There is disclosed a method and apparatus for mapping between logical and physical addresses in a solid state data storage device, particularly but not exclusively a magnetic random access solid state data storage device, in which a list of mappings between ranges of logical addresses and ranges of physical addresses are stored in a data table, the mappings being operated on to look up a physical address from a logical address and vice versa, and being operated on by a data processor, to amend the data mappings by introduction of new ranges of logical and physical addresses, upon ranges of individual physical memory elements becoming defective.