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  Adaptive read ahead method of data recorded on a sequential media readable via a variable data block size storage deviceUSPTO Application #: 20080010416Title: Adaptive read ahead method of data recorded on a sequential media readable via a variable data block size storage device Abstract: A read request of a sequential media from a host is executed with a read request data block size equal to a maximum recorded data block size parameter of the variable data block size storage device. Subsequently, if warranted, an adaptive read ahead data block size variable is set to equal a recorded data block size of data recorded on the sequential media that is responsive to the execution of the read request, and one or more read ahead requests of the sequential media are executed with a read ahead data block size equal to the adaptive read ahead data block size variable. The adaptive read ahead data block size variable is conditionally adjusted based on the recorded data block size(s) of data recorded on the sequential media that is responsive to the execution(s) of the read ahead request(s) (end of abstract)
Agent: Cardinal Law Group - Evanston, IL, US Inventors: Ralph T. Beeston, Cory G. Smith USPTO Applicaton #: 20080010416 - Class: 711137000 (USPTO) Related Patent Categories: Electrical Computers And Digital Processing Systems: Memory, Storage Accessing And Control, Hierarchical Memories, Caching, Look-ahead The Patent Description & Claims data below is from USPTO Patent Application 20080010416. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application claims benefit of, and priority to, U.S. patent application Ser. No. 11/119,968 filed May 2, 2005, the entirety of which is incorporated herein by reference, as a continuation application. FIELD OF INVENTION [0002] The present invention generally relates to executing a read ahead request of data recorded on a sequential media (e.g., tape) readable via a variable data block size storage device (e.g., a tape drive). The present invention specifically relates to executing the read ahead request based on a dynamic prediction of the recorded data block size of recorded data of the sequential media that is responsive to the execution of the read ahead request. BACKGROUND OF THE INVENTION [0003] FIG. 1 illustrates a conventional storage subsystem employing a host 20, a variable data block size storage device 30 (e.g., a tape drive system), and a storage controller 40 employing a sequential media read module 41 for executing read requests of data recorded on a sequential media 31 (e.g., a tape cartridge) readable by way of a device 30 as requested by host 20 and for autonomously executing read ahead requests of the data recorded on sequential media 31 on behalf of host 20. [0004] In operation, module 41 initially executes a read request RR.sub.20 of the data recorded on sequential media 31 as requested by host 20 and returns recorded data RCD.sub.20 responsive to the execution of read request RR.sub.20 to host 20. Thereafter, module 41 determines if the execution of one or more read ahead requests of the data recorded on sequential media 31 on behalf of host 20 is warranted. If so, as exemplarily illustrated in FIGS. 2 and 3, module 41 conservatively allocates space in a cache 42 for one or more read requests where a read ahead data block size ("RADBS") of each read ahead request equals a maximum recorded data block size ("MRCDBS") parameter of device 30. This allocation of space by module 41 is necessary in view of the facts that the recorded data block size of some or all of the data recorded on sequential media 31 may be less than the MRCDBS parameter, and module 41 will not know the largest recorded data block size of the data recorded on sequential media 31 when executing a read ahead request. Module 41 therefore executes an X number of read ahead requests RAR.sub.42(X) with the read ahead data block size RADBS of each read ahead request equaling the MRCDBS parameter. This conservative read ahead process is optimally performed by module 41 when the recorded data block size RCDBS.sub.42(X) of recorded data RCD.sub.42(X) responsive to an execution of a read ahead request RAR.sub.42(X) as stored in cache 42 equals the read ahead data block size RADBS.sub.42(X) of the read ahead request RAR.sub.42(X) as exemplarily shown in FIG. 2. Conversely, this conservative read ahead process is not optimally performed by module 41 when the recorded data block size RCDBS.sub.42(X) of recorded data RCD.sub.42(X) responsive to an execution of a read ahead request RAR.sub.42(X) as stored in cache 42 is less than the read ahead data block size RADBS.sub.42(X) of the read ahead request RAR.sub.42(X) as exemplarily shown in FIG. 3. The primary reason such a case is not optimal is the requirement by device 30 to execute an interrupt to build a special status and extra interface overhead to report to module 41 the difference between the recorded data block size RCDBS.sub.42(X) of recorded data RCD.sub.42(X) as stored in device 31 and the read ahead data block size RADBS.sub.42(X) of the read ahead request RAR.sub.42(X). [0005] A challenge therefore for the storage industry is to improve upon a performance of a read ahead processing of data recorded on a sequential media readable via a variable data block size storage device when the recorded data block size of recorded data responsive to a read ahead request does not equal the read ahead data block size of the read ahead request. SUMMARY OF THE INVENTION [0006] One form of the present invention is signal bearing medium tangibly embodying a program of machine-readable instructions executable by a processor to implement an adaptive read ahead of a sequential media readable via a variable data block size sequential storage device. The operations comprising an execution of a read request of the sequential media in response to an electrical communication of the read request from a host, wherein the read request is executed with a read request data block size equal to a maximum recorded data block size parameter of the variable data block size storage device, and subsequent to the execution of the read request of the sequential media, a setting of an adaptive read ahead data block size variable to equal a recorded data block size of data recorded on the sequential media that is responsive to the execution of the read request. [0007] A second form of the present invention is a system comprising a processor and a memory storing instructions operable with the processor for implementing an adaptive read ahead of a sequential media readable via a variable data block size sequential storage device. The instructions are executed for executing a read request of the sequential media in response to an electrical communication of the read request from a host, wherein the read request is executed with a read request data block size equal to a maximum recorded data block size parameter of the variable data block size storage device, and subsequent to the execution of the read request of the sequential media, setting an adaptive read ahead data block size variable to equal a recorded data block size of data recorded on the sequential media that is responsive to the execution of the read request. [0008] A third form of the present invention is method for implementing an adaptive read ahead of a sequential media readable via a variable data block size sequential storage device. The method comprising an execution of a read request of the sequential media in response to an electrical communication of the read request from a host, wherein the read request is executed with a read request data block size equal to a maximum recorded data block size parameter of the variable data block size storage device, and subsequent to the execution of the read request of the sequential media, a setting of an adaptive read ahead data block size variable to equal a recorded data block size of data recorded on the sequential media that is responsive to the execution of the read request. [0009] The forgoing forms and other forms, objects, and aspects as well as features and advantages of the present invention will become further apparent from the following detailed description of the various embodiments of the present invention, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the present invention, rather than limiting the scope of the present invention being defined by the appended claims and equivalents thereof. BRIEF DESCRIPTION OF THE DRAWINGS [0010] FIG. 1 illustrates a storage subsystem as known in the art; [0011] FIGS. 2 and 3 illustrates exemplary executions of a read ahead request by the storage subsystem illustrated in FIG. 1; [0012] FIG. 4 illustrates one embodiment of a storage subsystem in accordance with the present invention; [0013] FIG. 5 illustrates a flowchart representative of one embodiment of a read request execution method in accordance with the present invention; [0014] FIGS. 6 and 7 illustrate exemplary executions of a read request by the storage subsystem illustrated in FIG. 4 in accordance with the flowchart illustrated in FIG. 5; [0015] FIG. 8 illustrates a flowchart representative of one embodiment of a read ahead execution request method in accordance with the present invention; [0016] FIG. 9 illustrates a flowchart representative of one embodiment of a read ahead data block size adaptation method in accordance with the present invention; [0017] FIGS. 10-15 illustrates exemplary executions of read ahead requests by the storage subsystem illustrated in FIG. 4 in accordance with the flowcharts illustrated in FIGS. 8 and 9; [0018] FIG. 16 illustrates a flowchart representative of one embodiment of a read ahead termination method in accordance with the present invention; and [0019] FIG. 17 illustrates one embodiment of a storage controller in accordance with the present invention. 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