Methods of prefetching data in data storage systems

Abstract

The present invention relates to a cache memory management system suitable for use with snapshot applications. The system includes a cache directory including a hash table, hash table elements, cache line descriptors, and cache line functional pointers, and a cache manager running a hashing function that converts a request for data from an application to an index to a first hash table pointer in the hash table. The first hash table pointer in turn points to a first hash table element in a linked list of hash table elements where one of the hash table elements of the linked list of hash table elements points to a first cache line descriptor in the cache directory and a cache memory including a plurality of cache lines, wherein the first cache line descriptor has a one-to-one association with a first cache line. The present invention also provides for a method converting a request for data to an input to a hashing function, addressing a hash table based on a first index output from the hashing function, searching the hash table elements pointed to by the first index for the requested data, determining the requested data is not in cache memory, and allocating a first hash table element and a first cache line descriptor that associates with a first cache line in the cache memory.

1 . A method of prefetching data in a data storage system, comprising: 
 receiving a first read command from a host requesting data on a data storage subsystem, wherein the first read command includes a prefetch bit indicating data whose addresses are nearby the requested data;    staging the requested data from the data storage subsystem to the host; and    staging the nearby data to a cache of the data storage subsystem.    
   
   
       2 . The method of  claim 1 , further comprising: 
 receiving a second read command from a host requesting the nearby data; and    retrieving the nearby data from the cache of the data storage subsystem.