Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition
Reexamination Certificate
1999-09-15
2002-12-24
Yoo, Do Hyun (Department: 2187)
Electrical computers and digital processing systems: memory
Storage accessing and control
Specific memory composition
C711S154000, C711S217000
Reexamination Certificate
active
06499083
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
In general, this invention relates to a disk-based storage system; more particularly, it relates to such a system that receives a direction-selection signal and autonomously controls seeks in a sequence determined by the direction-selection signal and a locally-stored doubly linked list.
2. Description of the Related Art
A number of related markets exist for disk-based storage systems for supporting the playback of data streams such as audio/visual (“A/V”) streams. Among these are markets for image repositories, video on demand, networked video, and consumer TV time shifting.
Disk-based storage systems designed for these markets are described in various patents. Among these are: U.S. Pat. No. 5,701,383, titled “VIDEO TIME-SHIFTING APPARATUS”; U.S. Pat. No. 5,519,435, titled “MULTI-USER, ON-DEMAND VIDEO STORAGE AND RETRIEVAL SYSTEM INCLUDING VIDEO SIGNATURE COMPUTATION FOR PREVENTING EXCESSIVE INSTANTANEOUS SERVER DATA RATE”; U.S. Pat. No. 5,737,747, titled “PREFETCHING TO SERVICE MULTIPLE VIDEO STREAMS FROM AN INTEGRATED CACHED DISK ARRAY”; and U.S. Pat. No. 5,892,915, titled “SYSTEM HAVING CLIENT SENDING EDIT COMMANDS TO SERVER DURING TRANSMISSION OF CONTINUOUS MEDIA FROM ONE CLIP IN PLAY LIST FOR EDITING THE PLAY LIST.”
A performance requirement for substantially all such disk-based storage systems is to respond to user control. As used herein, the term “user control” refers to inputs provided by the user or operator (such as “play,” “fast forward,” “pause,” “rewind,” etc.). The “play” item indicates a forward direction and the “rewind” item indicates a reverse direction. A market requirement for substantially all such disk-based storage systems is to be cost effective, whereby a mass market consumer system needs to be extremely low in cost, but even a high-performance broadcast-market system needs to be cost competitive.
A problem commonly arising in the disk-based systems designed for these markets relates to reducing command-protocol latency and doing so in a cost-effective way.
With respect to cost effectiveness, a system design benefits from incorporating component subsystems that are, or are easily-modified versions of, mass-produced products. This is the case even in high-performance broadcast-market systems, as indicated in some of the above-identified patents that emphasize the advantage of building the system with component subsystems that constitute or are derived from commodity products such as commodity personal computers and commodity disk drives.
With respect to command-protocol latency, a system design benefits from reducing such latency, thereby to provide more bandwidth for handling the core functions needed for streaming. Command-protocol latency generally includes a number of elements that can be described with reference to communication between disk-drive structure and host structure. The term host structure is used in a very broad sense and includes without limitation standalone structure such as the commodity computers described as stream servers in some of the above-identified patents, and other structure such as programmable microprocessor-based circuitry integrated into the front end of a disk-based storage system such as that disclosed in U.S. Pat. No. 5,802,069, titled “IMPLEMENTING MASS STORAGE DEVICE FUNCTIONS USING HOST PROCESSOR MEMORY,” or in U.S. Pat. No. 5,809,337, titled “MASS STORAGE DEVICES UTILIZING HIGH SPEED SERIAL COMMUNICATIONS,” or in published European Patent Application No. EP 0 757 310 A2, titled “CONTROLLING DISK DRIVES,” (this published application describing a disk drive in column 11, lines 22 et seq., which includes a disk scheduler as part of an integrated disk drive. For brevity hereinafter, such host structure is referred to as a “host.” Similarly, the term “disk-drive structure” is used in a very broad sense to encompass hard disk drives having industry-standard interfaces such as IDE, SCSI, 1394, etc., and also to encompass head disk assemblies (“HDA's”) and associated electronics such portions of integrated drive/host systems; such disk-drive structure is hereinafter sometimes briefly referred to as a “drive.”
Command-protocol latency includes a number of elements. One of these elements is a software-associated latency relating to execution of instructions to organize and issue a host command. Two other elements are latencies that relate to the transmission and reception of the command while it propagates from the host and while it is received by the drive. An additional element relates to the latency involved in parsing of the command by the drive. For additional background regarding command-protocol latency, see U.S. Pat. No. 4,851,998, titled “METHOD FOR ANALYZING PERFORMANCE OF COMPUTER PERIPHERALS”; note particularly FIG. 2 and column 4, lines 22-54.
As for certain high-performance broadcast-market systems, the prior art (such as U.S. Pat. No. 5,892,915 cited above and hereinafter referred to as the '915 patent) teaches a hierarchical arrangement involving multiple levels of command-protocol latency. As shown in FIG. 28 of the '915 patent, the described system includes, at a first level of the hierarchy, a controller server; at a second level of the hierarchy, a stream server; and at a third level of the hierarchy, a cached disk array. Each of the controller servers and each of the stream servers is described as being a high-end commodity computer including an Intel processor such as a Pentium and including substantial amount of random access memory (RAM) such as 64 megabytes.
The hierarchical arrangement of the '915 patent involves a distribution among the levels of certain important control functions associated with storing control data, and involves communications between the various levels in which communications there are numerous dialogs and control-data transfers. In accord with this distribution important lists of control data are stored remotely from the drives in the cached disk array. These remotely stored lists are the subject of the following dialogs and control-data transfers between the various levels: One such dialog and transfer is the sending and delivery of a remotely-stored stripe set list from the controller server to a selected one of the steam servers. The controller server maintains a clip directory and numerous such remotely-stored stripe set lists. Each remotely-stored stripe set list is associated with a respective clip identified in the clip directory. Each remotely-stored stripe set list includes a doubly-linked list of entries, and each entry includes a starting stripe set number, an ending stripe set number, and a value indicating the number of data segments included in the terminal stripe set. Therefore, each entry in the list represents in sequence data segments beginning in the initial stripe set, continuing in any intermediate stripe set, and ending in the terminal stripe set. Multiple other such dialogs and transfers occur as the stream server controls the cached disk array. Each stream server remotely maintains a pointer to the current play position in the clip it is currently controlling for a client. The stream server repeatedly issues prefetch commands to the cached disk array so that the succession of stripe sets
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are prefetched one by one from the drives in the cached disk array. The command-protocol latencies involved are significant factors adversely affecting the overall performance of the system.
SUMMARY OF THE INVENTION
This invention can be regarded as a disk-based storage system for storing a plurality of data segments and for responding to a direction-selection signal by autonomously providing the data segments in a selected sequence so as to be concatenated together to define a continuous data stream. The direction-selection signal is preferably defined in response to user control for selecting direction including “forward” corresponding to “play” for an A/V stream; the form of the direction-control signal is subject to a broad range including but not limited to multi-bit commands (whe
Knobble, Martens, Olson & Bear, LLP.
Peugh B. R.
Shara, Esq. Milad G.
Western Digital Ventures, Inc.
Yoo Do Hyun
LandOfFree
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