Multi-tier cache and method for implementing such a system

A method for implementing a multi-tier caching system, said multi-tier caching system being implemented on a computer system having a random access memory (RAM), a portion of which is set aside and initialized as a RAM cache for storing first-tier data within a plurality of RAM data blocks, and at least one local non-volatile local mass storage device on which data can be alterably stored and on which a portion thereof functions as a non-volatile cache for storing second-tier data within non-volatile data blocks, said computer system having a data path to a mass storage device with an access speed slower than that of the local mass storage device, said slower mass storage device storing a full set of file data, said method comprising the steps of:

• whenever a received file input/output request involves data resident on said slower mass storage device, and the requested data is not available as first-tier data nor available as second-tier data, providing for determining whether or not all RAM data blocks are already filled with first-tier data;
• providing for purging first-tier data from a least-recently-used RAM data block if all RAM data blocks are already filled;
• providing for retrieving a quantity of third-tier data which includes the requested data;
• providing for writing all retrieved third-tier data to a non-volatile data block, as well as to an empty RAM data block;
• and
• providing for resolving the file input/output request from the retrieved third-tier data written to the empty RAM data block.

A computer program product comprising a computer usable medium having computer readable code embodied therein for implementing a multi-tier caching system on a computer system, said computer system having a random access memory (RAM), a portion of said RAM being is set aside and initialized as a RAM cache for storing first-tier data within a plurality of equal sized RAM data blocks, and at least one local non-volatile local mass storage device on which data can be alterably stored, a portion of said local mass storage device functioning as a non-volatile cache for storing second-tier data in non-volatile data blocks, said computer program product further comprising:

• computer readable program code devices configured to cause a computer, whenever a received input/output request involves data resident on a mass storage device identified for caching, and if the requested data is not available as first-tier data nor available as second-tier data, to effect determining whether or not all RAM data blocks are already filled with first-tier data, to effect purging first-tier data from a least-recently-used RAM data block if all RAM data blocks are already filled, to effect retrieving a quantity of third-tier data which includes the requested data, to effect writing retrieved third-tier data to a non-volatile data block, as well as to an empty RAM data block, and to effect resolving the file input/output request from the retrieved third-tier data written to the empty RAM data block.

A multi-tier caching system implemented in conjunction with a computer system having a random access memory (RAM), and at least one local non-volatile local mass storage device on which data can be alterably stored, said multi-tier caching system comprising:

• a mass storage device having a slower access time than that of said local mass storage device, said slower mass storage device having been designated for caching, and said slower mass storage device providing storage for third-tier data;
• a non-volatile cache established on a portion of said local mass storage device, said non-volatile cache providing storage for non-volatile blocks of second-tier data, said non-volatile cache having a total storage capacity less than that of said slower mass storage device, said second-tier data being a sub-set of said third-tier data always comprising at least the most recently used third-tier data;
• and
• a RAM cache established in a portion of the RAM, said RAM cache providing storage for RAM blocks of first-tier data, and said RAM cache having a total storage capacity less than that of said non-volatile cache, said first-tier data being a subset of said second-tier data comprising all of the most recently used third-tier data, said RAM cache coupled to supply all requests for data stored on said mass storage device having a slower access time.