Method and system for prefetching sequential data in a data storage system

A method in a RAID data storage system for reading stored data from said RAID data storage system, where said RAID data storage system comprises M data storage drives and an associated cache, where data and calculated parity are striped across said M data storage drives, where a stripe comprises a plurality of sectors on each of said M data storage drives, said method comprising the steps of:

• requesting data from said RAID data storage system;
• determining if said requested data resides in a cache and if said requested data sequentially follows a plurality of sectors also residing in said cache;
• fetching only said requested data into said cache if it is determined that said requested data does not reside in said cache and said requested data does not sequentially follow a plurality of sectors also residing in said cache;
• and
• fetching a predefined block of sectors including said requested data from said M data storage drives into said cache if it is determined that said requested data does not reside in said cache and said requested data does sequentially follow a plurality of sectors also residing in said cache, where said fetched predefined block of sectors sequentially follows said requested data.

A system in a data storage system for reading stored data from said data storage system, where said data storage system comprises M data storage drives and an associated cache, where data and calculated parity are striped across said M data storage drives, where a stripe comprises a plurality of sectors on each of said M data storage drives, said system comprises:

• means for requesting data from said data storage system;
• means for determining if said requested data resides in a cache and if said requested data sequentially follows a plurality of sectors also residing in said cache;
• means for fetching only said requested data into said cache if it is determined that said requested data does not reside in said cache and said requested data does not sequentially follows a plurality of sectors also residing in said cache;
• and
• means for fetching a predefined block of sectors including said requested data from said M data storage drives into said cache if it is determined that said requested data does not reside in said cache and said requested data does sequentially follow a plurality of sectors also residing in said cache, where said fetched predefined block of sectors sequentially follows said requested data.

A system in a RAID data storage system for reading stored data from said RAID data storage system, where said RAID data storage system comprises M data storage drives and an associated cache, where data and calculated parity are striped across said M data storage drives, where a stripe comprises a plurality of sectors on each of said M data storage drives, said system comprises:

• means for requesting data from said RAID data storage system;
• means for determining if said requested data resides in a cache and if said requested data sequentially follows a plurality of sectors also residing in said cache;
• means for fetching only said requested data into said cache if it is determined that said requested data does not reside in said cache and said requested data does not sequentially follow a plurality of sectors also residing in said cache;
• and
• means for fetching a predefined block of sectors including said requested data from said M data storage drives into said cache if it is determined that said requested data does not reside in said cache and said requested data does sequentially follow a plurality of sectors also residing in said cache, where said fetched predefined block of sectors sequentially follows said requested data.

A program product for fetching data into a cache associated with a data storage system, where said data storage system comprises M data storage drives and an associated cache, where data and calculated parity are striped across said M data storage drives, where a stripe comprises a plurality of sectors on each of said M data storage drives, said program product comprising:

• a data processing system usable medium;
• and
• a data fetching program encoded within said data processing system usable medium that, in response to receiving a request for data from said data storage system,
• determines if said requested data resides in a cache and if said requested data sequentially follows a plurality of sectors also residing in said cache,
• fetches only said requested data into said cache if it is determined that said requested data does not reside in said cache and said requested data does not sequentially follow a plurality of sectors also residing in said cache;
• and
• fetches a predefined block of sectors including said requested data from said M data storage drives into said cache if it is determined that said requested data does not reside in said cache and said requested data does sequentially follow a plurality of sectors also residing in said cache, where said fetched predefined block of sectors sequentially follows said requested data.