retrieval of data in a data store in which data is stored in data blocks. A group data store stores data by grouping together blocks that have at least one faulty bit into groups of at least two blocks. For each group of blocks at least one of the blocks has a non-faulty bit for each of the bit locations in the blocks. A selector data store stores indicators for each group indicating which bits of the blocks within a group are the non-faulty bits. When storing data to a data block within a group, the data is stored in each of the blocks within the group. When retrieving data from a data block within a group, the data is read from respective bits of the blocks within the group as indicated by the indicators.