A method and apparatus for cache coherency in storage system is disclosed. The
invention maintains cache coherency in the controller system of the storage system
in a manner to minimize the performance degradation to a host system, and to allow
the caches to be coherent without requiring data to be written to the backing disks.
Each controller manages an area of memory on the partner controller, but the area
is managed dynamically and is done with the information about the partner controller.
A first controller determines which mirror cache line on a second controller to
copy data into, and then mirrors the data from a first controller cache line to
a second controller cache line. A message is sent from the first controller to
the second controller informing the second controller of cache meta data associated
with the mirror cache line so that the cache line may be added to the second controller's
hash table.
