Selective memory duplication arrangement

An apparatus comprising:

• a plurality of memories, at least one of the memories comprising a plurality of memory blocks;
• means associated with the one memory, for indicating which ones of the plurality of memory blocks of the one memory are shadowed;
• means responsive to a memory block of the one memory being written, for determining from the indicating means whether the written memory block is shadowed;
• and
• means responsive to a determination that the written memory block is shadowed, for replicating the writing on others of the plurality of memories, and responsive to a determination that the written memory block is not shadowed, for forbearing from replicating the writing on the other memories.

An apparatus comprising:

• a memory comprising a plurality of memory areas;
• an information store associated with the memory for storing information indicating which ones of the plurality of memory areas are shadowed;
• a controller responsive to a memory area being written, for determining from the information store whether the written memory area is shadowed;
• and
• a controller responsive to a determination that the written memory area is shadowed, for causing the writing to be replicated on another memory, and responsive to a determination that the written memory area is not shadowed, for forbearing replication of the writing on the other memory.

A method of shadowing memory comprising:

• writing a memory area of a first memory comprising a plurality of memory areas;
• determining whether the written memory area is shadowed, from stored information indicating which ones of the plurality of memory areas are shadowed;
• in response to determining that the written memory area is shadowed, replicating the writing on a second memory;
• and
• in response to determining that the written memory area is not shadowed, forbearing from replicating the writing on the second memory.