Patent Publication Number: US-7725588-B2

Title: Switching method and switch device

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a switch logically disposed between a client and a server, and more specifically to a switch which is disposed in a client server system in which a remote file system is implemented for executing file processing through a network, and provides a single system image (SSI) transparent to the client and network traffic control such as load distribution. 
   2. Description of the Related Art 
   As a method for realizing a client server system through a network a famous method is known, which employs a network file system (NFS) protocol disclosed in RFC (Request For Comments) 1094 and RFC 1813. The NFS protocol provides basic operations as a file system such as creation, deletion, read/write operation, movement and the like of a file for a server located at a remote place through a network, and convenience such as sharing of files with other clients. In the NFS protocol, a client employs an object ID for identifying an object such as a file on a server to access the server through an application interface such as a remote procedure call (RPC). In the NFS, one called a file handle is employed as the object ID, for example. 
   In the following, conventional techniques concerning the switch device will be described for every item: 
   Layers 4 to 7 Switches: 
   As a implementation of a network file system there are widely known ones based upon an OSI (open Systems Interconnection) reference model of the so-called IP (Internet Protocol) network, and in an ordinary router and the like it is widely known that use is made of information up to a layer 3 of the OSI model, i.e., information on a physical layer, a data link layer and a network layer for path control. Further, in recent years, use is made of information from the layer 4 to the layer 7 of the OSI reference model, i.e., information on a transport layer, a session layer, a presentation layer, and an application layer for provision of varieties of convenience. 
   A network switch device for judging the kind of a protocol of a packet sent by making use of the information of the layer 4 and distributing it to a corresponding server for each protocol is widely utilized in, for example, web hosting services. Further recently, there is reported as a product one for realizing server distribution for each web content utilizing the layer 7 information. A major object of these techniques is load distribution of the server and control of an access policy to the server. The access policy includes execution of an SSL (Secure Socket Layer) processing for recognizing a user on a single server, and perusal limitation for every ages, and the like. Upon executing the SSL processing switching of servers for the purpose of load distributed and so on is generally prohibited. The switch device serves as logical packet switch. 
   Referring to  FIG. 1  there is provided a block diagram illustrating a function of a conventional web switch. Web switch  900  comprises packet processing unit  903 , and HTTP (Hypertext Transfer Protocol) processing unit  902 . After a received packet processing is executed in packet processing unit  903 , HTTP processing unit  902  collects information concerning the layer 4 to layer 7, and takes out information concerning URL (Uniform Resource Locator) classified to the layer 7. Further, HTTP processing unit  902  retrieves and specifies on the basis of information concerning the URL taken out a server to treat the URL, taking it&#39;s address, and policy of load distributed and the like. HTTP processing unit  902  further converts a MAC (Media Access Control) address and an IP address of an original packet by executing conversion from a global address to a local address, i.e., NAT (Network Address translator) conversion, and rewriting a MAC address by virtual IP clustering described later such that a packet is transferred to a server thereof, and corrects contradiction of security such as check sum following the conversion. Packet processing unit  903  sends a rewritten and corrected packet onto a network. 
   Besides the aforementioned switch device varieties of techniques for load distributed and the so on have been disclosed. There is widely known as such a technique a method wherein each DNS (Domain Name Server) disposed in each network area forces a plurality of IP addresses to bring into correspondence to one domain name, and selects an IP address with the round robin system and transmits it to a client, for example. 
   Virtual IP Clustering: 
   There is known a method wherein a coordinator who defines a virtual IP address as a cluster address, which virtual address is set to a plurality of servers as an IP alias, and serves as a switch redirects a packet to a proper server by rewriting a MAC address for load distribution. In such a method, each server sets the virtual IP address as the IP alias, so that a client looks that as if one server responds thereto. In the present method, a response can be returned directly from a client from a corresponding server without mediating the coordinator. The method that directly returns the response has an advantage that a bottleneck is unlikely to occur, compared with a method where a packet passes the coordinator even for a return path. The present method and methods where an improvement is added to the present method to some degree is widely known at present as one constituting method of a clustering system using an OS (Operating System) such as Linux. 
   Japanese Laid-Open Patent Publication No. 2001-51890 (JP, P2001-51890A) discloses another method in which a client may not recognize the number of a plurality of file servers dispersed on a network such as a LAN (Local Area Network) and a connection state of a storage device. As illustrated in  FIG. 2 , a client server system that executes the just-mentioned method includes a plurality of file servers  3  which are dispersed on network  2 , and connected with each other through inter-server exclusive line  7 , and further shares a multicast address in common virtual distributed file system  4  that operates over respective file servers  3  is implemented. A module on each file server  3  constituting the just-mentioned system, once receiving a multicast file operation request from client  1  judges whether or not a server of itself is an optimum server capable of processing the aforementioned request by making use of a mapping table of virtual distributed file system  4  and entire local file system  6 , and processes the requested file operation based upon a judged result without overlapping on other file servers  3 . Hereby, the plurality of file servers  3  distributed on the network can be treated as a single server, viewed from client  1 , so that a virtual distributed file server system can be provided, in which system the number of servers  3  and a connection state with the storage device are not recognized by client  1 . 
   However, when the aforementioned techniques are applied to a file system service through a distributed network, the following problems happen: 
   (1) Even a method employing a layer 4 to 7 switch and even a method employing virtual IP clustering suffer from a difficulty that contents rewritten upon redirection of a packet are limited to a MAC address or an IP address. For this, when in a protocol in which a client stores an object ID such as a file handle of NFS in a cache, an administrator executes an operation which does not require the need of informing a client for the purpose of load distribution and capacity distribution, for example when an object is moved from a server once allocated to a client to another server, the client accesses the server while accommodating an object ID of an old server in the packet. Accordingly, even though the switch transfers the packet to a new server, the new server fails to read the object ID in the packet and sends back an error to the client. More specifically, in the file system service mediating a load distributed network, transparency to the client can not been realized even when a conventional method of load distribution is applied; 
   (2) There is essential an improvement for a file server which is already utilized by a user upon setting the IP alias and introduction of the virtual distributed file system. Accordingly, when a file system of an existing client server is operated, for obtaining convenience provided while intactly utilizing a construction of the foregoing client server complicated installation work happens even when only a purpose of the load distribution is solved. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a switching method wherein it provides, provided that a client and a server support only a file system service protocol (e.g., NFS) through a standard network, a file service of a single system image to the client by integrally managing a plurality of servers without modifying those existing systems, and it realizes convenience of hiding relocation of an object due to management purposes of load distribution and capacity allocation thereby maintaining SSI processing or the like. 
   It is another object of the present invention to provide a switch device which provides a file service of a single system image to a client, provided that a client and a server support only a file system service protocol (e.g., NFS) mediating a standard network, by integrally managing a plurality of servers without modifying those existing systems, and realizes convenience of hiding relocation of an object due to control purposes of load distribution and capacity allocation thereby maintaining SSI processing or the like. 
   According to a first aspect of the present invention, there is provided a switching method, at a switch device which is logically disposed between at least one client and at least one server for managing at least one object, for transferring a request on the object transmitted from the client to the server which manages the object, and for transferring a reply against the request from the server to the client which is a source of the request, the switching method comprising the steps of: 
   rewriting, when in the transferred reply an original object ID which is generated by the server is contained for identifying the object, the original object ID to an information entraining object ID by inserting server identifying information for identifying the server for managing an object corresponding to the original object ID from other servers; 
   restoring the information entraining object to the original object ID when the information entraining object ID is contained in the transferred request; 
   estimating address information of the server corresponding to the server identification information contained in the information entraining object ID of the transferred request with reference to a first table for managing a combination of the address information of the server and the server identification information; and 
   determining a destination of the request based upon the address information. 
   According to a second aspect of the present invention there is provided a switching method, at a switch device which is logically disposed between at least one client and at least one server for managing at least one object, for transferring a request on the object transmitted from the client to the server which manages the object, and for transferring a reply against the request from the server to the client which is a source of the request, the switching method comprising the steps of: 
   estimating server identification information corresponding to an object ID contained in the request with reference to a first table for managing a combination of the object ID and server identification information for identifying a server for managing an object corresponding to the original object ID from other servers; 
   estimating address information of a server corresponding to the server identification information with reference to a second table for managing a combination of address information of the server and the server identification information; and 
   determining a destination of the request based upon the address information. 
   According to a third aspect of the present invention, there is provided a switch device disposed logically between at least one client and at least one server for managing at least one object, in which a request on the object transmitted from the client is transferred to the server for managing the object, and in which a reply to the request from the server is transferred to a client being the source of the transmission, the switch device comprising: 
   object ID rewrite means for rewriting, when an original object ID generated in the server for a purpose of identifying the object is contained in the request to be transferred, the original object ID to an information entraining object ID by inserting server identification information for identifying an object corresponding to the original object ID, and for restoring, when the information entraining object ID is contained in the request to be transferred, the information entraining object ID to the original object ID; 
   a first table for managing a combination of address information of the server and the server identification information; and 
   transfer means for estimating address information of a server corresponding to the server identification information contained in the information entraining object ID of the request to be transferred with reference to the first table, and determining a transfer destination based upon the address information. 
   In accordance with the switch device according to the present invention, the switch device includes a switch capable of bring into correspondence a server for managing an object and an object ID of the just-mentioned object, and provides the object ID transmitted to the client with identification information of a server for managing the object. With such arrangement, when the client tries to access its object in succession, server identification information for controlling the object is contained in an object ID in a request transmitted by the client, so that the switch device can determine a server of a destination from the server identification information contained in the request. Accordingly, application of the switch device of the present invention eliminates the need of specifying the server for managing the object on the side of the client, so that transparency to the client can be realized. 
   Even when the switch device of the present invention is applied, it is eliminated to need alteration of processings for the client and the server. Provided that the client and the server therefore support only a file system service protocol mediating a standard network, it is possible to integrally control a plurality of servers without modification of an existing system for providing a file service of the SSI to the client. 
   It is preferable in the switch device that common object unit identification information for identifying a common object unit being a unit where an object is exported to the public is contained in the foregoing server identification information. Hereby, very fine transfer control in the common object unit having further higher resolution than the server unit can be realized. 
   In the present invention, the switch device may further comprises: a classification table for associating the request and the reply, and managing a combination of tag information in an OSI model layer 4 or lower useable for uniquely specifying a combination of the client and the server and address information of the client; and second transfer means for estimating address information of the client to which a reply should be transferred, and determining a destination of the reply based upon the address information. Otherwise, the switch device may further comprises: a classification table for associating the request and the reply, and managing a combination of a communication session/port number with a server useable for uniquely specifying a combination of the client and the server and address information of the client; and second transfer means for estimating address information of the client to which a reply should be transferred with reference to the port number and the classification table, and determining a destination of the reply on the basis of the address information. By providing the classification table and the second transfer means the tag information of the OSI model layer 4 or lower to which hardware processing is possible becomes useable to ensure further higher processing. 
   Further, in the switch device of the present invention, it is desirable that insertion locations and data lengths of the algorithm identification information and the server identification information in the information entraining object IDs contained in all the request and reply are same. It is hereby made possible to reduce the time required for extracting and retrieving the information contained in the object ID. 
   In another switch device according to the present invention further comprises: a pseudo file system in which directory trees of an object exported to the public from the server are combined for managing them as one integrated directory tree; a second table for managing a combination of an object ID of an object corresponding to a joint of directory trees in each common object unit in the integrated directory tree and instruction information which is associated with the object ID and requires an access to a plurality of destinations; and file system control means for dividing, when a combination of an object ID and instruction information both contained in a request to be transferred is entered in the second table, the request to request transferred to each destinations, and assembling all requests received from each destination as a reply transferred to the client. In this switch device, there is executed a name solving processing only for a tree portion to which a plurality of servers or a plurality of file systems are combined with reference to the integrated directory tree of the pseudo file system, and other tree portions are entrusted to the server in their processing. Hereby, a load of the name solving processing can be distributed between the switch and the server. It is herein desirable in view of making the retrieval processing effective that an object ID registered in the second table is the same information entraining object ID as an object ID contained in the request. 
   Another switch device according to the present invention further comprises: a second table for managing a combination of a movement source object ID, when an object exported to the public by the server is subjected to movement, of the object before the movement, a movement destination object ID of the object after the movement, and movement destination server identification information being identification information for a server at a movement destination; data movement processing means for moving the object based upon a predetermined criteria with reference to an integrated directory tree managed by the pseudo file system, and entering the movement source object ID, the movement destination object ID and the movement destination server identification information of the object in the second table; and movement hiding means for altering, when an object ID contained in a request to be transferred is coincident with the movement source object ID in the second table, the object ID to a movement destination object ID corresponding to the coincident the movement source object ID, and determining a transmission destination server based upon movement destination server identification information corresponding to the movement source object ID. Since in this switch device then movement hiding means is provided which is capable of bring into correspondence the movement original object ID, movement destination object ID, and movement destination server, there can be realized convenience of hiding relocation of an object due to administrating purposes such as load distribution and capacity allocation, etc., from a user to maintain the SSI session. 
   Further another switch device according to the present invention further comprises: a second table for managing a combination of an advancement status of a movement processing for moving all objects upon executing a processing in which a group of objects exported to the public by the server to another server, update information required during the movement processing from the client, a movement source object ID of the object before the movement, a movement destination object ID of the object after the movement, and movement destination server identification information being identification information of a movement destination server; movement processing control means for moving the object on the basis of a predetermined criteria with reference to the pseudo file system, and entering an advancement status of the movement processing, update log in a copying processing, a movement source ID of the object, a movement destination object ID, and movement destination server identification information into the second table; and means for altering a transfer destination of a method of transferring a request to the moved object from the client upon executing the movement processing on the basis of the advancement state registered in the second table and contents of the request, and hiding that the operation is in the movement processing. 
   By adopting this arrangement, it is made possible to execute a management work by hiding a relocation work to the user without causing system interruption and file access service interruption even upon the object relocation work between servers by an administrator. 
   Although an object ID in the present invention is typically a file handle in the NFS, it is not limited thereto, and includes in an arbitrary file system capable of intervening of a network, all those identifying an object. Further, also for the file system, it is not limited to the NFS, and the present invention is applicable to other file systems. 
   Finally, in accordance with the present invention, provided that a client and a server support only a file system service protocol (e.g., NFS) mediating a standard network, an SSI file service can be realized for a client by integrally controlling a plurality of servers without modifying existing systems. Upon implementation of the switch device of the present invention, it is sufficient to only dispose the switch device logically between a client and a server, because any alteration of processings for the client and the server such as setting of IP alias and introduction of a virtual distributed file system is unnecessary. 
   The present invention can execute processings in a transparent fashion to a client when an administrator executes an operation not originally required to inform a client such as purposes of a load and of capacity distribution, for example when the administrator moves an object from a server which is once allocated to another server, and hence it can keep consistency of the SSI session presented to the client. The switch device of the present invention can bring into correspondence an object ID for specifying objects such as a directory and a file and a server for processing the object, and converts new and old object IDs. When the object is moved to be transparent to the client, and can distribute, on the basis of the result, a request from the client to a proper server and a reply containing an object ID from the server to a proper client. 
   The present invention is capable of processing a greater amount of object IDs without the use of the retrieving operation, and of transferring a packet to a proper server, and is hence advantageous for making processings a high speed and hardware implementation. 
   The present invention is capable of shortening time for a name solving processing by distributing a load of the name solving processing to a server and a switch device. The switch device of the present invention includes a pseudo file system, which system controls only a mount point and is capable of transferring name solving under the mount point to each server without contradiction. 
   In the present invention, when there is a movement request of an object including a joint in a directory tree in each common object unit in an integrated directory tree, a table is rewritten such that a client looks at it as if actual movement of an object at a joint or lower is prevented and the objects at the joint or lower are moved to a desired positions, and hence the movement can be completed at a very high speed. 
   In the present invention, when use can be made of tag information at the layer 4 or lower of the OSI reference model, rewriting of an object ID is ensured with a hardware using those pieces of tag information, and hence the processings are made a further high speed. 
   Further, in the present invention, even upon an object relocation work between servers by a controller the relocation work is masked to a user, whereby a control work can be executed without causing system interruption and file access service interruption. 
   The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate an example of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram illustrating a function of a web switch; 
       FIG. 2  is a block diagram illustrating the arrangement of a system that executes a method disclosed in JP P2001-51890A; 
       FIG. 3  is a block diagram of a network file system being a remote file system of a client/server type in which a switch device according to a first embodiment of the present invention is provided; 
       FIG. 4  is a block diagram illustrating the arrangement of the switch device of the first embodiment; 
       FIG. 5  is a block diagram illustrating the arrangement of a file access control unit; 
       FIG. 6  is a block diagram illustrating the arrangement of an object ID rewrite unit; 
       FIGS. 7A to 7C  are views each exemplarily illustrating formats of an original object ID, a compression type information entraining object ID and postscript type information entraining object ID rewritten in the object ID rewrite unit respectively; 
       FIG. 8  is a view illustrating the arrangement of an algorithm table; 
       FIG. 9  is a view illustrating the arrangement of a server information control table; 
       FIG. 10  is a view illustrating the arrangement of a transaction ID control table; 
       FIG. 11  is a flowchart illustrating the operation of an object rewrite unit upon reply data being received; 
       FIG. 12  is a block diagram illustrating the arrangement of a switch device according to a second embodiment of the present invention; 
       FIG. 13  is a block diagram illustrating the arrangement of a file access control unit in the switch device of the second embodiment; 
       FIG. 14  is a view exemplarily illustrating a directory tree of a pseudo file system; 
       FIG. 15  is a view illustrating the arrangement of a specific object ID control table; 
       FIG. 16  is a flowchart illustrating the operation of the switch device of the second embodiment; 
       FIG. 17  is a block diagram illustrating the arrangement of a switch device according to a third embodiment of the present invention; 
       FIG. 18  is a block diagram illustrating the arrangement of a file access control unit in the switch device of the third embodiment; 
       FIG. 19  is a view illustrating the movement of data; 
       FIG. 20  is a view illustrating the arrangement of a movement object ID control table; 
       FIG. 21  is a flowchart illustrating the operation of the switch device when a packet is received; . 
       FIGS. 22A to 22C  are views exemplarily illustrating formats of an original object ID, flag added compression type information entraining object ID and flag added postscript type information entraining object ID, respectively; 
       FIGS. 23A to 23C  are views exemplarily illustrating an original object ID, generation number added compression type information entraining object ID and generation number added postscript type information entraining object ID, respectively; 
       FIG. 24  is a view illustrating how to construct a pseudo file system in a sixth embodiment of the present invention in a concrete fashion; 
       FIG. 25  is a view exemplarily illustrating a case where a switch device executes directory movement by an ordinary file system processing in the sixth embodiment; 
       FIG. 26  is a view illustrating the operation of the sixth embodiment; 
       FIG. 27  is a block diagram illustrating the arrangement of a file access control unit in a switch device according to a seventh embodiment of the present invention; 
       FIG. 28  is a view illustrating the arrangement of a processing classifying table; 
       FIG. 29  is a block diagram illustrating a hardware construction of the switch device of the seventh embodiment; 
       FIG. 30  is a view exemplarily illustrating the arrangement of a directory tree assumed by a switch device according to an eighth embodiment of the present invention; 
       FIG. 31  a flowchart illustrating the operation of the eighth embodiment; 
       FIG. 32  is a view exemplarily illustrating a situation where an integrated directory tree environments by another method and a protocol are both arranged; 
       FIG. 33  is a view for describing incorporation of an integrated directory tree environment in a ninth embodiment of the present invention; 
       FIG. 34  is a block diagram illustrating the arrangement in a file access control unit in a switch according to a tenth embodiment of the present invention; 
       FIG. 35  is a view illustrating the arrangement of a movement object status control table in the tenth embodiment; 
       FIG. 36  is a view illustrating an outline of processings in the tenth embodiment; 
       FIG. 37  is a view illustrating, by a flowchart, a movement processing procedure for an object in a data movement processing unit in the switch device of the tenth embodiment; 
       FIG. 38  is a view illustrating, by a flowchart, processing procedure in the switch device for a request packet from a client during a movement processing of a data movement processing unit in the switch device of the tenth embodiment; 
       FIG. 39  is a view illustrating, by a flowchart, a processing procedure upon a read operation request; 
       FIG. 40  is a view illustrating, by a flowchart, a processing procedure upon an update operation request; 
       FIG. 41  is a view illustrating, by a flowchart, a processing procedure upon a newly creation operation request; 
       FIG. 42  is a view illustrating, by a flowchart, a processing procedure upon a delete operation request; and 
       FIG. 43  is a block diagram of a network file system being a client/server type remote file system to which a switch device according to the present invention is applied. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   First Embodiment 
   A switch device of a first embodiment of the present invention will first be described. 
   Referring to  FIG. 3 , a network file system that is a remote file system of a client server type in which a switch device of the first embodiment is provided is illustrated. As illustrated in  FIG. 3 , in the present network file system at least one client  1 , at least one server  3 , switch  100  that is one example of the switch device of the present embodiment are connected to network  2  that is a LAN (Local Area Network) or the Internet, etc. Each server  3  includes at least one file system  4  for managing data in a file or the like accessed by file access service and storage (or memory device)  5  for storing the foregoing data, and serves as a file server for providing file access service to each client  1 . 
   Although in  FIG. 3 , client  1 , server  3 , and switch  100  are connected with the same network  2 , switch  100  is logically disposed between each client  1  and each server  3 . In such a remote file system, all file access operations comprise a file access request transmitted from client  1  and a reply replied from server  3  for the file access request, and no request from server  3  is outputted. The file access request is generally a request with an NFS protocol, provided that it is a system with Unix® or its derivative for example. 
   In the file access request transmitted from client  1  an object ID is contained for the purpose of identifying objects of a directory and a file being access objective. Client  1  accesses to an object managed by server  3  by specifying an object ID for identifying an object such as a directory and a file in a file access request. The object ID is generated by server  3 , and client  1  has a list of objects accessible in the first place. Client  1  first transmits request data specifying an access path up to the object from the list, and obtains an object ID of an object accessible first from reply data of server  3 . For an object disposed at a lower rank of the object already obtaining the object ID, client  1  transmits the already obtained object ID and request data for specifying the name of an object to be file accessed, and obtains the object ID from reply data thereof. Otherwise, client  1 , unless it receives the reply data from server  3  and obtains an object ID contained in the reply data, can not operate an object bring into correspondence to the object ID. 
   In the network file system, existence of server  3  is hidden from client  1  by switch  100 , and a file access request from the client  1  is transmitted to the switch  100 . Switch  100  receives the file access request transmitted from client  1 , and distributes and transfers (routes) the file access request to proper server  3 , receives a reply for the foregoing file access request transmitted from server  3 , and transfers (routes) the reply to client  1  that transmitted the file access request. 
   Switch  100  analyzes an object ID contained in a file access request when it receives the file access request from client  1 , and determines server  3  to which the file access request should be transferred among a plurality of servers  3  on the basis of an analysis result, and further transmits the file access request to that server  3 . Since however an object ID generated in server  3  is constructed with a data train which only server  3  that generated the data train can interpret, that data can not be interpreted by switch  100  and client  1 . Further, there is the possibility that object IDs have the same data trains in different servers  3 . For this reason, unless the situation is changed, switch  100  could not execute routing proper for the file access request. Furthermore, client  100 , unless it receives reply data from server  3  and obtains an object ID contained in the reply data as described previously, fails to operate the object bring into correspondence to that object ID. 
   Hereupon, switch  100  inserts server identification information for identifying a server of a transmission source from other servers into an object ID contained in reply data transmitted from server  3 , reconstructs a packet with use of reply data which contains the object ID into which the server identification information is inserted, and further transfers the resulting packet to client  1  with such an arrangement, client  1  transmits a file access request containing an object ID into which server identification information is inserted to switch  100 , and switch  100  can then specify a server to which the file access request should be transferred with reference to the server identification information inserted in the object ID. Switch  100  should convert upon transferring a file access request to server  3  the object ID into which the server identification information is inserted to an original object ID generated by server  3  with provision of such switch  100  there is ensured a distributed processing by a plurality of servers in a network file system. 
   Referring here to  FIG. 4 , the arrangement of switch  100  is illustrated. Switch  100  includes object ID rewrite unit  101 , file access control unit  102 , and packet processing unit  103 . Packet processing unit  103  analyzes a packet received from client  1  and server  3  through network  2 , outputs data contained in the packet to file access control unit  102 , and further converts data outputted from the file access control unit  102  into a packet and transmits it to client  1  and server  3  mediating network  2 . File access control unit  102  inputs and analyzes data outputted from packet processing unit  103 , and determines a destination of the packet by packet processing unit  103 . Object ID rewrite unit  101  rewrites an object ID contained in the foregoing data in response to a destination of a packet determined by file access control unit  102 . 
   Referring to  FIG. 5 , the arrangement of file access control unit  102  is illustrated. File access control unit  102  includes data analysis unit  124 , transaction ID control table  125 , and server information control table  126 . Data analysis unit  124  analyzes request data and reply data and determines a proper destination of a received packet. In transaction ID control table  125  there is registered a transaction ID which associates respective request and reply data and is provided to discriminate individual request and reply data in client  1  and server  3 . In server control table  126  there are entered a combination of server identification information and address information of a server such as an IP address and a MAC address of server  3 , 
   Referring to  FIG. 6 , an arrangement of object ID rewrite unit  101  is illustrated. Object ID rewrite unit  101  includes request/reply distribution unit  120 , request processing unit  121 , reply processing unit  122 , and algorithm table  123 . Request/reply distribution unit  120  distributes when data transmitted from file access control unit  102  is request data, that data to request processing unit  121  while distributing, when the same is reply data, that data to reply processing unit  122 . In algorithm table  123  there is registered how to rewrite data. Request processing unit  121  and reply processing unit  123  rewrite an object ID on the basis of how to reply registered in algorithm table  123 , and transmits the written object ID to request/reply distribution unit  120 . Request/reply distribution unit  120  transmits the written object ID to the file access control unit  102 . 
   Object ID Format: 
   Referring here to  FIGS. 7A to 7C , a format of an object ID rewritten in object rewriting unit  101  is exemplarily illustrated. 
   Illustrated in  FIG. 7A  is an object ID generated by server  3 , i.e., original object ID  150 . Original object ID  150  has different definitions of data lengths depending upon the kinds and versions of network file access protocols such as NFS. More specifically, for original object ID  150  there are known ones having fixed data lengths, and ones where only maximum data lengths are determined and are variable within a range of the maximum data lengths. 
   Referring then to  FIG. 7B , a format of an information entraining object ID which is an object ID with fixed data length, and into which server identification information  154  and algorithm identification information  153  are inserted with the aid of object rewrite unit  101 . The information entraining object ID, since its data length is fixed, even if server identification information  154  and algorithm identification information  153  are inserted, the entire data length is fixed, i.e., it must be the same data length as original object ID  150 . Accordingly, object ID rewrite unit  101  upon generating the information entraining object ID, deletes part of original object ID  150  illustrated in  FIG. 7A  into compression data  152 , and adds server identification information  154  and algorithm identification information  153  to the head of the same. Algorithm identification information  153  is information for identifying a deletion algorithm use by object ID write unit  101  upon the part of original object ID  150  being deleted. The information entraining object ID rewritten as such is called compressed information entraining object ID  151 . 
   Referring further to  FIG. 7C , an information entraining object ID which is an object ID having a variable data length and into which server identification information and algorithm identification information are inserted. In the information entraining object ID, data of original object ID  150  is not deleted, but server identification information  154  and algorithm identification information  153  are added thereto. Such an information entraining object ID is called additionally added information entraining object ID  155 . Even if the data length thereof is variable, if it exceeds a maximum data length, compression information entraining object ID  152  is generated in object ID rewrite unit  101  instead of additional information entraining object ID  155 . 
   Server identification information  154  and algorithm identification information  153  illustrated in  FIG. 7B  and server identification information  154  and algorithm identification information  153  illustrated in  FIG. 7C  are desirable to be the same in data lengths, respectively, and server identification information  154  and algorithm identification information  153  are desirable to be set at the same data positions, respectively. The size of the object ID is large and is about 32 bite in an NFS version 2 protocol generally, and may change the foregoing size in NFS version 3. For this reason, time is required to extract information having various data lengths and data positions thereamong. It is therefore desirable to make those data same data length and same data position for extracting and retrieving each identification information contained in the information entraining object ID. 
   Referring to  FIG. 8 , the arrangement of algorithm table  123  is illustrated. Algorithm table  123  is a table having an entry constituted by a set of algorithm identification information  153 , delete data  156  that is an example of restored information, and delete data position  157  that is an example of the restoring information. With reference to this table then request processing unit  121  can restore compression data  152  to original object ID  150  with use of delete data  156  and delete data position  157 . In algorithm table  123 , an entry not including information concerning delete data  156  and delete data position  157  is an entry of the additional type information entraining object ID where server identification information  154  and algorithm identification information  153  are added to original object ID  150  without generating compression data  152 . 
   When original object ID  150  is generated with a predetermined generation rule in server  3 , original object ID  150  is an ID where a data train is periodic, i.e., an ID where the same bit train is generated at the same position in each original object ID  150 . In such a situation, it is possible to reduce the number of entries of algorithm table  123  by a method where delete data  156  and delete data position  157  are made equal to each other, and the same algorithm identification information  153  is employed. 
   Operation Upon Reception of Request Packet: 
   In the following, there will be described procedures of the operation in switch  100  where after a request packet sent from client  1  is received, a proper server is selected from a plurality of servers  3 , and a packet is transmitted to that server. 
   Packet processing unit  103  once receiving the request packet transmitted from client  1 , extracts file access request data, client IP address information  160  of client  1 , and client MAC address information  161  from that packet, and transmits those data to file access control unit  102 . 
   Data analysis unit  124  of file access control unit  102  once receiving those data, analyzes the file access request data, and extracts compression type information entraining object ID  151  or postscript type information entraining object ID  155 . 
   Data analysis unit  124  extracts server identification information  154  contained in compression type information entraining object ID  151  or postscript type information entraining object ID  155 , and reads server IP address information  158  and server MAC address information  159  of server  3  bring into correspondence to server identification information  154  with reference to server information control table  126  illustrated in  FIG. 9 . 
   In the file access request data there i&#39;s contained transaction ID  160  for discriminating respective request data. Data analysis unit  124  registers in transaction ID control table  125  illustrated in  FIG. 10  transaction ID  160 , client IP address information  161  and client MAC address information  162  received from packet control unit  103 , file access instruction information  163  such as read and write contained in the file access request data, and server identification information  154 . 
   Thereafter, data analysis unit  124  transmits compression type information entraining object ID  151  or postscript type information entraining object ID  155  to object ID rewrite unit  101  together with an information entraining object ID write instruction. These object IDs are, after being converted to original object ID  150  in object ID rewrite unit  101 , again transmitted to file access control unit  102 . 
   File access control unit  102  assembles original object ID  150  into the file access request. Reconstructed file access request data in file access control unit  102 , and server IP address information  158  of server  3  specified by retrieving server information control table  126 , and MAC address information  159  are transmitted to packet processing unit  103 . Packet processing unit  103  reconstructs those information as a request packet, and transmits the resulting packet to server  3 . 
   Operation of Object ID Rewrite Unit Upon Reception of Request Data: 
   Successively, there will be-described procedures of the operation in object ID rewrite unit  101  upon restoring compression type information entraining object ID  151  or additional description type information entraining object ID  155  contained in the request data from client  1  to original object ID  150 . 
   Once receiving, after analysis of the request data, compression type information entraining object ID  151  or postscript type information entraining object ID  155 , and an information entraining object ID rewrite instruction transmitted from file access processing unit  102 , request/reply distribution unit  120  transmits the received compression type information entraining object ID  151  or postscript type information entraining object ID  155  to request processing unit  121  based upon the information entraining object ID rewrite instruction. 
   Request processing unit  121  specifies delete data  156  and delete data position  157  of an entry bring into correspondence to algorithm identification information  153  contained in the received information entraining object ID with reference to algorithm  123 , and generates original object ID  150  based upon the foregoing specified data, and further transmits original object ID  150  generated in file access control unit  102  via request/reply distribution unit  120 . 
   Operation Upon Reception of Reply Packet: 
   Successively, there will be described procedures of an operation in switch  100  upon transferring the reply packet transmitted from server  3  by selecting a proper client from a plurality of clients  1 . Packet processing unit  103  extracts reply data, and server address information such as server IP address information  158  or server MAC address information  159  of server  3  from the reply packet from the received server  3 , and transmits it to file access control unit  102 . 
   Data analysis unit  124  of file access control unit  102  refers to server control table  126 , retrieves an entry having an equal value to server IP address information  158  or server MAC address information  159 , and obtains server identification information  154  of the entry. Further, data analysis unit  124  extracts transaction ID  160  contained in reply data by analyzing the reply data, and retrieves an entry where server identification information  154  and transaction ID  160  are coincident with each other, and further obtains client IP address information  161 , client MAC address information  162 , and file access instruction information  163  of client  1  that transmits a file access request corresponding to received reply data. 
   There is also an occasion where in the reply packet from server  3  no object ID is contained. In a protocol and a version of a specific file access service there is an occasion where file access instruction information is not demonstrated in reply data, so that data analysis unit  124  can judge whether or not the original ID is contained in the reply data using file access instruction information  163  to specify the kind of the instruction to which the reply data corresponds. 
   When original object ID is contained in the reply data, data analysis unit  124  transmits a definition method for data length, server identification information, and an original object rewrite instruction to object ID rewrite unit  101  together with original object ID  150 . Object ID rewrite unit  101  rewrites the received original object ID to compression type information entraining object ID  151  or postscript type information entraining object ID  155 , and data analysis unit  124  reconstructs the reply data. Data analysis unit  124  does not alter the reply data when no original object ID is contained in the reply data. Thereafter, data analysis unit  124  transmits client IP address information  161 , client MAC address information  162 , and reply data to packet processing unit  103 . Packet processing unit  103  generates a reply packet, and transmits the reply packet to client  1 . 
   Operation of Object Rewrite Unit Upon Reception for Reply Data: 
   Referring to  FIG. 11 , a flowchart for illustrating the operation of object rewrite unit  101  upon reception of the reply data. As illustrated in  FIG. 11 , request/reply distribution unit  120 , once receiving in step S 100  original object ID  150  as well as the definition method for data length, server identification information, and original object rewrite instruction contained in the reply data from file access control unit  102 , distributes all the received data to reply processing unit  122 . 
   Reply processing unit  122 , in step  101 , judges the definition method for the received data, and checks whether or not the data length of the original object ID is fixed length. In the case of the fixed length, reply processing unit  122 , in step S 102 , generates compression data by deleting part of a data train of the original object ID, and in step S 103 , registers deleted data  156 , deleted data position  157 , and algorithm identification information  153  provided to discriminate the deleted algorithm in algorithm table  123 . 
   After the registration into algorithm table  123  is finished, reply processing unit  122 , in step S 104 , generates the compression type information entraining object ID  151  by combining server identification information  154 , algorithm identification information  153 , and compression data  152 , and in step S 105  transmits compression type information entraining object ID  151  thereof to file access control unit  102  mediating request/reply distributing unit  120 . 
   In contrast, in step S 101 , in the case where the data length of original object ID  150  is not fixed length, reply processing unit  122 , in step S 106 , calculates the total sum of three data lengths of server identification information  154 , algorithm identification information  153 , and original object ID  150 , and calculates a resulting calculated value and the defined maximum data length. Herein, in the case where the total sum of the three data lengths is longer than the maximum data length, reply processing unit  122  executes processings in the same procedures as in the case of the data length being a fixed length shown in steps S 102  to S 105 . 
   In the case where the total sum of the three data lengths is shorter than the maximum data length in step S 106 , reply processing unit  122 , in step S 107 , generates algorithm identification information  153  as an entry where information of delete data  156  and delete data position  157  is not registered, and registers them in algorithm table  123 . Thereafter, reply processing unit  122 , in step S 108 , after the registration into algorithm table  123 , generates postscript type information entraining object ID  155  by combining server identification information  154 , algorithm identification information  153 , and original object ID  150 , and transmits, in step S 105 , postscript type information entraining object ID  155  to file access control unit  102  mediating request/reply distribution unit  120 . 
   In the switch device of the present embodiment, when an object is divided in the export unit for a plurality of objects exported to the public in server  3 , i.e., in the common object unit, ID items in the common object unit for identifying whether or not the objects are contained in the common object unit may be added as an entry of server information control table  126 . With such an arrangement, switch  100  can grasp not only server  3  for containing an object but also the common object unit containing an object, so that it is possible in switch  100  to realize very fine transfer control in the common object unit having a further higher resolution than in the server unit. 
   Second Embodiment 
   In the following, a switch device of a second embodiment according to the present invention will be described. The switch device is one used in a network file system illustrated in  FIG. 3  as the switch device of the first embodiment. 
   Referring to  FIG. 12 , an arrangement of the switch device of the second embodiment is illustrated. Switch device  100  comprises object ID rewrite unit  101 , file access control unit  102  and packet processing unit  103  which are provided in the switch according to the first embodiment, and pseudo file system  105 . Pseudo file system  105  is a system for managing a plurality of directory trees constituted with file systems  4  of a plurality of servers  3  in combination as one integrated directory tree. File system control processing unit  104  executes a control processing when a file access request from client  1  needs a file access over a plurality of destinations such as the plurality of servers  3  or a plurality of file systems  4 . 
   Referring to  FIG. 13 , an arrangement of file access control unit  102  in the present switch device is illustrated. File access control unit  102  comprises data analysis unit  124  provided in the switch device in the first embodiment, a transaction ID control table  125 , server information control unit  126 , and specific object ID control table  127 . Specific object ID control table  127  is a table for judging a file access request from client  1 , which requires a file access to a plurality of destinations of the plurality of servers  3  or the plurality of file systems  4 . Data analysis unit  124  in the switch device in the present embodiment is capable of not only data input/output with object ID rewrite unit  101  and packet processing unit  103 , but also of data input/output with file system control processing unit  104 . 
   In the following, the operation of switch  100  will be described. Similar to the switch device in the first embodiment, the present switch device has a function of properly distributing the request packet and the reply packet to client  1  or server  3 . Furthermore, the present switch device has a function of acting as an accessing only to pseudo file system  105  in switch  100  without client  1  taking care of the existence of individual file systems  4  in the plurality of servers  3  by integrating a plurality of directory trees formed on pseudo file system  4  of a plurality of servers  3  to a directory tree of pseudo file system  105 . 
   Pseudo file system  105  freely combines on pseudo file system  105  tree structures in a plurality of directory trees on file system  4  exported to the public as being accessible through network  2  by server  3 , and maps it to one directory tree. 
   Switch  100  not only distributes a file access request packet received from client  1  to a specific server  3 , but also transmits, when receiving a file access request to stride a plurality of servers  3  or different file systems  4 , one file access request to the plurality of servers  3  or file systems  4  by dividing the one file access request to a plurality of file access requests, and reconstructing all reply data transmitted from the plurality of servers  3  or file systems  4  to one reply data therein to transmit it back to client  1 . 
   Referring to  FIG. 14 , directory tree  200  of pseudo file system  105  is exemplarily illustrated. Pseudo file system  105  maps a tree structure of a directory tree from directory b ( 221 ) exported to the public in server A ( 250 ) and directory c ( 221 ) exported to the public in server B ( 251 ) as a directory tree from a sub directory of root directory  220  formed on pseudo file system  105 . Pseudo file system  105  generates pseudo file system directory tree  200  by registering a tree structure of a directory tree from directory e ( 224 ) exported to the public in server B ( 251 ) as a directory tree from a sub directory of directory f ( 223 ) existent on a lower layer of a directory tree from directory b ( 221 ). 
   In the switch device of the present embodiment, a directory name on pseudo file system directory tree  200  is not necessarily the same as a directory name set in file system  4  of server  3 , and another directory name may be set and exported to client  1 . 
   Pseudo file system  105  manages only a tree structure of directory tree  200  of pseudo file system  105 , and for tree structures other than data of an object, attribute information, and tree structures other than joint portions between respective file systems  4  the server  3  manages all of them. Accordingly, in switch  100 , there is performed a name solving processing only for a tree portion that couples a plurality of file systems  4 , and other tree portions are processed in server  3 , With such an arrangement a load of the name solving processing can be distributed between switch  100  and server  3 . 
   Switch  100 , when it receives a file access request packet using an object ID bring into correspondence to directory f ( 223 ) that is an instruction for obtaining an object ID and attribute information bring into correspondence to directory e ( 224 ) for example, generates a new request packet to reply correctly to that instruction, and transmits the request packet to server A ( 250 ) for storing data of directory f ( 223 ) and server B ( 251 ) for storing data of directory e ( 224 ). Pseudo file system  105  is used as control information for executing reconstruction processing for two reply packets returned from server A ( 250 ) and server B ( 251 ). 
   Switch  100 , excepting the case where a correct reply can not be returned unless there is executed such a control processing as sending request data to a plurality of servers  3  or file systems  4  on the basis of a file access request from client  1 , executes the processing in the same procedures as those in the switch of the first embodiment, and judges which processing should be executed with the aid of specific object ID control table  127  of file access control unit  102 . 
   Specific object ID control table  127  is constructed as illustrated in  FIG. 15  with an entry comprising object ID  164  of all directories bring into correspondence joints for trees existent on the different servers  3  of the directory tree such as directory b ( 221 ) and directory e ( 224 ) and all file access instruction information  165  which should undergo the control processing. In specific object ID control table  127  there are registered at the time directory tree  200  of pseudo file system  105  is generated all bring into correspondence directories. Object ID  164  registered in specific object ID control table  127  is an information entraining object ID, i.e., compression type information entraining object ID  151  or postscript type information entraining object ID  155  in order to collate an information entraining object ID contained in request data transmitted from client  1 . Hereby, collating time can be reduced. 
   In the following, procedures for the operation in switch  100  when a request packet from client  1  and a reply packet from server  3  are received will be described in detail using  FIG. 16 . 
   Packet processing unit  103 , once receiving a file access request packet from client  1 , extracts, in step S 110 , file access request data, client IP address information  160  and client MAC address information  161  of client  1  from the packet, and transmits it to file access control unit  102 . 
   Data analysis unit  124  of file access control unit  102  extracts, in step S 111 , instruction information such as read and write contained in the received request data, compression type information entraining object ID  151  or postscript type information entraining object ID  155 , and checks whether or not ones bring into correspondence to them is existent in an entry of object ID  164  and instruction information  165  registered in specific object ID control table  127 . When there is existent nothing bring into correspondence to even any one of two data of instruction information extracted from the request data and information entraining object ID  151  or  155  in specific object ID control table  127 , for a processing concerning a request packet in switch  100  described later and a processing concerning a reply packet bring into correspondence to the request packet they are executed, as shown in step S 112 , in the same procedure as in the switch device of the first embodiment. 
   In contrast, in step S 111 , when both two data of instruction information taken out from the request data and object ID  151  or  155  bring into correspondence to an entry of specific object ID control table  127 , data analysis unit  124 , in step S 113 , transmits, after registering required all data in transaction ID control table  125 , the received request data to file system control processing unit  104 . Thereafter, file system control processing unit  104  executes analysis for the received request data with reference to pseudo file system  105  in step S 114 , and then generates a plurality of the request data transmitted to the plurality of servers  3  or file systems  4 , and further transmits all the request packets to a plurality of or one associated servers  3  through packet control unit  103 . It is herein noted that the transmission of all the request packets to the one server  3  in step S 114  is limited to the situation where server  3  includes a plurality of file systems  4 , and mapping of the arrangement of directory tree  200  on pseudo file system  105  is constructed by joining the respective file systems  4 . 
   After execution of step S 114 , packet processing unit  103  of switch  100 , once receiving a reply packet for a request packet transmitted to server  3  in step S 115 , extracts reply data and address information  158 ,  159  of server  3  from its reply packet, and transmits them to file system control processing unit  104 . File system control processing unit  104 , when the reply data contains original object ID  150 , transmits a rewrite instruction of the object ID, original object ID  150 , and address information  168 ,  159  of server  3  to file access control unit  102 . 
   In succession, file access control unit  102  transmits, in step S 116 , original object ID  150  contained in all the received reply data to object ID rewrite unit  101 , and in the same fashion as in the first embodiment forces object ID rewrite unit  101  to rewrite compression type information entraining object ID  151  or postscript type information entraining object ID  155 , and generates reply data for the request data from client  1  using all the received reply data. Thereafter, file access control unit  102  retrieves in step S 117  an entry that is coincident with data registered in transaction ID control table  125 , and after obtaining address information of client  1  transmits the reply data and the address information to client  1 . 
   Packet processing unit  103  generates a reply packet based upon the received reply data and the address information of client  1 , and transmits the reply packet to client  1 . 
   Third Embodiment 
   In the following, a switch device of a third embodiment of the present invention will be described. The switch device of the present embodiment is applied to the network file system illustrated in  FIG. 3  as in the first and second embodiments. 
   Referring to  FIG. 17 , an arrangement of the switch device of the third embodiment will be described. Switch  100  includes object ID rewrite unit  101 , file access control unit  102  and packet processing unit  103  which are provided in the switch device of the first and second embodiments, and the file system control processing unit  104  and pseudo file system  105  which are provided in the second embodiment, and further includes data movement processing unit  106 . Data movement processing unit  106  moves data among a plurality of servers  3  without altering a directory structure of an integrated directory tree on pseudo file system  105  on the basis of a load of the file accessing processing of each server  3  and remaining capacity of storage  5 . 
   Referring to  FIG. 18 , an arrangement of file access control unit  102  is illustrated. File access control unit  102  includes transaction ID control table  125  and server information control table  126  both provided in the switch devices of the first and second embodiments, and specific object ID control table  127  and moving object ID control table  128  both provided in the second embodiment. In moving object ID control table  128  there is entered information where any inconvenience due to alteration of an object ID generated when data is moved among a plurality of servers  3 . In data analysis unit  124  there are ensured not only input/output operation of data among object ID rewrite unit  101 , packet processing unit  103 , and file system control processing unit  104  but also input/output operation of data with data movement processing unit  106 . 
   In succession, the operation of the switch device of the present embodiment will be described. The switch device, besides a function provided in the switch devices of the first, second embodiments, copies to another server  3  a tree structure originating from an exported directory of each server  3  constituting an integrated directory tree constructed on pseudo file system  105  unchanged while keeping the tree structure of the integrated directory tree, and executing data movement, and thereafter masks the movement of the data from client  1  by altering mapping of the tree structure, and reduces insufficient capacity in storage  5  of server  3  and a load of the file access processing in each server  3  while keeping the arrangement of the integrated directory tree unchanged. 
   There is the need of alteration of even an object ID bring into correspondence to an object of each directory and file following the data movement among servers  3 , so that in switch  100  an alteration history of the object ID before the data movement and after the data movement is controlled, and the operation of the data movement is masked from client  1  by preventing inconvenience due to the alteration of the object in client  1  and server  3  from happening. 
   In pseudo file system  105  illustrated in  FIG. 14 , for example, the situation is assumed that remaining capacity of the storage or memory device in server B ( 251 ) is a little, but remaining capacity of the storage or memory device in server A ( 250 ) is sufficient, and data in a directory tree from directory c ( 222 ) in server B( 251 ), a possessor of the object, and attribute information such as an access right are desired to be copied into server A ( 250 ) for every tree structure. The switch device of the third embodiment after updating information of pseudo file system  105  such that a directory tree from directory c ( 225 ) is again mapped without changing the structure of directory tree  200  of pseudo file system  105  as illustrated in  FIG. 19 , and then deletes the data of the directory tree from directory c ( 222 ). Hereby, the switch device can increase the remaining capacity while masking the movement of the data to client  1 , so that addition of any data is ensured in the directory tree from directory c ( 225 ) and the directory tree from directory e ( 224 ). 
   In the following, procedures of the operation of switch  100  concerning the data moving operation will be described. Data movement processing unit  106  monitors the data of the remaining capacities of storages  5  in all servers  3 , and records history data concerning the file access request packet and the reply packet processed in switch  100 . Data movement control unit  106 , when the remaining capacity is more reduced than a previously set reference, and when file access requests are concentrated only to a specific server  3 , refers to data registered in pseudo file system  105 , determines a directory tree of a movement source and a movement destination, and starts copying the data. 
   Upon executing copying of the data, data movement processing unit  106 , in order to deal with inconvenience when accessing data being an object of the movement data by making of information entraining object IDs  151 ,  155  already obtained by client  1 , registers information entraining object IDs  151 ,  155  obtained by rewriting original object ID  150  generated by the movement source server  3  in object ID rewrite unit  101 , original object ID  150  generated in the movement destination server  3 , and server identification information  154  bring into correspondence to the movement destination server  3  registered in server information control table  126  in movement object ID control table  128  illustrated in  FIG. 20  as information associated with all objects being objects for the movement of the data. Movement object ID control table  128  is constructed with an entry comprising information of movement source object ID  166 , movement destination object ID  167 , and movement destination server information  168 . 
   When an object registered in movement object ID control table  128  is again moved, movement destination object ID  167  in movement object ID control table  128  is added to items of movement source object ID  166 , and items of remaining movement destination object ID  167  and movement destination server information  168  are updated to the newest state. 
   As an object ID indicating an object in information registered in movement destination object ID  167 , in which object the processing in file system control processing unit  104  might be required compression type information entraining object ID  151  and postscript type information entraining object ID  155  are registered instead of original object ID  150 . Server identification information  154  is herein not registered in movement destination server information  168 . 
   When after copying for all data is finished, and data of server  3  of the movement source is deleted, setting of the exported directory making possible a file access through network  2  to a directory tree subjected to copying in server  3  of the movement destination, data movement processing unit  106  sets the export directory to the movement destination server  3 , updates mapping information of the tree structure in pseudo file system  105 , and updates entry data registered in specific object ID control table  127 . 
   In the following, there will be described in detail processing procedures in switch  100  when after the data movement is executed, the request packet from client  1  and the reply packet are received. Referring to  FIG. 21 , a flowchart indicating the operation of switch  100  when the packet is received is illustrated. 
   Packet processing unit  103 , once receiving a file access request packet from client  1 , extracts,-in step S 120 , file access request data, client IP address information  160  and client access MAC address information  161  of client  1  from the packet, and transmits them to file access control unit  102 . 
   Data analysis unit  124 , in step S 121 , analyzes the received request data, extracts compression type information entraining object ID  151 , or postscript type information entraining object ID  155 , and confirms whether or not its ID is registered in movement object ID control table  128 . When extracted compression type information entraining object ID  151  or postscript type information entraining object ID  155  is not registered as movement source object ID  166  of movement object ID control table  128 , as described in step S 122 , processings concerning request data thereafter and reply data bring into correspondence the just-mentioned request data are executed in the same fashion as processings from step S 111  of the second embodiment. 
   In contrast, when in step S 121 , extracted compression type information entraining object ID  151  or postscript type information entraining object ID  155  is registered as movement source object ID  166  in movement object ID control table  128 , data analysis unit  124  checks, in step S 123 , whether or not server identification information  154  is registered in movement destination server information  168 . When server identification information  154  is not registered in movement destination server information  168  as the result of the check, data analysis unit  124 , in step S 124 , alters compression type information entraining object ID  151  or postscript type information entraining object ID  155  contained in the request data to compression type information entraining object ID  151  or postscript type information entraining object ID  155  registered in movement destination object ID  167 . 
   A processing concerning the request data after the execution after step S 124  and reply data corresponding to the request data are executed, as shown in step S 125 , in the same fashion as the processings from step S 111  in the second embodiment. 
   When server identification information  154  is registered in movement destination server information  168  in step S 123 , data analysis unit  124  alters, in step  126 , compression type information entraining object ID  151  or postscript type information entraining object ID  155  to original object ID  150  registered in movement destination object ID  167 , and extracts server identification information  154  registered in movement destination server information  168 . Thereafter, data analysis unit  124  after registering all information required for an entry of transaction ID control table  125  in step S 127 , extracts server IP address information  158  and server MAC address information  159  from server information control table  126  on the basis of server identification information  154  obtained from movement object ID control table  128 , and transmits the request data altered to the original object ID  150 , server IP address information  158 , and server MAC address information  159 . 
   In step S 128 , Packet processing unit  103  generates a request packet using data transmitted from file access control unit  102 , and transmits it to server  3 . The processing of switch  100  concerning the request packet from server  3  for the request packet is executed, as shown in step S 129 , in the same fashion as the processing for the reply packet in the switch of the first embodiment. 
   Fourth Embodiment 
   In the following, a switch device according to a fourth embodiment of the present invention will be described. The switch device is obtained by modifying the switch device of the third embodiment. In the switch device of the third embodiment is adapted such that when the number of objects where data is moved once is very large, the number of entries of movement object ID control table  128  in file access control unit  102  is also very large to result in the time for retrieving those entries is increased. Accordingly, in the switch device of the fourth embodiment, as illustrated in  FIGS. 22A to 22C , data movement flag  169  indicative of a fact that the data is moved is assembled in the object ID together with algorithm identification information  153  and server identification information  154 , and object ID rewrite unit  101 , upon generating flag tagged postscript type information entraining object ID  171  or flag tagged postscript type information entraining object ID  172 , truly sets data movement flag  169  concerning the object that is a target. In the switch device in the fourth embodiment, upon analyzing, in data analysis unit  124 , flag tagged compression type information entraining object ID  171  or flag tagged postscript type information entraining object ID  172  contained in the request data from client  1 , if data movement flag is true, and only in that case, data movement object ID control table  128  is retrieved. Hereby, in the switch device in the fourth embodiment, more effective retrieving processing than in the case with the switch device in the third embodiment. 
   Fifth Embodiment 
   In the following, a switch device according to a fifth embodiment of the present invention will be described. The switch device is a modification of the switch device in the third embodiment. In the switch device of the third embodiment, when the number of objects where data is moved at a time is very large, the number of entries of movement object ID control table  128  in file access control unit  102  becomes very large to result in the time to retrieve an entry increased. Accordingly, in the switch device in the fifth embodiment, a generation number is applied to data movement by assuming the data movement of one time to be one generation, and the generation is incremented one by one every time data movement of one time is finished. A present generation number is stored in data analysis unit  124 , and in movement object ID control table  128  a table is prepared for each generation number. Further, in object ID rewrite unit  101 , as illustrated in  FIGS. 23A to 23C , assembles in the object ID data movement generation number  172  together with algorithm identification information  153  and server identification information  154 , and generates generation number tagged compression type information entraining object ID  173  or generation number tagged postscript type information entraining object ID  174 . Data analysis unit  124  retrieves, on the basis of a generation number obtained by analyzing in data analysis unit  124 , generation number involving compression type information entraining object ID  173  or generation number involving postscript type information entraining object ID  174  contained in the request data from client  1 , only a table of the foregoing generation number in movement object ID control table  128 . Hereby, the switch device in the fifth embodiment is capable of more effective retrieving processing than in the switch device in the third embodiment. 
   Sixth Embodiment 
   In the following, a sixth embodiment of the present invention will described. It is assumed that as the switch one illustrated in  FIG. 17  is employed. The directory tree of the pseudo file system according to the present invention will be described in a concrete manner. 
   Referring to  FIG. 24 , an example of the case where directory tree  200  of a pseudo file system is constructed in a concrete manner is illustrated. When directory e ( 224 ) in server B ( 251 ) is coupled to a lower portion of directory f ( 223 ) in server A ( 250 ), in the sixth embodiment dummy directory e′ is formed below directory f ( 223 ). An object below directory f ( 223 ) in specific object ID table  127  of file access control unit  102  on the basis of tree construction information of pseudo file system  105  is retrieved. An object ID of directory f ( 223 ) is registered such that a case where a command such as Lookup of NFS for example is issued from the client can be picked up. As a result, when the request is issues from the client, for forcing the client to look at that directory e ( 224 ) of server B ( 251 ) is constructed like directory tree  200  of the pseudo file system, file system control processing unit  104  divides and transmits a request to server A ( 250 ) and server B ( 251 ), and collects necessary information from the reply. Further, a specific processing is necessary even when a command of attribute setting is issued to directory e ( 224 ), so that an object ID of directory e ( 224 ) is also registered in specific object ID table  127 . In this case, for reflecting the command of the attribute setting also on dummy directory e′, file system control processing unit  104  divides and transmits the request to server A ( 250 ) and server B ( 251 ). 
   It is now assumed that a client issues a request for moving directory f ( 223 ) to a lower portion of directory g of server A ( 250 ). In this case, the just-mentioned movement is not a movement by an administrator, so that the arrangement of the pseudo file system is also actually changed. Referring to  FIG. 25 , there is illustrated a result that the switch device based upon the present invention exemplifies the movement. In this case, directory f ( 223 ) is moved to a lower portion of directory g to create directory new-f ( 300 ), and directory e ( 224 ) looked thereunder is actually moved to server A ( 250 ) from server B ( 251 ) in its actual state to clear contents in specific object ID table  127 . This is a result of normal operation, and a client recognizes that its operation is fulfilled, but file movement between the servers happens, so that very long period of time sometimes elapses until completion of the operation depending upon the size of a file to be moved. It is herein noted that although the name of a directory is not changed actually, an object ID corresponding thereto is changed, so that for the purpose of discrimination “n-” is added to the directory name. 
   Against this, referring to  FIG. 26 , a result of the same movement according to the sixth embodiment is illustrated. Although it is the same as an example illustrated in  FIG. 25  that directory f ( 223 ) becomes directory new-f ( 300 ), a client operation corresponding unit of data movement processing unit  106  is moved dummy directory e′ ( 225 ) at a lower portion of directory new-f ( 300 ) simultaneously as new dummy directory new-e′ ( 301 ). Further, a registered object ID in the contents in specific object ID table  127  is altered to that of directory new-f ( 300 ) from that of directory f ( 223 ). Hereby, the request of the client is likewise fulfilled, but a file belonging to directory e ( 224 ) of server B( 251 ) is not needed to be moved, so that the movement is completed at a very high speed. 
   Seventh Embodiment 
   In the following, a switch device according to a seventh embodiment of the present invention will be described. The present switch device s a modification of the switch devices of the first and second embodiments. The present embodiment has an object of speeding up the processings of the first and second embodiments. 
   In the first embodiment, switch device  100  needs, when an object ID is contained in reply data, to rewrite the object ID in object ID rewrite unit  101 , so that it retrieves and estimates that the reply data is one to which kind of instructions, from transaction ID control table  125  on the basis of a transaction ID contained in the reply data. Further, in the second embodiment, whether or not a reply packet is a reply to a request generated by file system control processing unit  104  by retrieving transaction ID control table  125  likewise the above description. The processing is, since the transaction ID belongs to the layers 5 to 7 of the OSI model, to extract the transaction ID with a software and hence successively compare the same with an entry of transaction ID control table  125 , which consumes much time. 
   In the seventh embodiment, use is made of information at the layer 4 or lower of the OSI model which is capable of being processed with a hardware to judge to which kind of instructions the reply is. As an example there will be described a case using a port number belonging to the layer of the OSI model. The just-mentioned port number includes, as an example, a port number in TCP (Transmission Control Protocol)/IP and in UDP (User Datagram Protocol). 
   Referring to  FIG. 27 , the file access control unit in the seventh embodiment is illustrated, processing classification table  129  that is an example of the classification table is newly added to the switch. Referring to  FIG. 28 , an example of an arrangement of processing classification table  129  is illustrated. 
   First, kinds of instructions are classified taking differences among processings which are executed for a reply packet from server  3 , to which processing classification information  176  is applied. The method of the classification may be executed for every instruction, or a plurality of instructions executing similar processings may be grouped taking differences of processings. There are classified the instructions at least into three instruction groups of an Instruction group where an object ID is not contained in reply data, an instruction group where an object ID is contained in reply data, and an instruction group generated in the file system control processing unit to ensure a high speed of the operation. 
   Switch  100  changes a port number from switch  100  to server  3  depending upon which kind of instructions it contains upon request data from client  1  being transferred to server  3 . Port number information  175  and processing classification information  176  are contained in processing classification table  129 , For selection of port numbers use may be made a method for allocating an empty port number for each request from client  1  or a method for determining a port number previously in a fixed fashion for any kind of instructions. It is noted here that the former method makes an entry of processing classification table  129  for each instruction, so that for speeding up the processings the latter method is desirable. 
   A reply packet from server  3  is sent to a port number to which switch  100  sends a request. File access control unit  102  retrieves processing classification table  129  on the basis of server identification information  154  and port number information  175  obtained by retrieving server information control table  126  to obtain processing classification information  176 , client IP address information  161 , and client MAC address information  162 . The processings described until now are capable of processing at a high speed provided that use can be made of an LSI (Large-scaled Integrated circuit) capable of retrieving the layer 4 or lower of the OSI model with a hardware. 
   In the case where an object ID is not contained in a reply packet from processing classification information  176 , the reply packet can be transferred only by converting an IP address and a MAC address on the basis of client IP address information  161  and client MAC address information  162  obtained as above, so that a very high speed processing is ensured. In the case of an instruction where it contains an object ID, the same processing as in the first embodiment is executed in object ID rewrite unit  101 . In the case of an instruction where it is generated in file system control processing unit  104 , the same processing as in the second embodiment is executed in file system control processing unit  104 . 
   A reply packet from server  3  is classified with the aid of processing classification information  176  in such a manner, and only necessary processings are executed, whereby the processings can be made a high speed. 
   With reference to  FIG. 29 , the above disclosure will be further described by dividing it to blocks adapted to an actual hardware arrangement. 
   Data analysis unit  124  can be divided into data analysis high speed processing unit  107  capable of high speed processing and data analysis non-high speed processing unit  108  consuming much time. To data analysis high speed processing unit  107 , server information control table  126  and processing classification table  129  are connected, and to data analysis non-high speed processing unit  108 , transaction ID control table  125  and specific object ID control table  127  are connected. An instruction where an object ID is not contained in reply data is transmitted to server  3  using port X, an instruction where an object ID is contained in reply data using port Y, and an instruction generated in file system control processing unit  104  using port Z. A reply from server  3  in the case of port X is capable of high speed processing because it is processed only in data analysis high speed processing unit  107 . In the case of port Y, it is processed in data analysis non-high speed processing unit  108 . Compared with the second embodiment in which such a reply passes through file system control processing unit  104 , it is capable of high speed processing. In the case of port Z, it is processed in file system control processing unit  104 . Since also in this situation it is known that such a reply is one to an instruction previously generated in file system control processing unit  104 , so that any excessive processing can be eliminated as the effect of the present invention. 
   Although in the present embodiment the case using the port numbers for discrimination of the instructions was described as an example, information on the OSI model layer 4 or lower such as an IP address, a VLAN (virtual LAN) tag, an MPLS (Multi-protocol Label switching) label, and a MAC address can be executed in the same fashion. 
   Eighth Preferred Embodiment 
   In the following, a switch device according to an eighth embodiment of the present invention will be described. The switch device is a modification of the switch device in the second embodiment. 
   The present embodiment is to speed up the processings of the second embodiment. 
   In the second embodiment, in step S 111 , it is necessary to check for all requests whether or not an object ID and instruction information contained in a request packet from client  1  correspond to an entry of specific object ID control table  127 . The object ID has 32 bite length in NFS for example, and belongs to the layer 5 to 7 of the OSI model, so that it is processed with a software, requiring much time. Further, in almost all cases the requests do not correspond to an entry of the specific object ID control table, so that processings which may not be executed are executed as a result. 
   In the present embodiment, specific attribute is registered in an object that provides a joint in a file system, and all requests are transferred without executing judgment in step S 111  to judge in switch  100  whether or not attribute contained in a reply packet is the foregoing specific attribute, and only for the case where the attribute is a specific attribute the file system control processing is executed to speed up the associated processings. 
   The embodiment will be described with reference to  FIG. 30  as an example. In the second embodiment, all requests for all objects in server A ( 250 ), server B ( 251 ) are compared to check whether or not an object ID corresponds to an entry of specific object ID control table  127 . However, object group A ( 226 ) and object group B ( 227 ) do not correspond the entry, so that processings, which may be not executed as a result, are executed. Thereupon, in the present embodiment, specific attribute is previously stored in dummy directory e′ ( 225 ) under directory f ( 223 ) in server A ( 250 ). Switch  100  executes the same processings as in the first embodiment for instructions for obtaining the object ID and attribute information corresponding to a directory e from client  1 , and transmits them to server A. Server A transmits to switch  100  a reply packet containing the specific attribute stored in pseudo file system  105  and the object ID of dummy directory e′ ( 225 ). Switch  100  judges whether or not the specific attribute is contained in the reply packet, and since in the present case it is contained, data is sent to the file system control processing unit for processings from step S 113  and later. If it is not contained, then the same processing as in the first embodiment is executed. A flowchart for the above description is illustrated in  FIG. 31 . In step S 130 , the same processings as in the first embodiment are executed, and a reply from server  3  is checked in its attribute in step S 131 . If it is the specific attribute, then the operation jumps to step S 113  in the second embodiment, but if it is not the specific attribute, then the same processing as in the first embodiment are executed in step S 132 . 
   In the present embodiment, as described above, switch  100  does not retrieve specific object ID control table  127  which may be not executed as a result upon reception of a request packet from client  1 , so that high speed processing is ensured. Instead of this, although it is necessary to judge whether or not the specific attribute is contained in the reply packet from server  3  in step S 131 , specific object ID control table  127  could have a plurality of entries while the judgment only compares a specific position of a reply packet and a specific attribute, and also for data length if an object ID is NFS, then comparison over 32 bits are required to a minimum, it is capable of being shortened depending upon implementation. Accordingly, if step S 111  and step S 131  are compared, then step S 131  ensures a high speed processing. 
   Ninth Embodiment 
   In the following, a ninth preferred embodiment of the present invention will be described. As the switch here one illustrated in  FIG. 17  is employed. 
   Referring to  FIG. 33 , server L ( 310 ) and server M ( 311 ) are a multiple protocol corresponding server, which can interpret protocol A and protocol B as protocols for servicing a file system through a network. The protocol A corresponds also to the switch device according to the present invention and server A. As illustrated in  FIG. 32 , in order to achieve the same object also other than the present invention, there is a modification where for accessing by the protocol B image  320  of another integrated directory tree is provided by refining the client or introducing a distributed file system into the server. In such a situation, the switch device in the present embodiment incorporates image  320  of another integrated directory tree for an access by the protocol B and provides image  320  of identical integrated directory tree also for an access by the protocol A. 
   To be concrete, an agent in pseudo file system  105  obtains information of image  320  of the integrated directory tree. Successively, it is determined on the basis of an instruction by an administrator at which directory A that is a root of the image  320  of the integrate directory tree is disposed on pseudo file system directory tree  200  on the switch device. In the present example, there will be described a situation where it is set to look at directory A below directory g of pseudo file system directory tree  200 , i.e., directory g in server A ( 250 ). 
   Herein, the switch device prepares dummy directory A′ ( 302 ) below directory g of server A, and further prepares dummy directory B′ ( 303 ) below directory A by accessing server L with the protocol A. In succession, information of joints between directories g and A and between directories A and B are registered as illustrated in  FIG. 33  for example such that contents in specific object ID control table  127  can be accessed from the client while making seamless a joint between two positions on the file system. For an access request associated with the joint, as described above, file system control processing unit  104  divides the request and sends it to a proper server, and collects necessary information from a reply thereto, and further returns a reply to the client, so that an integrated tree like the image of directory tree  200  of the pseudo file system can be provided. 
   Tenth Embodiment 
   In the following, a switch device according to a tenth embodiment of the present invention will be described. The switch device is applied to the network file system illustrated in  FIG. 3  likewise the first, second and third embodiments. The present embodiment is to achieve movement operation for a group of objects among a plurality of servers  3  without interruption of file access to a group of movement target objects from client  1 . More specifically, although the switch device according to the first to third embodiments can provide a file service of a single system image to a client by integrally managing a plurality of the servers, if any object is relocated in the course of an actual access (read and write) to any object or file on any server by a user, the user successively uses an object ID determined upon accessing during the access, so that the access by the user is interrupted or proper relocation can not be done. Accordingly, in the tenth embodiment, there is described a switch device, in which even in a timing when the user is accessing an object on the server at present, an administrator side can relocate the object, and it can be hidden to the user that relocation of the object and so on are done. 
   In the present embodiment, the switch device which is described using  FIG. 17  associated with the third embodiment is employed. More specifically, switch device  100  includes, additionally to object ID rewrite unit  101 , file access control unit  102 , packet processing unit  103 , all provided in the switch device in the first, second, and third embodiments, and file system control processing  104  and pseudo file system  105  provided in the second and third embodiments, data movement processing unit  106  provided in the third embodiment. 
   Referring to  FIG. 34 , file access control unit  102  in the tenth embodiment is illustrated in the form of a block diagram. File access control unit  102  includes, additionally to transaction ID control table  125  and server information control table  126  provided in the switch devices in the first, second, and third embodiments, and specific object ID control table  127  provided in the second and third embodiments, movement object status control table  130  for managing a group of objects each for executing the movement processing. 
   Operation of the switch device in the tenth embodiment will be described. The switch device masks, additionally to the function provided in the switch devices in the first, second, and third embodiments, a fact that the operation is in the course of a data moving processing by changing a transfer processing of a file access request such as read and write operations to a movement processing target object from client  1  when an object and a directory tree structure in each server  3  constituting an integrated directory tree constructed on pseudo file system  105  is copied to another server  3  and the movement processing is executed. 
   As described in the third embodiment, for example, a situation is assumed that data of a group of objects, owners of the objects, and attribute information such as an access right in a directory tree from directory c ( 222 ) in server B ( 251 ) are desired to be copied to server A for each tree structure owing to a reason of insufficient storage capacity or the like. Although the movement of the objects is finished by copying the data of the group of the objects, updating mapping information of pseudo file system  105  illustrated in  FIG. 14 , and deleting a copied portion from server B ( 251 ), it is possible to execute the movement processing without interruption of file accessing by controlling the file accessing with switch  100  from client  1  such that any disagreement of the data is prevented from happening when file access operation such as updating of data is required during the copying of the objects. 
   In the following, the operation of switch  100  relevant to the operation in the movement processing for the data will be described. Data movement processing unit  106  monitors remaining capacity data in storages  5  in all servers  3 , and records history data relevant to a file access request packet processed in switch  100  and a reply packet. Data movement processing unit  106  refers, when the remaining capacity is more reduced than a previously set criteria, and when file access requests are concentrated only on a specific server  3 , to data registered in pseudo file system  105 , and determines a directory tree on the movement source server  3  and a place to be moved ion the movement destination server  3 . 
   Prior to the execution of copying for data, data movement processing unit  106  extracts constituent information on a directory tree of a group of objects in a directory tree of the movement source, and all original object IDs  150 , and the original object ID  150  is converted in object ID rewrite unit  101  to compression type information entraining object ID  151  and postscript type information entraining object ID and then registered into movement object status control table  130  in file access control unit  102 . 
   Movement object status control table  130  is constructed with an entry, as illustrated in  FIG. 35 , which comprises movement source object ID  166  in which compression type information entraining object ID  151  or postscript type information entraining object ID  155  of the movement source is registered, movement destination object ID  167  in which postscript type information entraining object ID  151  and postscript type information entraining object ID  155  of the movement destination are registered, advancement status information  177  representative of information of an advancement status of the movement processing, parent object number  178  having as in formation, a number on movement object status control table  130  of an object corresponding to a parent object on a directory tree of a target object, updating log information  179  for registering updating history information from client  1  during copying operation, object attribute information  180  indicative of whether the target object is a directory or a file, and movement destination server information  168  for registering server identification information  154  corresponding to the movement destination server  3 . 
   In advancement status information  177  there are registered a non-copying status indicative of a fact that copying operation is not executed, an in-copying status indicative of a fact that copying processing is actually executed, a copying finish status indicative of a fact that copying is finished, and a movement finish status indicative of a fact that the movement processing is finished, and the registration is altered in the order of the non-copying status—in-copying status—copying finish status—movement finish status depending upon the statuses of the processings. 
   Accordingly, for all objects becoming movement targets before data is copied by data movement processing unit  106  there are registered movement source object ID  166 , parent object number  178  and object attribute information  180  as the directory constituting information, and movement destination server information  168 , and further advancement status information  177  is set to a non copy status. Further, for parent object number  178  of an entry of an object corresponding to a directory located at an uppermost level on directory trees of a group of objects for which the movement processing is executed “0” is registered. 
   An outline of processings of the present embodiment will described with reference to  FIG. 36 . First, an object being a target of the movement is determined, and information relevant to all objects that are the target of the movement is registered in movement object status control table  130  as a map. Then, the movement of the object is started, and following this mapping, i.e., updating of movement object status control table  130  is executed, and finish of the movement is confirmed. Thereupon, the object is divided into small movement processing units, which processing units are assumed to be copied to a movement destination one by one from the movement source to the movement destination, after the copying synchronization of copied objects is checked, and the directory in the aforesaid pseudo file system is replaced. Hereby, an FS branch is formed. Thereupon, updating to a copying finish region is blocked by data movement processing unit  106 . The movement is finally finished by repeating copying the movement processing unit one by one, a source object existent at the movement source is deleted. 
   In the following, the movement processing for a group of objects executed in data movement processing unit  106  will be described in detail with reference to a flow chard illustrated in  FIG. 37 . Object movement processing unit  106  first registers in step S 140 , pieces of information relevant to all objects that are movement targets to movement object status control table  130 , and then starts, in step S 141 , the movement processing for objects that are uppermost rank directory on a directory hierarchy judged from parent object number  178  and for all the objects corresponding to one hierarchy involved in a lower layer of the aforesaid objects judged from parent object number  178 , and executes, in step S 142 , copying from the movement source server  3  to the movement destination server  3 . Data movement processing unit  106  registers one obtained by converting original object ID  150  extracted from the movement destination server  3  to compression type information entraining object ID  151  and postscript type information entraining object ID  155  with the aid of object ID rewrite unit  101  to movement destination object ID  167  in movement object status control table  130  of the object executing actually the copying processing, and thereafter sets advancement status information  177  to the in-copying status and starts copying from the movement source to the movement destination. Advancement status information  177  is set to a copying finish status after the copying processing to the processing movement destination is finished. When an updating request from client  1  is generated to an object where advancement status information  177  in the in-copying status, data analysis unit  124  adds write position information other than the updating data and the like to updating log information  179  as the history information. Data movement processing unit  106  after the first copying processing is finished checks, in step S 143 , whether or not any information is registered in updatinglog information  179 . If any information is registered, data movement processing unit  106  executes, in step S 144 , copying processing of only an updating difference fraction from updating log information  179 , and clears updating log information  179 , and then sets advancement status information  177  to the copying finish status. 
   In contrast, when any updating log information is not registered in step S 143 , advancement status information  177  of the objects corresponding to the one hierarchy fraction is all set to the copying finish status, and thereafter data movement processing unit  106  alters, in step S 145 , as mapping to an object of the movement destination, mapping of an object fraction of the movement source of a portion for which copying is finished in integrated directory tree information registered in pseudo file system  105 , and thereafter sets advancement status information  177  of the object to movement finish status where the mapping of the object is altered. Data movement processing unit  106  checks, in step S 146 , whether or not there is existent an object where information registered in object attribute information  180  is attribute of the directory among the objects of one hierarchy fraction contained in a lower layer of an object corresponding to the aforesaid uppermost directory, i.e., an object that becomes a subdirectory is existent. Herein, when the subdirectory is existent, data movement processing unit  106  copies in step S 147 , all objects corresponding to one hierarchy fraction from objects that become the just-mentioned subdirectory in the same fashion as the case of the uppermost directory, and alters mapping information of pseudo directory  105 . When the subdirectory is not existent in step S 146 , i.e., when all processings are finished, the operation jumps to step S 148  to delete the data of the movement source. 
   In such a manner, the presence of the subdirectory is checked, and the movement processing is executed following the directory trees for every directory for each one hierarchy, and further advancement status information  177  of all objects registered in movement object status control table  130  is set to the movement finish status, and thereafter all objects that are movement targets existent in the movement source server  3  are deleted, and all movement processings are finished. 
   In the following, how to treat a file access request packet from client  1  when the movement processings are executed by data movement processing unit  106  and a reply packet in switch  100  will be described. The file access request from client  1  includes read operation for executing reading of data and attribute, updating operation for executing data writing and attribute alteration and the like, new preparation operation for preparing an object anew, and deleting operation for deleting an object, and switch  100  alters processing methods depending upon the respective operations. 
   In the following, a processing method in switch  100  in each operation will be described with reference to flow charts illustrated in  FIGS. 38 to 42 . 
   Packet processing unit  103 , once receiving the file access request packet of client  1 , extracts from the request packet in step S 150 , the file access request data, and client IP address information  160  and client MAC address information  161  of client  1 , and transmits them to file access control unit  102 . Data analysis unit  124  analyzes received request data in step S 151 , and extracts server identification information  154  contained in compression type information entraining object ID  151  or postscript type information entraining object ID  155 , and further checks whether or not server identification information  154  coincident with movement destination server information  168  of movement object status control unit  130  is existent. When server identification information  154  is not existent in movement destination server information  168 , the operation in switch  100  takes the same method as the processings for a request packet and a reply packet in the second embodiment as illustrated in step S 152 . 
   In contrast, when server identification information  154  is existent in movement destination server information  168  in step S 151 , in step S 153  the entry is retrieved and checked on whether or not compression type information entraining object ID  151  or postscript type information entraining object ID  155  are registered in movement source object ID  166  in movement object status control table  130 . When compression type information entraining object ID  151  or postscript type information entraining object ID coincident with movement source object ID  166  is not existent, as indicated in step S 154  the operations in switch  100  takes the same method as the processings of the request packet and reply packet in the second embodiment. In contrast, when compression type information entraining object ID  151  or postscript type information entraining object ID is existent in movement source object ID  166 , data analysis unit  124  judges what the operation request is from the request data in step S 155 . 
   When in step S 155  the operation request obtained from the request data is read operation as indicated in box S 160 , in step S 161  reference is made to advancement status information  177  of the entry of movement source object ID  166  corresponding to movement object status control table  130  to find the status being any of the non copying status, in-copying status, and copying finish status, in step S 162  the request packet is transferred to the movement source server  3 , so tat as indicated in step S 163  later operations in switch  100  takes the same method as in the processings for the request packet and the reply packet in the second embodiment. 
   When in step S 161  the operation is not any of the non-copying, in-copying, and copying finish, the situation is the operation finish status as indicated in box S 164 , and in step S 165  the request packet to the movement destination server  3  is transferred, and in step S 166  the request packet is converted to compression type information entraining object ID  151  or postscript type information entraining object ID  155  registered in movement destination object ID  167  of the entry of corresponding movement source object ID  166 . 
   Operations thereafter in switch  100 , as illustrated in step S 163 , employ the same method as in the processings for the request packet and the reply packet in the second embodiment. 
   When in step S 155  an operation request obtained from the request data is an updating operation as illustrated in box S 170 , in step S 171  advancement status information  177  is referred to of the entry of movement source object ID  166  corresponding to movement object status control table  130 , and when the operation is in the non-copying status, in step S 172  the request packet to the movement source server  3  is transferred, so that the operations thereafter in switch  100  employs the same method as the processings for the request packet and the reply packet in the second embodiment as indicated in step S 173 . 
   When the operation is not in the non-copying status in step S 171 , it is judged from advancement status information  177  in step S 174  that an operation target is in copying, and when the operation is in the in-copying status, the request packet is transferred to the movement source server  3  in step S 175 , and in step S 176  meta-information other than the updating data such as the write position information is added to updating log information  179  of the corresponding entry. The operations thereafter in switch  100  employ the same method as in the processings of the request packet and the reply packet in the second embodiment as indicated in step S 177 . However, when the reply data from the movement source server  3  suffers from an error owing to a reason that the client  1  does not have a deletion right, the reply data is transferred to client  1 , and data registered in updating log information  179  in movement object status control table  130  is deleted. 
   When the operation is not in the in-copying in step S 174 , it is judged in step S 178  whether or not the operation target is in the copying finish with reference to advancement status information  177 , and hence when it is in the copying finish status, the request packet is transferred to both of the movement source server  3  and the movement destination server  3  in step S 179 , and after necessary information is registered in transaction ID control table  125 , on the basis of compression type information entraining object ID  151  contained in the request packet or original object ID  150  obtained by converting postscript type information entraining object ID  155  in object ID rewrite unit  101 , and compression type information entraining object ID  151  or server identification information  154  extracted from postscript type information entraining object ID  155  transfer destination address information such as the IP address of the movement source server  3  extracted from server information control table  126  and the MAC information is sent to file system control processing unit  104 . In the same fashion, on the basis of original object ID  150  obtained by converting compression type information entraining object ID  151  or postscript type information entraining object ID  155  registered in movement destination object ID  167  of the entry of movement source object ID  166  in object ID rewrite unit  101 , and on server identification information  154  registered in movement destination server information  168 , transfer destination address information such as the IP address and the MAC address information extracted of the movement destination server  3  from server information control table  126  are sent to file-system control processing unit  104 . 
   In file system control processing unit  104 , in step S 180 , on the basis of data directed to the movement source server  3  and data directed to the movement destination server  3  received from file access control unit  102 , the request packet is transmitted from switch  100  to the movement source server  3  and the movement destination server  3  through packet processing unit  103 . The respective reply packets from the movement source server  3  and the movement destination server  3  are received in switch  100 , and the respective reply data are extracted in packet processing unit  103  and are sent to file system control processing unit  104 . In file system control processing unit  104 , in step S 181 , after it is confirmed that the two reply data are received, the reply data are sent to file access control unit  102 . Operations thereafter in switch  100  employ the same method as the processing method for the reply packet in the first embodiment, and the reply packet is returned to client  1 . 
   When the operation is not in the copying finish in step S 178 , the operation target is in the movement finish status as indicated in box S 182 , so that the request packet is transferred to the movement destination server  3  in step S 183  and is converted in step S 184  to compression type information entraining object ID  151  or postscript type information entraining object ID  155  registered in movement destination object ID  167  of the entry of movement source object ID  166  corresponding to movement object status control table  130 . Operations thereafter in switch  100  employ the same method as the processings for the reply packet and the reply packet in the second embodiment, as illustrated in step S 185 . 
   When in step S 155  an operation request obtained from the request data is a newly prepared operation as indicated in box S 190 , in step S 191  advancement status information  177  of the entry of movement source object ID  166  corresponding to an object corresponding to a newly prepared directory in movement object status control table  130  is referred to, and it is judged whether or not the operation is in the non-copying status, in-copying status, and copying finish status. When the operation is in any of the non-copying status, in-copying status, and copying finish status, in step S 192  the request packet is transferred to the movement source server  3 , and hence a later packet transfer operation in switch  100  employs the same method as in the processings for the request packet and the reply packet in the second embodiment as indicated in step S 193 , and data movement processing unit  106  adds an entry of a prepared object to movement object status control table  130  in step S 194 . 
   When the operation is not any of the non-copying status, in-copying status, and copying finish status, i.e., when the operation is in the movement finish status as indicated in box S 195 , in step S 196  the request packet is transferred to the movement destination server  3 , and hence in step S 197  the request packet is converted to compression type information entraining object ID  151  or postscript type information entraining object ID  155  registered in movement destination object ID  167  of the entry of movement source object ID  166  corresponding to movement object status control table  130  in step S 197  operations thereafter in switch  100  employ the same method as in the processings for the request packet and the reply packet in the second embodiment, as illustrated in step S 198 . 
   When in step S 155  an operation request obtained from the request data is a deletion operation as indicated in box S 200 , in step S 201  advancement status information  177  of the entry of movement source object ID  166  corresponding to movement object status control table  130  is referred, and it is judged whether or not the operation is in the non-copying status. When it is in the non-copying status, in step S 202  the request packet is transferred to the movement source server  3 , and hence later packet transfer operation in switch  100  employs the same method as in the processings for the request packet and the reply packet in the second embodiment as indicated in step S 203 , and data movement processing unit  106  deletes an entry of an object to be deleted that is registered in movement object status control table  130  in step S 204 . But, when reply data replied from the movement source server  3  is an error owing to a reason that client  1  does not have a delete right, the reply data is transferred to client  1 , and hence deletion of the corresponding object from movement object status control table  130  is not executed. 
   When the operation is not in the non-copying status in step  201 , it is judged by advancement status information  177  in step S 205  whether or not the operation is in the in-copying status, and if it is in the in-copying status, in step S 206  the request is sent to the movement source server  3  and the movement destination serve  3 , and hence in step S 207  a copying processing of an object corresponding to data movement processing unit  106  is interrupted. In the same manner as in the case of the write operation, in step S 208 , transmission of the request packet to the movement source server  3  and to the movement destination serve  3  and reply packet processing returned respectively therefrom are executed, and thereafter data movement processing unit  106  deletes the entry of movement object status control table  130  of a corresponding object in step S 209 . But, when the reply data replied from the movement source server  3  and the movement destination server  3  is an error owing to a reason tat client  1  does not have a right of delete, the reply data is transferred to client  1 , and deletion of the corresponding object from movement object status control table  130  is not executed, and copying for a corresponding object in data movement processing unit  106  is restarted. 
   When the operation is not in the in-copying status in step S 205 , it is judged with the aid of advancement status information  177  in step S 210  whether or not it is in the copying finite status, and if it is in the copying finite status, in step S 211  the reply packet is transferred to the movement source server  3  and the movement destination server  3 , and hence as in the same fashion as in the in-copying status, in step S 212  the transmission of the request packet to the movement source server  3  and the movement destination server  3  and the reply packet processing replied respectively are executed in the same manner as in the steps S 180  to S 181 . 
   Thereafter, the operation jumps to step S 204 , and data movement processing unit  106  deletes the entry of movement object status control table  130  of the corresponding object. However, when reply data replied from the movement source server  3  and the movement destination server  3  undergoes an error owing to a reason that the client  1  does not have a delete right, the reply data is transferred to client  1 , and deletion of the corresponding object from movement object status control table  130  is not executed. 
   Further, when an object of an operation target obtained from the request data is a directory, and advancement processing status information  177  is in the in-copying status or in the copying finish status, a method of transmission of requests to the movement source server  3  and the movement destination server  3  is not simultaneous transmission of the requests, but a delete request to the movement source server  3  is first transmitted, and only when the delete operation request is successful, the request is transmitted to the movement destination, and when an error happens on the movement source server  3 , the delete request is not transmitted to the movement destination server  3 . 
   When the operation is not in the copying finish status in step S 210 , it is the case where an operation target is in the movement complete status as illustrate in box S 213 , so that in step S 214  a request packet is transferred to the movement destination server  3 , and in step S 215  the request packet is converted to compression type information entraining object ID  151  or postscript type information entraining object ID  155  registered in movement destination object ID  167  of the entry of movement source object ID  166  corresponding to movement object status control table  130 . Operations thereafter in switch  100  employ the same method as in the processings for the request packet and the reply packet in the second embodiment as indicated in step S 216 . 
   All movement processings for an object group with the data movement processing unit  106  are complete, and an object corresponding to the movement source server  3  is deleted, and thereafter the processings for the request packet and the reply packet using movement object status control table  130  is effective until the entry of movement object status control table  130  is deleted with data movement processing unit  106  after a predetermined time. 
   Eleventh Embodiment 
   The present embodiment is an embodiment in which the tenth embodiment is further altered. Although in the tenth embodiment after the finish of the movement processing for all objects that are operation targets, the movement target object of the movement source server  3  is deleted, in the eleventh embodiment deletion of the movement target object of the movement source server  3  is not done. Further, when an operation request of any of the update operation request, new preparation request, and a delete request from client  1  comes during the movement processing, even if advancement status information  177  of movement object control table  130  of an operation target object is the movement settled status, the same processing as the copying finish status is executed in switch  100 , whereby there is ensured synchronism between the object of the movement target of the movement source and an object of a movement target of the movement destination that is a duplication of the just-mentioned object. 
   Twelfth Embodiment 
   The present embodiment is an embodiment obtained by further altering the tenth embodiment and the eleventh embodiment. In the tenth and eleventh embodiments, when an update operation request comes from client  1  during the movement processing in switch  100 , not only the update meta-information but also the update data are registered in update log information  179  in movement object status control table  130  for an object that is an operation target, and in the course of copying processing for a later updated portion reading from the movement source server  3  is not executed, and the update processing is directly executed for an update operation target object. 
   The preferred embodiments according to the present invention were described. As described previously, although the switch devices in the respective embodiments are applicable to the network file system of a network construction illustrated in  FIG. 3 , those switches can provide the just-mentioned function even with the construction where server  3  is directly connected with switch  100 , not network  2 . With such a network construction which is illustrated in  FIG. 43 , any access from client  1  to server  3  without mediating switch  100  can be completely interrupted, so that system-down can be prevented from happening by directly accessing incorrectly to server  3  from client  1 . 
   In switch device  100  in the respective embodiments, there may be provided a table having an entry composed of a combination of original object ID  150  prepared by server  3  and server identification information  154  instead of object ID rewrite unit  101 . In this situation, data analysis unit  124  estimates server identification information corresponding to an object ID contained in a file access request with reference to the table, and estimates address information of a server corresponding to the server identification information with reference to server information control table  126 , and determines a transfer destination of the file access request based upon the resulting address information. With the construction, even if original object ID  150  is transferred to client  1  as it is, the same function can be realized. However, when in this situation there is also the possibility that original object ID  150  having the same data train is generated, so tat when an object ID having the same data train as that of original object ID  150  already registered in the table thereof is received with switch  100 , there are necessary processings where the object ID is rewritten to another data train, and there is provided an entry in which the rewritten data train is registered. 
   Although in the switch devices of the aforesaid respective embodiments they are applied to a network file system, the present invention is not limited thereto, and if there is a system where a resource (object) possessed by a plurality of servers is utilized by a client, the present invention is applicable to the system excepting the network file system. 
   In switch  100  a program is recorded for executing the operation of switch  100 . The program is to control the operation of a hardware of switch  100  that is a computer server, by which program all processings of switch  100  is specified. 
   While preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.