Method and apparatus for operating an array of storage devices

A storage apparatus for a computer system, comprising:

• a write assist data storage unit;
• a plurality of service data storage units;
• means for maintaining clam redundancy among said plurality of service dam storage units;
• means for receiving write dam, said write data being data to be written to said plurality of service data storage units;
• selection means for selectively determining whether said write data should be temporarily stored in said write assist unit, wherein said write data is contained in a plurality of write commands, said write data being of varying length, said selection means selectively determining whether individual ones of said plurality of write commands should be written to said write assist unit based upon the length of said write data associated with each respective write command;
• means for temporarily storing said write data in said write assist unit, wherein said means for temporarily storing said write data in said write assist unit selectively writes said write data to said write assist unit in response to said determination made by said selection means;
• means for reconstructing data stored on a service data storage units in the event of failure of said unit;
• and
• means for storing said reconstructed data on said write assist unit.

A method for storing data in a computer system, comprising the steps of:

• storing data redundantly on a plurality of service data storage units;
• selectively determining whether updated data to be written to said plurality of service units should be written to a write assist data storage unit, said updated data associated with a plurality of write commands, said updated data being of varying length;
• writing said updated data to said write assist data storage unit, said writing step being performed in response to said selectively determining step determining that said updated data should be written to said write assist unit, wherein said selectively determining step selectively determines whether individual ones of said plurality of write commands should be written to said write assist unit based upon the length of the updated data associated with each respective write command;
• signalling that said updated data has been written to said plurality of service data storage units;
• writing said updated data redundantly to said plurality of service data storage units, wherein said step of writing said updated data to said plurality of service data storage traits is completed after said signalling step;
• reconstructing data stored in a service data storage unit in the event of failure of said service data storage unit;
• and
• storing said reconstructed data on said write assist unit, and thereafter operating said write assist unit as said service unit which failed, in the event of said failure of said service data storage unit.

A storage subsystem controller for a computer system, comprising:

• a processor;
• a memory;
• a host interface for communicating with a host computer system;
• a storage unit interface for communicating with at least four data storage units coupled to said controller, wherein at least one of said data storage units is a write assist data storage unit, and at least three of said data storage units are service data storage units,
• wherein said service data storage units comprise at least one stripe of storage blocks, each stripe comprising a plurality of data storage blocks for containing data and at least one data redundancy storage block for containing data redundant of the data stored in said data storage blocks, each of said storage blocks being contained on a respective service data storage unit;
• means for maintaining said data redundancy storage block on said stripe of storage blocks;
• means for receiving write data from said host computer system, said write data being data to be written to said data storage units, said write data having varying lengths, said write data associated with a plurality of write commands;
• selection means, responsive to said means for receiving write data from said host computer system, for selectively determining whether said received write data should be written to said write assist unit, said selection means selectively determining whether individual ones of said plurality of write commands should be written to said write assist unit based upon the length of said write data associated with each respective write command,
• means for writing said write data to said write assist unit, wherein said means for writing said write data to said write assist unit selectively writes said write data to said write assist unit in response to said determination made by said selection means;
• means for signalling operation complete to said host computer system after writing said write data to said write assist unit and before writing said write data to any of said service data storage units;
• means for reconstructing said write data in the event any one of said data storage units fails after signalling operation complete;
• and
• means for reconstructing said write data in the event the contents of said memory are lost after signalling operation complete.