Abstract:
The present invention decreases the burden of operation required for specifying the continuity status and the cause of failure of a network storage device. A host computer accepts the specification of the device identifier, that is an identifier of the network storage device in the host protocol which positions in a higher hierarchy than the network communication protocol, and a volume identifier, that is an identifier of the volume. Then based on the specified device identifier, the host computer specifies the network identifier, that is an identifier of the network storage device in the network communication protocol. And continuity is confirmed in the network communication protocol in which the specified network identifier is the destination. Also continuity is confirmed in the host protocol in which the device identifier is the destination. And the volume specified by the volume identifier is accessed.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     This application relates to and claims priority from Japanese Patent Application No. 2004-066978, filed on Mar. 10, 2004, the entire disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a technology for confirming continuity between a network storage device and a host computer.  
         [0004]     2. Description of the Related Art  
         [0005]     This is a network storage device for providing volumes to a host computer via a network. The network storage device communicates with the host computer according to the network communication protocol used by the network to be connected. There are many types of networks, and the IP (Internet Protocol) network is one of them.  
         [0006]     The protocol of the IP network has been standardized by the IETF (Internet Engineering Task Force), and protocols are hierarchical. For example, iSCSI (Small Computer Systems Interface protocol over the Internet) is a protocol for using the network storage device to be connected to the IP network, and is a host protocol which positions in the higher hierarchy of the IP.  
         [0007]     In the IP network, Ping, which confirms continuity using the ICMP (Internet Control Message Protocol) standardized by the IETF, is widely known as a means for the host computer to confirm continuity with the network connection device. The host computer can confirm continuity with the device having a specified IP address in the IP layer, by using Ping (J. Postel, “RFC-792 Internet Control Message Protocol,” IETF, 1981).  
       SUMMARY OF THE INVENTION  
       [0008]     If continuity is disabled in the host protocol or if the host computer cannot access (mount) the volume of the network storage device, the host computer cannot access the network storage device even if continuity is confirmed in the network communication protocol.  
         [0009]     Accessibility of the host computer to the network storage device can also be manually confirmed by the user, sequentially performing continuity confirmation in the network communication protocol, continuity confirmation in the host protocol and access confirmation to the volume. With this method, however, the user must input a command for confirming continuity in each hierarchy into the host computer by specifying the identifier of the network storage device in the network communication protocol (e.g. IP address in the case of IP), the identifier of the network storage device in the host protocol (e.g. iSCSI name in the case of iSCSI) and the identifier of the volume of the network storage device (e.g. LUN: Logical Unit Number). So if the number of network storage devices and the number of volumes of the network storage device increases, the number of times of operation increases, and the operation becomes complicated. Also if some failure occurs, operation to specify the cause thereof becomes complicated, and the failure cannot be handled quickly.  
         [0010]     With the foregoing in view, it is an object of the present invention to decease the burden of operation required for confirming the continuity status of the network storage device and specifying the cause of failure.  
         [0011]     To solve the above problem, according to the present invention, the specification of an identifier of a network storage device (called device identifier) in a host protocol that positions in a higher hierarchy than a network communication protocol, and an identifier of the volume (called the volume identifier) provided by the network storage device is accepted from a user. Then based on the specified device identifier, the identifier of this network storage device (called network identifier) in the network communication protocol is specified. And continuity confirmation is executed in the network communication protocol of which destination is the specified network identifier, and the execution result thereof is output. If the continuity in the network communication protocol is confirmed, the continuity confirmation is executed in the host protocol of which the destination is the device identifier specified by the user, and the execution result thereof is output. Finally, if the continuity in the host protocol is confirmed, access (mount) to the volume specified by the specified volume identifier is executed, and the execution result is output.  
         [0012]     For example, the present invention is a continuity confirmation method for a network storage device for a host computer to confirm continuity with the network storage device for providing a volume via the network, the method performing: an acceptance step for accepting the specification of a device identifier, that is, an identifier of a network storage device in a host protocol that positions in a higher hierarchy than a network communication protocol used by the network, and a volume identifier that is an identifier of the volume, from a user via an input device; and a volume accessibility decision step for deciding whether the host computer can access the volume of the network storage device specified by the device identifier and the volume identifier accepted in the acceptance step, wherein the volume accessibility decision step further comprises: a network continuity confirmation step for specifying a network identifier corresponding to the device identifier accepted in the acceptance step using a storage management table in which the correspondence relationship between the network identifier, that is an identifier of the network storage device in the network communication protocol, and the device identifier is registered, executing confirmation continuity processing in the network communication protocol between the network storage device having the specified network identifier and the host computer, and outputting the result to an output device; a storage connection confirmation step for executing the connection confirmation processing in the host protocol between the network storage device having the device identifier accepted in the acceptance step and the host computer, and outputting the result to the output device; and access confirmation step for executing access confirmation processing for confirming whether the host computer can access the volume of the network storage device specified by the device identifier and the volume identifier accepted in the acceptance step, and outputting the result to the output device.  
         [0013]     According to the present invention, the network identifier is specified by the user specifying the device identifier and the volume identifier, so the user need not know the network identifier. The continuity confirmation in the network communication protocol, the continuity confirmation in the host protocol and the access confirmation to the volume are sequentially executed, and the results thereof are output, so the continuity status of the network storage device and the cause of the failure can be easily specified. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a schematic diagram depicting the computer system to which the first embodiment of the present invention is applied;  
         [0015]      FIG. 2  is a table showing a registration content example of the access management table  3123 ;  
         [0016]      FIG. 3  is a table showing a registration content example of the storage management table  124 ;  
         [0017]      FIG. 4  is a flow chart depicting the volume accessibility decision processing;  
         [0018]      FIG. 5  is a flow chart depicting the network continuity confirmation processing;  
         [0019]      FIG. 6  is a flow chart depicting the storage connection confirmation processing;  
         [0020]      FIG. 7  is an example of the data format of the data to be transmitted to the storage device for continuity confirmation;  
         [0021]      FIG. 8  is an example of the data format of the response data to the data for continuity confirmation;  
         [0022]      FIG. 9  is a flow chart depicting the access confirmation processing; and  
         [0023]      FIG. 10A  shows a display example when all of network continuity confirmation processing, storage connection confirmation processing and access confirmation processing succeeded in confirmation, and  FIG. 10B  shows a display example when the network continuity confirmation processing failed in confirmation. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     A computer system according to an embodiment of the present invention will now be described using an example when IP is used for the network communication protocol and iSCSI is used for the host protocol of the network communication protocol in the storage area network (SAN) between the host computer and the network storage device.  
         [0025]     (1) System Configuration  
         [0026]      FIG. 1  is a schematic diagram depicting a computer system to which the first embodiment of the present invention is applied.  
         [0027]     As  FIG. 1  shows, the computer system of the present embodiment is comprised of a host computer  1  and network storage device  3  which are connected to the SAN  2 .  
         [0028]     The network storage device  3  provides a volume  34  to the host computer  1  via the SAN  2 . Here the volume  34  is a logical storage area which is comprised of at least one disk device  32 . As  FIG. 1  shows, the network storage device  3  is comprised of a storage control device  31  and at least one disk device  32 . The storage control device  31  is further comprised of a CPU  311 , memory  312 , an NIC (Network Interface Card)  313  to be connected to the SAN  2 , a storage connection device  314 , and an internal bus  315  for connecting these elements  311  to  314 . The storage connection device  314  controls the data transfer to the volume  34  according to the instructions from the CPU  311 .  
         [0029]     In the memory  312 , the communication control (PG) program  3121 , storage control (PG) program  3122  and access management (TL) table  3123  are stored.  
         [0030]     The access management table  3123  is a table for managing the host computer  1  which can access the volume  34 .  FIG. 2  is a table showing a registration content example of the access management table  3123 . As  FIG. 2  shows, an entry  31230  is registered for each volume  34  in the access management TL table  3123 . The entry  31230  is comprised of a field  31231  for registering the LUN of the volume  34 , a field  31232  for registering the iSCSI name of the host computer  3  which can access the volume  34 , and a field  31233  for registering the IP address of the host computer  3  which can be connected to the local network storage device  3  which provides the volume  34 .  
         [0031]     The CPU  311  performs the processing of TCP/IP required for communication with the host computer  1  by executing the communication control program  3121 . Also [the CPU  311 ] returns a reply to the Ping command addressed from the host computer  1  to the local network storage device  3 . The CPU  311  also executes the storage control program  3122 , so as to control the storage connection device  314  and the read/write data to the volume  34 . [The CPU  311 ] also performs the iSCSI processing required for a iSCSI target. [The CPU  311 ] also performs authentication processing for the Login command from the host compute  3  and access (mount) possibility decision processing to the volume  34  of the host computer  3  using the access management table  3123 .  
         [0032]     The host computer  1  accesses the volume  34  of the network storage device  3  via the SAN  2 , and reads/writes data stored in the volume  34 . As illustrated, the host computer  1  is comprised of the CPU  11 , memory  12 , I/O  13  for connecting the display device  16  and input device  17 , NIC  14  for connecting to the SAN  2 , and internal bus  15  for connecting these elements  11  to  15 .  
         [0033]     In the memory  12 , the communication control (PG) program  121 , storage control processing (PG) program  122 , continuity confirmation processing (PG) program  123  and storage management (TL) table  124  are stored.  
         [0034]     The storage management table  124  is a table for managing the network storage device  3  to which the local host computer  1  can connect.  FIG. 3  is a table showing a registration content example of the storage management table  124 . As  FIG. 3  shows, in the storage management TL  124 , the entry  1240  is registered for each iSCSI name of the network storage device  3 . The entry  1240  is comprised of a field  1241  for registering the IP address of the network storage device  3 , and a field  1242  for registering the iSCSI name of the network storage device  3 .  
         [0035]     The CPU  11  executes the communication control program  121  for executing TCP/IP processing required for communication with the network storage device  3 . [The CPU  11 ] also sends the Ping command to the IP address specified by the continuity confirmation processing program  123 , receives the response thereof, and transfers it to the continuity confirmation processing program  123 . The CPU  11  also executes the storage control program  122  to execute the iSCSI processing required for an iSCSI initiator. [The CPU  11 ] also sends the Login command to the iSCSI name specified by the continuity confirmation processing program  123 , receives the response data thereof, and transfers it to the continuity confirmation processing program  123 . [The CPU  11 ] also sends the mount command to the iSCSI name and the LUN specified by the continuity confirmation processing program  123 , receives the response data thereof, and transfers it to the continuity confirmation processing program  123 . Also the CPU  11  executes the continuity confirmation processing program  123  to execute the processing for confirming whether the volume  24  provided by the network storage device  3  can be accessible (called volume accessibility decision processing).  
         [0036]     (2) Volume Accessibility Decision Processing  
         [0037]     Now the volume accessibility decision processing executed by the host computer  1  will be described.  FIG. 4  is a flow chart depicting the volume accessibility decision processing. This flow is started in the host computer  1  by the CPU  11  executing the continuity confirmation processing PG program  123 .  
         [0038]     At first, the CPU  11  accepts the input of the number of times of execution for the volume accessibility decision, the LUN of the volume  34  for which accessibility is decided, and the iSCSI name of the network storage device  3  which provides this volume, from the user via I/O  13  and input device  17 . Then using the storage management table  124 , [the CPU  11 ] searches the IP address registered in the entry  1240  with the iSCSI name received from the user (S 101 ). Also [the CPU  11 ] sets the number of times of execution N of the accessibility decision to 1.  
         [0039]     Then the CPU  11  executes continuity confirmation processing with the network storage device  3  having the searched IP address in the IP layer (called network continuity confirmation processing) (S 102 ). Details of the network continuity confirmation processing will be described later.  
         [0040]     Then the CPU  11  analyzes the result of the network continuity confirmation processing (S 103 ). If the processing result indicates “No continuity”, [processing] moves to S 108 . If the processing result indicates “Continuity”, on the other hand, the CPU  11  executes connection confirmation processing with the network device  3  having the iSCSI name received from the user in the iSCSI layer (called storage connection confirmation processing) (S 104 ). Details of the storage connection confirmation processing will be described later.  
         [0041]     Then the CPU  11  analyzes the result of the storage connection confirmation processing (S 105 ). If the processing indicates “No connection”, [processing] moves to S 108 . If the processing result indicates “Connection”, on the other hand, the CPU  11  executes processing for confirming whether the volume  34  specified by the iSCSI name and the LUN received from the user is accessible (called access confirmation processing) (S 106 ). Details of the access confirmation processing will be described later.  
         [0042]     Then the CPU  11  executes disconnection processing of the iSCSI session established with the iSCSI target by the storage connection confirmation processing (S 107 ), and [processing] moves to S 108 .  
         [0043]     Then in S 108 , the CPU  11  judges whether the number of times of the execution N of the accessibility decision reaches the number of times of the execution of the accessibility decision received from the user. If reached, this flow is ended. If not reached, the number of times of the execution N of the accessibility decision is incremented by 1, and [processing] returns to S 102 .  
         [0044]     (3) Network Continuity Confirmation Processing  
         [0045]     Now the network continuity confirmation processing executed in S 102  of  FIG. 4  will be described.  FIG. 5  is a flow chart depicting the network continuity confirmation processing.  
         [0046]     At first, the CPU  11  generates a Ping command (echo request of ICMP) to the IP address searched in S 101  of  FIG. 4  according to the communication control program  121  (S 1021 ). Then [the CPU  11 ] sends the generated Ping command to the SAN  2  via the NIC  14 , and acquires the transmission time based on the internal timer, which is not illustrated (S 1022 ). And the CPU  11  waits for the response to the Ping command for a predetermined time (S 1023 , S 1024 ). In the storage control device  31 , if the CPU  311  receives the Ping command via the NIC  313 , [the CPU  311 ] generates the response according to the communication control program  3121 , and sends it to the transmission source of the Ping command.  
         [0047]     In S 1023  and S 1024 , if the response to the Ping command is not received within a predetermined time, the CPU  11  judges that there is no continuity with the transmission destination of the Ping command in the IP layer, generates a message to notify this (S 1025 ), and displays it on the display device  16  (S 1028 ). For example, such a message as “S-ID network continuity confirmation failed (NS-ID)” is displayed on the display device  16 . Here, “S-ID” is an iSCSI name of the network storage device  3  received from the user in S 101  of  FIG. 4 , and “NS-ID” is an IP address of this network storage device  3  searched in S 101  of  FIG. 4 .  
         [0048]     If a response to the Ping command is received within a predetermined time in S 1023  and S 1024 , the CPU  11  judges that continuity exists with the transmission destination of the Ping command in the IP layer. And [the CPU  11 ] acquires the reception time from the internal time, which is not illustrated, subtracts the transmission time from this reception time, and calculates the processing time required for the continuity confirmation (S 1026 ). Then the CPU  11  generates a message to indicate “Continuity”, including the processing time (S 1027 ), and displays it on the display device  16  (S 1028 ). For example, such a message as “S-ID network continuity confirmation succeeded. Processing time t.” is displayed on the display device  16 . Here the processing time t is the time calculated in S 1026 .  
         [0049]     (4) Storage Connection Confirmation Processing  
         [0050]     Now the storage connection confirmation processing to be executed in S 104  of  FIG. 4  will be described.  FIG. 6  is a flow chart depicting the storage connection confirmation processing.  
         [0051]     At first, the CPU  11  generates the iSCSI login command for the network storage device  3  of which continuity was confirmed by the above mentioned network continuity confirmation processing according to the storage control program  121  (S 1041 ).  
         [0052]      FIG. 7  is an example of a data format of the data which is sent for confirming the continuity for the storage device. As  FIG. 7  shows, the data to be sent for confirming continuity comprises an overall data length  501  for indicating the length of the entire data, NS-ID  502  which is an IP address of the network storage device  3  at the transmission destination, NH-ID  503  which is an IP address of the host computer  1  at the transmission source, S-ID  505  which is an iSCSI name of the network storage device  3  at the transmission destination (iSCSI target), H-ID  506  which is an iSCSI name of the host computer  1  at the transmission source (iSCSI initiator), command  507  for specifying the processing content (one of 01: connect (login); 02: disconnect (logout); 03: mount; and 04: unmount) of which execution is requested to the storage device  3 , LUN  508  of the volume  34  to be a target when the command  507  is mount or unmount, and data length  504  of S-ID  505 , H-ID  506 , command  507  and LUN  508 . Here the iSCSI login command is generated, so “01” is stored in the command  507 . In the case of the disconnect processing in S 107  in  FIG. 4 , an iSCSI logout command where “02” is stored in the command  507  is sent to the iSCSI target during the iSCSI session.  
         [0053]     Then the CPU  11  sends the generated iSCSI login command to the network storage device  3  of which continuity is confirmed by the above mentioned network continuity confirmation processing. Also [the CPU  11 ] acquires the transmission time from the internal timer, which is not illustrated (S 1042 ). And the CPU  11  waits for the response data to the iSCSI login command for a predetermined time (S 1043 , S 1044 ).  
         [0054]     In the storage control device  31 , the CPU  311  which received the iSCSI login command via the NIC  313  decides the authentication method (e.g. RFC 1510, RFC 2025, RFC 2945, RFC 1944) by negotiation with the iSCSI initiator (storage control program  122  of the host computer  1 ) according to the storage control program  3122 , and executes the authentication processing. And [the CPU  311 ] generates the response data including the authentication result, and sends it to the iSCSI initiator.  
         [0055]      FIG. 8  is an example of the data format of the response data to the data for confirming continuity. As  FIG. 8  shows, the response data to the data for confirming continuity comprises an overall data length  601  which indicates the length of the entire response data, NS-ID  602  which is an IP address of the network storage device  3  at the transmission source, NH-ID  603  which is an IP address of the host computer  1  at the transmission destination, S-ID  605  which is an iSCSI name of the network storage device  3  at the transmission source (iSCSI target), H-ID  606  which is an iSCSI name of the host computer  1  at the transmission destination (iSCSI initiator), result  607  for specifying the execution result of the command (one of 11: normal end; 12: authentication error; 13: LUN error), and data length  604  of S-ID  605 , H-ID  606  and the result  607 . In this case, the data to be transmitted for confirming continuity, which was transmitted from the host computer  1 , is a login command, so either “11” or “12” is stored in the result  607  of the response data.  
         [0056]     In S 1043  and S 1044 , if the response data to the iSCSI login command is not received within a predetermined time, the CPU  11  judges this as no continuity with the transmission destination of the iSCSI login command (iSCSI target) in the iSCSI layer, generates a message to indicate “No continuity” (S 1045 ), and displays it on the display device  16  (S 1050 ). For example, such a message as “S-ID storage connection confirmation failed (no response)” is displayed on the display device  16 .  
         [0057]     If the response data to the iSCSI login command is received within the predetermined time in S 1043  and S 1044 , on the other hand, the CPU  11  analyzes the command execution result stored in the result  607  of this response data (S 1046 ). If the execution result is the authentication error “12”, the CPU  11  judges that the transmission destination of the iSCSI login command (iSCSI target) rejected the establishment of the iSCSI session, generates a message to indicate “No connection” (S 1047 ), and displays it on the display device  16  (S 1050 ). For example, a message such as “S-ID storage connection confirmation failed (authentication error)” is displayed on the display device  16 .  
         [0058]     If the execution result of the login command is normal end “11” in S 1046 , on the other hand, the CPU  11  judges that an iSCSI session was established with the transmission destination of the iSCSI login command (iSCSI target). And [the CPU  11 ] acquires the reception time from the internal timer, which is not illustrated, and calculates the processing time required for confirming connection by subtracting the transmission time from this reception time (S 1048 ). Then the CPU  11  generates a message to indicate “Connection” including the processing time (S 1049 ), and displays it on the display device  16  (S 1050 ). For example, a message such as “S-ID storage connection confirmation succeeded. Processing time t.” is displayed on the display device  16 . Here the processing time t is the time calculated in S 1048 .  
         [0059]     (5) Access Confirmation Processing  
         [0060]     Access confirmation processing to be executed in S 106  of  FIG. 4  will be described.  FIG. 9  is a flow chart depicting the access confirmation processing.  
         [0061]     At first, the CPU  11  generates the iSCSI mount command for the network storage device  3  of the iSCSI target of which iSCSI connection was established by the above mentioned storage connection confirmation processing according to the storage control program  121  (S 1061 ). This mount command has the data format of the data to be sent for confirming continuity shown in  FIG. 7 , where “03” is stored in the command  507 , and the LUN received from the user in S 101  in  FIG. 4  is stored of the LUN  508 .  
         [0062]     Then the CPU  11  sends the generated iSCSI mount command to the network storage device  3  of the iSCSI target of which the iSCSI connection is established by the above mentioned storage connection confirmation processing. And the transmission time is acquired from the internal timer, which is not illustrated (S 1062 ). And the CPU  11  waits for the response data to the iSCSI mount command for a predetermined time (S 1063 , S 1064 ).  
         [0063]     In the storage control device  31 , the CPU  311 , which received the iSCSI mount command via the NIC  313 , decides whether the mounting of the volume  34  having the LUN, specified by the mount command, is enabled by referring to the access management table  3123  according to the storage control program  3122 . Specifically, if the entry  31230  which has the LUN specified by the mount command, iSCSI name of the iSCSI initiator (H-ID) and IP address of the host computer  1 , which is the iSCSI initiator (NH-ID), are registered in the access management table  3123 , the mounting of the LUN is enabled. If not registered, mounting thereof is not enabled. The CPU  311  generates the response data including the decision on mountability, and sends it to the iSCSI initiator. Here, in this response data, “11” is stored in the result  607  in the data format shown in  FIG. 8  if mounting is enabled. If mounting is rejected, “12” is stored in the result  607 . If the network storage device  3  does not have the LUN specified by the mount command, then “13” is stored in the result  607 .  
         [0064]     In S 1063  and S 1064 , if the response data to the iSCSI mount command is not received within the predetermined time, the CPU  11  judges that continuity does not exist with the transmission destination of the iSCSI mount command (iSCSI target) in the iSCSI layer, generates a message to indicate “No continuity” (S 1065 ), and displays it on the display device  16  (S 1070 ). For example, such a message as “LUN (S-ID) access confirmation failed (no response)” is displayed on the display device  16 . Here LUN is the LUN received from the user in S 101  of  FIG. 4 .  
         [0065]     If the response data to the iSCSI mount command is received within the predetermined time in S 1063  and S 1064 , on the other hand, the CPU  11  analyzes the command execution result stored in the result  607  of this response data (S 1066 ). If the execution result is the authentication error “12” or the LUN error “13”, the CPU  11  judges that the transmission destination of the iSCSI mount command (iSCSI target) rejected the mounting of LUN or that there is no mounting target LUN, and generates a message to indicate the reason (S 1067 ), and displays it on the display device  16  (S 1070 ). For example, such a message as “LUN (S-ID) access confirmation failed (LUN error)” (in the case of no LUN) or “LUN (S-ID) access confirmation failed (authentication error)” (in the case of rejecting a mount) is displayed on the display device  16 .  
         [0066]     If the mount command execution result is the normal end “11” in S 1066 , on the other hand, the CPU  11  judges that the transmission destination of the iSCSI mount command (iSCSI target) mounted the LUN received from the user in S 101  in  FIG. 4 . And [the CPU  11 ] acquires the reception time from the internal timer, which is not illustrated, and calculates the processing time required for confirming access by subtracting the transmission time from this reception time (S 1068 ). Then the CPU  11  generates a message to indicate “mounting succeeded” including the processing time (S 1069 ), and displays it on the display device  16  (S 1070 ). For example, such a message as “LUN (S-ID) access confirmation succeeded. Processing time t” is displayed on the display device  16 . Here the processing time t is the time calculated in S 1068 .  
         [0067]     (6) Message Output  
         [0068]      FIG. 10  shows examples of the messages to be output to the display device  16  by the volume accessibility decision processing shown in  FIG. 4 .  FIG. 10A  shows a display example when confirmation succeeded in all of the above mentioned network continuity confirmation processing, storage connection confirmation processing and access confirmation processing, and  FIG. 10B  shows a display example when confirmation failed in the above mentioned network continuity confirmation processing.  
         [0069]     As  FIG. 10A  shows, a success message  701  is output each time confirmation succeeds in the respective network continuity confirmation processing, storage connection confirmation processing and access confirmation processing. The examples shown in  FIG. 10A  are success messages  701  when the volume accessibility decision is executed for iSCSI name “A” and LUN “1” of volume  34  of the network storage device  3 . Each message  701  includes the processing time, so that the guideline for throughput can be set.  
         [0070]     As  FIG. 10B  shows, if confirmation failed in a confirmation processing, a failure message  702  is output, and confirmation processing after this confirmation is omitted. The example shown in  FIG. 10B  is a failure message  702  which was output in the network continuity confirmation processing when the volume accessibility decision is executed for the iSCSI name “B” of the network storage device  3 . The message  702  includes not only the iSCSI name of the network storage device  3  but also the IP address (192.169.2.10).  
         [0071]     An embodiment of the present invention was described above.  
         [0072]     In the present embodiment, continuity confirmation between the host computer  1  and the network storage device  3  in the IP layer (network continuity confirmation processing), connection confirmation between the host computer  1  and the network storage device  3  in the iSCSI layer (storage connection confirmation processing), and mountability confirmation for the volume  34  of the network storage device  3  by the host computer  1  (access confirmation processing) are sequentially executed. Therefore when the host computer  1  cannot access the volume  34  of the network storage device  3 , the cause can be easily identified. Also when a new host computer  1  or a new network storage device  3  is installed, setup can be easily confirmed. Also the processing time required for the respective confirmation processing is displayed, so the guideline of communication throughput between the host computer  1  and the network storage device  3  can be known. In this way, according to the present embodiment, the burden of operation required for specifying the continuity status and the cause of failure of the network storage device  3  can be decreased.  
         [0073]     The present invention is not limited to the above mentioned embodiment, but can be modified in various ways within the scope of the essential characteristics thereof.  
         [0074]     For example, in the above embodiment, the volume accessibility decision processing is executed in the sequence of network continuity confirmation processing, storage connection confirmation processing and access confirmation processing, but the present invention is not limited to this. However the cause of failure can be specified more quickly by executing the volume accessibility decision processing in the above sequence.  
         [0075]     Also in the above embodiment, an example of SAN  2  where an IP is used as the network communication protocol and an iSCSI is used as a host protocol of the network communication protocol was described. However the present invention is not limited to this. A protocol other than IP may be used as the network communication protocol. In the same way, a protocol other than the iSCSI protocol may be used as the host protocol.  
         [0076]     The present invention can be applied in the same way when the connection status between the network device other than the network storage device  3  and the host computer  1  is confirmed.