Patent Publication Number: US-7908418-B2

Title: Storage system, storage device, and host device

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a technique of constructing a multipath of a storage system in consideration of redundancy for hot-swap of firmware in a storage device. 
     2. Description of the Related Art 
     A storage system is composed of a host and a storage device connected to the host. Upon hot-swap of firmware in such a storage device, if plural control modules (hereinafter referred to as “CMs”) having firmware components installed thereto are provided, the firmware components are exchanged in two stages, the first half and the second half. For example, if the storage device includes four CMs, firmware components of two CMs are first exchanged at the same time. After the completion of the exchange, firmware components of the remaining two CMs are exchanged. The storage device and the host constitute multipath construction. Each path is connected to each CM to thereby enable hot-swap of firmware without stopping an operation. Next, an example of hot-swap of firmware in a device including two CMs is described. 
       FIGS. 1A to 1D  are explanatory views of firmware exchange of the related art. A storage system is composed of a host  101  and a storage device  102  having two paths connected to the host  101 . ( FIG. 1A ) In a general state, data can be transferred to the storage device  102  from the host  101  through the two paths. ( FIG. 1B ) During exchange of firmware of the first half (CM  0 ), data is transferred between the host  101  and the storage device  102  only through the path on the CM  1  side. ( FIG. 1C ) During exchange of firmware of the second half (CM  1 ), data is transferred between the host  101  and the storage device  102  through the path on the CM  0  side where firmware exchange is completed. ( FIG. 1D ) After the completion of exchange of firmware of the second half, data can be transferred through the two paths. 
     As described above, the storage device  102  and the host  101  constitute multipath construction. Each path is connected to each CM to thereby enable hot-swap of firmware components without stopping an operation. 
     However, if firmware exchange is carried out under the following circumstances, connectivity of all paths between the storage device and the host is abnormal. As a result, data transfer is disabled and an operation is stopped. 
     (1) All cables connected between the storage device and the host are connected to the first half, the CM  0 . 
     (2) All cables connected between the storage device and the host are connected to the second half, the CM  1 . 
     In the environment where multipath information has been already generated, if active firmware exchange is carried out under this condition, an operation is stopped. However, the host needs to be reactivated in order to change path construction. As a result, the operation is further suspended. Therefore, in this case, this firmware exchange is the same as inactive firmware exchange. 
     SUMMARY 
     Accordingly, it is an object of the present technique to provide a storage system, which construct redundant multipath for hot-swap of firmware. 
     According to an aspect of an embodiment, a storage system includes a host device and a storage device connected to the host device through a multipath and configured to perform hot-swap of firmware. 
     The host device includes a command control unit for generating a inquiry command about whether to allow firmware exchange, a command transmitting unit for transmitting the generated inquiry command to the storage device, a response information receiving unit for receiving a response information from the storage device as a response to the inquiry command, a determination unit for determining whether to allow the firmware exchange of the storage device in accordance with the response information, and a path information generating unit for generating multipath information regarding the multipath with the storage device upon determining the firmware exchange being enabled. 
     The storage device includes a receiving unit for receiving the inquiry command, a response information generating unit for generating information about whether to allow the firmware exchange as response information to the received inquiry command, and a transmitting unit for transmitting the generated response information to the host device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A to 1D  are explanatory views of firmware exchange of prior art; 
         FIG. 2  is a diagram of a storage system according to an embodiment; 
         FIG. 3  is an explanatory view of an I/O control unit of a host; 
         FIGS. 4A and 4B  are explanatory views of a path configuration table; 
         FIG. 5  is a diagram of an example of erroneous connection; 
         FIG. 6  is an explanatory view of a management table; 
         FIG. 7  is a flowchart of processing A of a host; 
         FIG. 8  is a flowchart of processing B of a host; and 
         FIG. 9  is a flowchart of processing of a storage device. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 2  is a diagram of a storage system according to an embodiment. 
     A storage system  1  includes, for example, two hosts  11  and  61 , and a storage device  2 . The host  11  and the host  61  each include two paths. 
     The host  11  includes a control unit  13 , an input/output (hereinafter referred to as “I/O”) control unit  14 , a port  15 , and a port  16 . 
     The host  61  includes a control unit  63 , an I/O control unit  64 , a port  65 , and a port  66 . 
     The host  11  or the host  61  performs multipath control on connection with the storage device  2 . 
     The multipath control means to connect the host  11  or the host  61  with one or more storage devices  2  through plural paths. In general, the host  11  or the host  61  accesses the storage device  2  through a main path connected thereto. If any failure occurs in the main path, the host accesses the storage device  2  through a sub path connected thereto. According to such multipath control, even if a failure occurs in one path of any storage device  2 , the host  11  or the host  61  can access the storage device through another path connected to the storage device. Thus, system&#39;s fault-tolerance for a path failure can be enhanced. 
     On the other hand, the storage device  2  includes a channel adaptor (hereinafter referred to as “CA”)  21 , a CA  31 , a controller module (hereinafter referred to as “CM”)  22 , a CM  32 , a disk control module  41 , a disk control module  42 , and disks  71  to  73 . 
     A main path between the host  11  and the storage device  2  is a connection route of the port  15 , the CA  21 , and the CM  22 . Further, a sub path therebetween is a connection route of the port  16 , the CA  31 , and the CM  32 . A combination of the paths is set as the default. 
     On the other hand, a main path between the host  61  and the storage device  2  is a connection route of the port  66 , the CA  31 , and the CM  32 . Further, a sub path therebetween is a connection route of the port  65 , the CA  21 , and the CM  22 . A combination of the paths is set as the default. 
     (Explanation of Host) 
     The control unit  13  controls the entire host  11 . The control unit  63  controls the entire host  61 . Therefore the control units  13  and  63  control start-up processing and job processing. The control units  13  and  63  each include a processor for controlling an operation. 
     The I/O control units  14  and  64  issue an I/O command to control data read/write from/to the storage device  2 . Examples of the I/O command include an inquiry command to check a connection state of a path of the storage device  2 , a write command to write data to the storage device  2 , and a state notification command to notify a user of a connection state. 
     The ports  15 ,  16 ,  65 , and  66  are interface ports connected to the storage device  2  through a fibre channel or the like. The ports control data communication between the host  11  or  61  and the storage device  2 . The ports transmit a command as a command transmitting unit or receive response information as a response information receiving unit, for example. Moreover, each port is given a unique 8-byte serial number WWN (world wide name). For example, the port  15  is given a WWN-A, the port  16  is given a WWN-B, the port  65  is given a WWN-C, and the port  66  is given a WWN-D. 
       FIG. 3  is an explanatory view of an I/O control unit of a host. 
     The I/O control unit  14  is described next. The I/O control unit  14  includes a command control unit  81 , a connection control unit  82 , an error display unit  83 , a path configuration table  84 , and a path information generating unit  85 . The I/O control unit  64  has similar configuration. The command control unit  81  issues a write command, a read command, etc. to each path between the host  11  or  61  and the storage device  2  in response to an instruction from the control unit  13 . Further, the command control unit  81  issues a state notification command and an inquiry command in response to an instruction from the connection control unit  82 . In addition, the command control unit  81  receives response information from the storage device  2  as a response to the inquiry command and passes the information to the connection control unit  82 . 
     The inquiry command to the storage device  2  is to inquire about a CM number for identifying the CM  22  or CM  32  connected to a path and the exchange order of each firmware of the CM  22  or CM  32 . The response information from the storage device  2  to the inquiry command includes CA-WWN information of the port  51  or  52  of the CA  21  or WWN information of the port  53  or  54  of the CA  31 . The CM number refers to an identification number of the CM. 
     The exchange order refers to the order in which CMs are subjected to controller firmware loading (hereinafter referred to as “CFL”). The CFL means exchange of each firmware installed to the CM  22  or  32 . The CFL is executed in two stages, the first half and the second half. For example, if the first half of the CFL is targeted at the CM  22 , the exchange order thereof is set to “1”. If the second half of the CFL is targeted at the CM  32 , the exchange order thereof is set to “2”. If two or more CMs in the storage device  2  are provided, the CMs are divided into several groups, and the firmware exchange order is determined on a group basis. 
     Referring back to  FIG. 3 , a detailed description is given below. 
     The connection control unit  82  has a redundancy check unit  92  and a failure processing unit  93 . The redundancy check unit  92  issues inquiry command for checking redundancy of path between the storage device  2  and the host  11 . And the redundancy check unit  92  checks redundancy of the path based on the response information from the storage device  2  to the inquiry command transmitted to the storage device  2 . In addition, the connection control unit  82  prepares the path configuration table  84  based on path-specific CM number and exchange order number included in the response information from the storage device  2  in order to check redundancy. After the completion of generating the path configuration table  84  for all paths, the redundancy check unit  92  checks whether the exchange orders are the same exchange orders. 
     If the exchange orders are the same exchange orders, the paths are considered as not redundant, and the redundancy check unit  92  sends an error message for warning toward the error display unit  83 . When the paths are considered as not redundant for failure of the path, the redundancy check unit  92  sends an error message for warning toward the error display unit  83 . Then the redundancy check unit  92  requests the command control unit  81  to issue a state notification command to notify the storage device  2  of abnormal state. 
     If the exchange order differs between the paths, the paths are considered as redundant, and the redundancy check unit  92  requests the path information generating unit  85  to construct multipath and then, requests the command control unit  81  to issue a state notification command to notify the storage device  2  about a normal state. The failure processing unit  93  regularly issues the inquiry command in the job processing and detects the failure of the path or recovery of the path. Furthermore the failure processing unit  93  determines to be failure of the storage device  2 , for example, when normal response information from the storage device  2  to the inquiry command transmitted to storage device  2  is not received. The failure is, for example, the failure of the disks  71  to  73 . And the failure processing unit  93  determines to be recovery of the path when the normal response information to the inquiry command transmitted to the storage device  2  after the failure of the path is received. A maintenance person recovers the failure of the path by replacement of failed units. 
     When the failure processing unit  93  determines to be the failure of the path, the failure processing unit  93  sends an error message for warning toward the error display unit  83 . And when the failure processing unit  93  determines to be the recovery of the path, the failure processing unit  93  sends a recovery message toward the error display unit  83 . 
     The error display unit  83  displays the error message and the recovery message to the maintenance person. The path configuration table  84  shows path-specific connection construction. The path information generating unit  85  generates path information about a path among the control unit  13  and the CM  22  or  32  of the storage device  2  and the disks  71  to  73  based on the response information from the storage device  2 . The control unit  13  controls data read/write from/to the disks  71  to  73  based on the generated path information. 
       FIGS. 4A and 4B  are explanatory views of the path configuration table. 
     The path configuration table  84  of the host  11  is described next. The path configuration table  84  includes a path number, a host-WWN, a CM number, and the exchange order number. 
       FIG. 4A  shows the path configuration table  84  under a normal condition. 
     As for a path number  1 , WWN-A is set as the host WWN, CM  22  is set as the CM number, and “1” is set as the exchange order number. 
     As for a path number  2 , WWN-B is set as the host WWN, CM  32  is set as the CM number, and “2” is set as the exchange order number. 
       FIG. 4B  shows the path configuration table  84  under an abnormal condition. 
     As for a path number  1 , WWN-A is set as the host WWN, CM  22  is set as the CM number, and “1” is set as the exchange order number. 
     As for a path number  2 , WWN-B is set as the host WWN, CM  32  is set as the CM number, and “1” is set as the exchange order number. 
       FIG. 5  is a diagram of an example of erroneous connection. 
       FIGS. 4A and 4B  indicate to be different about CM number, and the exchange order number. 
     The connection between the host  11  and the storage device  2  is described as an example of the erroneous connection. The path configuration table  84  in  FIG. 5  is shown in  FIG. 4B . 
     The host  11  includes the ports  15  and  16  for communication control. 
     The port  15  is connected to the CM  22  through the port  51  of the CA  21 . This path is the path numbered “ 1 ”. The port  16  is connected to the CM  22  through the port  52  of the CA  21 . This path is the path numbered “ 2 ”. To be specific, the path numbered “ 1 ” and the path numbered “ 2 ” are both connected to the CM  22 . In this case, if the CM  22  is subjected to CFL, the storage device  2  cannot receive data from the host  11 . As a result, an operation is stopped. Thus, the host  11  displays an error message and notifies a maintenance person about the error. Then, the host  11  instructs the maintenance person to reconnect a connection cable. 
     (Explanation of Storage Device) 
     Referring back to  FIG. 2 , a detailed description is given below. 
     The CA  21  is connected to the hosts  11  and  61 . The CA  21  controls communications between the hosts  11  and the storage device  2 . The CA  21  controls communications between the hosts  61  and the storage device  2 . Further, the CA  21  is connected to the CM  22 . The CA  21  includes the ports  51  and  52  for communication control, which are connected to the host  11  or the host  61 . The ports  51  and  52  receive a command as a receiving unit or transmit response information as a transmitting unit. The ports  51  and  52  each have a CA-WWN. 
     The CA  31  is connected to the hosts  11  and  61 . The CA  31  controls communications between the hosts  11  and the storage device  2 . The CA  31  controls communications between the hosts  61  and the storage device  2 . Further, the CA  31  is connected to the CM  32 . The CA  31  includes the ports  53  and  54  for communication control, which are connected to the host  11  or  61 . The ports  53  and  54  receive a command as a receiving unit or transmit response information as a transmitting unit. The ports  53  and  54  each have a CA-WWN. 
     The disk control modules  41  and  42  control data read/write from/to the disks  71  to  73 . The disks  71  to  73  are data storage devices. The CMs  22  and  32  execute control to store data received from the host  11  or  61  in the disks  71  to  73  through the disk control module  41  or  42  and to transmit data read from the disks  71  to  73  to the host  11  or  61  through the disk control module  41  or  42 . Further, the CMs  22  and  32  control the CFL or the like. 
     The CM  22  includes a response information generating unit  23 , a CFL control unit  24 , a read/write control unit (hereinafter referred to as “R/W control unit”)  25 , and an MPU  26  as a control unit of the storage device  2 . For example, the response information generating unit  23 , the CFL control unit  24 , and the read/write control unit (hereinafter referred to as “R/W control unit”)  25  are firmwares that operate by MPU  26 . 
     The CM  32  includes a response information generating unit  33 , a CFL control unit  34 , a R/W control unit  35 , and an MPU  36  as a control unit of the storage device  2 . For example, the response information generating unit  33 , the CFL control unit  34 , and the read/write control unit (hereinafter referred to as “R/W control unit”)  35  are firmwares that operate by MPU  36 . 
     The response information generating units  23  and  33  generate response information as a response to an inquiry command. The response information includes a CA-WWN, a CM number, and the firmware exchange order number. 
     The CFL control units  24  and  34  perform firmware exchange for revision. 
     The CFL is first performed on the first half, the CM  22 . Next, the CFL is performed on the second half, the CM  32 . Thus, a management table  91  for determining whether to allow firmware exchange is set. The management table  91  (reference to  FIG. 6 ) stores a normal/abnormal path state corresponding to a state notification command from the host  11  or  61 . 
       FIG. 6  is an explanatory view of the management table. 
     The management table  91  lists a host ID, a host-WWN, and state information. 
     The host ID represents an identification number of the host  11  or  61 . The host-WWN represents an identification number of the port  15 ,  16  or the port  65 ,  66 . 
     The state information “normal” represents that a path is normal. The state information “abnormal” represents that a path is abnormal. 
     In the management table  91  of  FIG. 6 , all paths are normal. Thus, firmware exchange can be performed when all paths are normal. Here, CFL is carried out under such a condition that one side of the redundant configuration is assured. For example, during revision of the firmware of the CM  22 , the CM  32  is put into a general state. During revision of the firmware of the CM  32 , the CM  22  is put into a general state. The general state means a state of being communicable with the host  11  or  61 . 
     Referring back to  FIG. 2 , a detailed description is given below. 
     The R/W control units  25  and  35  control data read/write between the disks  71  to  73  and the host  11  or  61  through the disk control module  41  or  42 . 
     The MPU  26  controls the entire CM  22 . The MPU  36  controls the entire CM  32 . 
     (Explanation of Operation) 
     Upon firmware exchange in the storage device  2 , required is a function of executing revision of the firmware without stopping I/O control of the host  11  or  61 . Upon the CFL in the storage device  2 , firmware revision is controlled utilizing the redundant configuration in the storage device  2  without disconnecting paths to the disks  71  to  73 . 
     In order to effectively execute the CFL, the host  11  or  61  automatically communicates with the storage device  2  in a boot sequence of the host  11  or  61  to check redundancy for the CFL. If the check result shows that path connection configuration has no redundancy, a warning message is output. As a result, a maintenance person can find a defect in the configuration at an early stage and detect an error before the CFL. 
     To elaborate, at the time of automatically constructing multipath in the start-up processing of the host  11  or  61 , a connection state of each cable between the host  11  or  61  and the storage device  2  is checked. If all cables are connected to the CM  22  subjected to the CFL on the first half, a message to that effect is output. As a result, when all cables are connected to the CM  22  subjected to the CFL on the first half, multipath is not constructed. If all cables are connected to the CM  32  subjected to the CFL on the second half, a message to that effect is output. As a result, when the all cables are connected to the CM  32  subjected to the CFL on the second half, multipath is not constructed. On the other hand, if a connection state of each cable is normal, the host  11  or  61  constructs multipath. 
     As discussed previously, the host  11  or  61  constructs the multipath when the redundancy of the path in the start-up processing is detected. 
     However, if the failure of the path occurs in the job processing after the start-up processing and the CFL is performed, the job processing might stop. Therefore when the host  11  or  61  detects the failure of the path, the host  11  or  61  checks the redundancy of the path for CFL. As a result, when the host  11  or  61  determines that the storage system  1  has not the redundancy of the path for CFL, the host  11  or  61  sends the error message for warning toward the error display unit  83 . 
     And when the host  11  or  61  detects the recovery of the path, the host  11  or  61  checks the redundancy of the path for CFL. When the host  11  or  61  determines that the storage system  1  has the redundancy of the path for CFL, the host  11  or  61  sends the recovery message toward the error display unit  83 . 
     The above-mentioned processing is the explanation of the failure of the path and recovery of the path. However, the same processing of host  11  or  61  is executed if the path is increased or decreased. 
       FIG. 7  is a flowchart of processing A of a host. The following explanation is explanation of the processing A of host  11 . Explanation of processing of host  61  is omitted for the explanation similar to the processing A of host  11 . 
     First of all, the I/O control unit  14  checks whether state of processing of the host  11  is start-up processing (step S 1 ). 
     When the state of processing is start-up processing, processing B is executed (step S 2 ). The I/O control unit  14  advances the processing to step S 3  when processing B ends. The processing B is processing that checks the redundancy of path between host  11  and storage device  2 . 
       FIG. 8  is a flowchart of processing B of the host. First, the I/O control unit  14  transmits an inquiry command on a port basis (step S 11 ). The inquiry command is to inquire of a CM number for identifying the CM  22  or  32  connected to a path and the exchange order of each firmware of the CM  22  or  32 . 
     The I/O control unit  14  waits for the storage device  2  to receive response information (step S 12 ). The I/O control unit  14  determines to be the failure of the path if the response from the storage device  2  is not received. 
     If the I/O control unit  14  receives response information from the storage device  2 , the I/O control unit  14  checks whether all paths have been examined (step S 13 ). If all paths have been examined, the path configuration table  84  is generated based on the response information (step S 14 ). Next, the I/O control unit  14  checks redundancy (step S 15 ). Under the following conditions, the check result shows that paths are considered as no redundancy (step S 16 ). To be specific, if the exchange orders in the path configuration table  84  are all set to “1”, all paths are connected to the first half, the CM  22  as in the path configuration table  84  of  FIG. 4B . Further, if the exchange orders in the path configuration table  84  are all set to “2”, all paths are connected to the second half, the CM  32 . In such cases, since firmware exchange cannot be performed, the I/O control unit  14  stops constructing multipath and displays an error message indicating improper connection. And when the response information from the storage device  2  is not received, the I/O control unit  14  displays an error message indicating the failure of the path (step S 17 ). Then, the I/O control unit  14  of the host device  11  notifies the storage device  2  of the abnormal state using a state notification command (step S 18 ). As a result, multipath is not constructed. The maintenance person recoveries the error between the host  11  and the storage device  2  based on the error message. 
     On the other hand, in the connection state shown in the path configuration table  84  of  FIG. 4A , for example, path connection configuration is considered redundant. The exchange orders in the path configuration table  84  are set to “1” and “2” and thus different, not identical. In this case, since firmware exchange can be performed based on the path configuration table  84 , multipath is constructed. Then, the I/O control unit  14  of the host device  11  notifies the storage device  2  of the normal state using a state notification command (step S 19 ). 
     However, if one path is a failure and the other two paths are normal when the storage system  1  has, for example, three paths, the paths can be determined to be redundancy. 
     Referring back to  FIG. 7 , a detailed description is given below. The I/O control unit  14  transmits the inquiry command to the storage device  2  when the state of processing of the host  11  is not start-up processing (step S 3 ). 
     Next, the I/O control unit  14  determines whether the failure of the path occurs (step S 4 ). 
     The I/O control unit  14  determines to be the failure of the path when the normal response information to the inquiry command transmitted to the storage device  2  is not received. 
     Next, the processing B is executed for the rest of the paths when the failure of the path occurs (step S 5 ). 
     The I/O control unit  14  determines whether the path is recovered after the processing B ends (step S 6 ). 
     When the I/O control unit  14  determines that the path is recovered, the I/O control unit  14  executes the processing B (step S 7 ). 
     The I/O control unit  14  displays the recovery message after the end of the processing B (step S 8 ). 
     The I/O control unit returns to the step S 3  after the end of the processing B. 
       FIG. 9  is a flowchart of processing of a storage device. In  FIG. 9 , the following explanation is explanation of the processing of CM  22 . Explanation of processing of CM  32  is omitted for the explanation similar to the processing of CM  22 . The CM  22  determines whether a received command is the inquiry command (step S 21 ). When the received command is the inquiry command, the CM  22  obtains a CM number of the CM  22  and a CA-WWN (step S 22 ). Next, the device acquires the exchange order number (step S 23 ). The exchange order number is assigned to each CM in advance. 
     Next, the CM  22  generates response information (step S 24 ). In this embodiment the response information includes a CA-WWN, a CM number, and the exchange order number. The CM  22  transmits the generated response information to the host  11  through the CA  21  or  31  ((step S 25 ). Meanwhile, the CM  22  determines whether the received command is a state notification command when the received command is not the inquiry command (step S 26 ). When the received command is the state notification command, the CM  22  determines whether the state notification command notifies the abnormal state (step S 27 ). If abnormal state is notified, the CFL is disabled. Thus, the CFL is not performed even if a maintenance person issues an instruction to execute CFL (step S 28 ). If normal CFL is notified, the CFL is enabled (step S 29 ). Thus, the storage device  2  starts CFL in response to an instruction to execute CFL. 
     When the received command is not the state notification command, the processing ends. Next, an operation of the CFL is described. 
     (Explanation of Firmware Exchange Operation) 
     Referring to  FIG. 2 , firmware exchange in the storage device  2  is described. 
     In this example in  FIG. 2 , cable connection involves no error. 
     The storage system  1  assures connectivity of a path between the storage device  2  and the hosts  11  and  61 , and then performs firmware exchange. On the host  11  or  61  side, connectivity with the storage device  2  is monitored. When connection with the storage device  2  is established, any failure occurs, or any failure is eliminated, the storage system issues a state notification command to notify the storage device  2  of each state of the hosts  11  and  61 . 
     The storage device  2  side has plural paths connected with the hosts  11  and  61  connected to the storage device  2 . The storage device  2  registers state information received from the connected hosts  11  and  61  in the management table  91  for each path of the hosts  11  and  61 . In response to a request to start firmware exchange from a maintenance person, the storage device  2  first exchanges firmware of the CM  22  if a path state of the host  11  or  61  in the management table  91  is “normal”. At this time, the storage device  2  can perform an operation via paths of the CM  32 . After the completion of firmware exchange in the CM  22 , firmware of the CM  32  is next exchanged. At this time, the storage device  2  can perform an operation via paths of the CM  22 . 
     On the other hand, in response to a request to start firmware exchange, the storage device  2  does not perform firmware exchange if a path state of the host  11  or  61  in the management table  91  is “abnormal”. 
     In this way, the host  11  or  61  can construct multipath in consideration of redundancy for hot-swap of firmware. 
     Further, the following configuration may be employed. That is, at the time of determining whether to allow firmware exchange, if exchange is disabled, multipath is constructed and a warning message is output. In this case, multipath that disallows firmware exchange is constructed. 
     Further, in the storage system  1 , multipath would not be automatically constructed during a boot sequence of the host  11  or  61  depending on the type of an OS. In this case, a maintenance person inputs an instruction to generate multipath information to thereby determine whether to allow firmware exchange and then construct multipath.