Patent Publication Number: US-7587506-B2

Title: Computer system and data backup method in computer system

Description:
CLAIM OF PRIORITY 
   The present application claims priority from Japanese Application P2005-64690 filed on Mar. 9, 2005, the content of which is hereby incorporated by reference into this application. 
   BACKGROUND 
   The present invention relates to a technique for backing up data stored on storage servers in a computer system comprising individual storage servers for each client connected over the Internet. 
   Storage servers which store data used by servers and clients are important for periodically backing up data in order to prevent accidental loss of data. Data can be backed up, for example, to certain recording media by sending the data to a media server connected by a fiber network to the storage servers (see, for example, U.S. Pat. No. 6,460,113). Examples of backup recording media which can be used include portable recording media such as tape media, optical disks, and opticomagnetic disks, as well as stationary recording media such as magnetic disks and semiconductor memory devices. 
   Recently there has been continuing development of services which involve exclusive maintenance and management of storage servers, web servers, and the like, and which give clients access to the functions of such devices over the Internet. Ordinarily, such servers are located in facilities referred to as data centers managed by service providers. Storage servers located in data centers are sometimes individually prepared for each client to limit access by other clients. 
   An example of a method for backing up data stored in storage servers in such a data center is to individually prepare media servers for each client in the same manner as storage servers. In this method, however, the increase in facility resources and the greater complexity of the facilities can result in the risk of less maintenance. One possible solution is to connect one media server over a network to a plurality of storage servers. However, in that method, the storage servers for which pains have been taken to individually provide each client end up being connected to each other over the network, with the danger of client data leaking over the network during data backup to other clients. 
   SUMMARY 
   In view of these various problems, an object of the present invention is to control the increase in facility resources and to properly back up client data while controlling data leaks. 
   The computer system of the present invention is constructed in the following manner based on the above objectives. Specifically, the gist of the invention is a computer system that is equipped with individual storage servers for predetermined sections that are accessed over the Internet, comprising: 
   a backup device that backs up data stored in the storage servers; 
   a data intermediate server that is connected to the storage severs and backup device, and that reads data from the storage servers according to backup commands received from the backup device and transmits the read data to the backup device; and 
   backup channels that connect the storage servers and data intermediate server, and that exchange data based on a communication procedure that is different from the protocol used by the Internet in cases where data is read from the storage servers by the data intermediate server. 
   In the computer system of the invention, a data intermediate server is located between the storage servers and backup device. The data intermediate server and the storage servers are connected by backup channels in which the exchange of data is based no a communication procedure that is different from the protocol used by the Internet. Client computers which connect over the Internet to the computer system thus have limited access to the backup device beyond the storage server. That is, according to the present invention, during the backup of data stored on the storage servers, client data transmitted between the data intermediate server and backup device can be prevented from leaking or being improperly accessed by other clients, and the data can be properly backed up. According to the structure of the present invention, a computer system can be built at a lower cost, without the need for setting up individual backup devices for each storage server. The predetermined sections can also be divided, for example, according to client or differences such as client departments. 
   In a computer system with the above structure, the data intermediate server and backup device may be connected by a network that communicates based on the same protocol as the protocol used by the Internet. This will allow the backup device and data intermediate server to be connected using a general purpose network machine. 
   Here, the protocol used by the Internet can be the Internet Protocol. The Internet Protocol is a communication protocol located at the network layer of the OSI reference model defined by the International Standards Organization, and communicates between nodes based on IP addresses assigned to each node on a network. 
   The storage servers and data intermediate server may also be connected by a channel from among USB, serial interfaces, Infiniband, and fiber channels as the backup channels. Serial bus interface standard defined as IEEE1394, which offer high-speed communications and isochronous real-time data services may be used for the backup channels. Only protocols that are not compatible with Internet protocols, such as IPX/SPX or NetBEUI, for example, should be used for communications on such channels, which may be physically connected by a channel with the same standards to the network used to connect the backup device and data intermediate server (such as Ethernet (registered trademark)). 
   In the computer system with the above structure, the storage servers may be constructed by software in a single server device by means of certain programs run by the CPU. The data intermediate server may also be constructed by software in the single server device by means of certain programs run by the CPU. These structures will allow systems to be built at lower cost because the computer system architecture can be simplified. 
   In such a structure, the server device keeps reception buffer areas for the storage servers and data intermediate server to use in exchanging data, in the memory of the server device, and the storage servers and data intermediate server use the reception buffer areas as backup channels. 
   This sort of structure can prevent unauthorized intrusions or the like that use Internet protocols, because the data itself can be exchanged through the reception buffer. Data can also be efficiently transmitted because there is no need for a process to divide the data into packets or to attach protocol headers, as in data transmission based on communications protocols. 
   Here, the server device may control the allocation of physical devices for the server device used by the data intermediate server and storage servers constructed by software, based on certain resource allocation tables. 
   The physical device can include, for example, at least any one of a CPU, memory, magnetic disk, and network interface, and the resource allocation tables can define at least any one of appropriable CPU utilization, appropriable memory area, appropriable disk area, and usable network interface for each storage device and data intermediate server. 
   Such resource allocation tables can be used to allow the functions of the storage servers and the functions of the data intermediate server to be efficiently realized by software by means of one server device. 
   In computer systems with the various structures described above, the backup device may store lists in which the locations of data targeted for backup are registered, and may send backup commands to the data intermediate server based on the lists. 
   For example, locations of data targeted for backup may be registered in the lists by means of a directory structure comprising identification paths for individually identifying the storage servers and paths specific to the storage servers, and the data intermediate server can specify the storage server in which the data targeted for backup is stored, and can read the stored data from the storage server to the specific path. 
   Such a structure allows identifiers for specifying the storage server targeted for backup and the locations of data stored in the storage servers to be registered in the lists in a uniform format, thus allowing the locations of the data targeted for backup to be efficiently managed. 
   In computer systems with the various structures described above, the storage servers may store start paths that serve as the basis of where data targeted for backup will be stored, specify data indicated by the data intermediate server, and output the specified data to the data intermediate server. Such a structure will make it possible to set a range of data which is backed up by the storage device as well as the backup device. 
   In a computer system with such a structure, the storage servers may comprise means for modifying the details in the start paths by means of a computer connected over the Internet. This will allow clients more flexibility to set the range of data to be backed up using a storage server over the Internet. 
   In computer systems with the various structures described above, the backup device may comprise a media server for outputting the data to certain recording media, and a backup control device for storing the data to the media server for secondary backup. 
   In this sort of structure, the backup control device can establish a data socket to the media server before sending the backup command to the data intermediate server, and can establish a connection between the media server and data intermediate server. 
   Here, the recording media to which the backup device backs up the data can be tape media. Because tape media generally has a greater storage capacity than magnetic disks or the like, more data can be backed up. 
   The storage servers, backup device, and data intermediate server may also be located in the same data center. 
   In addition to the various computer system structures described above, the present invention can also be worked in the form of an invention of the following method, specifically, a method for backing up comprising; 
   providing the computer system with storage servers that are accessed over the Internet and that are individually prepared for predetermined sections, a backup device for backing up data stored in the storage servers, and a data intermediate server connected to the storage servers and backup device, wherein 
   receiving backup commands sent from the backup device by the data intermediate server, 
   reading data from the storage servers, according to the backup commands that the data intermediate server received, through channels where data is exchanged based on a communication procedure that is different from the protocol used in the Internet, and sending the read data to the backup device, and 
   storing the data by the backup device. 
   In this type of backup method, during the backup of data stored on the storage servers, client data transmitted between the data intermediate server and backup device can be prevented from leaking or being improperly accessed by other clients, and the data can be properly backed up, in the same manner as the computer system described above. 
   In addition to the embodiments of computers systems and back up methods described above, the present invention can also be worked in the form of computer programs for allowing a computer to run data back up. Such computer programs may also be embodied in the form of data signals in carrier waves, and may be recorded on computer-readable recording media. Examples of recording media include CD-ROMs, floppy disks, opticomagnetic disks, and DVDs. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates the basic structure in an embodiment of the invention. 
       FIG. 2  illustrates the structure of the system as a whole in a first embodiment. 
       FIG. 3  illustrates and example of a resource allocation table TB 1 . 
       FIG. 4  illustrates the theoretical structure of the data server  600 . 
       FIG. 5  illustrates an example of a storage server table TB 2 . 
       FIG. 6  is a flow chart of the backup process. 
       FIG. 7  is a flow chart of the backup process. 
       FIG. 8  illustrates an example of a file list FL. 
       FIGS. 9   a  through  9   c  illustrate file lists after allocation. 
       FIG. 10  illustrates the structure of the system as a whole in a second embodiment. 
       FIG. 11  illustrates an example of a storage server table TB 2   b.    
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the invention are given in the following order to further elucidate the operation and effects of the above inventions.
         A. Embodiments   B. First Embodiment   (B1) System Structure as a Whole   (B2) Backup Process   (B3) Effects   C. Second Embodiment   D. Variants       

   A. Embodiments 
     FIG. 1  illustrates the basic structure in an embodiment of the invention. As illustrated, the computer system in this embodiment comprises a data center DC, and client computers connected over the Internet INT to the data center DC. In this embodiment, a computer  100 A of company A, a computer  100 B of company B, and a computer  100 C of company C are connected to the data center DC. The data center DC is equipped with a system  200 A for company A, system  200 B for company B, and system  200 C for company C, corresponding to each client, and is also equipped with a backup system BS for backing up data in these systems. Although there are three clients in this embodiment, the number is not limited. 
   The system  200 A for company A is constructed by connecting a router RT 1 , web server SV 1 , and storage server ST 1  to each other by a local area network LAN 1 . The computer  100 A of company A is connected over the Internet INT to the router RT 1 . The storage server ST 1  is constructed in the form of an NAS (Network Attached Storage) comprising a disk device DK 1 , and HTML (Hyper Text Markup Language) data or the like used by the web server SV 1  is stored in the disk device DK 1 . 
   Meanwhile, the system  200 B for company B is constructed by connecting a router RT 2 , web server SV 2 , and storage server ST 2  to each other by a local area network LAN 2 . The computer  100 B of company B is connected over the Internet INT to the router RT 2 . The storage server ST 2  is constructed in the form of an NAS comprising a disk device DK 2 , and a data base or the like used by the web server SV 2  is stored in the disk device DK 2 . 
   The system  200 C for company C is also constructed by connecting a router RT 3 , FTP server SV 3 , and storage server ST 3  to each other by a local area network LAN 3 . The computer  100 C of company C is connected over the Internet INT to the router RT 3 . The storage server ST 3  is also constructed in the form of an NAS comprising a disk device DK 3 , and various types of data available in file transmission by the FTP server SV 3  is stored in the disk device DK 3 . 
   The backup system BS is constructed by connecting a data intermediate server  300 , backup control device  400 , and media server  500  to each other by means of a local area network LAN 4 . The above storage servers ST 1  through ST 3  are also each connected by backup channels BK 1  through BK 3  to the data intermediate server  300 . 
   The backup control device  400  is a device for comprehensively controlling file backup carried out between the storage servers ST 1  through ST 3 , data intermediate server  300 , and media server  500 . The backup control device  400  stores a file list FL in which the locations of files targeted for backup have been registered by the system administrator, and controls file backup based on this file list FL. The back up control device  400  can make use of NDMP (Network Data Management Protocol), for example, which works on an Internet protocol as the protocol for backing up files. 
   The backup control device  400  is a device which, based on backup commands from the data intermediate server  300 , reads files stored in the storage servers ST 1  through ST 3  and transmits the files through the local area network LAN 4  to the media server  500 . 
   The media server  500  is a device for recording data transmitted from the data intermediate server  300  through the local area network LAN 4  to tape media. 
   In the computer system in this embodiment, the Internet Protocol (IP) is used as the communication protocol for communication between devices via the local area networks LAN 1  through LAN 4  or the Internet INT. However, the data intermediate server  300  and the storage servers ST 1  through ST 3  are connected by the backup channels BK 1  through BK 3 , which do not permit Internet protocol traffic but only data targeted for backup and control data assigned thereto. A specific example of such backup channels BK 1  through BK 3  is illustrated in an embodiment below. 
   According to the embodiment with this structure, access by the Internet Protocol from the Internet INT side to the local area network LAN 4  side is limited, making it possible to prevent unauthorized retrieval of backup data circulating in the backup system BS. Several embodiments in which the present embodiment is applied are described below. 
   B. First Embodiment 
   (B1) System Structure as a Whole 
     FIG. 2  illustrates the structure of the system as a whole in a first embodiment. In this embodiment, the functions of the storage servers ST 1  through ST 3  and the functions of the data intermediate server  300  among the above embodiments are realized by software in one server device. Such a server device is referred to as the data server  600  in the following description. 
   As illustrated, the data server  600  is composed in the form of a computer comprising a CPU  610 , memory  620 , network interfaces NIC 1  through NIC 4 , a host bus adapter HBA, and the like. The local area networks LAN 1  through LAN 4  are each connected to the network interfaces NIC 1  through NIC 4 . Three disk devices DK 1  through DK 3  are meanwhile connected to the host bus adapter HBA. 
   A process control program PCP, a resource allocation table TB 1  used by the process control program PCP, a virtual data intermediate server program VDP, and virtual storage server programs VSP 1  through VSP 3  which are run by the CPU  610  are stored in memory  620 . These programs may also be installed on any of the disk devices DK 1  through DK 3 , in which case they are read from the physical disk to memory  620  and run by the CPU  610 . 
   The virtual storage server programs VSP 1  through VSP 3  are programs for executing the functions of the storage servers ST 1  through ST 3  in the above embodiments. The virtual data intermediate server program VDP is a program for executing the functions of the data intermediate server  300  in the above embodiment. 
   The process control program PCP is a program for allocating specific resources to processes produced when the above programs are run, and for controlling the process operations. Resources are allocated with reference to the resource allocation table TB 1 . 
     FIG. 3  illustrates an example of a resource allocation table TB 1 . As illustrated, usable memory space or disk areas, network interfaces, maximum occupiable CPU utilization, and the like are established in the resource allocation table TB 1 . A reception buffer memory area is also established for the exchange of data between the virtual storage server programs VSP 1  through VSP 3  and the virtual data intermediate server program VDP. In this embodiment, as illustrated, paths where the magnetic disks DK 1  through DK 3  are mounted (such as “/mnt/dk 1 /”) are assigned as disk areas allocated for each process. In contrast, however, ranges of physical addresses in the magnetic disks may be allocated, and virtual drives kept in the magnetic disks may be individually allocated. Optional directories or partitions may also be allocated. 
     FIG. 4  illustrates the theoretical structure of the data server  600  realized by running the various programs described above. As illustrated, the virtual storage server program VSP 1  is run so that the virtual storage server ST 1 V for company A is constructed by software in the data server  600 . Similarly, the virtual storage server program VSP 2  is run so that the virtual storage server ST 2 V for company B is constructed, and the virtual storage server program VSP 3  is run so that the virtual storage server ST 3 V for company C is constructed. The virtual data intermediate server program VDP is also run so that the virtual data intermediate server  300 V is constructed by software. 
   As illustrated, the individual network interfaces NIC 1  through NIC 3 , disk areas DK 1 V through DK 3 V, or reception buffers A through C are allocated to the virtual storage servers ST 1 V through ST 3 V based on the resource allocation table TB 1 . The virtual storage servers ST 1 V through ST 3 V also store a “start path” in the memory space or disk area allocated to each. Paths that serve as the basis of where data targeted for backup will be stored are established in the start paths. 
   The network interface NIC 4  is allocated to the virtual data intermediate server  300  based on the resource allocation table TB 1 , and the individual reception buffers  1  through  3  are also allocated to the virtual storage servers ST 1 V through ST 3 V. The virtual data intermediate server  300 V stores a storage server table TB 2  to manage the virtual storage servers ST 1 V through ST 3 V in the memory space or disk area allocated based on the resource allocation table TB 1 . 
     FIG. 5  illustrates an example of a storage server table TB 2 . As illustrated, the corresponding relations between “identification paths,” “storage paths names,” and “interfaces” are defined in the storage server table TB 2 . “Identification paths” are identifiers which are used when the backup control device  400  indicates a virtual storage server targeted for backup in the backup process described below. “Storage server names” are names given individually to the virtual storage servers ST 1 V through ST 3 V. In this embodiment, the virtual storage server ST 1 V is designated “vnas 1 ,” the virtual storage server ST 2 V is designated “vnas 2 ,” and the virtual storage server ST 3 V is designated “vnas 3 .” Reception buffers used by the virtual storage servers ST 1 V through ST 3 V during the exchange of data with the virtual data intermediate server  300 V are indicated in the “interfaces.” 
   As noted above, in this embodiment, the storage servers ST 1  through ST 3  and data intermediate server  300  in  FIG. 1  are constructed by software in one data server  600 , and the virtual backup channels VBK 1  through VBK 3  in  FIG. 4  are thus also realized virtually by the exchange of data using the data given in the table in  FIG. 5 . The storage servers and data intermediate server can also be individually established, and can be connected by actual channels using a protocol other than the Internet Protocol. 
   (B2) Backup Process 
     FIGS. 6 and 7  are flow charts of a backup process carried out between the virtual storage servers ST 1 V through ST 3 V, virtual data intermediate server  300 V, backup control device  400 , and media server  500 . The backup process starts when the system administrator carries out back up operations in regard to the backup control device  400 . 
   When the backup process is executed, the backup control device  400  first requests a connection to the media server  500  through the local area network LAN 4  (step S 100 : “Connect”). The media server  500  replies that a connection is possible (“OK”) upon receiving the request while connected (step S 110 ). 
   Upon receiving the notification from the media server  500  that connection is possible, the backup control device  400  requests the establishment of a data socket to the media server  500  (step S 120 : “Open Data Port”). the media server  500  establishes the data socket upon receiving the command, and ends the port number of the established data socket (step S 130 : “Data Port Number”). 
   Upon receiving the port number from the media server  500 , the backup control device  400  requests a connection to the virtual data intermediate server  300 V through the local area network LAN 4  (step S 140 : “Connect”). Upon receiving the request while connected, the virtual data intermediate server  300 V responds that a connection is possible (“OK”) (step S 150 ). 
   Upon receiving the response that a connection is possible from the virtual data intermediate server  300 V, the backup control device  400  sends the port number given by the media server  500  in step S 130  to the virtual data intermediate server  300 V, and requests connection to the data socket corresponding to the port number (step S 160 : “Connect Data Port”). 
   Upon receiving the request, the virtual data intermediate server  300  connects to the data socket established by the media server  500 . When the connection to the data socket is complete, a reply that the connection is complete (“OK”) is sent to the backup control device  400  (step S 170 ). 
   In the above process, a connection is established between the virtual data intermediate server  300 V and the media server  500  through the local area network LAN 4 . Data can thus be sent from the virtual data intermediate server  300 V to the media server  500  through the local area network LAN 4 . 
   With reference to  FIG. 7 , when the above process results in the establishment of a connection between the virtual data intermediate server  300 V and the media server  500 , the backup control device  400  sends a backup request through the local area network LAN 4  to the virtual data intermediate server  300 V (step S 180 ). At that time, the backup control device  400  sends the file list in which the list of files targeted for backup are registered, along with the backup request, to the virtual data intermediate server  300 V. 
     FIG. 8  illustrates an example of a file list FL. As illustrated, the files targeted for backup are registered by means of a directory structure in the file list FL. For example, “/vnas 1 /secret.txt” is the first registered file in the list targeted for backup in the illustrated list. This indicates that “vnas 1 ,” that is, a file referred to as “secret.txt” stored on the virtual storage server ST 1 V, is targeted for backup. Also, for example, “/vnas 3 /log/*” is indicated sixth in the list. This indicates that “vnas 3 ,” that is, all the files stored in a directory referred to as “log on the virtual storage server ST 3 V, are targeted for backup. 
   With reference to  FIG. 7  again, upon receiving the backup command and the file list F from the backup control device  400  (step S 190 ), the virtual data intermediate server  300 V matches the identification path sections in the file list FL with the identification paths in the storage server table TB 2 , and divides the file list FL that has been received into file lists for the virtual storage servers ST 1 V through ST 3 V (step S 200 ). For example, when the file list FL includes an identification path “/vnas 1 ,” the list is divided as a file list for vnas 1 . 
     FIGS. 9   a  through  9   c  illustrate examples in which the file list FL in  FIG. 8  has been divided.  FIG. 9   a  shows a file list FL 1  for vnas 1 , and  FIG. 9   b  shows a file list FL 2  for vnas 2 .  FIG. 9   c  shows a file list FL 3  for vnas 3 . As illustrated, the virtual data intermediate server  300  deletes a portion of the identification path referred to as “/vnas 1 ” or “/vnas 2 ” from the file lists FL 1  through FL 3  when dividing the file list FL. 
   With reference to  FIG. 7  again, when the virtual data intermediate server  300 V divides the file list FL, the file lists FL 1  through FL 3  are sent to the virtual storage servers ST 1 V through ST 3 V (vnas 1  through vnas 3 ), and a file transfer is requested (step S 210 ). The file transfer request is sent through the interfaces (see  FIG. 5 ) established in the storage server table TB 2 . That is, in this embodiment, the request is sent through the reception buffers a through c allocated to the virtual storage servers and the reception buffers  12  through  3  allocated to the virtual data intermediate server  300 V. 
   Upon receipt of the file lists and file list transfer requests from the virtual data intermediate server  300 V through the reception buffers (step S 220 ), the virtual storage servers ST 1 V through ST 3 V add the “start paths” in  FIG. 4  to the file lists (step S 230 ) . When, for example, a path “/usr/local/” is established in the “start path” and a file “database/customer.db” is registered in the file list, the file list after the addition of the start path would be “/usr/local/database/customer.db.” When no “start path” is established on the virtual storage server, the process in step S 230  is skipped. 
   When the virtual storage servers ST 1 V through ST 3 V add start paths to the file lists, the files corresponding to the files registered in the file lists are retrieved from the respective disk areas and sent to the virtual data intermediate server  300 V (step S 240 ). the files are transmitted through the reception buffers in the same manner as in step S 210 . 
   Upon receipt of the files from the virtual storage servers ST 1 V through ST 3 V through the reception buffers (step S 250 ), the virtual data intermediate sever  300 V sends the received files to the data socket of the media server  500  where a connection was established in step S 170  above (step S 260 ). The files are transferred through the local area network LAN 4 . 
   Upon receipt of the files from the virtual data intermediate server  300 V (step S 270 ), the media server  500  writes all the received files to the tape media (step S 280 ). When the writing is finished, the virtual data intermediate server  300 V is notified through the local area network LAN 4  that the writing is complete (step S 290 ). 
   Upon receiving notification from the media server  500  that the writing is complete (step S 300 ), the virtual data intermediate server  300  notifies the backup control device  400  through the local area network LAN 4  that backup is complete (step S 310 ). When the backup control device  400  receives notification that backup is complete (step S 320 ), the backup process is complete. 
   (B3) Effects 
   In the computer system of the embodiment described above, the exchange of data between the virtual storage servers ST 1 V through ST 3 V and the virtual data intermediate server  300 V is managed through the reception buffers established in the memory  620  of the data server  600 . Although the Internet Protocol is used as the communication protocol on the local area networks LAN 1  through LAN 3  and Internet INT, this type of communication protocol is not used in the reception buffers, and the data itself is handled directly, thus limiting direct access to the local area network LAN 4  constructed on the backup system BS side from the web server SV 1  or client computers  100 A through  100 C connected over the Internet INT. Thus, during the backup of the above files, client files transmitted over the local area network LAN 4  can be prevented from leaking or being improperly accessed by other client computers, and the data can be properly backed up. 
   In this embodiment, the functions of the storage servers ST 1  through ST 3  and the functions of the data intermediate server  300  are realized by software by means of one data server  600 , allowing the system to be constructed at a lower cost. 
   C. Second Embodiment 
     FIG. 10  illustrates the structure of the system as a whole in a second embodiment. In the first embodiment, the functions of the storage servers ST 1  through ST 3  and the functions of the data intermediate server  300  were realized by software by means of one data server  600 , but in this embodiment, the storage servers ST 1  through ST 3  and the data intermediate server  300  are separate devices in the same manner as the basic structure in the embodiment. 
   The storage servers ST 1  through ST 3  each comprise a CPU, memory, network interface NIC, host bus adapter HBA, communication port COM, and the like. The network interfaces NIC of the storage servers ST 1  through ST 3  are connected to local area networks LAN 1  through LAN 3 , and the host bus adapters HBA are connected to the disk devices DK 1  through DK 3 . Start paths are also stored in memory. 
   the data intermediate server  300  comprises a CPU, memory, network interface NIC for connection to the local area network LAN 4 , and three communication ports COM. The storage server table TB 2   b  is stored in memory. 
     FIG. 11  illustrates an example of a storage server table TB 2   b.  As illustrated, the contents of the storage server table TB 2   b  are virtually the same as those in the storage server table TB 2  in  FIG. 5  of the first embodiment, but the “interface” details are different. That is, reception buffers were used s interfaces in the transfer of data in the first embodiment, but communication ports COM are used in this embodiment. 
   IEEE1394 ports are used as the communication ports COM in this embodiment. In IEEE1394 ports, data is transferred based on the IEEE1394 protocol, not the Internet Protocol. Other examples of communication ports include bidirectional serial ports such as RS-232C, and USB ports, Infiniband, fiber channels, and the like. When only protocols that are not compatible with Internet protocols, such as IPX/SPX or NetBEUI, for example, are used, then Ethernet (registered trademark) ports can be used as the communication ports COM. 
   In the computer system of this embodiment constructed in the manner described above, the backup process is the same as that described using  FIGS. 6 and 7  in the first embodiment. However, the process carried out by the virtual storage servers ST 1 V through ST 3 V in  FIGS. 6 and 7  are carried out by the storage servers ST 1  through ST 3  in  FIG. 10 , and the process carried out by the virtual data intermediate server  300 V in  FIGS. 6 and 7  is carried out by the data intermediate server  300  in  FIG. 10 . 
   In the backup process, the process of sending the file transfer requests and the file lists shown in step S 210  of  FIG. 7  is carried out through the communication ports COM in the present embodiment. The file transmission process in step S 240  is similarly carried out through the communication ports COM. 
   In the second embodiment constructed in the above manner, the exchange of data between the storage servers ST 1  through ST 3  and the data intermediate server  300  is carried out through the communication ports COM based on the IEEE1394 protocol. The Internet Protocol is used as the communication protocol on the local area networks LAN 1  through LAN 3  or the Internet INT, but the Internet Protocol is not used in communications through the communication ports COM, thus limiting direct access to the local area network LAN 4  constructed on the backup system BS side from the web server SV 1  or client computers  100 A through  100 C connected over the Internet INT. Client files transmitted over the local area network LAN 4  during the file backup process can thus be prevented from leaking or being improperly accessed by other client computers, and the data can be properly backed up. 
   D. Variants 
   A few embodiments of the invention were described above, but the invention can be worked in a variety of forms without departing from the spirit and scope of the invention. The following variants are possible, for example. 
   In the above embodiments, reception buffers or communication ports COM were used to block Internet Protocol traffic and to limit access from client computers  100 A through  100 C and the like to the backup system BS in the data center DC. By contrast, in structures where, for example, the storage servers ST 1  through ST 3  and the data intermediate server  300  are connected by the Ethernet (registered trademark), the data intermediate server  300  can monitor all packets transmitted from the storage servers ST 1  through ST 3  so as to permit only data corresponding to file transfer requests from the backup control device  400 . In such cases, the data intermediate server  300  cancels all packets spontaneously sent from the storage servers ST 1  through ST 3  or client computers  100 A through  100 C. This form of control can control access from the storage servers ST 1  through ST 3  or Internet INT to the backup system BS side even though the data transferred between the storage servers ST 1  through ST 3  and the data intermediate server  300  are based on the Internet Protocol. 
   In the above embodiments, “start paths” stored in the storage servers ST 1  through ST 3  and virtual storage servers VST 1  through VST 3  may optionally be established from the client computers  100 A through  100 C. A method of establishment, for example, is to have the client computers  100 A through  100 C read the start paths from the respective storage servers over the Internet INT, and to edit the contents of the start paths using a text editor or the like installed on the client computers  100 A through  100 C. Optional start paths can also be established by being written back to the respective storage servers. When the start paths can be edited in this manner, the client has more flexibility in establishing ranges targeted for backup. 
   Data may also be transferred between the storage servers and data intermediate server using a unique protocol instead of an existing protocol. The backup communications channels can also be uniquely constructed. 
   Having described a preferred embodiment of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to the embodiments, and that various changes and modifications could be effected therein by one skilled in the art without departing from the spirit or scope of the invention as defined in the appended claims.