Patent Publication Number: US-2004049553-A1

Title: Information processing system having data migration device

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to an apparatus for managing and controlling, in an information processing system including a storage subsystem, the storage subsystem, and more particularly to a data migration technique for migrating data of a storage area which a first storage subsystem has to a second storage subsystem.  
       [0002] The data migration technique that moves data of a storage area existing within a first storage subsystem to a second storage subsystem to change a storage subsystem to be used by a computer from the first storage subsystem to the second storage subsystem is effective when changing the storage subsystem from an old type of machine to a new type of machine and when no access should be obtained to the storage subsystem currently in use in order to maintain the machine and the like. As a conventional technique concerning such a data migration technique, there has been disclosed in U.S. Pat. No. 6,108,748 a technique that performs data migration between storage subsystems while a computer is continuing access to the storage subsystem.  
       [0003] Also, in recent years, as a protocol for performing storage I/O between the storage subsystem and the computer, iSCSI (internet Small Computer System Interface) whose specification is currently being laid down by IETF (Internet Engineering Task Force) has been drawing attention. The iSCSI is a protocol that performs exchange of the SCSI command, control of transmission, authentication and the like on a network on which the iSCSI communicates with the TCP/IP protocol.  
       [0004] In the above-described technique of the U.S. Pat. No. 6,108,748, in any other computer than a computer in which a specified OS (for example, MVS: Multiple Virtual Storage) has been installed, switching of the access target from the first storage subsystem to the second subsystem is performed by interchanging the cables. For this reason, it has been necessary for a maintenance worker to work at a place where the host is installed, and the remote work has been difficult.  
       [0005] Also, since it is possible in recent years to mix a multiplicity of storage areas of plural types having different capacity and device emulation within the storage subsystem, it is complicated to configure the storage subsystem and wrong configuration is prone to be made. However, since the above-described technique of the U.S. Pat. No. 6,108,748 has not disclosed the technique for solving this point, the maintenance worker of the storage subsystem should configure the second storage subsystem, which becomes a movement target, by means of handwork, and there is the possibility that a failure in data migration due to wrong configuration is caused.  
       SUMMARY OF THE INVENTION  
       [0006] It is an object of the present invention to provide a data processing system capable of easily performing a change in an accesses path of the storage subsystem associated with the data migration.  
       [0007] It is another object of the present invention to reduce, by automatically performing an operation of configuring the migration target storage subsystem through the use of software, complicated input operations for configuration items which have been conventionally required and to reduce failure in data migration due to wrong configuration concerning the migration target storage subsystem.  
       [0008] It is a further object of the present invention to make it easy for a system supervisor to grasp the condition of the system during data migration by displaying the condition of an event which occurs as the data migration, on a display screen.  
       [0009] The present invention is realized in a system including: a host computer connected to a network, having a function for issuing an I/O; a first storage subsystem in which a storage area for storing data is formed, for processing an I/O request to be transmitted from the host computer through the network to the storage area; a second storage subsystem which becomes an object for processing the I/O request to be transmitted from the host computer through the network, and becomes a migration target of data from the first storage subsystem; and a data migration device connected to the first and second storage subsystems through a management network, for processing data migration. This data migration device configures the second storage subsystem and forms a storage area on the basis of configuration information concerning the first storage subsystem, instructs for refusing an I/O request from the host computer to the first storage subsystem, and instructs for changing the access target from the first storage subsystem to the second storage subsystem by changing an information that a network communication protocol of the host computer has and that concerns the first storage subsystem.  
       [0010] In a preferred example, said information that a network communication protocol is an ARP information that TCP/IP protocol stack has.  
       [0011] In a preferred example, a management computer for managing a system concerning the data migration is connected through a network. This management computer has means for receiving a notice concerning data migration from a data migration device, and display means for displaying a condition of data migration from the first storage subsystem to the second storage subsystem. The display means is preferably capable of displaying a condition of the data migration through an icon. Also, this management computer has a function of determining whether or not an event that has occurred is an event that occurs as a result of the data migration, and when it is an event as a result of the data migration, it is displayed on the display means together with a message concerning that event. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0012]FIG. 1 is a block diagram showing hardware of a data processing system using iSCSI;  
     [0013]FIG. 2 is a view showing functional structure of each device of a data processing system according to the present embodiment;  
     [0014]FIG. 3 is a view showing outline of data migration processing between a migration source storage subsystem  100  and a migration target storage subsystem  110 ;  
     [0015]FIG. 4 is a flowchart showing a portion where data migration is performed in a storage area in which LUN has been assigned;  
     [0016]FIG. 5 is a flowchart showing a portion where data migration is performed in a storage area in which no LUN has been assigned;  
     [0017]FIG. 6 is a flowchart showing an operation of an I/O connection restoring function  222 ;  
     [0018]FIG. 7 is a flowchart showing addition or a change of information of ARP cache when a TCP/IP stack receives an ARP packet;  
     [0019]FIG. 8 is a view showing structure of a network information processing system according to another embodiment;  
     [0020]FIG. 9 is a flowchart showing a portion where data migration is performed in a storage area in which LUN has been assigned;  
     [0021]FIG. 10 is a flowchart showing processing of a notice receiving function  814 ; and  
     [0022]FIG. 11 is an example showing screen display for displaying a condition during data migration. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
     [0023] With reference to a block diagram showing hardware of a storage data processing system using the SCSI shown in FIG. 1, the description will be made of one embodiment of the present invention.  
     [0024] The present embodiment is an information processing system including a migration source storage subsystem  100  and a migration target storage subsystem  110  which have been connected to a local network segment  150 .  
     [0025] The migration source storage subsystem  100  is a storage subsystem, has one or more I/O processors  101 , a memory B 102  and a storage device  103  like a RAID disk device, and is connected to a storage subsystem inner network  104 .  
     [0026] The migration target storage subsystem  110  is a storage subsystem, and has a similar hardware structure to that of the migration source storage subsystem  100 . For this reason, display of the contents of the storage system  100  has been omitted.  
     [0027] A local network segment  150  is a network to which the migration source storage subsystem  100  and the migration target storage subsystem  110  have been connected through a NIC (Network Interface Card)  199 . Network node including the storage subsystem, the host computer and a relay computer (ex. router  140 ), which are connected to the local network segment  150 , can communicate to other network nodes without passing through the relay computer by acquiring MAC address which is identifier of NIC  199  from IP address.  
     [0028] An indirect connection network  160  is a network which has been connected to the local network segment  150  through the computer which relays the IP datagram. Communication between a network node to be connected to the indirect connection network  160  and a network node to be connected to the local network segment  150  is performed through the computer which relays the IP datagram. In this case, the indirect connection network  160  may be composed of one or more segments, and any network equipment may be used. Also, the indirect connection network  160  may be an internet or another wide area network, or include this or be one part thereof.  
     [0029] The router  140  is a computer for relaying the IP datagram, and has a NIC  199  for connecting to the local network segment  150  and the indirect connection network  160 .  
     [0030] A host A  120 A connected to the local network segment  150  and a host B  120 B which is connected to the indirect connection network  160  and communicate with the migration source storage subsystem  100  or the migration target storage subsystem  110  through the medium of the router  140 , are connected to such a system and perform storage I/O. The host A  120 A and the host B  120 B are computers such as a main frame computer, a server, a personal computer, a client terminal, a storage subsystem issuing I/O request, a work station and the like, which are accessible to the storage subsystem, any of which has CPU  121 , a memory  122 , and the NIC  199 , and these are connected through a computer internal bus  123 .  
     [0031] In the drawing, there have been described only the host A  120 A and the host B  120 B as a computer for performing storage I/O, but the present embodiment is not limited thereto. It is also possible to use a system to which one or more hosts A  120 A are connected, a system to which one or more hosts B  120 B are connected, or a system to which two or more hosts including hosts A  120 A and hosts B  120 B are connected together.  
     [0032] A migration processing computer  130  is a computer having a function of integrating and controlling the data migration of the present embodiment. This migration processing computer  130  is a computer such as, for example, a server, a personal computer, a client terminal, and a work station, and has CPU  121 , a memory  122  and the like.  
     [0033] To a management network  170 , there are connected the migration source storage subsystem  100  and the migration target storage subsystem  110 . Also, for the management network  170 , any network may be used, and further for the management network  170 , the local network segment  150  or the indirect connection network  160  maybe used. Also, all network nodes to be connected to the management network  170  are capable of performing communication for management with an IP address different from the IP address for storage I/O, but communication for management may be performed through the use of the IP address for storage I/O. In that case, however, since in the present embodiment, the IP address for storage is transferred to a different storage subsystem, another network node for performing communication through the use of the network for management must recognize the transfer of the IP address.  
     [0034] Next, with reference to FIG. 2, the description will be made of the functional structure of each device of a data processing system according to the present embodiment.  
     [0035] A host  120 A and a host  120 B have an I/O request issuing function  221 , an I/O connection restoring function  222 , a TCP/IP stack  223 , and an ARP cache  224  respectively, and these functions or information can be realized by the CPU  121  or the memory  122  operating.  
     [0036] A router  140  is a computer having the TCP/IP stack  223 , the ARP cache  224 , and a routing function  241 , and these functions or information can be realized by operation of the CPU  121  or the memory  122 .  
     [0037] The migration source storage subsystem  100  has a storage configuration function  201 , an I/O connection cutting function  202 , an access control function  204  and an I/O processing function  203 , which are realized when an I/O processor  101 , a memory B  102  and a storage device  103  operate. In this respect, the access control function  204  is used in order to restrict the access after an I/O request issuing target is switched from the migration source storage subsystem  100  to the migration target storage subsystem  110 , but is not essential. Also, the migration source storage subsystem  100  may have any other function than this.  
     [0038] The migration target storage subsystem  110  is realized when the I/O processor  101 , the memory B  102  and the storage device  103  operate, and has the storage configuration function  201 , a route switching information transmission function  211 , a data migration function  212 , and an I/O processing function  203 . In this respect, the migration target storage subsystem  110  may have any other function than this.  
     [0039] Next, the details of each of these functions will be described.  
     [0040] First, concerning the function of the host  120 A or  120 B, the I/O request issuing function  221  issues an I/O request based on the iSCSI protocol to the migration source storage subsystem  100  and the migration target storage subsystem  110 .  
     [0041] When the I/O connection with the migration source storage subsystem  100  and the migration target storage subsystem  110  is cut or the I/O processing ends in failure, the I/O connection restoring function  222  makes an attempt to re-establish the I/O connection in order to start the I/O processing again.  
     [0042] The TCP/IP stack  223  performs communication based on the TCP/IP protocol. In this respect, the TCP/IP stack  223  and the ARP cache  224  are also included in each of the migration source storage subsystem  100  and the migration target storage subsystem  110 , but the illustration has been omitted.  
     [0043] An ARP (Address Resolution Protocol) cache  224  is a cache for holding corresponding information between the IP address of a network node connected to the local network segment  150  and the MAC address. In this respect, for operation of information to be included in the ARP cache  224 , there are conceivable a method by transmission and reception of a packet based on the ARP protocol, a method for deleting, this information when a fixed time period has elapsed at a time when the corresponding information is received on is utilized, and a method by manual input, but information of the ARP cache may be operated through the use of any other method than this.  
     [0044] Concerning the function of the router  140 , a routing function  241  relays the IP datagram between the local network segment  150  and the indirect connection network  160 .  
     [0045] In the storage subsystem  100  or  110 , the storage configuration function  201  receives a configuration request, a configuration reference request or a functional operation request from the outside of the devices of the migration source storage subsystem  100  and the migration target storage subsystem  110 , and on the basis of these, configures and performs information output and functional execution of each storage subsystem. In this respect, there are an IP address which the storage subsystem allocates to the NIC  199 , a request of cutting the I/O connection, an access control configuration and the like, and in addition to these, information and the like for authentication and encipherment that each storage has may be configured, referred to and requested for processing. Also, if the size and identifier of the storage area can be determined by the administrator or the management software when the migration source storage subsystem  100  and the migration target storage subsystem  110  provide the host A  120 A and the host B  120 B with a storage area respectively, these may be configured or referred to. In this respect, the storage configuration function  201  is a function for management in which SNMP (Simple Network Management Protocol) defined by RFC  1157  is regarded as an interface with the outside of the device, but any other interface than this may be used.  
     [0046] The I/O connection cutting function  202  cuts the I/O connection which is being connected to the migration source storage subsystem  100 . In the case of the iSCSI, the present function can be realized by returning termination notice of the TCP connection to the host, but if the I/O connection restoring function  222  can detect cutting of the I/O connection or failure of I/O, it may be used. Also, the I/O connection cutting function  202  may exist on a network equipment such as a switch constituting the local network segment  150 .  
     [0047] The I/O processing function  203  processes I/O request issued to the migration source storage subsystem  100  or the migration target storage subsystem  110 .  
     [0048] The access control function  204  limits a host or a storage subsystem to perform I/O access to the migration source storage subsystem  100 . In this respect, the IP address, the MAC address, and authentication information to be exchanged before and at issuing I/O request is used as information for identifying the host or storage subsystem. But any other information than that may be used.  
     [0049] In the migration target storage subsystem  110 , the route switching transmission function  211  notifies a node, including the host  120 A and the router  140 , of an IP address or MAC address corresponding to the IP address thereto. In this respect, in the present embodiment, the information has been transmitted through the use of the ARP packet, but any other method than this may be used for transmission.  
     [0050] The data migration function  212  moves data of the storage area existing in the migration source storage subsystem  100  to the migration target storage subsystem  110 . The data of the migration source storage subsystem  100  is transferred through the local network segment  150 . Data management for, for example, an I/O request from the host  120 A during data migration may be performed as described in, for example, the U.S. Pat. No. 6,108,748. In other words, an array of bit (bit map) is provided correspondingly to a data block to be transferred, and by referring to a bit flag of this bit map, it is determined whether or not the data block has been transferred. If a data block requested from host  120 A is not transferred to the migration transfer target storage subsystem  110 , the I/O request may be transferred to the original storage subsystem  100  to read the data block from there for transmitting to the host  120 A.  
     [0051] A migration configuration function  231  controls migration of configuration from the migration source storage subsystem  100  to the migration target storage subsystem  110 , and the entire data migration including switching of the communication route. Furthermore, the migration configuration function  231  controls the migration source storage subsystem  100  and the migration target storage subsystem  110  by communicating with the storage configuration function  201 . In this respect, this function  231  is provided within the migration processing computer  130 , and may exist in any other place than this. This function  231  may be provided within, for example, the migration source storage subsystem  100  or the migration target storage subsystem  110 . For example, when this function  231  exists within the migration target storage subsystem  110 , it is also possible to directly configure the migration target storage subsystem  110  without through the medium of the storage configuration function  201  of the storage subsystem.  
     [0052] In the present embodiment, the storage subsystem  100  is a migration source and the storage subsystem  110  is a migration target as described above, but there is also a case where the storage subsystem  110  becomes a migration source and the storage subsystem  100  becomes a migration target. When such a case is also taken into account, the storage subsystems  100  and  110  have both the above-described functions  201  to  204 ,  211  and  212 .  
     [0053] Next, with reference to FIG. 3, the description will be made of outlined operation of the present embodiment.  
     [0054]FIG. 3 shows a general outline of processing for migrating to the migration target storage subsystem  110  in an environment having the migration source storage subsystem  100  in which a storage area  301  and a storage area  302  have been provided within the storage subsystem, and a host  120 A connected through the local network segment  150 . In this case, it is assumed that the storage area  301  and the storage area  302  are assigned LU_A and LU_B respectively as an identifier (hereinafter, referred to as LUN) to be designated by the host to perform I/O processing. It is assumed that the MAC address of the NIC  199  of the migration source storage subsystem  100  is HWAddrOld, and the MAC address of NIC  199  of the migration target storage subsystem  110  is HWAddrNew. Further, it is assumed that IP address AddressA is configure to the NIC  199  of the migration source storage subsystem  100 . In this respect, although in the figure, there exist only two storage areas and one host, the present invention is not limited thereto.  
     [0055] Hereinafter, the general outline of the operation will be described.  
     [0056] (1) Before the data migration, the migration source storage subsystem  100  is assigned Address A as the IP address like the box  330 , and the host  120 A obtains access to the storage area  301  and the storage area  302  through the Address A (access route  310 ). Also, the migration target storage subsystem  110  is not assigned such an Address A as the box  332 , but a state in which even configuration for creating the storage area  303  and the storage area  304  has not been made will be brought about. Also, in the ARP cache  224  of the host  120 A, a state in which HWAddrOld has been registered or has not been registered with the IP address as MAC address corresponding to the Address A will be brought about.  
     [0057] (2) In the migration target storage subsystem  110 , there will be provided the same storage area (storage area  303  and storage area  304 ) as the storage area (storage area  301  and storage area  302 ) which the migration source storage subsystem  100  has. (copy of configuration  321 )  
     [0058] (3) Next, there will be cut the I/O connection (access route  310 ) which has been established between the migration source storage subsystem  100  and the host  120 A.  
     [0059] (4) Next, the IP address which has been assigned to the migration source storage subsystem  100  will be changed from such Addrress A as the box  330  to such a different Address B as the box  331 .  
     [0060] (5) Next, the IP address of the migration target storage subsystem  110  will be assigned to Address A (box  332 ).  
     [0061] (6) Next, from the migration target storage subsystem  110 , the IP address will broadcast an ARP packet  312  indicating that the MAC address corresponding to the Address A is HWAddrNew to the local network segment  150 . Thereby, in the ARP cache  224  of the host A  120 A, the IP address Address A is brought into correspondence with the MAC address HWAddrNew, and it becomes possible to obtain access to the migration target storage subsystem  110  through the use of the Address A as in the case of the access route B  311 .  
     [0062] In this respect, if the host  120 A cannot receive the ARP packet  312  for some reason such as when the ARP packet  312  is broadcast during stoppage of the system or cutting of the network and the like, the host  120 A operates as below on the basis of the ARP protocol.  
     [0063] (A) The host  120 A deletes the correspondence between the IP address (Address A) and the MAC address (HWAddrOld) which has been scheduled to be changed by the ARP packet  312  from the ARP cache. In this respect, an opportunity for this deletion process depends upon the implementation of the software installed on the host  120 A. As its representative example, the execution when a fixed time period has elapsed since the host  120 A ceased the use of the IP address concerned is conceivable. Also, as a different condition, when the host  120 A sends the IP datagram having the Address A to the migration source storage subsystem  100  instead of the migration target storage subsystem  110 , the migration target storage subsystem  100  sends a message of ICMP to be defined in RFC  792 , and it is conceivable to perform the deletion process of the above-described (A) with the reception of that message as a turning point. However, even at any other opportunity for the implementation than this, the deletion process may be performed. However, if there is no correspondence concerned with the ARP cache  224  immediately after starting of the OS or the like, the present step may not be performed.  
     [0064] (B) Thereafter, when the host  120 A obtains access to the storage subsystem having the Address A, the information on the correspondence between the Address A and the MAC address has already been deleted from the ARP cache  224  by the process described in (A). Thus, in order to obtain the MAC address corresponding to the Address A, the host  120 A will broadcast the ARP request.  
     [0065] (C) The migration target storage subsystem  110  will broadcast, in response to the ARP request, an ARP reply meaning that HWNewAddr that is MAC address of its own corresponds.  
     [0066] (D) The host  120 A receives the ARP reply to change the ARP cache  224 . If it cannot receive the ARP reply even after a lapse of a fixed time period after the execution of (B), the host  120 A may repeat from (B) again. Also, when another host performs the same step and has the ARP reply broadcast although not shown, it may receive this reply to change the ARP cache  224 .  
     [0067] Therefore, even if the host  120 A cannot receive the ARP packet  312  for some reason, it is possible to obtain an ARP packet including correspondence between the MAC address and the IP address to be transmitted from the migration target storage subsystem  110  again.  
     [0068] (7) Finally, the migration target storage subsystem  110  copies data of the storage area  301  and the storage area  302  to the storage area  303  and the storage area  304  while transferring the I/O request from the host  120 A to the migration source storage subsystem  100  (data copy  322 ).  
     [0069] Since it is not necessary for all the hosts to change the ARP information at the same time, even though one host may fail in change of access path route of the storage subsystem associated with the data migration, the remaining hosts can switch normally, and as regards a host which fails, it will be possible to change the access path route later.  
     [0070] Next, the description will be made of the processing of the migration configuration function  231 .  
     [0071]FIG. 4 is a flowchart showing a portion where data migration is performed in a storage area to which LUN has been assigned in the process of the migration configuration function  231 .  
     [0072]FIG. 5 is a flowchart showing a portion where data migration is performed in a storage area to which no LUN has been assigned in the process of the migration configuration function  231 .  
     [0073] In this respect, although not clearly described in the description of each step, when the migration configuration function  231  refers to and controls each function and the configuration information inside the migration source storage subsystem  100  and the migration target storage subsystem  110 , the migration configuration function  231  performs through the storage configuration function  201 .  
     [0074] Hereinafter, the flow of FIG. 4 will be described.  
     [0075] (1) Readout configuration information from the migration source storage subsystem  100  to configure the migration target storage subsystem  110  and to create a storage area on the basis of the information. As information to be read out and configured configure, there are capacity, emulation type and LUN that each storage area has, required to create the storage area, but in addition to these, authentication information required to certify the migration source storage subsystem  100 , configuration of access control that the migration source storage subsystem, and the like may be regarded. As regards a configuration method, there is a process for automatically configuring all values of information read out from the migration source storage subsystem  100  as they are. But it may be added to retain items of attribute that is not migrated, check the configuration information whether the configuration information includes the appropriate items before configuring the migration target storage subsystem  110 , and if the appropriate item is included, it does not use for configuring the migration target storage subsystem  110 , and other process may be used. Also, the correspondence between the storage area created in the migration target storage subsystem  110  and the storage area in the migration source storage subsystem  100  which become a data migration source will be retained (Step  401 ).  
     [0076] (2) Request the I/O connection cutting function  202  of the migration source storage subsystem  100  to cut the I/O connection between the network node and the migration source storage subsystem  100 . Thereby, for example, the I/O connection between the host  120 A and the migration source storage subsystem  100  will be cut (Step  402 ).  
     [0077] (3) After the I/P address assigned to the migration source storage subsystem  100  is stored, another IP address not used by other network nodes is assigned to the migration source storage subsystem  100  (Step  403 ). In this respect, at this point of time, a renewal of the authentication information may be applied to a computer for handling the authentication information.  
     [0078] (4) When the migration source storage subsystem  100  has the access control function  204 , request the access control function  204  of the migration source storage subsystem  100  to configure preventing the I/O request from being received from any other than the migration target storage subsystem  110  (Step  404 ).  
     [0079] (5) Assign the previous IP address of the migration source storage subsystem  100  stored in the Step  403  to the migration target storage subsystem  110  (Step  405 ).  
     [0080] (6) Request the route switching information transmission function  211  of the migration target storage subsystem  110  to transmit a route switching information (Step  406 ). The route switching information is the MAC address of the migration target storage subsystem  110  and the IP address stored in the Step  403 , and these addresses are transmitted to notify the node including the host  120 A or the router.  
     [0081] (7) Pass the correspondence information retained in the Step  401  to the data migration function  212  of the migration target storage subsystem  110 , and request the migration target storage subsystem  110  so as to move data of the storage area existing in the migration source storage subsystem  100  to the migration target storage subsystem  110  (Step  407 ).  
     [0082] Next, the description will be made of FIG. 5. In this respect, the flow of FIG. 5 will be performed after the process of FIG. 4 is executed, but if the process of the Step  401  could be executed in advance, it may be executed at a timing independent of the process of FIG. 4.  
     [0083] (1) Select storage areas which are not configured as accessible from the host  120 A, in the migration source storage subsystem (Step  501 ).  
     [0084] (2) Configure non-accessible storage areas as accessible storage areas by assigning accessible LUNs which are currently unused (Step  502 ).  
     [0085] (3) The I/O request from the migration target storage subsystem  110  to the storage area is issued to thereby request the data migration function  212  of the migration target storage subsystem  110  for processing, and to migrate data of the storage area selected in the Step  501  through the use of the LUN assigned (Step  503 ).  
     [0086] Next, with reference to the flowchart of FIG. 6, the description will be made of the operation of the I/O connection restoring function  222 .  
     [0087] (1) In accordance with the process described below, detect the cutting I/O connection and I/O process failure. In the case of the iSCSI, since TCP is used as a transport layer, the cutting can be detected by requesting the TCP/IP stack  223  to confirm the state of the TCP session. Also, the failure in the I/O process can be confirmed by inquiring of the I/O request issuing function  221  (Step  601 ).  
     [0088] (2) If the applicable I/O connection is not in a cut state, perform a cutting process (Step  602 , Step  603 ).  
     [0089] (3) Repeat an establishment process until I/O connection with the migration source storage subsystem  100  or the migration target storage subsystem  110  is established (Step  604 , Step  605 ).  
     [0090] Next, with reference to the flowchart of FIG. 7, the description will be made of the addition or change of the information of the ARP cache  224  when the TCP/IP stack  223  receives the ARP packet.  
     [0091] (1) Receive an ARP packet representing the ARP request or the ARP reply (Step  701 ).  
     [0092] (2) Extract the IP address and the corresponding MAC address from the ARP packet received (Step  702 ).  
     [0093] (3) Add a pair of the IP address and the MAC address to the ARP cache  224  extracted by the Step  702 , and if the MAC address corresponding to the IP address has already been registered, renew it to a new MAC address (Step  703 ).  
     [0094] Next, with reference to FIG. 8, the description will be made of another embodiment of the present invention.  
     [0095] The present embodiment is an information processing system obtained by adding means for conducting system management to the information processing system of the first embodiment described above.  
     [0096] The present embodiment differs from the first embodiment in that a computer for management  810  is added, that accordingly a host agent  821  is added to the host  120 A, that a migration notifying function  832  is added to the migration processing computer  130 , and that the configuration migration function  231  is changed to a migration configuration function B  831 .  
     [0097] The computer for management  810  is such a computer as a work station or a personal computer which becomes important when conducting management such as obstacle observation and performance management of the entire information processing system, and has a display input function  811 , a database  812 , an information collecting function  813  and a notice receiving function  814 . In this respect, the computer for management may have any other function than these, for example, an alarm notifying function to the administrator, a function for configuring the host and storage, or a function for requesting its configuration.  
     [0098] Hereinafter, the description will be made of each function that the computer for management  810  has.  
     [0099] The database  812  accumulates information of the host, the storage subsystem, network equipment and the like which are to be managed by the computer for management  810 , and provides information in response to request from the display input function.  
     [0100] The information collecting function  813  collects information of hosts, storage subsystems, network equipment and the like including the host A 120 , the migration source storage subsystem  100  and the migration target storage subsystem  110 . In the information collecting method of the present embodiment, the information collecting function  813  obtains information by requesting the host agent  821  and the storage configuration function  201  to acquire information, but information may be obtained by any other method than this one.  
     [0101] The display input function  811  has a display unit and an input unit, and forms an operating display environment for managing the entire information processing system. In this respect, the display screen of the display unit displays kinds of events such as restarting of the process, obstacles, and changes in performance in the information processing system resulting from the data migration process. Also, as kinds of events to be displayed, there are re-establishment of I/O connection in the host  120 A, an increase in amount of data that passes through the local network segment  150 , changes in access performance to the storage area which exists within the migration source storage subsystem  100 , and the like.  
     [0102] The notice receiving function  814  receives an event notice to be issued from the migration notifying function  832 , and in response thereto, controls the information collecting function  813  and the display input function  811 . However, the notice receiving function  814  may perform any other process than this one. In this respect, a trap of SNMP (Simple Network Management Protocol) defined in RFC  1157  as means for notifying of events can be used, and any other method than this one may be used.  
     [0103] The host agent  821  acquires the system configuration, configuration information, obstacle information, performance information and the like of the host  120 A, and transfers to the computer  810  for management. In this respect, the host agent  821  may have any other function as this one, for example, a function for changing the configuration of the host  120 A in response to a request from a remote place, and the like.  
     [0104] The configuration migration function B  831  is equal to the configuration migration function  231  in the first embodiment, and has a new process for controlling the migration notifying function  832  added.  
     [0105] The migration notifying function  832  notifies the notice receiving function  814  of events. In this respect, the present function may exist in any other than the migration processing computer  130 , and may exist in the migration source storage subsystem  100  and the migration target storage subsystem  110 .  
     [0106] Next, with reference to the flowchart of FIG. 9, the description will be made of the process of the configuration migrating function  831  where data migration is performed in a storage area in which LUN has been assigned.  
     [0107] (1) Before starting data migration, request the migration notifying function  832  to issue a notice of commencement of data migration. In this respect, together with the notice of commencement of migration, information indicating storage subsystems which become the migration source and migration target (in this case, the migration source storage subsystem  100  and the migration target storage subsystem  110  respectively) may also be transmitted (Step  901 ).  
     [0108] (2) Perform the data migration process. In this respect, the contents of the process are equal to Steps  401  to  407  of FIG. 4 (Steps  401  to  407 ).  
     [0109] (3) Request the migration notifying function  832  to issue a notice of termination of data termination. Even in this case, together with the notice, information indicating storage subsystems which become the migration source and migration target (in this case, the migration source storage subsystem  100  and the migration target storage subsystem  110  respectively) may also be transmitted (Step  902 ).  
     [0110] In this respect, if in the migration source storage subsystem  100  there exists a storage area in which no LUN has been assigned, the flow of FIG. 5 according to the first embodiment will be executed. As the process in that case, before the event notification of the Step  902  is performed, the process of FIG. 5 will be executed, and the event notification will be performed at this point of time whereat the entire migration of storage area has been completed.  
     [0111] Next, with reference to the flowchart of FIG. 10, the description will be made of the process of the notice receiving function  814 .  
     [0112] (1) Receive an event notice. If the kind of the event notice is commencement of migration, the sequence will proceed to a Step  1003 , and if termination of migration, the sequence will proceed to a Step  1004  (Step  1001 ,  1002 ).  
     [0113] (2) Notify the display input function  811  that data migration has commenced. In this respect, if the event notice includes an identifier indicating storage subsystems of the migration source and the migration target, the display input function  811  may be notified of these pieces of information (Step  1003 ).  
     [0114] (3) Request the information collecting function  813  to renew the information concerning the information processing system which the computer for management  810  has (Step  1004 ).  
     [0115] (4) Notify the display input function  811  that the data migration has been terminated. In this respect, if the event notice includes an identifier indicating storage subsystems of the migration source and the migration target, the display input function  811  may be notified of these pieces of information (Step  1005 ).  
     [0116] Next, with reference to FIG. 11, the description will be made of a display example of the display screen during data migration. A host icon  1101  is an icon meaning the host.  
     [0117] A storage area icon  1103  is an icon indicating a storage area.  
     [0118] A path  1102  is a line drawn from or to a storage area to be used by the host. In this respect, as a method for determining the storage area to be utilized by the host, there is a method for determining whether or not there arose access from the host to the storage area within a fixed time period in the past, or whether or not the host performed a log-in process of the storage subsystem including the storage area, and any other criterion than this one may be used.  
     [0119] A host event  1105  is a message to be displayed when some event occurs in a host corresponding to the host icon  1101 . The host event  1105  includes a general message  1111  to be displayed when an event occurs, and an explanatory message  1112 . The explanatory message  1112  is displayed only concerning an event in which there is the possibility that it has occurred as a result of a data migration process, and indicates that there is the possibility that the event has occurred because of the data migration process. This can be distinguished by providing an operation or a function for determining, when, for example, an event occurs, whether or not the event occurred as a result of data migration, and whether or not the event occurred during a data migration period. It is displayed that it is an event that occurred as a result of the data migration process, whereby any side effect of the data migration can be easily determined.  
     [0120] In this respect, the host event  1105  may include any other information than the general message  1111  and the explanatory message  1112 . In the present screen example, when path switching according to the first embodiment has been performed, re-establishment of I/O connection which may be issued from the host A  120 A is shown as an example of the event.  
     [0121] Storage area information  1104  has an area displaying information of a storage area corresponding to the storage area icon  1103 , and at least storage area positional information  1115 . In this respect, the storage area information  1104  may include any other information than this one, and includes, in the present screen example, IP information and LUN information, which are parameters required in order to access to the storage area.  
     [0122] The storage area positional information  1115  is information concerning a storage subsystem in which there exists a corresponding storage area. Before the data migration, the present information indicates the migration source storage subsystem  100 , and after the data migration, the migration target storage subsystem  110 . In the case of during the data migration, this information displays either the migration source storage subsystem  100  or the migration target storage subsystem  110 , and displays a message, like message  1116 , indicating that the storage area concerned is migrating from the migration source storage subsystem  100  to the migration target storage subsystem  110 .  
     [0123] In this respect, the present invention is not restricted to the above-described embodiments, and can assume further various constructions without departing from the gist of the present invention. The function  231 , and the functions  831 ,  832  in the migration processing computer  130  shown in, for example, FIG. 1 or FIG. 8 may be intensively provided within the computer for management  810 . If performed in this manner, the migration processing computer  130  will become unnecessary to reduce the amount of hardware.  
     [0124] According to the present invention, since the access target is switched from the migration source storage subsystem to the migration target storage subsystem by changing the ARP information of the host and further by the migration source storage subsystem refusing access from the host, there is no need to replace cables connected to the host which uses the storage subsystem, and for the administrator to execute the command for each host.  
     [0125] Also, since a configuration operation of the migration target storage subsystem that becomes a complicated operation is automatically performed by means of the software, it is possible to reduce failures in the data migration process based on wrong configuration.  
     [0126] Further, a condition of the data migration is displayed on the display screen connected to the network, and it is displayed that there is the possibility that the even occurs as a result of the data migration, whereby the system administrator is capable of monitoring the storage while taking into account the data migration.