1. An apparatus comprising a solid state storage device in which a solid state storage in the solid state storage device comprises erasable blocks each erasable block comprising a plurality of data write locations, the apparatus comprising memory and control logic adapted to: store input data in successive groups of data write locations, each group comprising write locations in a set of erasable blocks in each of a plurality of logical subdivisions of the solid state storage; error correction encode the input data such that each group contains an error correction code for the input data in that group; maintain, in the memory, metadata indicating the location of input data in the solid state storage; maintain an indication of validity of data stored in each data write location; and prior to erasing a block, recover valid input data from each group containing write locations in that block and re-store the recovered data as new input data.