The present disclosure includes systems and techniques relating to solid state drive controllers. In some implementations, a device includes a buffer that holds a block of data corresponding to a command from a host. The command identifies the block of data and a logical sequence in which the identified block of data is to be transmitted. In response to the command, a data retriever included in the device retrieves the portions of the block of data from non-volatile memory units in a retrieval sequence that is different from the logical sequence. When the device receives multiple commands identifying multiple blocks of data, the device services the commands in parallel by retrieving portions of blocks of data identified by both commands.