Abstract:
A method and apparatus for dynamically balancing the loading of data storage facilities is described. A listing is acquired of locations and loading of all segments of a requested data object including all copies of the segments of the requested data object. Those storage devices containing copies of each segment of the data object having a least loading is selected. If the loading of the storage devices is greater than the maximum loading for the storage devices, the segment is designated to be copied. The presence of all segments of the requested data object is determined. If there are missing segments of the requested data object, each of those missing segments is assigned a file identification and file location, such that those missing segments are assigned to data storage devices having the least loading. The missing segments are retrieved from a back-up storage device.

Description:
BACKGROUND OF THE INVENTION 
   Related Patent Applications 
   Title “A Video Distribution System Using Segments with Disk Load Balancing,” Ser. No. 09/748,442, Filing Date Dec. 27, 2000, assigned to the same assignee as this invention. 
   Title “A Video Distribution System Using Dynamic Segmenting of Video Files,” Ser. No. 09/748,304, Filing Date Dec. 27, 2000, assigned to the same assignee as this invention. 
   Title “A Video Distribution System Using Dynamic Disk Load Balancing with Variable Segmenting,” Ser. No. 10/027,991, Filing Date Dec. 20, 2001, assigned to the same assignee as this invention. 
   “Streaming While Fetching of Video Objects,” Ser. No. 10/804,658, Filing Date Mar. 19, 2004, assigned to the same assignee as this invention. 
   Title “A Hardware Independent Hierarchical Cluster of Heterogeneous Media Servers,” Ser. No. 10/804,657, Filing Date Mar. 19, 2004, assigned to the same assignee as this invention. 
   Field of the Invention 
   This invention relates to the field of broadcasting quality video data over a packet switched network in such a way that the video is played in a smooth (not jerky) manner. 
   Description of Related Art 
   In the past video streaming servers required that a file be fully present before the sever could start streaming the file. This imposed a considerable restriction as typical DVD or broadcast quality videos may be several Gigabytes in size and thus imposed a large latency before a viewer could start viewing a video. 
   Video is the most dominant medium in entertainment and is rapidly becoming a critical part of computing as well. Video is often used in CD-ROM titles, for example, to mimic personal or virtual environments, increasing an application&#39;s appeal and usability. Video has a large information carrying capacity and is heavily used in capturing and conveying complicated situations such as news events, live interviews, scientific experiments, tourist attractions, and many others. 
   With the increasing availability of high bandwidth networks, video on-demand applications are gaining popularity on global digital communications networks such as the Internet as well as private and corporate digital communication internal networks commonly referred to as Intranets. Example applications include online training, news broadcasts, educational programming, corporate information, and virtual seminars directly to every desktop computing system or workstation. Similarly, video kiosks can be set up in enterprises and university campuses to display live video and up-to-the-minute news, without ever needing an on-site upgrade. 
   Video files, however, occupy huge amounts of space on computers. It requires about 10 MB to store one minute of video in most standard compression and decompression video formats, including Motion Picture Experts Group standard MPEG-1, the Apple Computer Inc. Indeo, Intel Corp. QuickTime, and Super Mac, Inc Cinepak. That translates into 1.2 GB of space for two hours of video, the length of an average feature film. These tremendous storage requirements make effective on-demand sharing of video files at least as important as conventional file sharing. 
   However, conventional file servers do not address video&#39;s unique requirements and cannot effectively support video sharing. Full-motion video, inherited from analog TV, is a sequence of images played out at constant intervals. The two most common analog video formats are the National Television Standards Committee (NTSC), used in the United States and Japan, and Phase Alternation Standard (PAL), used in Europe. NTSC plays video at 30 frames per second, while PAL plays it at 25 frames per second. The sequence of images in a video clip must be relayed at a constant interval, or else the perceptual quality degrades rapidly: the motion jumps and the sound breaks. This rigid periodic timing property is referred to as the isochronous requirement. Referring now to  FIG. 1 , conventional file servers  10  are designed for minimal transfer latency. Files  15  are thus transferred to maintain the minimum latency and are transferred as quickly as possible. The files  15  will be interleaved with other digital communication traffic on the network and thus non-isochronously. Without explicit mechanisms to ensure isochronism, delivery rates are irregular, resulting in erratic playback quality at the client computing system  20 : 
   To avoid erratic playback, the usual approach is to download whole files  15  from the server  10  to the client computing system  20  before starting video playback. This approach results in unacceptable delays for most video files, which are large. For example, even with transfer rates as fast as 1.5 Mb/second, the initial start-up delay is 60 seconds for a one-minute video clip. 
   It is thus desirable to deliver video streams isochronously, as depicted in  FIG. 2 , so that video playback is guaranteed to have smooth motion and sound. The file server  10  must now transfer or stream the files  25  such that the time between each section of the file is transferred at a period of time τ The even interval allows the file  25  to arrive isochronously with the first section to be displayed before any of the remaining sections of the file  25  have arrived at the client system  25 . This allows a video clip to begin practically instantaneously. 
   The rapid advances in the speeds of microprocessors, storage, and network hardware may give a false impression that video on-demand (VOD) solutions do not need special purpose video streaming software. Video streaming as shown in  FIG. 2  allows efficient playback of full motion videos over networks with guaranteed quality using isochronous timing. 
   When an operating system&#39;s default file transfer mode is used to stream a video file, faster hardware may accelerate the operating system&#39;s transfer rate, but this improved hardware still cannot change the fundamental, erratic behavior of a file transfer as shown in  FIG. 1 . By default, the file transfer process does not respect the isochronous nature of a video stream. This typically results in a jerky and poor-quality playback of a video stream. The dominant factors of a system&#39;s overall streaming performance are the higher level client/server and networking processes, and are not the raw power of the low level physical devices. 
   When an application at a Windows client accesses a file in a Windows NT server, the data are automatically cached by WFS at both Windows client and Windows NT server. This is a commonly used technique for reducing the amount of disk access when the cached data can be reused by subsequent requests. This technique does not work for most video-on-demand applications for two reasons. The first reason is that the cached data is hardly used again. VOD applications have very low “locality profile” because they tend to have high data rate and massive volume of videos for users&#39; interactive playback. The second reason is that the constant video caching leads to intensive memory paging and, thus, severely limits performance. 
   U.S. Pat. No. 6,101,546 (Hunt) describes a method and system for providing data files that are partitioned by delivery time and data type. A file is logically partitioned into data channels where each data channel holds a sequence of data of a particular data type. The data channels are logically partitioned into delivery times. The format of the file explicitly sets forth the synchronization between the data channels and the delivery times of data held within the channels. The file format is especially well adapted for use in a distributed environment in which the file is to be transferred from a server to a client. Channel handlers are provided at the client to process respective data channels in the file. The channel handlers are data type specific in that they are constructed to process data of an associated data type. The data in the file may be rendered independently of the delivery time of the data. 
   U.S. Pat. No. 6,018,359 (Kermode, et al.) illustrates a system and method for multicast video-on-demand delivery system. The video-on-demand system divides video files into sequentially organized data segments for transmission and playback. Each segment is repeatedly transmitted in a looping fashion over a transmission channel. The rate of transmission is equal to or greater than the playback rate, and the lengths of the segments are chosen such that:
         the receiver tunes into no more than a fixed number of channels (preferably two) at any one time;   the receiver tunes into a new channel only after an entire segment has been received from a previous channel; and   until a maximum segment length is attained, data is received from no fewer than two channels.
 
The segments are sequentially presented even as new segments are being downloaded. When the display rate is equal to the transmission rate, it is found that the foregoing conditions are satisfied when the relative lengths of the segments form a modified Fibonacci sequence.
       

   U.S. Pat. No. 5,930,473 (Teng, et al.) discloses a video application server for mediating live video services. The video application server is to be used in a network including source clients and viewer clients connected to one or more shared transmission media. A video server is connected to one of the transmission media and is operative to control the broadcast and storage of multiple live or previously stored video streams. The control may be provided via remote procedure call (RPC) commands transmitted between the server and the clients. In one embodiment, a video presentation system is provided in which a video stream from a source client is continuously broadcast to a number of viewer clients. One or more of the viewer clients may be authorized by the source client to broadcast an audio and/or video stream to the other clients receiving the source video stream. In another embodiment, a multicast directory is provided to each of a plurality of viewer clients by transmitting directory information in a packet corresponding to a predetermined multicast address. The multicast directory indicates to a particular viewer client, which of a number of video programs are available for broadcast to that client. 
   U.S. Pat. No. 6,101,547 (Mukherjee, et al.) describes an inexpensive, scalable and open-architecture media server. The multi-media server provides client systems with streaming data requiring soft real-time guarantee and static data requiring a large amount of storage space. The servers use a pull-mode protocol to communicate with client systems through a real-time network. Separate data and control channels enhance the soft real-time capability of the server. The data channel conforms to an open standard protocol such as such as Transmission Control Protocol (TCP), User Datagram Protocol (UDP), or Real-time Transport Protocol (RTP). A switched data link layer for the control channel permits separate intrahost control messages that may be multicast and broadcast. The distributed file system selects a specific data block size based upon the compression technique employed to enhance soft real-time guarantee. A hierarchical data structure combined with merging empty data blocks minimizes disk fragmentation. Data blocks are striped across multiple disks to improve disk utilization. A local buffer and a queue for both read and write requests provides support for simultaneous read and write data streams. 
   U.S. Pat. No. 5,805,821 (Saxena, et al.) teaches a video optimized media streamer user interface employing non-blocking switching to achieve isochronous data transfers. The media streamer includes at least one control node; a user interface having an output coupled to the at least one control node; at least one storage node for storing a digital representation of at least one video presentation; and a plurality of communication nodes each having an input port for receiving a digital representation of at least one video presentation therefrom. The video presentation requires a time T to present in its entirety, and is stored as a plurality of N data blocks. Each data block stores data corresponding to a T/N period of the video presentation. Each communication nodes further has a plurality of output ports for outputting a digital representation. A circuit switch is connected between the at least one storage node and the input ports of communication nodes for coupling one or more input ports to the at least one storage node. The user interface includes a capability for specifying commands for execution, and the at least one control node is responsive to individual ones of the commands for controlling at least one of the at least one storage node and at least one of the plurality of communication nodes, in cooperation with the circuit switch, so as to execute a function associated with individual ones of the commands. The commands may include videocassette recorder-like commands that include commands selected from a group that includes a Load command, an Eject command, a Play command, a Slow command, a Fast Forward command, a Pause command, a Stop command, a Rewind command, and a Mute command. The commands may also include commands selected from a group that includes a Play List command, a Play Length command, and a Batch command. A synchronous application program interface (API) is provided for coupling, via the user interface, a user application program to the at least one control node. The API includes Remote Procedure Call (RPC) procedures. 
   U.S. Pat. No. 5,550,577 (Verbiest, et al.) illustrates a video on demand network, including a central video server and distributed video servers with random access read/write memories. The video on demand network transmits video signals to user stations pursuant to the receipt of control signals issued by these user stations. In order to optimize the retrieval costs, this video on demand network maintains a large video library in a central video server and stores locally popular video signals in a plurality of local distributed video servers from which the latter video signals are transmitted to the user stations. The video signals provided by the local distributed servers are updated from the central server based upon the changing popularity of the video signals. The video on demand network of Verbiest proposes in particular to store the video signals in the local distributed servers in random access read/write memories, e.g., electronic RAMs, magnetic or optical disks from which the video signals can flexibly be supplied on-line to the user stations and to store the video signals in the central server in sequential access memories, e.g. Digital Audio Tapes (DAT) and CD-ROMs (CDR), providing cheap mass storage. 
   “Performance Evaluation of QuickVideo OnDemand (QVOD) Server,” InfoValue Computing, Inc. Technical Report IV-TR-QVOD-1999-07-1-1, Jul. 8, 1999, InfoValue Computing, Inc., Elmsford, N.Y. describes a video on-demand system developed for high performance, effective and flexible, network-based, on-demand sharing of videos. QuickVideo on Demand provides streaming throughput for broadband applications. Further, QuickVideo On Demand allows a linearly scalable clustering mechanism, which provides support for higher throughputs, if required. QuickVideo On Demand supports all video formats, codecs, networks and applications, and is compatible with any open application platform. 
   “Network Video Computing Via QuickVideo Suite,” InfoValue Technical White Paper, InfoValue Computing, Inc., Elmsford, N.Y., 1999, describes Network Video Computing the core of which is video streaming. Video streaming allows the efficient playing of full-motion video content over networks with guaranteed quality. The rigid timing property of full motion video is referred to as the isochronous timing. File servers are designed to minimize transfer latency during conventional network transfers, and are insensitive to video&#39;s unique timing requirement. As a result, delivery rates are irregular and produce erratic playback as described above. Video streaming technologies are real-time network transfers that maintain the video&#39;s critical timing property throughout the entire delivery period, as depicted in  FIG. 2 . This white paper describes an open architecture with a streaming core. 
   “Web Distribution Systems: Caching and Replication” Chandbok, Ohio State University, 1999, found http://www.cis.ohio-state.edu/˜jain/cis788-99/web 13  caching/index.html, Aug. 15, 2000, provides an overview of the current techniques for caching and replication of digital data on computer systems interconnected through a global or local digital communication network. Refer now to  FIG. 3  for a summary of caching in large distributed digital processing networks. Multiple server computing systems  100   a,    100   b,  . . . ,  100   f  are high performance computing systems such as the IBM Corporation RS-6000-SP, The Sun Microsystems, Inc. Enterprise 10000 Server, the Hewlett-Packard Netserver AA-6200, or other server systems. The computer systems  100   a,    100   b,  . . . ,  100   f  are each connected to multiple storage devices  105   a,    105   b,  . . . ,  105   r.  The storage devices  105   a,    105   b,  . . . ,  105   r  are magnetic disk devices, compact disk read only memory (CD-ROM) “juke boxes,” or tapes drives. A group of the server systems  100   a,    100   b,    100   c  or  100   d,    100   e,    100   f  are respectively interconnected through the digital communications cluster network  110  and  115  to form the server cluster  1   120  and the server cluster  2   125 . The server cluster  1   120  and the server cluster  2   125  may be resident with in the same enterprise data center or placed at different geographical locations either within the enterprises or even in different enterprises. 
   The cluster networks  110  and  115  are connected respectively to the network routers  130  and  135 . The network routers  130  and  135  are further connected to a public or global digital communications network  155 . The global network  155  may be the public Internet or an enterprise&#39;s private Intranet. 
   The server computer systems  100   a,    100   b,  . . . ,  100   f  contain database information systems, storage for files such as audio or video files, and other data files to be accessed by large numbers of people either publicly or privately within an enterprise through the client systems  150   a,    150   b,    150   c.    
   Edge servers  140   a,    140   b,    140   c  are connected to the global network  155  and thus provide access portals for the client systems  150   a,    150   b,    150   c  to the global network  155  to communicate with each other, with other edge servers  140   a,    140   b,    140   c,  or with the server computer systems  100   a,    100   b,  . . . ,  100   f.  Each edge servers  140   a,    140   b,    140   c  is connected has attached data storage device  145   a,    145   b,  . . . ,  145   i.  The attached data storage device  145   a,    145   b,  . . . ,  145   i  is generally a magnetic disk storage device, but may also include a CD-ROM, magnetic tape, or other storage media. 
   If a server computer systems  100   a,    100   b,  . . . ,  100   f  has data  160  that is requested by many of the client systems  150   a,    150   b,    150   c,  the network traffic to the server computer system  100   a  may to great for either the global network  155  or the cluster network  110  to carry and maintain a reasonable quality of service. Quality of service in this context means that the original data  160  is transferred repetitively relatively quickly and if the original data  160  is audio or video files, that the isochronous nature of the transfer of the data is maintained. 
   If the server clusters  120  and  125  are separated geographically, it may cost less to maintain the quality of service by placing a copy  165  of the original data  160  in a disk  105 I on a second server system  100   d.  If the copy  165  of the original data  160  is permanent, it is referred to as being replicated. If the copy  165  of the original data  160  is temporary it is referred to as cached. As the demand for the original data  160  is increased, it may be desirable to either replicate or cache  170  or  175  the data even within the disks  145   b  or  145   i  of the edge servers  150   a  or  150   c.    
   There are many policies developed regarding which of the original data  160  is replicated or cached  165 ,  170 , or  175 . Further, the replacement of cached data  165 ,  170 , or  175  by other data that is demanded more often is known and generally follows a least recently used protocol, where the cached data  165 ,  170 , or  175  that has not been requested is replaced by data that is more requested. 
   U.S. Pat. No. 6,088,721 (Lin, et al.) teaches an efficient unified replication and caching protocol. The protocol provides assurance of consistent replication of objects from a central server to caching servers, for example, over data communication networks such as the Internet. It is an application-layer protocol, which guarantees delivery of objects such as files. This protocol insures that objects sent by a source machine such as a server to any number of destination machines such as caching servers actually arrive at the intended caching servers even when the caching servers are temporarily unavailable, for example, due to failure or network partition. 
   U.S. Pat. No. 6,061,504 (Tzelnic, et al.) illustrates a video file server using an integrated cached disk array and stream server computers. The video file server includes an integrated cached disk array storage subsystem and a multiple stream server computers linking the cached disk storage system to the data network for the transfer of video data streams. The video file server further includes a controller server for applying an admission control policy to client requests and assigning stream servers to service the client requests. The stream servers include a real-time scheduler for scheduling isochronous tasks, and supports at least one industry standard network file access protocol such as Simple Network Management Protocol (SNMP) and one file access protocol Network File System (NFS) for continuous media file access. The cached disk storage subsystem is responsive to video prefetch commands, and the data specified for a prefetch command for a process are retained in an allocated portion of the cache memory from the time that the cached disk storage subsystem has responded to the prefetch command to the time that the cached disk storage subsystem responds to a fetch command specifying the data for the process. The time between prefetching and fetching is selected based on available disk and cache resources. The video file server provides video-on-demand service by maintaining and dynamically allocating sliding windows of video data in the random access memories of the stream server computers. 
   “Network Caching Guide,” Goulde, Patricia Seybold Group for Inktomi Corp., Boston, Mass., March 1999, describes the various types of caching approaches and the different ways for caches to be implemented. Implementations vary depending on where the cache is placed, who is accessing the cache, and the quantity and type of content that is being cached. Goulde describes the Inktomi Traffic Server from Inktomi Corporation. The Inktomi Traffic Server is capable of delivering fresh content to large numbers of users around the world from a large number of Web servers around the world. 
   “Inktomi Traffic Server—Media Cache Option”, Inktomi Corporation, San Mateo Calif., 1999, found http://www.inktomi.com, Aug. 15, 2000, describes the caching option for the Inktomi Traffic Server to support streaming of video data files. 
   “Implementing Multiplexing, Streaming, and Server Interaction for MPEG-4” Kalva et al., IEEE Transactions On Circuits And Systems For Video Technology, Vol. 9, No. 8, December 1999, pp. 1299–1312, describes the implementation of a streaming client-server system for object-based audio-visual presentations in general and MPEG-4 content in particular. The system augments the MPEG-4 demonstration software implementation (IM1) for PC&#39;s by adding network-based operation with full support for the Delivery Multimedia Integration Framework (DMIF) specification, a streaming PC-based server with DMIF support, and multiplexing software. The MPEG-4 server is designed for delivering object-based audio-visual presentations. The system also implements an architecture for client-server interaction in object-based audio-visual presentations, using the mechanism of command routes and command descriptors. 
   “New Solution for Transparent Web Caching: Traffic Server 2.1 Supports WCCP,” Inktomi Corporation, San Mateo Calif., 2000, found http://www.inktomi.com/products/network/traffic/tech/wccp, Aug. 15, 2000 describes the use of the Web Cache Control Protocol (WCCP) from Cisco Systems, Inc. within Inktomi Corporation&#39;s Traffic Server. 
   “API Overview,” Inktomi Corporation, San Mateo Calif., 2000, found http://www.inktomi.com/products/network/traffic/tech/wccp, Aug. 15, 2000, describes the application program interface tools that are available for the Inktomi Corporation&#39;s Traffic Server which allow customization or the Traffic Server&#39;s event processing thus allowing manipulation of hypertext transaction protocol (HTTP) transactions at any point in their lifetime. 
   “Web Cache Communication Protocol v2,” Cisco Systems, Inc., San Jose, Calif., found http://www/cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120t/120t3/wccp.htm, Aug. 15, 2000, describes the protocol that allows the use a Cisco Cache Engine to handle web traffic, reducing transmission costs and downloading time. This traffic includes user requests to view pages and graphics on World Wide Web servers, whether internal or external to a network, and the replies to those requests. When a user requests a page from a web server (located in the Internet), the router sends the request to a cache engine. If the cache engine has a copy of the requested page in storage, the cache engine sends the user that page. Otherwise, the cache engine retrieves the requested page and the objects on that page from the web server, stores a copy of the page and its objects, and forwards the page and objects to the user. WCCP transparently redirects Hypertext Transfer Protocol (HTTP) requests from the intended server to a cache engine. 
   “A Practical Methodology For Guaranteeing Quality Of Service For Video-On-Demand,” Zamora et al.,  IEEE Transactions On Circuits And Systems For Video Technology,  Vol. 10, No. 1, February 2000, describes an approach for defining end-to-end quality of service (QoS) in video-on-demand (VoD) services. A schedulable region for a video server, which guarantees end-to-end QoS, where a specific QoS required in the video client, translates into a QoS specification for the video server. The methodology is based on a generic model for VoD services, which is extendible to any VoD system. In this kind of system, both the network and the video server are potential sources of QoS degradation. The effects that impairments in the video server and video client have on the video quality perceived by the end user are examined. 
   As described above, video files may be very large, on the order of 1.2 GB for a two-hour movie or video presentation. In the digital communication networks  110 ,  115 , and  155  of  FIG. 3 , the files are generally formed into data packets for transfer. These data packets may not arrive to a designated client system  150   a,    150   b,    150   c  in correct order for processing. This requires reception of the complete file before processing may begin. If the file is an audio or video file requiring isochronous presentation of the file, the files must be totally received before processing or the files must be segmented or partitioned into portions to allow smaller units of the files to be processed. 
   U.S. Pat. No. 5,926,649 (Ma, et al.) teaches a Media server for storage and retrieval of voluminous multimedia data. The Media server provides storage and retrieval of multiple data streams in a multimedia distribution system. A given data stream is separated into a plurality of portions, and the portions are stored in a multi-disk storage system with Y disks each having X zones such that the ith portion of the given stream is stored in zone (i mod X) of disk (i mod Y). The number X of zones per disk and the number Y of disks are selected as relatively prime numbers. The stored data are retrieved using Y independent retrieval schedulers, which are circulated among the Y disks over a number of scheduling intervals. Each retrieval scheduler processes multiple requests separated into X groups, with the requests of each group accessing the same disk zone during a given scheduling interval. The retrieval schedulers are also configured such that the retrieval requests of a given retrieval scheduler access the same disk during a given scheduling interval. The data stream placement techniques in conjunction with the retrieval schedulers provide sequential-like parallel retrieval suitable for supporting real-time multimedia data distribution for large numbers of clients. 
   U.S. Pat. No. 5,936,659 (Viswanathan, et al.) illustrates a method for broadcasting movies within channels of a wide band network by breaking the communications path into a number of logical channels and breaking each movie up into a number of segments of increasing size. The first segment of each movie is the smallest segment is transmitted in sequence over the first logical channel and repeated. The second segment of each movie, which is proportionately larger than the first segment of each movie, is transmitted in sequence over the second logical channel and repeated. This is repeated for the total number of segments, which equals the total number of logical channels. The segments are broadcast in such a way that, once the first segment is received at a client location, the subsequent segments are also received in time, so that the movie can be viewed continuously. 
   U.S. Pat. No. 5,973,679 (Abbott, et al.) describes an indexing method for allowing a viewer to control the mode of delivery of program material. By mapping from time to data position, data delivery can begin at any selected time in the program material. The indexing method also provides for controlling data delivery to begin at the beginning of a frame of data. A synchronizing method is provided to minimize a time offset between audio and video data, particularly in environments using groups of pictures. 
   U.S. Pat. No. 5,996,015 (Day, et al.) describes a method of delivering seamless and continuous presentation of multimedia data files to a target device by assembling and concatenating multimedia segments in memory. The method provides a multimedia server connected in a network configuration with client computer systems. The multimedia server further includes various functional units which are selectively operable for delivering and effecting the presentation of multimedia files to the client such that a plurality of multimedia files are seamlessly concatenated on the fly to enable a continuous and uninterrupted presentation to the client. In one example, client selected video files are seamlessly joined together at the server just prior to file delivery from the server. The methodology includes the analog to digital encoding of multimedia segments followed by a commonization processing to ensure that all of the multimedia segments have common operating characteristics. A seamless sequential playlist or dynamically created playlist is assembled from the selected and commonized segments and the resources needed to deliver and play the playlist are reserved in advance to assure resource availability for continuous transmission and execution of the playlist. At a predetermined point prior to an end point of each selected multimedia segment, the next selected segment is initialized and aligned in memory in preparation for a seamless switch to the next segment at the end of a previous segment, thereby providing a seamless flow of data and a continuous presentation of a plurality of selected multimedia files to a client system. 
   U.S. Pat. No. 5,608,448 (Smoral, et al.) describes a hybrid architecture for a video on demand server. The processing requirement at each computing element in a video server for a video on demand (VOD) system is reduced to only those needed for VOD, resulting in a less expensive processor with less memory and, hence, lower cost. A hybrid video server architecture combines the features of massive parallel processor (MPP) and workstation designs. Since it is not necessary to run a parallel relational database program in order to accomplish VOD data distribution, a unique type of switch element that is well matched to the VOD server problem is employed. By matching this switch element technology to an appropriate data storage technique, a full featured, responsive VOD server is realized. 
   U.S. Pat. No. 6,061,732 (Korst, et al.) describes a data streaming system utilizing an asynchronous technique for retrieving data from a stream server. In an audio/video server blocks of data are read from a storage medium by a reader and supplied to users in the form of data streams. The storage medium comprises a plurality of record-carrier based storage units. A reader reads a batch of data units from a storage unit in a single relative movement of a reading head of the storage unit with respect to the record-carrier of the storage unit. A scheduler controls reading of blocks from the storage medium by determining from which storage unit(s) data unit(s) need to be read for the block and placing a corresponding carrier access request in a read queue. The scheduler extracts for each of the storage units a batch of carrier access requests from the queue and issues the batch to the reader in an asynchronous manner, in response to the reader having substantially completed reading data units for a previous batch for the storage unit. 
   U.S. Pat. No. 5,414,455 (Hooper, et al.) teaches a segmented video on demand system. In the system for distributing videos, multiple videos are stored on a mass storage device. Each video includes a plurality of frames of digitized video data for playback on a viewing device. The system includes a memory buffer for storing a segment of a selected one of the videos. The segment includes a predetermined number of frames representing a predetermined time interval of the selected video. In addition, the memory buffer includes a write pointer and a read pointer. Software controlled servers are provided for writing and reading video data of the selected video to and from the memory buffer, independently, at locations indicated by the write and read pointers to transfer the selected video to the viewing device. 
   When any of the multiple client systems  150   a,    150   b,  and  150   c  requests access to the original data  160  present, each request if fulfilled and the original data is routed through the server computing system  100   a,  the cluster network  110 , the router  130 , to the global digital communications network  155 , to the edge servers  140   a,    140   b,    140   c  to the requesting client systems  150   a,    150   b,  and  150   c.  Each transfer of the original data  160  consumes a portion of the available transfer rate (Bytes/sec) or bandwidth of the connections from the storage device  105   a  to the server computing system  100   a,  from the server computing system  100   a  to the cluster network  110 , from the cluster network  110  to the router  130 , from the router  130  to the global digital communication network  155 , from the global communications network  155  to the edge servers  140   a,    140   b,    140   c,  from the edge servers  140   a,    140   b,    140   c  to the requesting client systems  150   a,    150   b,  and  150   c.  The smallest bandwidth of this chain is generally the determining factor of the loading. In this case the loading determinant will be from the storage device  105   a  to the server computing system  100   a.  If there are no copies of the original data  160 , as the number of requests for the original data increases, the available bandwidth decrease or loading on the storage device  105   a  increases. The loading of the data transfer  160  to and from the data storage device  105   a  must be in balance or the requests for the transfer may not be honored. In the case of video-on-demand, this causes interruptions or at least degradation of the quality of service in viewing the demanded video. 
   “DASD Dancing: A Disk Load Balancing Optimization Scheme for Video-on-Demand Computer,” Wolf, et al., ACM SIGMETRICS 1995, pp. 157–166 proposes a scheme to dynamically perform load-balancing of DASDs: (direct access storage devices), which is referred to as a DASD dancing algorithm. The algorithm consists of two components. The static component assigns movie files to DSGs (disk-striping groups) initially, and it also reassigns movies periodically, for example every day or every week. The dynamic component performs the real-time movie stream scheduling. (A disk-striping group, or DSG, is a group of disks, which contains a number of movies). 
   “Load Balancing For a Video-On-Demand Server,” DO, Information and Computer Science Dept, University of California, Irvine, 1998, found Oct. 1, 2000, http://www.ics.uci.edu/˜tdo/loadVOD/loadVOD.html, is an overview of the state of the art of load balancing for video-on-demand server systems, the problems that are involved with the server systems, and solutions for those problems. 
   “Random Duplicated Assignment: An Alternative to Striping in Video Servers,” Korst, Electronic Proceedings ACM Multimedia 97, November 1997, found http://info.acm.org/sigmm/MM97/Papers/korst/RDA.html, Oct. 2, 2000, describes an approach for storing video data in large disk arrays. Video data is stored by assigning a number of copies of each data block to different, randomly chosen disks, where the number of copies may depend on the popularity of the corresponding video data. The use of the approach results in smaller response times and lower disk and RAM costs if many continuous variable-rate data streams have to be sustained simultaneously. 
   U.S. Pat. No. 5,544,313 (Shachnai, et al.) describes a baton passing optimization scheme for load balancing/configuration planning in a video-on-demand computer system. A video on demand computer system includes multiple storage devises each storing many video data files. The storage devices in this case are disks attached to a computer system. The computer system plays the videos on demand by reading out the videos from the disks as data streams to play selected video data files in response to user requests. The computer system is programmed to monitor the numbers of video data files being performed for each of the disks. Based on the monitoring function performed by the computer system, the computer system performs a load balancing function by transferring the current transfer of a video data file in progress from the disk having the original video data file being transferred to another disk having a copy of the video data file. The computer system periodically performs a reassignment function to transfer videos between the disks to optimize load balancing based on the user performance requests for each of the video data files. There are two phases to the load balancing performed by the computer system; a static phase and a dynamic phase. In the static phase, video data files are assigned to memory and disks, and in the dynamic phase there is provided a scheme for playing video data files with minimal and balanced loads on the disks. The static phase supports the dynamic phase, which insures optimal real-time operation of the system. A process of “baton passing” accomplishes dynamic phase load balancing. 
   “U.S. Pat. No. 5,333,315 (Saether, et al.) describe a computer system of device independent file directories using a tag between the directories and file descriptors that migrate with the files. The computer file system has a multiple disk storage devices which includes a multiple of file directories, stored on various disks. Each file directory is used to translate file names into corresponding tag values. For each disk there is a file descriptor table with a file descriptor entry for every file stored on the disk. A single tag directory contains one tag entry for every file stored in the system. The tag directory is used by the file system to find a file by translating a tag value into a pointer to the disk on which the file is stored and a pointer to the file&#39;s file descriptor entry. To move a file from a first disk to a second disk, the file is copied to the second disk, a new file descriptor entry for the copied file is generated in the file descriptor table for the second disk, the copy of the file on the first disk is de-allocated, and the tag entry for the file is updated to point to the second disk and to the file&#39;s new file descriptor entry. Thus, a file can be moved from a first disk to a second without having to locate and update all the corresponding file directory entries. In a preferred embodiment, the file system includes a routine that monitors disk loading and unused disk capacity. It determines when disk usage is imbalanced and automatically moves files among the disks so as to better balance disk usage. 
   U.S. Pat. No. 5,631,694 (Aggarwal, et al.) describes a maximum factor selection policy for batching VOD requests. A VOD scheduler maintains a queue of pending performance for each video. Using the notion of queue selection factor, a batching policy is devised that schedules the video with the highest selection factor. Selection factors are obtained by applying discriminatory weighting factors to the adjusted queue lengths associated with each video where the weight decreases as the popularity of the respective video increases and the queue length is adjusted to take defection into account. 
   SUMMARY OF THE INVENTION 
   An object of this invention is to provide a method and apparatus to dynamically balance the loading of data storage facilities containing video data files. 
   Further, another object of this invention is to provide a method and apparatus to balance the loading of data storage facilities containing video data files to facilitate the transfer of the video data files or portions of video data files from a file server system to client computing system. 
   To accomplish these and other objects a method for balancing a loading of a storage device attached to multiple computing systems begins by acquiring a listing of locations of all segments of a requested data object including all copies of the segments of the requested data object. The loading of the storage devices attached to the multiple computing systems containing all copies of all segments of a requested data object is evaluated and those storage devices containing copies of each segment of the data object having a least loading, which is less than a maximum loading for the storage devices, is selected. If the loading of the storage devices is greater than the maximum loading for the storage devices, segment resident on the storage device having loading greater than the maximum loading is designated to be copied to an alternate storage device. 
   The presence of all segments of the requested data object is determined. If there are missing segments of the requested data object, each of those missing segments is assigned a file identification and file location, such that those missing segments are assigned to data storage devices having the least loading. The missing segments are retrieved from a back-up storage device. 
   An alternate storage device is selected and the segment is copied to the alternate storage device. The segments of the requested data object are then transferred to a requesting computer system. 
   To select the storage devices containing copies of the segments of the requested data object and having the least loading, a current segment indicator is first set to indicate which of the segments of the data object is to be transferred next. Then a current storage device indicator is set to specify a primary location of the segment to be transferred next. If the transfer of the segment causes the loading of the storage device containing the segment to be exceeded, the current storage device indicator is incremented to a next location of the segment to be transferred. If the loading for each storage device containing a copy of the segment of the data exceeds the maximum loading, the next copy is examined until one of the storage devices does not have excess loading. If all copies of the segment exceed the loading, a copy of the segment is made to a storage device having light loading. 
   The transfer of the segments of the data object is defined as reading the segments from the data storage device, writing the segments to the data storage device, and copying the segments from a the data storage device to an alternate data storage device. The loading of the data storage device is allocated between the reading, writing, and copying of the segments to prevent interference with the reading of the segments. 
   The data objects as described for this invention are video data files to be streamed isochronously to the requesting computer system. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram of the transfer of files on a digital communications network of the prior art requiring minimal latency. 
       FIG. 2  is a diagram of the transfer of files on digital communications network of the prior art illustrating isochronous file transfer. 
       FIG. 3  is a diagram of a distributed computer network system illustrating replication of files in caches of the prior art. 
       FIG. 4  is a diagram of a distributed computer network system illustrating load balancing of data storage devices of this invention. 
       FIGS. 5 ,  6 , and  7  are flow diagrams illustrating the method of load balancing of data storage devices of this invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Refer now to  FIG. 4  for a description of a video distribution system of this invention. The client computing systems  400   a,    400   b,    400   c  are connected through a communications link to an edge server  405   a,    405   b,  and  405   c.  Each edge server  405   a,    405   b,    405   c  acts as an interface for the client computing systems  400   a,    400   b,    400   c  to a global communications network  415 . The edge servers  405   a,    405   b,    405   c  are at the boundary between the “front-end” and the “backend” of the video distribution system. The front-end being the client computing systems  400   a,    400   b,    400   c  that are the terminal points whereby the users can access the video distribution system. Further the edge servers  405   a,    405   b,    405   c  are generally Internet service providers to which the client computing systems  400   a,    400   b,    400   c  are in communication. 
   The backend of the video distribution system has server systems  420   a,  . . . ,  420   f  that are grouped together to form server clusters  410   a,  . . . ,  410   b.  The server systems  420   a,    420   b,  and  420   c  are interconnected together through the cluster network  455 . The server systems  420   d,    420   e,  and  420   f  are interconnected together through the cluster network  460 . The router  425  provides an interface for the server cluster  1   410   a  to the global communication network  415 . Likewise, the router  430  provides an interface for the server cluster n  410   b  to the global communication network  415 . 
   The gateway server  475  is connected through the global communication network  415  to the edge servers  405   a,    405   b,    405   c  and thus to the client computing systems  400   a,    400   b,    400   c.  The gateway server  475  is the central point of contact for incoming requests to the system from the client computing systems  400   a,    400   b,  and  400   c.  When a client computing systems  400   a,    400   b,    400   c  requests a video data file (on demand) or join a broadcast (multicast) of a video data file, it first contacts the gateway server  475 . The gateway server  475  maintains an updated list of the server systems  420   a,  . . . ,  420   f  in the system. Based on the location of the client computing systems  400   a,    400   b,    400   c  and the type of request, it routes the request to the appropriate server systems  420   a,  . . . ,  420   f.    
   A large-scale system containing thousands of video data files must offer an efficient and easy to use content management service to the client computing systems  400   a,    400   b,    400   c.  Such a content management service includes capabilities to add/delete, categorize, and browse video data files and is provided by the title server  450 . In presence of a dedicated title server  450 , the gateway server  475  redirects the client computing systems  400   a,    400   b,    400   c  requests to the title server  450 . In the absence of such a dedicated title server  450 , the gateway server  475  can be configured to provide content management services to client computing systems  400   a,    400   b,  and  400   c.  Client computing systems  400   a,    400   b,    400   c,  then, browse video data file in the gateway server. 
   In a geographically distributed broadband video distribution system of this invention, there will be multiple title servers  450 , each for a service region. The gateway server  475  will route the client computing systems  400   a,    400   b,    400   c  requests to appropriate title servers  450  based on the location of the client computing systems  400   a,    400   b,    400   c.    
   A distribution server  470  is used to introduce new contents in the video distribution system of this invention. Once a new video data file is available, a media distributor uses this service to propagate the title to different service regions of a geographically distributed system. The distribution server  470  consists of four distinct components. A Distribution Center, which is a remote service, is used by media distributors to push new video data files to regional server systems  420   a,  . . . ,  420   f.  A Distributor Console, a web based remote graphical user interface (GUI), is used to specify locations and contents to be pushed to remote server systems  420   a,  . . . ,  420   f.  A set of Asset Managers, which are local to regional server systems  420   a,  . . . ,  420   f,  is responsible for managing and tracking contents in the regional server systems  420   a,  . . . ,  420   f.  A set of asset databases, one database per regional server system  420   a,  . . . ,  420   f,  which stores the meta data for the available contents (video data files) in that regional server systems  420   a,  . . . ,  420   f.  Asset managers use this database to keep track of local video data files. Multiple asset managers can share one asset database. The title server  450  also uses this database to generate a categorized, browsable list of video data files. 
   A media distributor uses the distributor console to schedule distribution of new media data objects (video data files) to the a video distribution system of this invention. The new video data files generally reside in a tertiary storage  445  such as a robotic DVD. The media distributor specifies when to push the title, the list of target regional sites, and the textual meta data related to the video. Among other things, the meta data of a title will possibly contain information required to categorize it as well as a set of searchable strings, which can be used to search the content of the video data files. The distributor console connects with the remote distribution center  470  and delivers the schedule. The distributor console contacts the asset managers in the specified target server systems  420   a,  . . . ,  420   f,  and schedules the delivery of the new content. Once a server system  420   a,  . . . ,  420   f,  receives the new video data file, it first stores the content in any available space in a local disk  480   a,  . . . ,  480   r.  Then, it updates the asset database with the information on the new video data file (including the received meta data on the video data file). If it does not have any available space, it replaces an old video data file using a programmed policy. 
   Based on the client computing systems  400   a,    400   b,    400   c  request (browsing by category, or searching using a string), the title server  450  queries the asset database, and creates a list of video data files for the client computing systems  400   a,    400   b,    400   c  to browse. The title server  450  uses aggressive caching techniques to improve the performance of the query. When new information is added in the asset database, the cache in the title server  450  is invalidated. 
   It is sometimes possible for a title server  450  to have information on a video data file, which is not wholly available in the local storage  480   a,  . . . ,  480   r,  for various reasons. Portions of the video data file may have been replaced because the asset manager needed space for a new video data file, or only a portion of a video data file was propagated from the distribution center. Once a client computing systems  400   a,    400   b,    400   c  requests such a video data file, server system  420   a,  . . . ,  420   f,  is fetches the video data file to the local storage  480   a,  . . . ,  480   r.  The server system  420   a,  . . . ,  420   f  allocates free space in the local storage  480   a,  . . . ,  480   r  possibly by replacing a portion of a resident video data file. The server system  420   a,  . . . ,  420   f  contacts the distribution server  470  providing the name of the video data file and the remaining portion of the video data file. Once the distribution server  470  is ready, the server system  420   a,  . . . ,  420   f  fetches the remaining portion of the video data file, stores it in the allocated free space, and updates the asset database. 
   When a user of a client computing systems  400   a,    400   b,    400   c  selects a video data file to be viewed, the client computing systems  400   a,    400   b,    400   c  contacts the admission server  435 , which based on the bandwidth requirements and the file location of the video data file, assigns a video server system  420   a,  . . . ,  420   f  from the server clusters  410   a,    410   b.    
   The admission server  435  provides a set of mechanisms, which are used to implement different policies for load balancing. The admission server  435  maintains a cluster topology, a disk usage table, a node usage table, and a cluster map. The cluster topology maintains the connection information of the cluster. It itemizes a list of server systems  420   a,  . . . ,  420   f  of a server cluster  410   a,    410   b,  which can access any of the disks  480   a,  . . . ,  480   r.  The cluster topology contains the server system  420   a,  . . . ,  420   f  identification that is the mount point where a disk  480   a,    480   r  is mounted, and the access status of the disk  480   a,  . . . ,  480   r.    
   The disk usage table maintains the capacity (maximum data rate in Mbps) and the current load (data rate in Mbps) for each disk  480   a,  . . . ,  480   r  in the server cluster  410   a,    410   b.  The node usage table maintains the streaming capacity (maximum data rate in Mbps) and the current load for each node in the server cluster  410   a,    410   b.  The cluster map maintains an up to date list of network address (internet protocol address), port and the status of the important server system  420   a,  . . . ,  420   f  in the distribution system, and it maintains a list of server systems  420   a,  . . . ,  420   f  in the cluster  410   a,    410   b,  their network addresses and their status. A server system  420   a,  . . . ,  420   f  can be in one of two states: Live (L) and Failed (D). Additionally, the admission server  435  maintains a supporting data structure, required to provide fault tolerance and authenticated access to the server cluster  410   a,    410   b.  The data structure maintains a table containing the list of active sessions per server system  420   a,  . . . ,  420   f,  and a similar table for active sessions per disk  480   a,  . . . ,  480   r.    
   The configuration server  485  allows an administrator to define and to configure server clusters  410   a,    410   b  and the distributed server installations. It maintains an up to date information of the distributed installation using a periodic monitoring mechanism and asynchronous update events from the servers  420   a,  . . . ,  420   f  in the system. 
   As described, the video data files may be several gigabytes in size. In order to facilitate the transfer of the video data files to client computing systems  400   a,    400   b,    400   c  for viewing by a user, it is desirable to fragment the video data file into smaller segments. Each segment is assigned a file name and a location within any of the disks  480   a,  . . . ,  480   r,  and  495   a,  . . . ,  495   x.  When a client computing system  400   a,    400   b,    400   c  requests a video data file, the admission server  435  retrieves the listing of the segments of the requested data file from the disk usage table. It should be noted, that the requested video data file may in fact be any portion of a larger video data file not just the whole video data file. It should further be noted that the portion of the video data file requested may not encompass whole segments by may also contain fractional segments. 
   Refer now to  FIGS. 5 ,  6 , and  7  for a description of the method for balancing of the loading on storage devices of this invention. The video data files or segments of the video data files are copied and distributed to other disks  480   a,  . . . ,  480   r,  and  495   a,  . . . ,  495   x  according to the activity of the disks  480   a,  . . . ,  480   r,  and  495   a,  . . . ,  495   x  and the request patterns for the video data file by the client computing system  400   a,    400   b,    400   c.  The client  400   a,    400   b,  and  400   c  requests (Box  500 ) a video data file (or portion of a video data file) according to an identification (file name) of the requested video data file and a range or indication of the beginning location and size of the requested video data file. The admission server  435  retrieves (Box  510 ) a disk usage table describing the segments contained within the range of the requested video data file. Further, the admission server  435  retrieves (Box  520 ) locations on the disks  480   a,  . . . ,  480   r,  and  495   a,  . . . ,  495   x  of the segments of the video data file. The contents of the disk usage table are interrogated (Box  530 ) to verify the presence of all the requested segments or the total video data file. 
   If the results of the interrogation (Box  530 ) of the disk indicates the video data file or a segment of the video data file are not present on the disks  480   a,  . . . ,  480   r,  and  495   a,  . . . ,  495   x,  the admission server  435  requests (Box  532 ) the missing video data file or segments of the video data file from the backing store  445  through the distribution server  470 . The admission server  435  assigns (Box  534 ) a disk  480   a,  . . . ,  480   r,  and  495   a,  . . . ,  495   x  that is to receive the video data file or the segments of the video data file based on the available space and disk activity. If the video data file is segmented, the admission server  435  assigns (Box)  536 ) segment file names to the individual segments of the video data file. The video data files are fetched (Box  538 ) from the tertiary or backing store  445  and placed in the assigned locations. 
   The admission server  435  then requests (Box  510  and Box  520 ) an updated list of the segments of the requested range of the video data file. Once the interrogation (Box  530 ) by the admission server  435  verifies the presence of the complete video data file, a current segment counter in the admission server  435  is set (Box  540 ) to request the first segment of the requested range of the video data file. The current disk pointer in the admission server  435  is assigned (Box  550 ) the location of the first segment of the requested range. 
   Since the request of the video data is being scheduled at this point, only a portion of the loading P or over all bandwidth for the requested video data file is allocated to the loading (bandwidth) factor L CD  of the disks  480   a,  . . . ,  480   r,  and  495   a,  . . . ,  495   x.  There is, for purposes of this embodiment, an equal probability that any of the video data files or segments of the video data files will be transferred at a given time to the requesting edge server  405   a,    405   b,  and  405   c  and streamed to the client  400   a,    400   b,  and  400   c.  Therefore, a new loading factor for one of the disks  480   a,  . . . ,  480   r,  and  495   a,  . . . ,  495   x  becomes
 
{dot over ( L )} CD   =L   CD   +P/n    Eq. 1
 
where:
         {dot over (L)} CD  is the new loading factor or amount of bandwidth of the disk allocated with the requested segment.   L CD  is the current loading factor or bandwidth of the disk being consumed by the current disk activities.   P is the required bandwidth of the segment being requested.   n is the number of copies of the requested video data file.       

   The new loading factor {dot over (L)} CD  is compared (Box  560 ) to a maximum loading factor (MaxL). If the new loading factor {dot over (L)} CD  exceeds the maximum bandwidth of loading factor (MaxL), the current disk pointer is set (Box  565 ) to the location of the disk containing the next location of the first segment of the requested video data file. The admission server  435  schedules the transfer and sends the disk location of the first segment of the requested video data file to the edge server  405   a,    405   b,  and  405   c  requesting the video data file. The edge server  405   a,    405   b,  and  405   c  contains the player program that streams the requested video data file to a client or clients  400   a,    400   b,  and  400   c  the video data file. The player state is assigned (Box  570 ) the location of the first segment of the video data file. 
   Referring to  FIG. 6 , the admission server  435  transmits (Box  575 ) an authorization to the edge server  405   a,    405   b,  and  405   c  granting the edge server  405   a,    405   b,  and  405   c  permission to admit or request the range (R) with the beginning location (P 1 ) and the ending location (P 2 ) for the segment. The edge server  405   a,    405   b,  and  405   c  assigns (Box  580 ) the event register the code whether the client  400   a,    400   b,  and  400   c  is going to start to stream the segment, to continue to stream the segment, or if the current segment has been viewed sufficiently, to start the processing for accessing the next segment (admit forward). 
   The event register is tested (Box  585 ) and if the segment is to be streamed, the current loading factor L CD  of the disk containing the segments to be streamed is assigned (Box  590 ) the loading factor as determined by Eq. 1. The requested segment is transferred from the disk  480   a,  . . . ,  480   r,  and  495   a,  . . . ,  495   x  location to the edge server  405   a,    405   b,  and  405   c  and then streamed (Box  595 ) to the client or clients  400   a,    400   b,  and  400   c  for viewing. The event register is then assigned (Box  580 ) the codes for the next event of the process and tested (Box  585 ). 
   If, in this case, the client  400   a,    400   b,  or  400   c  has requested that the viewing be stopped, the load factor L CD  is assigned a non-active value of Eq. 1. The admission server  435  allocates the load across all copies of the segment in anticipation of the client  400   a,    400   b,  and  400   c  resuming the request to view the segment of the requested video data file, while recognizing that the request may be rerouted to another copy of the segment of the requested video data file. 
   The event register is assigned (Box  580 ) the code for the next event and tested (Box  585 ). If the current segment is streamed to a predetermined location (approximately midway through the segment) within the video data file, the next segment is scheduled for transfer. If the event register is assigned a code for the admit forward operation, the current segment register is tested (Box  605 ) to determine if the last segment of the range of the requested data file is being streamed. If it is the last segment, the process ends, (Box  610 ). 
   Referring now to  FIG. 7 , if there are more segments to be streamed, the current segment counter is incremented (Box  615 ) and the current disk register is assigned (Box  620 ) the disk location of the next segment to be processed. 
   The disk-loading factor L CD  with the additional loading of the requested segment is assigned as determined by Eq. 1. The newly allocated disk loading factor L CD  is compared (Box  625 ) to the maximum available loading or bandwidth (MaxL). If there is not sufficient allocable bandwidth, the listing of available copies is queried (Box  635 ) to find an available copy of the current requested segment. If all the disks  480   a,  . . . ,  480   r,  and  495   a,  . . . ,  495   x  containing copies of the current segment have their loading factors L CD  or bandwidths fully allocated, the admission server  435  assigns (Box  640 ) a new disk location for the segment to a more lightly loaded disk  480   a,  . . . ,  480   r,  and  495   a,  . . . ,  495   x.  The admission server  435  then directs the distribution server  470  to copy (Box  650 ) the requested segment from the tertiary or backing store  445 . If there is a copy of the currently requested segment or the distribution server  470  has copied the segment to a new disk location, the current disk counter is incremented to point to the location of the next copy (newly copied) of the currently requested segment of the video data file. 
   The loading factor L CD  for the current disk containing the copy of the currently requested segment is again compared  625  to the maximum loading factor (MaxL) of the disk. If the allocated current loading factor L CD  is less than the maximum loading factor (MaxL) or maximum bandwidth of the disk  480   a,  . . . ,  480   r,  and  495   a,  . . . ,  495   x  containing the currently requested segment, the player state is assigned (Box  630 ) the point to the disk location of the currently requested segment. The currently requested segment is processed as described above for  FIG. 5  and the process is repeated until the last segment of the requested range is streamed to the client  400   a,    400   b,  and  400   c,  where the processing ends (Box  630 ). 
   It is apparent that there can be not only multiple copies of a video data file within the video distribution system of this invention, but multiple copies of the segments of the video data file that are further divided into sub-segments as the requests video data files or portions of video data files indicate that new segment sizes are required. The copying of the video data files or segments of the video data files are dynamically copied dependent on the bandwidth allocation of the disks  480   a,  . . . ,  480   r,  and  495   a,  . . . ,  495   x.  Thus, various segments of a video data file may have various numbers of copies on multiple disks  480   a,  . . . ,  480   r,  and  495   a,  . . . ,  495   x  to allow the segments to have the appropriate bandwidth to stream the segments to the clients  400   a,    400   b,  and  400   c.  This allows the viewers to select various segments and the system to adjust the bandwidth accordingly to allow the viewer (client  400   a,    400   b,  and  400   c ) demand. 
   The video distribution system as shown in  FIG. 4  illustrates a system having local cluster networks  455 , and  460 , and the global communication network  415 . It is apparent that the server clusters  410   a  and  410   b  do not require the cluster networks  455  and  460  to virtually construct the server clusters  410   a  and  410   b.  Further, the disks  480   a,  . . . ,  480   r  may be grouped in such fashion that they can be associated with one or more of the server systems  420   a,  . . . ,  420   f.  The generalized structure allows the configuration server  485  to allocate the functions of the system to any of the server systems  420   a,  . . . ,  420   f.  For instance the admission server  435  and the gateway server  475  may in fact be the same computing system and additionally, may be one of the server systems  420   a,  . . . ,  420   f.  Also, any of the edge servers  405   a,    405   b,  or  405   c  may physically be on of the server systems  420   a,  . . . ,  420   f.    
   The segments of the video data files  490   a  are shown as distributed over multiple disks  480   a,    480   b,  and  480   c,  associated with the server system  420   a.  Depending on the file usage factors, and the interactivity factors, various segments or copies of segments  490   a,  . . . ,  490   h  may be placed at other server systems  420   a,  . . . ,  420   f,  on the admission server  435 , the configuration server  485 , or even an edge server  405   a,    405   b,  or  405   c.  The distribution of the segments  490   a,  . . . ,  490   h  allows the balancing of the loading (the amount of data being transferred) of the disks  480   a,  . . . ,  480   r  and disks  495   a,  . . . ,  495   w.  The admission server  435  controls the placement of the segments and sub-segments and will eliminate segments of video data file based on a policy that will erase those segments that are least recently used, starting at the end of a video data file. Thus certain video data files may have a low number of segments present on the disks  480   a,  . . . ,  480   r  of the server systems  420   a,  . . . ,  420   f.  A request for a video data file having segments missing requires that the distribution server  470  recreate the segments of the video data file requested and transfer them to the server systems  420   a,  . . . ,  420   f.  However, those video data file segments at the beginning of the video data file can be transferred to the client system  400   a,    400   b,    400   c  for viewing, while the distribution server  470  is recreating those missing segments. 
   The load or the amount of data being transferred to or from an individual disks  480   a,  . . . ,  480   r  and  495   a,  . . . ,  495   w  is allocated between a read action (transferring the video data file isochronously to a client system  400   a,    400   b,    400   c  for viewing by a user), a write action (transferring the video data file to a disk  480   a,  . . . ,  480   r  and  495   a,  . . . ,  495   w ), or a copy action (a disk to disk transfer of the video data file). The total bandwidth or transfer rate for a single disk is thus divided in the read action, the write action, or the copy action. The load of the is the amount of the total bandwidth consumed for the transfer of the requested video data files resident on the disk. Therefore, the segment size is determined by the number of disks  480   a,  . . . ,  480   r  and  495   a,  . . . ,  495   w  available to contain the video data file (some maybe off line or too full to accept the video data file) and the loading of the available disks. 
   It is well known in the art that while the above describes a system to distribute video data files to client systems, the apparatus is implemented as a program code for execution on a computing system. The program code maybe obtained from media such as storage nodes of the cluster network or the global communication network, or stored on storage media such a read only memory (ROM), or a magnetic disk. The program code executed by the computing system executes the method for segmenting video data files to facilitate the transfer of the video data files. The program executed is as described in  FIG. 6 . 
   While this invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.