Abstract:
A file system for distributing content in a data network, includes a file replication and transfer system and a replicated file receiver system. The file replication and transfer system includes an interface file system which looks for changes made to contents of a file created and stored in an associated work file system; and a file system monitor communicatively associated with the interface filing system for monitoring events occurring with the interface file system and causing copies of the new files to be transferred over the data network to the replicated file receiver system. The interface file system also looks for changes made to the contents of files already stored in the work file system and creates an update file in a mirror file system if a change to the contents of a file stored in the work file system is observed by the interface file system. A collector file system communicatively associated with the mirror file system is provided for temporarily storing a copy of the update file. The replicated file receiver system includes a file construction system for constructing a new version of the file from a copy of the file and the update file; a receiver collector file system for storing the new version of the file; and a receiver interface file system for enabling work to be conducted with an old copy of the file if an open request for the file has been made prior to the construction of the new version of the file, and for enabling work to be conducted with the new version of the file if an open request for the file has been made after the notification that the new version of the file has been constructed.

Description:
PROVISIONAL APPLICATIONS 
     This application claims the benefit of Provisional application 60/211,645 filed Jun. 14, 2000. 
    
    
     RELATED APPLICATIONS 
     Commonly-assigned, copending U.S. patent application, No. 09/439,980, entitled “Nonintrusive Update Of Files”, filed Nov. 12, 1999. 
     FIELD OF THE INVENTION 
     This invention relates to data network systems, and more particularly to file system for distributing content in a data network and methods relating to the same. 
     BACKGROUND OF THE INVENTION 
     Data network usage is growing rapidly due, in part, to the ease of distributing content over the Internet and the World Wide Web (the “Web”), which has been simplified by the emergence of the Hypertext Markup Language (“HTML”) and the Hypertext Transfer Protocol (“HTTP”). Increased data network usage is also due to recent advances in networking technology, which provide ever-increasing storage capacity for content providers, and ever-increasing connection bandwidth for end users. 
     The Internet is an internetwork of networks, routers, backbones, and other switches and connections that separate a source of content from a user. Providing content from a single source to a single user becomes complex for a large, distributed network such as the Internet. Responding to requests from numerous users, who may be widely geographically distributed, and who may present widely varying traffic demands over time, becomes very complex. Inadequate management of network resources may result in the sluggish performance that is familiar to Internet users as slow page loading or outright failure of a request to a server. 
     One approach to this difficulty is to provide “mirror sites,” which are content servers that supply identical content on one or more sites associated with an original content provider. However, mirror sites do not function well in highly dynamic environments, where frequent content changes require frequent mirror updates. Mirror sites are particularly deficient in environments where there are small changes to large files, since there is no efficient mechanism for transmitting incremental file changes to mirrors. 
     Accordingly, a system and/or method is still needed for efficiently distributing content in a data network. Such a system should be scalable to the Internet and transparent to users and content providers. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a file system for distributing content in a data network, comprises a file replication and transfer system and a replicated file receiver system. The file replication and transfer system includes an interface file system which looks for changes made to contents of a file created and stored in an associated work file system. A file system monitor is communicatively associated with the interface filing system monitors events occurring with the interface file system and causes copies of the new files to be transferred over the data network to the replicated file receiver system. 
     According to another aspect of the invention, the interface file system looks for changes made to the contents of files already stored in the work file system and creates an update file in a mirror file system if a change to the contents of a file stored in the work file system is observed by the interface file system. 
     According to a further aspect of the invention, a collector file system communicatively associated with the mirror file system can be provided for temporarily storing a copy of the update file. 
     According to a further aspect of the invention, the replicated file receiver system includes a file construction system for constructing a new version of the file from a copy of the file and the update file. 
     According to a further aspect of the invention, the replicated file receiver system further includes a receiver collector file system for storing the new version of the file. 
     According to a further aspect of the invention, the replicated file receiver system further includes a receiver interface file system for enabling work to be conducted with the copy of the file if an open request for the copy of the file has been made prior to the construction of the new version of the file, and for enabling work to be conducted with the new version of the file if an open request for the copy of the file has been made after the notification that the new version of the file has been constructed. 
     According to a further aspect of the invention, a method for distributing content in a data network comprises creating an update file which records changes made to contents of a file stored in a work file system; generating a notification that the at least one change has been made to the contents of the file stored in the work file system, the notification indicating that the update file reflects all the changes of a version of the file; and distributing the update file over the data network to a receiver work file system. 
     According to a further aspect of the invention, a method for distributing content in a data network, comprises looking for changes made to contents of a file stored in a work file system; creating an update file which records only changes made to the contents of the file stored in the work file system; and distributing the update file over the data network to a receiver work file system; wherein the looking and creating steps are performed in a kernel mode. 
     According to a further aspect of the invention, a method for distributing content in a data network, comprises creating and storing a file in a work file system; generating a notification that the file has been created and stored in the work file system; and distributing a copy of the file over the data network to a receiver work file system. 
     According to a further aspect of the invention, a method for distributing content in a data network, comprises looking for files created and stored in a work file system; and distributing copies of the files over the data network to a receiver work file system operating at a second location; wherein the looking step is performed in a kernel mode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The advantages, nature, and various additional features of the invention will appear more fully upon consideration of the illustrative embodiments now to be described in detail in connection with accompanying drawings wherein: 
     FIG. 1 is a diagram of a file system for distributing content on a data network according to an exemplary embodiment of the present invention; 
     FIG. 2 is a block diagram of the file replication and transfer system according to an exemplary embodiment of the present invention; 
     FIG. 3 is a block diagram of the file system monitor application according to an exemplary embodiment of the present invention; 
     FIG. 4A is a diagram of an update file having a file map appended as a list to an end thereof; 
     FIG. 4B is an enlarged diagram of three file maps; 
     FIG. 4C is an enlarged diagram of a file map created by combining the file maps illustrated in FIG. 4B; 
     FIG. 5 is a timing diagram that illustrates how the file replication and transfer system processes write, read and delete requests generated from one or more application processes; 
     FIG. 6 is a timing diagram that illustrates how the file update replication and transfer system of the present invention processes close requests generated from one or more application processes and prepares the update file for transfer; 
     FIG. 7 is a block diagram of the replicated file receiver system according to an exemplary embodiment of the present invention; and 
     FIGS. 8A and 8B illustrate how the replicated file receiver system on each of the servers at the mirror sites works with both the new and old versions of a file. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The file system of the present invention, as described with reference to following illustrative embodiments, is especially applicable to data networks such as the Internet. It should be understood, however, that the file system described herein may be suitably adapted to any other data network used for distributing content, including wide area networks, metropolitan area networks, virtual private networks, and the like. The file system of the present invention is particularly applicable to those environments requiring distribution of large amounts of data that may be changed from time to time. Furthermore, the file system of the present invention can be adapted for use with virtually any conventional operating system including but not limited to Microsoft Windows 95, Microsoft Windows NT, or Unix and its variants. 
     As used herein, the term content can be any media that may be stored in a digital form, including text, data files, program files, application documents such as word processing or spread sheet documents, still or moving graphical images, sound files, applications, applets, HTML documents, DHTML documents, XML documents, forms, or any combination of these. Content may also be real-time media such as streaming media. 
     FIG. 1 diagrammatically illustrates a file system for distributing content on a data network according to an exemplary embodiment of the present invention. The file system comprises a file replication and transfer system  10  on a file storing and serving device  20  at a master site  30  and a plurality of replicated file receiver systems  40  on respective file storing and serving devices  50  at remotely located mirror sites  60 . The file storing and serving devices  20 ,  50  typically comprise conventional file servers or any other suitable device for storing and serving files. The file storing and serving devices  20 ,  50  at the master and mirror sites  30 ,  60  are communicatively connected by a network, which may be any private or public network, or any mix thereof, suitable for carrying data. The mirror sites  60  may be geographically distributed, for example, on regional backbones of the Internet. The file storing and serving devices  50  at each mirror site  60  may include a copy of the files stored on the file storing and serving device  20  at the master site  30 . The file storing and serving device  50  at the mirror sites  60  may also be communicatively connected with one another so that file changes can be distributed among the file storing and serving devices  50  at the mirror sites  60 . One of the primary goals of the file system of the present invention is to look for changes made to existing files on the file storing and serving device  20  at the master site  30  and new files created on the file storing and serving device  20  at the master site  30 , replicate these files changes and new files and transfer the replicated file changes and new files to one or more of the file storing and serving devices  50  at the mirror sites  60  as will be described in greater detail below. 
     FIG. 2 is a block diagram of the file replication and transfer system  10  according to an exemplary embodiment of the present invention. The file replication and transfer system  10  comprises: an interface file system  101 ; a mirror file system  102 ; a collector file system  103 ; and a file system monitor  104 . The interface file system  101  is mounted or stacked on top of the file storing and serving device&#39;s  20  work file system  105  and responds to calls from, and returns data to, an input/output (I/O) library  106  which converts user mode requests or commands from an application process  124  into kernel mode system calls that invoke certain events from the interface file system  101 . 
     The work file system  105 , on top of which the interface file system  101  is mounted, may include a work directory  107 , a disk driver  108  and a disk drive  109 . The mirror file system  102  may include a mirror directory  110 , a disk driver  111  and a disk drive  112 . The collector file system  103  may include a collector directory  113  a disk driver  114  and a disk drive  115 . The file system monitor  104  may include a file system monitor application  116 , a spool directory  117 , a disk driver  118 , a disk drive  119 , and an input/output (I/O) library  120 . The operations and interactions which take place between the directories  107 ,  110 ,  113 ,  117  and their associated disk drivers  108 ,  111 ,  114 ,  118  and disk drives  109 ,  112 ,  115 ,  119  are well known in the art and, therefore, need not be discussed further herein. The file system monitor&#39;s input/output (I/O) library  120  converts user mode file system monitor application requests or commands into kernel mode system calls that invoke certain events from the spool directory  117 . 
     It should be noted that the disk drives  109 ,  112 ,  115 ,  119  utilized in the work, mirror, and collector file systems  105 ,  102 ,  103  and the file system monitor  104  are exemplary and may be replaced by other physical or virtual memory devices in other embodiments of the present invention. For example the disk drives  109 ,  112 ,  115 ,  119  may be partitions or directories of a single disk drive. However, persons of ordinary skill in the art will recognize that separate physical memory devices are preferred as they usually improve efficiency where access to the disk drives  109 ,  112 ,  115 ,  119  is made independently or simultaneously, or if the mirror and collector disk drives  112 ,  115  actually share the same physical disk device. 
     FIG. 3 is a block diagram of the file system monitor application  116  according to an exemplary embodiment of the present invention. The file system monitor application, which is a key component of the file system monitor  104 ,  116  may include a compression utility  121 , an output queue  122  and a network transfer utility  123 . The file system monitor application  116  and the interface file system  101  communicate with each other through any suitable protocol. This permits the file system monitor application  116 , which runs in the user mode, to monitor asynchronous events occurring with the interface file system  101  in the kernel mode. With the knowledge of events occurring with the interface system  101 , the file system monitor  104  causes the collector, mirror, and work file systems in the kernel mode to transfer replicated file updates and/or replicated newly created files (generated in the work file system) to the file system monitor&#39;s the spool directory  117 , where they will then be transferred at the appropriate time to the replicated file receiver systems on the servers at the mirror sites. 
     Referring collectively now to FIGS. 2 and 3, the general operation of the file replication and transfer system  10  of the present will now be described. In the user mode, the application process  124  generates a request or command for a file. The application process  124  may be any computer application that might operate on a file. The application process  124  may dictate a specific user mode request for a file, by which a user or process may read data from, or write data to a file. The I/O library  106  on the user level converts the file request into a system call suitable for a kernel mode. System calls may include, for example, open calls, close calls, read calls, write calls, create file calls, delete file calls, rename file calls, change attribute file calls, truncate file calls, and the like. The file storing and serving device&#39;s  20  operating system kernel (not illustrated), in response to the system call generated in the kernel mode by the I/O library  106 , sends the call to the interface file system  101 . The interface file system  101  passes the system call to the work file system  105  for conventional processing without any interruption. The interface file system  101  will also replicate the system call, if it relates to a file change or deletion, and send the replicated call to the mirror file system  102 . In response to the system call, the mirror file system  102  will create and store a record representative of the file change (update file). The update file replicates the changes made to the corresponding file stored in the work file system. 
     At an appropriate time as requested by the file system monitor  104 , update files may be copied from the mirror file system  102  to the collector file system  103 . When appropriate, the file system monitor  104  will then request the update file to be copied from the collector file system  103  to its spool directory  117 . In the case of a new file written to the work file system  105 , when appropriate, the file system monitor  104  will request the new file to be copied directly from the work file system  105  to its spool directory  117 . As the update file or replicated new file is copied to the spool directory, the compression utility  121  of the file system monitor application  116  may be employed to compress the file if necessary. For example, if the file is already well compressed, such as in the case of a MPEG or JPEG encoded file, compression via the compression utility  121  would not ordinarily be required. The file system monitor application  116  may also perform additional functions, such as encryption of the update files and new files, and may include any other control, authentication, or error correction information along with the update file data for transmission therewith, or in a header appended thereto. For example, authentication may be performed using MD4, MD5, double MD5 (e.g., E=MD5(key1,MD5(key2, pass)), or any other one-way hash function or other suitable authentication scheme. 
     A further function of the file system monitor  104  includes using the information obtained from the knowledge of the events occurring with the interface file system  101 , which may contain details concerning control information, file size, and offsets, to create a file map of the update file. The file map and possible other subsequent file maps corresponding to changes made to the update file are generated by the network transfer utility  123  and appended as a list to the end of the update file as shown in FIG. 4A, when the network transfer utility  123  transfers the file from the spool directory  117  to the replicated file receiver systems  40  on the servers  50  at the mirror sites  60 . A pointer, which comprises some type of data, is used to identify where the list begins, i.e., identifies the list offset. The file map enables the replicated file receiver systems  40  on the servers  50  at the mirror sites  60  to construct a new version of the corresponding existing file stored thereon using the data from the update file and the data from the existing file. A truncate file call may be presented in the map as a separate field. 
     The file map also enables the file system monitor  104  to optimize the update file prior to its transfer to the mirror sites. For example, if the file system generates three maps for a particular update file (indicative of two subsequent changes made to the update file), as illustrated in FIG. 4B, data in two or more of these maps may be combined into a single map as illustrated in FIG. 4C, if the data in the maps overlap. Thus, only the single map need be appended to the update file when it is transferred. 
     Referring again to FIGS. 2 and 3, as the replicated update file (or replicated new file) is copied to the spool directory  117  of the file system monitor  104 , file information is transmitted to the queue  122  in the file system monitor application  116 . The network transfer utility  123  of the file system monitor application uses queuing information obtained from the queue  122  to transfer the update files and/or replicated new files stored in the spool directory over the network to the replicated file receiver systems  40  running on the servers  50  at the mirror sites  60 . 
     The file replication and transfer system  10  of the present invention uses the transparency of the kernel mode to the user mode in a manner that permits it to transparently track changes made to files stored in the server  20  at the master site  30  or track new files created on the server  20  at the master site  30 . By tracking changes in the kernel mode, user mode application processes may make changes to files stored in the server hardware level, and these changes may be tracked without any explicit action in the user mode. Tracking changes in the kernel mode in accordance with the present invention, also permits incremental changes to be sent to the replicated file receiver systems  40  operating on the servers  50  at the mirror sites  60  without transmitting and replacing potentially large files. 
     FIG. 5 illustrates how the file replication and transfer system  10  of the present invention may process write, read and delete requests generated from one or more application processes. At time T 1 , the application process  124  submits a write request to write to a file stored in the work file system  105 , and the I/O library  106  (FIG. 2) outputs an appropriate call such as write (fd, offset, *data, data_size) to the kernel  125 . The write call may include a file descriptor fd (generated in a previously processed open call open(fname)) that provides a method for identifying which file stored in the work file system  105  is to be changed. The write call will also include information about what is going to be written to the file, i.e., offset, *data, and data_size. At time T 2 , the kernel  125  sends the write call to the interface file system  101 . At time T 3 , the interface file system  101  passes the write call to the work file system  105 , which responds to the call by writing the data_size bytes of data pointed to by the pointer, *data, to the file stored therein identified by fd, at a location within that file defined by the offset. 
     At time T 3 , the interface file system  101  also replicates the write call write (fd, offset, *data, data_size) and sends it to the mirror file system  102 . In response thereto, the mirror file system  102  creates and stores an update file that replicates only the new data just written to the file fd in the work file system  105 . The update file has a size equal to the file fd stored in the work file system  105 , i.e., data_size plus the offset, but includes only the new data submitted in the write call. Since the update file includes only data changes resulting from the write call, it is highly compressible. Any subsequent changes written to the file fd in the work file system  105  will be recorded in the update file in the mirror file system  102 , while subsequent changes to different files in the work file system  105  will respectively result in the creation of additional update files in the mirror file system  102 . 
     At time T 4 , the interface file system  101  sends an event to the file system monitor  104  which indicates that the mirror file system  102  has created and stored an update file which represents the new data written to file fd in the work file system  105 . This event includes parameters for generating a file map. As discussed earlier, this and any other maps corresponding to changes made in the update file will be appended as a list to the end of the update file. 
     The interface file system  101  is transparent for read system calls. For example, at time T 5 , the application process  124  may submit a read request to read the file fd stored in the work file system  105 . In response thereto, the I/O library  106  outputs an appropriate call such as read(fd) to the kernel  125 . At time T 6 , the kernel sends the read call to the interface file system  101 . At time T 7 , the interface file system  101  simply passes the read call to the work file system  105  where it is conventionally processed. Because read system calls require no changes to the file fd, no action is taken by the interface file system  101 , therefore no event is sent to the file system monitor  104 . 
     At time T 8 , the application process may then submit a delete request to delete the file fd stored in the work file system  105 . The I/O library  106 , therefore, outputs an appropriate call such as delete (fd) to the kernel. At time T 9 , the kernel sends the delete call to the interface file system  101 . At time T 10 , the interface file system  101  passes the delete call to the work file system  105 , which results in deletion of the file fd. The interface file system  101  also replicates the delete call and sends it to the mirror file system  102 , which results in deletion of the corresponding update file from the mirror file system  102 . (The interface file system  101  takes no action if no corresponding update file exists in the mirror file system  102 .) At time T 11 , the interface file system  101  sends an event to the file system monitor  104  which indicates that the mirror file system  102  has deleted the update file. When this happens, file map information corresponding to that file is deleted from the file system monitor  104 . Note that the system actions from time T 8  to time T 11  also take place when a file is renamed, truncated or its attributes are changed. 
     FIG. 6 illustrates how the file update replication and transfer system of the present invention may process close requests generated from one or more application processes and may prepare the update file for transfer. For the sake of clarity, only critical interactions are described as one of ordinary skill in the art will recognize that other less critical interactions may be taking place, such interactions being well known in the art. At some moment in time, it will become desirable to transfer an update file stored in the mirror file system to the replicated file receiver systems  40  of the servers  50  at the mirror sites  60  (FIG.  1 ). If the update file is transferred at this time, it may still be open and receiving writing changes from one or more application processes and, therefore, may be inconsistent. Thus, in order to ensure the consistency of the data in the update file, i.e., the update file reflects all the changes of some version of the a file fd, when possible (just as the version of the file fd comes into existence), the kernel  125  sends a clean-up event or any other equivalent notice to the update file system  101 . This will typically happen when close calls close(fd) are received by the kernel via the I/O library  106  (FIG. 2) from each open application process  126 ,  127 ,  128  such as at times T 1 , T 2 , and T 3 . When the last application process  128  has closed the file in the work file system  105 , such as at time T 4  the kernel  125  will then send the aforementioned cleanup event to the interface file system  101 . The cleanup event enables the interface file system  101  to know that the file in the work file system  105  is finally closed. At time T 5 , the interface file system  101  passes the cleanup event to the work file system  105  for processing. At time T 6 , the interface file system sends a request to the kernel  125  to close the update file in the mirror file system  102 . At time T 7 , the kernel sends a cleanup event to the mirror file system  102 , which closes the update file, resulting in a version thereof (with consistent data) in the mirror file system  102 . At time T 8 , the interface file system  101  sends an event to the file system monitor  104 , which indicates that some version of the update file is now stored in the mirror file system  102 . 
     At some time T 9 , the transfer process commences under the control of the file system monitor  104 , which sends a special request to the interface file system  101 . In response thereto, the interface file system  101  may copy the update file in the mirror file system  102  to the collector file system  103 , or it may postpone the copy if the file in working file system  105  and the update file in the mirror file system  102  are open again by some application. At some time T 10  the interface file system  101  copies the update file in the mirror file system  102  to the collector file system  103 . At some time T 11  the interface file system sends an event to the file system monitor  104 , which indicates that some version of the update file is now stored in the collector file system  103 . The copy command may alternatively result in only a renaming of the update file when the file systems reside on the same partitions of a disk drive and no physical relocation is required to reflect the file&#39;s reassignment to the new file system. 
     Then at some other moment in time T 12 , the file system monitor  104  may send a second copy command to the kernel  125 . This copy command causes the update file to be copied from the collector file system  103  to the spool directory  117  of the file system monitor  104 . As the update file is copied to the spool directory  117 , it may be compressed by the compression utility  121  of the file system monitor application  116  if deemed necessary. Once in the spool directory  117 , the update file can be transferred to the replicated file receiver systems  40  on the servers  50  at the mirror sites  60 . 
     FIG. 7 is a block diagram of the replicated file receiver system  40 , on each of the servers at the mirror sites, according to an exemplary embodiment of the present invention. The replicated file receiver system  40  typically comprises: a receiver interface file system  201 ; a receiver collector file system  202 ; and a file construction system  203 . The receiver interface file system  201  is mounted or stacked on top of the mirror server&#39;s  50  receiver work file system  204  and responds to calls from, and returns data to, an input/output (I/O) library  215  which converts user mode requests or commands from an application process  217  into kernel mode system calls that invoke certain events from the receiver interface file system  201 . 
     The receiver work file system  204  may include a receiver work directory  205 , a disk driver  206  and a disk drive  207 . The receiver collector file system  202  may include a receiver collector directory  208  a disk driver  209  and a disk drive  210 . The file construction system  203  may include a file construction application  211 , a receiver spool directory  212 , a disk driver  213 , a disk drive  214 , and an input/output (I/O) library  216 . The operations and interactions which take place between the directories  205 ,  208 ,  212  and their associated disk drivers  206 ,  209 ,  213  and disk drives  207 ,  210 ,  214  are well known in the art and, therefore, need not be discussed further herein. The input/output (I/O) library  216  of the file construction system  203  converts user mode file construction system application requests or commands into kernel mode system calls that invoke certain events from the receiver spool directory  212 . 
     It should be noted that the disk drives  207 ,  210 ,  214  utilized in the receiver work and collector file systems  204 ,  202  and the file construction system  203  are exemplary and may be replaced by other physical or virtual memory devices in other embodiments of the present invention. For example the disk drives  207 ,  210 ,  214  may be partitions of a single disk drive. However, persons of ordinary skill in the art will recognize that separate physical memory devices are preferred as they usually improve efficiency where access to the disk drives  207 ,  210 ,  214  is made independently or simultaneously. 
     The file construction system  203  receives data pertaining to update files or new files from the network (transferred from the file replication and transfer system  10  on the master site server  20 ). The file construction application  211  decodes this data to create a copy of the update file in the receiver spool directory  212 . The file construction application  211  can be adapted to decode data encoded in any conventional manner. 
     In the case of new files, the file construction application  211  copies the new file stored in the receiver spool directory  212  directly to the receiver work file system  204  and sends a notification of this to the receiver interface file system  201 . In the case of update files, the file construction application  211  reads the update file stored in the receiver spool directory  212  and reads the corresponding existing or “old” version of the file stored in the receiver work file system  204  and constructs a new version of the file in the receiver collector file system  202 . The file construction application  211  then deletes the update file from the receiver spool directory  212  and sends a notification of this to the receiver interface file system  201 . 
     FIGS. 8A and 8B illustrate how the replicated file receiver system  40  on each of the servers  50  at the mirror sites  60  works with both the new and old versions of a file. Referring first to FIG. 8A, assume for example, in an initial state, the receiver work file system  204  is storing one or more “old” files and that the receiver collector file system  202  is empty. At time T 1 , a first application process  218  submits an open request to open an old file (fname), and the receiver I/O library  215  outputs an appropriate system call such as open (old fname) to the receiver kernel  220 . At time T 2 , the receiver kernel  220  (mirror site file storing and serving device  40  operating system kernel) sends the open call to the receiver interface file system  201 . At time T 3 , the receiver interface file system  201  passes the open call to the receiver work file system  204  which responds to the call at time T 4  by returning a file descriptor (fd 1 ) to the receiver interface file system  201 . At time T 5 , the receiver interface file system  201  returns the file descriptor (fd 1 ) to the receiver kernel  220  and at time T 6 , the receiver kernel  220  returns the file descriptor (fd 1 ) to the first application process  218 . At time T 7 , the first application process  218  submits a read request to read the file (fd 1 ), and the receiver I/O library  215  outputs an appropriate system call such as read (fd 1 ) to the receiver kernel  220 . At time T 8 , the receiver kernel  220  sends the read call to the receiver interface file system  201 . At time T 9 , the receiver interface file system  201  passes the read call to the receiver work file system  204  which responds to the call at time T 10  by sending “old” data (fd 1 ) to the receiver kernel  220  (the “old” data passes through the receiver interface file system  201 ) and at time T 11 , the receiver kernel  220  sends the “old” data (fd 1 ) to the first application process  218 . 
     At time T 12 , an event is sent by the file construction application  211  indicating that a new version of the file name) has been created and stored in the receiver collector file system  202 . At time T 13 , a second application process  219  submits an open request to open the old file (fname), and the receiver I/O library  215  outputs open call open (old fname) to the receiver kernel  220 . At time T 14 , the receiver kernel  220  sends the open call to the receiver interface file system  201 . Because the receiver interface file system  201  is aware of the new version of the file fname) stored in the receiver collector file system  202 , at time T 15 , the receiver interface file system  201  generates and sends an open call open (new fname) to the receiver collector file system  202  and does not pass the open call open (old fname) to the receiver work file system  204 . At time T 16 , the receiver collector file system  202  by returns a file descriptor (fd 2 ) to the receiver interface file system  201 . At time T 17 , the receiver interface file system  201  returns the file descriptor (fd 2 ) to the receiver kernel  220  and at time T 18 , the receiver kernel  220  returns the file descriptor (fd 2 ) to the second application process  219 . At time T 19 , the second application process  219  submits a read request to read the file (fd 2 ), and the receiver I/O library  215  outputs a read call read (fd 2 ) to the receiver kernel  220 . At time T 20 , the receiver kernel  220  sends the read call directly to the receiver collector file system  202 , which responds to the call at time T 21  by sending “new” data (fd 2 ) to the receiver kernel  220  and at time T 22 , the receiver kernel  220  sends the new data (fd 2 ) to the second application process  219 . 
     As should now be apparent, when the receiver interface file system  201  becomes aware of a new file version in the receiver collector file system  202 , it modifies all open system calls from subsequent application processes and opens the new version of the file stored in the receiver collector file system  202 . Accordingly, all application processes generating open system calls prior to the creation of the new file version work with the receiver work file system  204  and read the old version of the file and all application processes generating open system calls after the creation of the new file version work with the receiver collector file system  202  and read the new version of the file. Consequently, if at time T 23  the first application process  218  submits another read request to read the file (fd 1 ), at time T 24  the receiver kernel  220  will send the read call to the receiver interface file system  201  which in turn will pass the read call at time T 25  to the receiver work file system  204 . Thus, old data (fd 1 ) will be returned to the first application process  218 . 
     Referring now to FIG. 8B, at time T 26 , the first application process  218  submits a close request to close the old file (fd 1 ), and the receiver I/O library  215  outputs a close call close (fd 1 ) to the receiver kernel  220 . If the first application process  218  is the last application process to closed the file, at time T 26  the receiver kernel  220  will send a cleanup event for old file (fd 1 ) to the receiver interface file system  201 . At time T 28 , the receiver interface file system  201  sends a command to the receiver kernel  220  to copy the new version of the file, which results copying of the new version of the file to the receiver work file system  204  at time T 29 . Thus, the new version of the file takes on the status of the “old” or existing version of the file in the receiver work file system  204 . The copying process is similar to the copying process described earlier in the discussion of the file replication and transfer system  10 . 
     At time T 30 , the second application process  219  submits a read request to read the file (fd 2 ), and the receiver I/O library  215  outputs a read call read (fd 2 ) to the receiver kernel  220 . At time T 31 , the receiver kernel  220  sends the read call directly to the receiver collector file system  202 , which responds to the call at time T 32  by sending new data (fd 2 ) to the receiver kernel  220  and at time T 33 , the receiver kernel  220  sends the new data (fd 2 ) to the second application process  219 . 
     At time T 34 , a third application process  221  submits an open request to open the old file (fname), and the receiver I/O library  215  outputs open call open (old fname) to the receiver kernel  220 . At time T 35 , the receiver kernel  220  sends the open call to the receiver interface file system  201 . At time T 36 , the receiver interface file system  201  sends the open call to the receiver work file system  204 . At time T 37  the receiver work file system  204  returns a file descriptor (fd 3 ) to the receiver interface file system  201 . At time T 38 , the receiver interface file system  201  returns the file descriptor (fd 3 ) to the receiver kernel  220  and at time T 39 , the receiver kernel  220  returns the file descriptor (fd 3 ) to the third application process  221 . 
     At time T 40 , the second application process  219  submits a close request to close the new file (fd 2 ), and the receiver I/O library  215  outputs a close call close (fd 2 ) to the receiver kernel  220 . If the second application process  219  is the last application process to closed the new file (fd 2 ), at time T 41  the receiver kernel  220  will send a cleanup event for the new file (fd 2 ) to the receiver interface file system  201 . At time T 42 , the receiver interface file system  201  sends a command to the receiver kernel  220  to delete the new version of the file, which results in the deletion of the new version of the file from the receiver collector file system  202  at time T 43 . 
     While the foregoing invention has been described with reference to the above embodiments, various modifications and changes can be made without departing from the spirit of the invention. Accordingly, all such modifications and changes are considered to be within the scope of the appended claims.