Coded write masking

The controller has a host interface to receive a block of write data values and a set of mask values. A mask logic circuit (550) generates a coded block of write data values by substituting a key value for each masked data value within the block of write data values. A memory interface outputs the coded block of write data values to the storage subsystem upon receiving the values from the logic circuit. The mask value is capable of indicating whether a corresponding one of the write data values is a masked data value to be excluded from storage within a storage subsystem. Independent claims are also included for the following: (1) a memory system (2) a method of operation within a memory system.