Data processing system and method for efficient storage of metadata in a system memory

A cache coherent data processing system, comprising:

• a plurality of processing units each having at least an associated cache;
• a system memory;
• a memory controller that is coupled to and controls access to said system memory;
• wherein said system memory includes:
• a plurality of storage locations for storing a memory block of data, wherein each said plurality of storage locations is sized to store a sub-block of data;
• metadata storage for storing metadata describing the memory block, said metadata storage including a first metadata storage location for storing a first item of metadata and a second metadata storage location for storing a second item of metadata, wherein said first item and second item of metadata provide different types of information regarding the memory block;
• and
• wherein said memory controller, responsive to a failure of a storage location for a particular sub-block among said plurality of sub-blocks, overwrites said second item of metadata in said second metadata storage location with said particular sub-block of data while retaining the first item of metadata in the first metadata storage location.