Method and apparatus for efficient management of non-aligned I/O write request in high bandwidth raid applications

Associated with a RAID storage subsystem having a plurality of disk drives and a cache memory, a RAID controller comprising:

• means for identifying a middle Portion of said data which begins and ends aligned with a stripe of said RAID storage subsystem, wherein said data comprises a data portion of a single I/O write request and is substantially larger than the size of a stripe in said RAID storage subsystem;
• means for identifying a non-aligned starting portion of said data, wherein said non-aligned starting portion includes the start of said data and wherein said non-aligned starting portion ends at the start of said middle portion:
• means for identifying a non-aligned ending portion of said data, wherein said non-aligned ending portion includes the end of said data and wherein said non-aligned ending portion starts at the end of said middle portion;
• and
• means for writing said middle portion to said plurality of disk drives using at least one stripe write operation in a cache memory write through mode.

A method for storing data in a RAID storage subsystem having a plurality of disk drives and a cache memory, said method comprising the steps of:

• identifying a middle portion of said data which begins and ends aligned with a stripe of said RAID storage subsystem, wherein said data comprises a data portion of a single I/O write request and is substantially larger than the size of a stripe in said RAID storage subsystem;
• identifying a non-aligned starting portion of said data, wherein said non-aligned starting portion includes the start of said data and wherein said non-aligned starting portion ends at the start of said middle portion;
• identifying a non-aligned ending portion of said data, wherein said non-aligned ending portion includes the end of said data and wherein said non-aligned ending portion starts at the end of said middle portion;
• writing said middle portion to said cache memory with indicia of a high priority;
• and
• writing said middle portion from said cache memory to said plurality of disk drives using at least one stripe write operation, wherein said writing of said middle portion occurs prior to writing of other information from said cache memory having indicia of lower priority relative to said indicia of high priority associated with said middle portion.

Associated with a RAID storage subsystem having a plurality of disk drives and a cache memory, a RAID controller comprising:

• means for identifying a middle portion of said data which begins and ends aligned with a stripe of said RAID storage subsystem, wherein said data comprises a data portion of a single I/O write request and is substantially larger than the size of a stripe in said RAID storage subsystem;
• means for identifying a non-aligned starting portion of said data, wherein said non-aligned starting portion includes the start of said data and wherein said non-aligned starting portion ends at the start of said middle portion;
• means for identifying a non-aligned ending portion of said data, wherein said non-aligned ending portion includes the end of said data and wherein said non-aligned ending portion starts at the end of said middle portion;
• means for writing said middle portion to said cache memory with indicia of a high priority;
• and
• means for writing said middle portion from said cache memory to said plurality of disk drives using at least one stripe write operation, wherein said writing of said middle portion occurs prior to writing of other information from said cache memory having indicia of lower priority relative to said indicia of high priority associated with said middle portion.