Abstract:
A storage system, method and program product, the system comprising: storage devices; and a controller configured to: provide virtual volumes to a host computer; manage logical units on the storage device and storage pools; allocate, in response to receiving a write request to a virtual volume, a storage region of the storage pools; and store data related to the write request in the storage region allocated, wherein the controller is further configured to: allocate first storage region in first storage pool to first virtual volume based on first size of the first storage region or the first virtual volume; allocate a second storage region in a second storage pool to a second virtual volume of the plurality of virtual volumes based on a second size of the second storage region or the second virtual volume.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a storage system, and a method of controlling a storage system. 
       BACKGROUND ART 
       [0002]    Patent Literature (PTL) 1 discloses a technique for improving the availability of an information system. Specifically, first and second storage apparatuses, coupled to a host computer, have set therein a remote copy pair for copying data of a first volume in the first storage apparatus to a second volume in the second storage apparatus, and associate a third volume in a third storage apparatus with the remote copy pair. When an I/O request to the first volume ends in an error, the host computer sends the second storage apparatus an I/O request to the second volume. When the first or second storage apparatus detects a failure in its partner first or second storage apparatus or detects a coupling failure between the first and the second storage apparatuses, the first or second storage apparatus stores in the third volume a failure information flag indicating the detection of the failure. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         PTL 1: US Patent Application Laid-open Publication No. 2009/0271582 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0004]    In the information system disclosed in PTL 1, when a failure occurs in the first storage apparatus, the information system is recovered to an original high-availability operational status by replacing the first storage apparatus with another storage apparatus, for example. However, information uniquely set for each storage apparatus is changed before and after the replacement. Accordingly, the host computer has to change settings or be rebooted, which affects the tasks or services provided by the host computer. 
         [0005]    The present invention has been made in view of such background, and an object thereof is to provide a storage system capable of recovering to the high-availability operational status without affecting a host computer, and method of controlling the storage system. 
       Solution to Problem 
       [0006]    One aspect of the present invention for achieving the above object is a storage system including: a first storage apparatus communicatively coupled to a host computer and capable of providing a first storage volume; a second storage apparatus communicatively coupled to the host computer and the first storage apparatus and capable of providing a second storage volume and a third storage volume; and a third storage apparatus communicatively coupled to the host computer and the second storage apparatus and capable of providing a fourth storage volume, wherein the first storage apparatus provides the host computer with a first virtual apparatus ID set for the first storage apparatus, a first virtual volume ID set for the first storage volume, and a first virtual port ID set for a network port in the first storage apparatus, as information for identifying a first path the host computer uses when sending a data I/O request to the first storage volume, the second storage apparatus provides the host computer with a second virtual apparatus ID set for the second storage apparatus, a second virtual volume ID set for the second storage volume, and a second virtual port ID set for a network port in the second storage apparatus, as information for identifying a second path the host computer uses when sending a data I/O request to the second storage volume, the second storage apparatus provides the host computer with the second virtual apparatus ID set for the second storage apparatus, a third virtual volume ID set for the third storage volume, and a third virtual port ID set for a network port in the second storage apparatus, as information for identifying a third path the host computer uses when sending a data I/O request to the third storage volume, the third storage apparatus provides the host computer with a third virtual apparatus ID set for the third storage apparatus, a fourth virtual volume ID set for the fourth storage volume, and a fourth virtual port ID set for a network port in the third storage apparatus, as information for identifying a fourth path the host computer uses when sending a data I/O request to the fourth storage volume, the first storage apparatus, the second storage apparatus, and the third storage apparatus provide the host computer with a common virtual apparatus ID as the first virtual apparatus ID, the second virtual apparatus ID, and the third virtual apparatus ID, the first storage apparatus, the second storage apparatus, and the third storage apparatus provide the host computer with a common virtual volume ID as the first virtual volume ID, the second virtual volume ID, the third virtual volume ID, and the fourth virtual volume ID, when the first storage apparatus is normally operating, the first storage apparatus receives the data I/O request from the host computer via the first path to perform data I/O to and from the first storage volume and performs management using a remote copy function for a pair of the first storage volume and the second storage volume, and when an error occurs in the first storage apparatus: the second storage apparatus starts to receive the data I/O request from the host computer via the second path, and starts to perform data I/O to and from the second storage volume, the second storage apparatus starts management using a local copy function for a pair of the second storage volume and the third storage volume; the second storage apparatus and the third storage apparatus start management using a remote copy function for a pair of the third storage volume and the fourth storage volume; the second storage apparatus starts to receive the data I/O request from the host computer via the third path and starts to perform data I/O to and from the third storage volume; and the third storage apparatus starts to receive the data I/O request from the host computer via the fourth path and starts to perform data I/O to and from the fourth storage volume. 
         [0007]    Other problems disclosed in the present specification and the solutions thereof are made clear in the section of Description of Embodiments, drawings, and the like. 
       Advantageous Effects of Invention 
       [0008]    According to the present invention, the storage system can be recovered to a high-availability operational status without affecting the host computer. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is a diagram showing a schematic configuration of a storage system  1 . 
           [0010]      FIG. 2  is a diagram for explaining a unique information virtualization function in detail. 
           [0011]      FIG. 3  shows an example of a path management table  300 . 
           [0012]      FIG. 4  is a diagram showing various tables managed in a first storage apparatus  10 . 
           [0013]      FIG. 5  is a diagram showing various tables managed in a second storage apparatus  10 . 
           [0014]      FIG. 6  is a diagram for explaining an overview of processing performed in the storage system  1  in a time-series order. 
           [0015]      FIG. 7  is a diagram schematically showing the operations of the respective stages in  FIG. 6 . 
           [0016]      FIG. 8  shows an example of the path management table  300 . 
           [0017]      FIG. 9  shows an example of the remote pair management table  540 . 
           [0018]      FIG. 10  is a diagram for explaining a third stage. 
           [0019]      FIG. 11  is a flowchart for explaining local copy start command processing S 1100 . 
           [0020]      FIG. 12  is a flowchart for explaining local copy start processing S 1200 . 
           [0021]      FIG. 13  shows an example of a local pair management table  1300 . 
           [0022]      FIG. 14  is a diagram for explaining a fourth stage. 
           [0023]      FIG. 15  shows examples of a quorum drive management table  550  and a quorum drive management table  650 . 
           [0024]      FIG. 16  is a flowchart for explaining remote copy start command processing S 1600 . 
           [0025]      FIG. 17  is a flowchart for explaining remote copy start processing S 1700 . 
           [0026]      FIG. 18  shows examples of an own virtual port management table  510  and a partner virtual port management table  520 . 
           [0027]      FIG. 19  shows examples of a remote pair management table  540  and a unique information conversion table  570 . 
           [0028]      FIG. 20  is a flowchart for explaining remote copy start preparation processing S 2000 . 
           [0029]      FIG. 21  shows examples of an own virtual port management table  610 , a partner virtual port management table  620 , a remote pair management table  640 , and a unique information conversion table  670 . 
           [0030]      FIG. 22  is a diagram for explaining a fifth stage. 
           [0031]      FIG. 23  shows an example of the path management table  300 . 
           [0032]      FIG. 24  is a flow chart for explaining data I/O processing (second storage apparatus) S 2400 . 
           [0033]      FIG. 25  is a flow chart for explaining data I/O processing (third storage apparatus) S 2500 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0034]    Hereinafter, an embodiment will be described with reference to the drawings. 
         [0035]      FIG. 1  shows a schematic configuration of a storage system  1  which will be described as one embodiment. As shown in  FIG. 1 , the storage system  1  includes one or more host computers  3  (external apparatuses), four storage apparatuses  10  (hereinafter, each of which are referred to as a first storage apparatus  10 , a second storage apparatus  10 , a third storage apparatus  10 , and a fourth storage apparatus  10 ), and a management apparatus  4 . Note that, the four storage apparatuses  10  described above are simply collectively called the storage apparatus  10  in the explanation below. 
         [0036]    The host computer  3  is a computer which provides services such as automated teller services in banks and Web page browsing services in the Internet, for example. The storage apparatus  10  is an apparatus which provides a data storage area for an application program or the like executed in the host computer  3 , and is a disk array apparatus, for example. 
         [0037]    The host computer  3  is communicatively coupled to each of the first storage apparatus  10  and the second storage apparatus  10  via a first communication network  5 . Furthermore, the first storage apparatus  10 , the second storage apparatus  10 , the third storage apparatus  10 , and the fourth storage apparatus  10  are communicatively coupled to one another via the first communication network  5 . 
         [0038]    The first communication network  5  is, for example, a LAN (Local Area Network), a WAN (Wide Area Network), a SAN (Storage Area Network), the Internet, a public communication network, lease line, or the like. Furthermore, communication between the host computer  3  and the storage apparatus  10  is performed in accordance with a protocol such as TCP/IP, iSCSI (internet Small Computer System Interface), Fibre Channel Protocol, FICON (Fibre Connection) (registered trademark), ESCON (Enterprise System Connection) (registered trademark), ACONARC (Advanced Connection Architecture) (registered trademark), and FIBARC (Fibre Connection Architecture) (registered trademark), for example. 
         [0039]    The management apparatus  4  is communicatively coupled to each of the host computer  3 , the first storage apparatus  10 , the second storage apparatus  10 , the third storage apparatus  10 , and the fourth storage apparatus  10  via a second communication network  6 . The second communication network  6  is, for example, a LAN, a WAN, the Internet, a public communication network, lease lines, or the like. 
         [0040]    When accessing the storage area provided by the storage apparatus  10 , the host computer  3  sends a data frame (hereinafter, abbreviated as frame) including a data I/O request (a data write request, a data read request, or the like) to the storage apparatus  10 . The frame sent from the host computer  3  to the storage apparatus  10  is a frame of a fibre channel (FC frame (FC: Fibre Channel)), for example. 
         [0041]    As shown in  FIG. 1 , the host computer  3  includes a CPU  31  (CPU: Central Processing Unit), a memory  32  (RAM (Random Access Memory), ROM (Read Only Memory), NVRAM (Non Volatile RAM), or the like), a storage device  33  (HDD (Hard Disk Drive), a semiconductor memory (SSD (Solid State Drive), or the like), a first network interface (hereinafter, referred to as first network I/F  34 ), and a second network interface (hereinafter, referred to as second network I/F  35 ). As shown in  FIG. 1 , the first network I/F  34  includes multiple network ports  341  for coupling to the first communication network  5 . 
         [0042]    Among these components, the first network I/F  34  is an interface for coupling to the first communication network  5 , and is, for example, an HBA (Host Bus Adapter), an NIC (Network Interface Card), or the like. Furthermore, the second network I/F  35  is an interface for coupling to the second communication network  6 , and is an NIC, for example. Specific examples of the host computer  3  include a personal computer, a mainframe, an office computer, and the like. 
         [0043]    As shown in  FIG. 1 , the memory  32  (or the storage device  33 ) in the host computer  3  stores programs such as an operating system (hereinafter, referred to as OS  321 ), a device driver  322 , alternate path software (hereinafter, referred to as alternate path software  323 ), and an application program  324 . When the CPU  31  in the host computer  3  reads and executes the programs stored in the memory  32  (or the storage device  33 ), various functions provided by the host computer  3  are implemented. 
         [0044]    The alternate path software  323  is a program for implementing functions related to setting of a path being a route followed by the data I/O request when the host computer  3  sends the data I/O request to the storage apparatus  10 , or a selection of a path to be used (switching (alternating) a path). 
         [0045]    As shown in  FIG. 1 , the storage apparatus  10  includes a controller  101  and a storage device unit  102 . The controller  101  includes one or more first communication I/Fs  11 , one or more microprocessors (hereinafter, referred to as MP  12 ), a cache memory (hereinafter, referred to as CM  13  (CM: Cache Memory)), a shared memory (hereinafter, referred to as SM  14  (SM: Shared Memory)), one or more disk adapters (hereinafter, referred to as DKA  15  (DKA: Disk Adaptor) (drive controller), a coupling device  16 , and a maintenance device (hereinafter, referred to as SVP  17  (SVP: SerVice Processor)). As shown in  FIG. 1 , the first communication I/F  11 , the MP  12 , the CM  13 , the SM  14 , and the DKA  15  are communicatively coupled to one another via the coupling device  16 . 
         [0046]    The first communication I/F  11  (front-end) is an interface for coupling to the first communication network  5 . As shown in  FIG. 1 , the first communication I/F  11  includes a plurality of network ports  111  for coupling to the first communication network  5 . The first communication I/F  11  receives a frame sent from the host computer  3 , and sends the host computer  3  a frame including a response of processing (for example, data read from the storage device unit  102 , a read completion report, and a write completion report) related to the data I/O request included in the received frame. 
         [0047]    The MP  12  includes a CPU, an MPU (Micro Processing Unit), a DMA (DMA: Direct Memory Access), or the like. In response to the data I/O request included in the frame which the first communication I/F  11  has received from the host computer  3 , the MP  12  transfers data at high speed among the first communication I/F  11 , the CM  13 , the SM  14 , and the DKA  15 . This data transfer is performed, for example, at the time of passing data read from the storage device unit  102  (hereinafter, referred to as read data), passing data to be written into the storage device unit  102  (hereinafter, referred to as write data), and staging (reading of the data from the storage device unit  102  to the CM  13 ) and destaging (writing of the data into the storage device unit  102  from the CM  13 ) by the CM  13 . 
         [0048]    The CM  13  (cache memory) includes a RAM, a ROM, an NVRAM, or the like. The CM  13  temporally stores data being a target of the data I/O request. 
         [0049]    The SM  14  includes a RAM, a ROM, an NVRAM, or the like. The SM  14  stores data used for controlling processing related to the data I/O request (hereinafter, referred to as control information). 
         [0050]    The DKA  15  communicates with the storage device unit  102  when data is read from the storage device unit  102  and when data is written into the storage device unit  102 . 
         [0051]    The coupling device  16  includes a high-speed cross bar switch or a bus, for example. Communication via the coupling device  16  is performed in accordance with a protocol such as Fibre Channel, iSCSI, and TCP/IP, for example. 
         [0052]    The storage device unit  102  includes multiple storage drives  18  which are physical storage media. Each of the storage drives  18  is, for example, a hard disk drive (a hard disk drive in conformity to the standards such as SAS (Serial Attached SCSI), SATA (Serial ATA), FC (Fibre Channel), PATA (Parallel ATA), or SCSI), or a semiconductor storage device (SSD). The storage device unit  102  may be housed in the same enclosure as the storage apparatus  10 , or may be housed in an enclosure which is different from an enclosure in which the storage apparatus  10  is housed. 
         [0053]    The storage device unit  102  provides the host computer  3  with a storage area in units of logical device (LDEV  181  (LDEV: Logical Device)) which is configured using an RAID (Redundant Arrays of Inexpensive (or Independent) Disks) group (Parity Group) based on the storage areas in the storage drives  18 . 
         [0054]    The storage apparatus  10  provides the host computer  3  with a logical storage area (hereinafter, referred to as LU (Logical Unit, Logical Volume) (storage volume) configured using the LDEV  181 . The storage apparatus  10  manages correspondence between the LU and the LDEV  181 . The relation between the LU and the LDEV  181  may be a relation of one-to-one or one-to-a plurality. 
         [0055]    A unique identifier (hereinafter, referred to as LUN (Logical Unit Number)) is assigned to each LU. The host computer  3  specifies a storage area to be accessed by setting a LUN and a block address to a frame to be sent to the storage apparatus  10 . Upon receiving the data I/O request from the host computer  3 , the storage apparatus  10  identifies the LDEV  181  configuring the specified LU, and performs processing specified in the data I/O request. 
         [0056]    The SVP  17  includes a personal computer, an office computer, or the like. The SVP  17  communicates with the components (the first communication I/F  11 , the MP  12 , the CM  13 , the SM  14 , the DKA  15 , and the storage device unit  102 ) in the storage apparatus  10 , via the coupling device  16  or a communication means provided separate from the coupling device  16 . The SVP  17  is coupled to the second communication network  6 , and communicates with the management apparatus  4 , the host computer  3 , and the storage apparatus  10 . The SVP  17  collects information that is used for performance monitoring or state monitoring of the storage apparatus  10 , and provides the management apparatus  4  with the collected information as needed. Furthermore, the SVP  17  sets the storage apparatus  10  or controls the storage apparatus  10 , spontaneously or passively in response to the command sent from the management apparatus  4 . 
         [0057]    As shown in  FIG. 1 , the management apparatus  4  includes a CPU  41 , a memory  42  (RAM, ROM, NVRAM, or the like), a storage device  43  (HDD, a semiconductor storage device (SSD), or the like), a second network interface (hereinafter, referred to as second network I/F  45 ) (NIC or the like), and a user interface (hereinafter, referred to as UI  46 ) (a keyboard, a mouse, a touchpanel, a liquid crystal monitor, an organic EL panel, or the like). 
         [0058]    As shown in  FIG. 1 , the memory  42  or the storage device  43  in the management apparatus  4  stores programs such as an operating system (hereinafter, referred to as OS  4021 ), a device driver  4022 , and management path software (hereinafter, referred to as management path software  4023 ). 
         [0059]    &lt;Basic Function of Storage Apparatus&gt; 
         [0060]    Next, basic processing performed by the storage apparatus  10  when the storage apparatus  10  receives a data I/O request from the host computer  3  will be described. 
         [0061]    Firstly, processing performed by the storage apparatus  10  when the storage apparatus  10  receives a frame including a data write request from the host computer  3  will be described. Upon receiving the frame, the first communication I/F  11  in the storage apparatus  10  notifies the MP  12  of the reception. When receiving the notification from the first communication I/F  11 , the MP  12  creates a drive write request based on the data write request in the frame, stores the created write data in the CM  13 , and responds by notifying the first communication I/F  11  that the notification has been received. Furthermore, the MP  12  sends the created drive write request to the DKA  15 . 
         [0062]    Upon receiving the response from the MP  12 , the first communication I/F  11  sends a completion report to the host computer  3 . When receiving the drive write request from the MP  12 , the DKA  15  registers the received drive write request in a write processing queue. 
         [0063]    The DKA  15  reads the drive write request from the write processing queue as needed. Furthermore, the DKA  15  reads, from the CM  13 , the write data specified in the drive write request thus read, and writes the write data thus read in the storage drive  18 . Furthermore, the DKA  15  notifies the MP  12  by reporting that the writing of the write data specified in the drive write request has been completed (completion report). The MP  12  receives the completion report sent from the DKA  15 . 
         [0064]    When the storage apparatus  10  receives the frame including the data write request from the host computer  3 , data is written to the storage drives  18  basically in accordance with the flow described above. 
         [0065]    Next, processing performed by the storage apparatus  10  when the storage apparatus  10  receives a frame including a data read request from the host computer  3  will be described. Upon receiving the frame sent from the host computer  3 , the first communication I/F  11  notifies the DKA  15  of the reception. When receiving the notification from the first communication I/F  11 , the DKA  15  reads, from the storage drives  18 , data specified in the data read request included in the frame (for example, specified in LBA (Logical Block Address)). Note that, when the read data is present in the CM  13  (when staging has been performed), the reading from the storage drives  18  is omitted. 
         [0066]    The MP  12  writes the data read by the DKA  15  into the CM  13 , and transfers the data having been written into the CM  13  to the first communication I/F  11  as needed. 
         [0067]    The first communication I/F  11  receives the read data sent from the MP  12 , and transmits the received read data to the host computer  3 . When the transmission of the read data to the host computer  3  is completed, the first communication I/F  11  sends a completion report to the host computer  3 . 
         [0068]    When the storage apparatus  10  receives the frame including the data read request from the host computer  3 , the data is read from the storage drive  18  basically in accordance with the flow described above. 
         [0069]    &lt;Local Copy Function&gt; 
         [0070]    The storage apparatus  10  is provided with a mechanism (hereinafter, referred to as local copy function) in which duplication of data that is stored in a certain LU (hereinafter, referred to as source LU), is also stored in a LU (hereinafter, referred to as target LU) different from the certain LU. The local copy function is used in the storage apparatus  10  in order to ensure safety and integrity of data and the like. The local copy function is achieved by hardware included in the storage apparatus  10  or by the MP  12  in the storage apparatus  10  reading and executing a program stored in the shared memory (the SM  14 ). Note that, as described above, because the LUs are configured using the LDEVs  181 , duplication between the LUs in the local copy function is performed by duplicating data between the LDEVs  181  configuring the respective LUs. 
         [0071]    The storage apparatus  10  manages local pair management information, local pair difference information (source), and local pair difference information (target), as tables related to the local copy function. These pieces of information are stored, for example, in the shared memory (the SM  14 ) in the storage apparatus  10 . 
         [0072]    The local pair management information includes mapping between a source LU and a target LU (hereinafter, a pair of a source LU and a target LU mapped to the source LU is referred to as local pair), and control states of the local pair. Note that, an operator manipulates the management apparatus  4  to set contents of the local pair management information, for example. 
         [0073]    Main examples of the control states of the local pair include a pair state, a split state, and a re-sync state. 
         [0074]    In the pair state, duplication from the source LU to the target LU is performed in real time. In other words, if data in the source LU is changed by the data I/O request from the host computer  3 , the changed data is also immediately reflected in the target LU. 
         [0075]    In the split state, even if data in the source LU is changed, the changed data is not immediately reflected in the target LU, but is reflected in the target LU at a timing when the local pair is transitioned from the split state to the pair state (hereinafter, referred to as re-sync). Note that, when change of data of the target LU is allowed in the split state, the data of the target LU is reflected in the source LU at the timing of re-sync of the local pair. 
         [0076]    In the local pair difference information (source), managed is whether or not data in each of the data blocks in the source LU is changed during a period when the local pair is in the split state. The local pair difference information (source) includes, for example, a set of bits corresponding to the respective data blocks in the source LU. For example, when data in a certain data block in the source LU is changed by the data I/O request from the host computer  3 , a bit corresponding to the data block is set ON (set). Meanwhile, when the re-sync is completed, the corresponding bit is set OFF (reset). 
         [0077]    In the local pair difference information (target), managed is whether or not data in each of the data blocks in the target LU is changed during a period when the local pair is in the split state. The local pair difference information (target) includes, for example, a set of bits corresponding to respective data blocks in the target LU. For example, when data in a certain data block in the target LU is changed by the data I/O request from the host computer  3 , a bit corresponding to the data block is turned ON (set). Meanwhile, when the re-sync is completed, the corresponding bit is turned OFF (reset). 
         [0078]    The control state of the local pair can be changed from the management apparatus  4 . For example, when the management apparatus  4  sends a command to cause a local pair to transition to the split state (hereinafter, referred to as split command), the storage apparatus  10  causes the control state of the local pair to transition from the pair state to the split state. Furthermore, when the management apparatus  4  sends a command to cause a local pair in a split state to transition to the pair state (hereinafter, referred to as re-sync command), the storage apparatus  10  causes the control state of the local pair to transition from the split state to the pair state. 
         [0079]    &lt;Remote Copy Function&gt; 
         [0080]    The storage apparatus  10  includes a function (hereinafter, referred to as remote copy function) in which duplication of data stored in a certain LU (hereinafter, referred to as primary LU) in the storage apparatus  10  (hereinafter, referred to as primary apparatus) is further stored in a LU (hereinafter, referred to as secondary LU) in another storage apparatus  10  (hereinafter, referred to as secondary apparatus) different from the storage apparatus  10  being the primary apparatus. The remote copy function is achieved by hardware included in each of the storage apparatuses  10  or by the MP  12  in each storage apparatus  10  reading and executing a program stored in the shared memory (the SM  14 ). Note that, because the LUs are configured using the LDEVs  181 , duplication between the LUs in the remote copy function is performed by duplicating data between the LDEVs  181  configuring the respective LUs in storage apparatuses  10 . 
         [0081]    The remote copy function is employed in the storage apparatus  10  in order to ensure safety and integrity of data and the like. The remote copy function is achieved by hardware included in the storage apparatus  10 , or, by the MP  12  in the storage apparatus  10  reading and executing a program stored in the SM  14 . 
         [0082]    The storage apparatus  10  manages remote pair management information, remote pair difference information (primary), and remote pair difference information (secondary), as tables related to the remote copy function. Note that, these pieces of information are stored, for example, in the shared memory (the SM  14 ) in the storage apparatus  10 . 
         [0083]    The remote pair management information includes mapping between a primary LU in the primary apparatus and a secondary LU in the secondary apparatus (hereinafter, a pair of a primary LU in the primary apparatus and a secondary LU, mapped to primary LU, in the secondary apparatus is referred to as a remote pair), and control states of the remote pair. Note that, an operator manipulates the management apparatus  4  to set the contents of the remote pair management information, for example. 
         [0084]    Main examples of the control states of the remote pair include a pair state, a split state, and a re-sync state. 
         [0085]    In the pair state among the control states, duplication from the primary LU to the secondary LU is performed in real time. In other words, when data in the primary LU is changed by the data I/O request from the host computer  3 , the changed data is also immediately reflected in the secondary LU. 
         [0086]    In the split state, even if data in the primary LU is changed, the changed data in not immediately reflected in the secondary LU, but are reflected in the secondary LU at a timing when the remote pair is transitioned from the split state to the pair state (hereinafter, referred to as re-sync). Note that, when change of data in the secondary LU is allowed in the split state, the data in the secondary LU is reflected in the primary LU at the timing of re-sync of the remote pair. 
         [0087]    In the remote pair difference information (primary), managed is whether or not data in each of the data blocks in the primary LU is changed during a period when the remote pair is in a split state. The remote pair difference information (primary) includes, for example, a set of bits corresponding to the respective data blocks in the primary LU. For example, when data in a certain data block in the primary LU is changed by the data I/O request from the host computer  3 , a bit corresponding to the data block is turned ON (set). Meanwhile, when the re-sync is completed, the corresponding bit is turned OFF (reset). 
         [0088]    In the remote pair difference information (secondary), managed is whether or not data in each of the data blocks in the secondary LU is changed during a period when the remote pair is in a split state. The remote pair difference information (secondary) includes, for example, a set of bits corresponding to the respective data blocks in the secondary LU. For example, when data in a certain data block in the secondary LU is changed by the data I/O request from the host computer  3 , a bit corresponding to the data block is turned ON (set). Meanwhile, when the re-sync is completed, the corresponding bit is turned OFF (reset). 
         [0089]    The control state of each remote pair can be changed by a command from the management apparatus  4 , for example. In other words, when a command to cause a remote pair to transition to the split state (hereinafter, referred to as split command) is issued by the management apparatus  4 , the storage apparatus  10  causes the control state of the remote pair to transition from the pair state to the split state. Furthermore, when a command to cause a remote pair in a split state to transition to the pair state (hereinafter, referred to as re-sync command) is issued by the management apparatus  4 , the storage apparatus  10  causes the control state of the remote pair to transition from the split state to the pair state. 
         [0090]    Furthermore, as for each remote pair, a control method thereof can be set to be a synchronous method or an asynchronous method. An operator manipulates the management apparatus  4  to set the control method, for example. 
         [0091]    In the synchronous method, upon receiving from the host computer  3  a data write request to the primary LU, the primary apparatus writes data specified in the data write request into the primary LU. Furthermore, the primary apparatus sends data same as the written data to the secondary apparatus. Upon receiving the data from the primary apparatus, the secondary apparatus writes the received data into the secondary LU, and notifies the primary apparatus that the received data has been written. Upon receiving the notification, the primary apparatus sends a completion notification to the host computer  3 . 
         [0092]    In this manner, in the synchronous method, the completion notification is sent to the host computer  3  after it is confirmed that the data has been written into both the primary LU and the secondary LU. Accordingly, in the synchronous method, at the time when the host computer  3  receives the completion notification, coincidence between the data in the primary LU and the data in the secondary LU is always secured. 
         [0093]    On the other hand, in the case of the asynchronous method, upon receiving from the host computer  3  a data write request to the primary LU, the primary apparatus writes data specified in the data write request into the primary LU, and sends a completion notification to the host computer  3 . Furthermore, the primary apparatus sends data same as the written data to the secondary apparatus. Upon receiving the data from the primary apparatus, the secondary apparatus writes the received data into the secondary LU, and notifies the primary apparatus that the received data has been written. 
         [0094]    In this manner, in the case of the asynchronous method, upon writing the data in the primary LU, the primary apparatus sends a completion notification to the host computer  3  irrelevant to whether or not the data has been written into the secondary LU. Therefore, coincidence between the data in the primary LU and the data in the secondary LU is not always secured, which is different from the synchronous method. 
         [0095]    &lt;Unique Information Virtualization Function&gt; 
         [0096]    The storage apparatus  10  includes the following function (hereinafter, referred to as unique information virtualization function). In a case where the remote copy function described above is performed, information (hereinafter, referred to as unique information) is virtualized and shown to the host computer  3  when the host computer  3  sends the data I/O request to the secondary apparatus, the information being referred to in order to identify a target of the data I/O request. The unique information virtualization function is achieved by hardware included in each storage apparatus  10 , or, by the MP  12  in each storage apparatus  10  reading and executing a program stored in the shared memory (the SM  14 ). 
         [0097]    Here, the unique information is information included in inquiry information which is information used as a response from the storage apparatus  10  to the host computer  3  when the host computer  3  sends to the storage apparatus  10  an inquiry command complying with the SCSI (Small Computer System Interface) standard, for example. 
         [0098]    Specific examples of unique information include the network port  111  in the first communication I/F  11 , a serial number assigned to the storage apparatus  10  (an identification number assigned to each storage apparatus  10  by a manufacturer, a vendor, or the like, of the storage apparatus  10 ) (apparatus ID), and the like. Note that, in the explanation below, unique information that is actually assigned to an apparatus is called real unique information, and virtualized unique information that is shown to the host computer  3  is called virtual unique information. 
         [0099]    The unique information virtualization function is used, for example, when an error occurs in the primary apparatus, so that the secondary apparatus can take over (a failover can be performed) the service having been provided to the host computer  3  by the primary apparatus only by switching a path with the alternate path software  323  in the host computer  3 . 
         [0100]      FIG. 2  is a diagram for explaining the unique information virtualization function in detail, and is a schematic diagram of the storage system  1  illustrated in a simplified manner. As shown in  FIG. 2 , the storage system  1  includes a first storage apparatus  10  with serial number “1111”, and a second storage apparatus  10  with serial number “2222”. 
         [0101]    The first storage apparatus  10  has a network port  111  with identifier (hereinafter, referred to as port ID) “1A” which is coupled to the host computer  3 , and LDEVs  181  with identifiers (hereinafter, referred to as LDEV numbers) “#10:00” and “#10:01”, respectively. Furthermore, the second storage apparatus  10  has a network port  111  with port ID “2A” which is coupled to the host computer  3 , and LDEVs  181  with LDEV numbers “#21:00” and “#21:01”, respectively. 
         [0102]    In the storage system  1  shown in  FIG. 2 , a remote copy function is employed in which the first storage apparatus  10  is set as the primary apparatus and the second storage apparatus  10  is set as the secondary apparatus. The LDEVs  181  (LDEVs  181  with LDEV numbers “#10:00” and “#10:01”) in the first storage apparatus  10  configure the primary LU, and the LDEVs  181  (LDEVs  181  with LDEV numbers “#21:00” and “#21:01”) in the second storage apparatus  10  configure the secondary LU. 
         [0103]    Data is transferred between the LDEV  181  with LDEV number “#10:00” in the first storage apparatus  10  and the LDEV  181  with LDEV number “#21:00” in the second storage apparatus  10  to make the data therein equal to each other by the remote copy function. Furthermore, data is transferred between the LDEV  181  with LDEV number “#10:01” in the first storage apparatus  10  and the LDEV  181  with LDEV number “#21:01” in the second storage apparatus  10  to make the data therein to equal to each other by the remote copy function. 
         [0104]    Furthermore, the unique information virtualization function of the first storage apparatus  10  shows “FFF0” to the host computer  3  as its own serial number (first virtual apparatus ID), “FFF0” being a serial number (hereinafter, referred to as virtual serial number (virtual apparatus ID)) virtually set for “1111” which is a serial number actually assigned to the first storage apparatus  10  (hereinafter, referred to as real serial number). Accordingly, for example, when the host computer  3  sends the inquiry command, the first storage apparatus  10  returns “FFF0” as its own serial number to the host computer  3 . 
         [0105]    In addition, the unique information virtualization function of the second storage apparatus  10  shows “FFF0” (the same virtual serial number as the virtual serial number which the first storage apparatus  10  is showing to the host computer  3 ) to the host computer  3  as its own serial number (second virtual apparatus ID), “FFF0” being a serial number virtually set for “2222” which is a serial number actually assigned to the second storage apparatus  10  (hereinafter, referred to as real serial number). Accordingly, for example, when the host computer  3  sends the inquiry command, the second storage apparatus  10  returns “FFF0” as its own serial number to the host computer  3 , “FFF0” being the same virtual serial number as the virtual serial number which the first storage apparatus  10  is showing to the host computer  3 . 
         [0106]    Moreover, the unique information virtualization function of the first storage apparatus  10  shows “#10:00” to the host computer  3  as the LDEV number of its own LDEV  181  (first virtual volume ID), “#10:00” being a LDEV number (hereinafter, referred to as virtual LDEV number) virtually set for “#10:00” which is a LDEV number actually assigned to the LDEV  181  of the first storage apparatus  10  (hereinafter, referred to as real LDEV number). Accordingly, for example, when the host computer  3  sends the inquiry command, the first storage apparatus  10  returns “#10:00” as the LDEV number of the LDEV  181  which the first storage apparatus  10  manages. 
         [0107]    Moreover, the unique information virtualization function of the first storage apparatus  10  shows “#10:01” to the host computer  3  as the LDEV number of its own LDEV  181  (second virtual volume ID), “#10:01” being a virtual LDEV number virtually set for “#10:01” which is a real LDEV number assigned to the LDEV  181  of the first storage apparatus  10 . Accordingly, for example, when the host computer  3  sends an inquiry command, the first storage apparatus  10  returns “#10:01” as the LDEV number of the LDEV  181  which the first storage apparatus  10  manages. 
         [0108]    Moreover, the unique information virtualization function of the second storage apparatus  10  shows “#10:00” to the host computer  3  as the LDEV number of its own LDEV  181 , “#10:00” being a virtual LDEV number virtually set for “#21:00” which is a real LDEV number assigned to the LDEV  181  of the second storage apparatus  10 , and being the same virtual LDEV number as the LDEV number of the LDEV  181  of the first storage apparatus  10 . Accordingly, for example, when the host computer  3  sends an inquiry command, the second storage apparatus  10  returns “#10:00” as the LDEV number of the LDEV  181  which the second storage apparatus  10  manages, “#10:00” being the same virtual LDEV number as the virtual LDEV number which the first storage apparatus  10  is showing the host computer  3 . 
         [0109]    Moreover, the unique information virtualization function of the second storage apparatus  10  shows “#10:01” to the host computer  3  as the LDEV number of its own LDEV  181 , “#10:01” being a virtual LDEV number virtually set for “#21:01” which is a real LDEV number assigned to the LDEV  181  of the second storage apparatus  10 , and being the same virtual LDEV number as the LDEV number of the LDEV  181  of the first storage apparatus  10 . Accordingly, for example, when the host computer  3  sends the inquiry command, the second storage apparatus  10  returns “#10:01” as the LDEV number of the LDEV  181  which the second storage apparatus  10  manages, “#10:01” being the same virtual LDEV number as the virtual LDEV which the first storage apparatus  10  is showing the host computer  3 . 
         [0110]    Furthermore, the unique information virtualization function of the first storage apparatus  10  shows “1A” and “1X” to the host computer  3  as its own port IDs (first virtual port IDs), “1A” and “1X” being port IDs (hereinafter, referred to as virtual port IDs) virtually set for “1A” which is a port ID actually assigned to the network port  111  of the first storage apparatus  10  (hereinafter, referred to as real port ID). Accordingly, for example, when the host computer  3  sends an inquiry command, the first storage apparatus  10  returns virtual port ID “1A” or “1X” as its own port ID. 
         [0111]    Furthermore, the unique information virtualization function of the second storage apparatus  10  shows “2A” and “2X” to the host computer  3  as its own port IDs (second virtual port IDs), “2A” and “2X” being virtual port IDs virtually set for “2A” which is a real port ID assigned to the network port  111  of the second storage apparatus  10 . Accordingly, for example, when the host computer  3  sends an inquiry command, the second storage apparatus  10  returns virtual port ID “2A” or “2X” as its own port ID. 
         [0112]    Here, the settings described above are made in the storage system  1 , the remote copy function is employed for the LDEVs  181  in the first storage apparatus  10  and the LDEVs  181  in the second storage apparatus  10  as described above, and both the first storage apparatus  10  and the second storage apparatus  10  show the same LDEV number (virtual LDEV number) to the host computer  3 . Therefore, the host computer  3  sees as if a storage apparatus  10  with serial number (virtual serial number) “FFF0” exists, and each of the LDEVs  181  with respective LDEV numbers “#10:00” and “#10:01” is provided with a plurality of paths (a path including network port  111  with real port ID “1A” (hereinafter, referred to as first path) and a path including network port  111  with real port ID “2A” (hereinafter, referred to as second path)). 
         [0113]    Accordingly, for example, when an error occurs in the first storage apparatus  10  in a state where the first storage apparatus  10  is receiving the data I/O request sent from the host computer  3 , a rapid and easy failover from the first storage apparatus  10  to the second storage apparatus  10  can be performed simply by switching a path so that the data I/O request from the host computer  3  is sent to the second storage apparatus  10  (switching from the first path to the second path). 
         [0114]    Note that, a data transfer does not occur between the LDEVs  181  in the failover because the remote copy function is employed for the LDEVs  181  in the first storage apparatus  10  and the LDEVs  181  in the second storage apparatus  10 . Furthermore, because both the first storage apparatus  10  and the second storage apparatus  10  show to the host computer  3  a common (same) virtual serial number and a common (same) virtual LDEV number, the settings of the unique information do not have to be changed and the host computer  3  does not have to be rebooted to reflect the unique information. Thus, the failover can be performed without affecting the service of the host computer  3 . 
         [0115]    &lt;Table in Host Computer&gt; 
         [0000]      FIG. 3  shows a table managed in the host computer  3 , and is a table (hereinafter, referred to as path management table  300 ) in which information related to a path to be used when the host computer  3  accesses the storage apparatus  10  is managed. The path management table  300  is stored, for example, in the memory  32  or the storage device  33  in the host computer  3 . 
         [0116]    As shown in the  FIG. 3 , the path management table  300  has one or more records including items of path ID  311 , path type  312 , LUN  313 , LDEV number  314 , serial number  315 , port ID  316 , path state  317 , and currently-used flag  318 . For example, the host computer  3  acquires setting contents of the items in the path management table  300  by sending an inquiry such as an inquiry command to the storage apparatus  10  as needed. Note that, an operator or the like can set the contents of items in the path management table  300  from the management apparatus  4 . 
         [0117]    In the path ID  311 , an identifier assigned to each path (hereinafter, referred to as path ID) is set. Eight paths are managed in the path management table  300  shown in  FIG. 3 . 
         [0118]    In path type  312 , information indicating whether a path is an owner path or a non-owner path is set. Here, the owner path is a path preferentially used compared to the non-owner path. Under the circumstance where both the owner path and the non-owner path are available, the host computer  3  preferentially uses the owner path to send the data I/O request to the storage apparatus  10 . The non-owner path is set as a standby path of the owner path, for example, to achieve a redundant configuration. As shown in  FIG. 3 , “Owner” is set for the owner path in path type  312 , while “Non-Owner” is set for the non-owner path in path type  312 . 
         [0119]    Note that, the eight paths with respective path IDs “1” to “8” are set in the path management table  300  shown in  FIG. 3 . Among the paths, paths with respective path IDs “1” to “4” are set as owner paths. Meanwhile, paths with respective path IDs “5” to “8” are set as non-owner paths. 
         [0120]    In LUN  313 , a LUN of a LU being a target of a certain path (an access target when the certain path is used) is set. 
         [0121]    In LDEV number  314 , a LDEV number of the LDEV  181  being a target of the certain path (an access target when the certain path is used) is set. Note that, when the storage apparatus  10  is showing a virtual LDEV number to the host computer  3  by the unique information virtualization function described above, the virtual LDEV number is set in LDEV number  314 . 
         [0122]    In serial number  315 , a serial number of the storage device  10  providing a LU (or the LDEV  181 ) being a target of the certain path (an access target when this path is used) is set. 
         [0123]    In port ID  316 , a port ID of the network port  111  of the storage device  10  which configures the certain path is set. Note that, when the storage apparatus  10  is showing a virtual port ID to the host computer  3  by the unique information virtualization function described above, a virtual port ID is set in port ID  316 . 
         [0124]    In path state  317 , information indicating whether or not the certain path is currently available (online or offline) is set. If the certain path is available, “Online” is set, while if the certain path is not available, “Offline” is set. For example, when there is an error in the first communication network  5  or in the storage apparatus  10 , “Offline” is set in path state  317 . 
         [0125]    In currently-used flag  318 , information indicating whether or not the certain path is currently used to actually send the data I/O request is set. If the certain path is currently used to actually send the data I/O request. “1” is set, while if the certain path is not currently used, “0” is set. 
         [0126]    &lt;Table in First Storage Apparatus&gt; 
         [0127]      FIG. 4  shows various tables managed in the first storage apparatus  10 . As shown in  FIG. 4 , the first storage apparatus  10  manages own virtual port management table  410 , partner virtual port management table  420 , LU management table  430 , remote pair management table  440 , quorum drive management table  450 , serial number management table  460 , and unique information conversion table  470 . These tables are stored in the shared memory (the SM  14 ) in the first storage apparatus  10 , for example. An operator manipulates the management apparatus  4  to set the contents of the tables, for example. 
         [0128]    As shown in  FIG. 4 , the own virtual port management table  410  has one or more records each including items of own real port ID  411 , own virtual port ID  412 , and enabled/disabled  413 . 
         [0129]    Among the items, in own real port ID  411 , a real port ID of a certain network port  111  in the first storage apparatus  10  is set. In own virtual port ID  412 , a virtual port ID set for the real port ID is set. 
         [0130]    In enabled/disabled  413 , information indicating whether or not the certain network port  111  is currently available is set. If the certain network port  111  is available, “Enabled” is set, while if the certain network port  111  is not available, “Disabled” is set. For example, when an operator has manipulated the management apparatus  4  to disable the certain network port  111 , “Disabled” is set in enabled/disabled  413 . Furthermore, when there is an error in a communication function of the first communication network  5  or the storage apparatus  10  (the first storage apparatus  10  or the second storage apparatus  10 ), “Disabled” is also set in enabled/disabled  413 . 
         [0131]    As shown in  FIG. 4 , the partner virtual port management table  420  has one or more records each including items of partner serial number  421 , partner real port ID  422 , partner virtual port ID  423 , and enabled/disabled  424 . 
         [0132]    Among the items, in partner serial number  421 , a serial number of the second storage device  10  is set, the second storage device  10  being the secondary device which is the partner of this first storage device  10  being the primary device in the remote copy function. 
         [0133]    In partner real port ID  422 , a real port ID of a certain network port  111  of the second storage device  10  being the secondary device is set. In partner virtual port ID  423 , a virtual port ID set for the real port ID is set. 
         [0134]    In enabled/disabled  424 , information indicating whether or not the certain network port  111  is currently available is set. If the certain network port  111  is available, “Enabled” is set, while if the certain network port  111  is not available, “Disabled” is set. For example, when an operator has manipulated the management apparatus  4  to disable the certain network port  111 , “Disabled” is set in enabled/disabled  424 . Furthermore, when there is an error in the first communication network  5  or the storage apparatus  10 , “Disabled” is also set in enabled/disabled  424 . 
         [0135]    In the LU management table  430  shown in  FIG. 4 , a correspondence between the LUs and the LDEVs  181  (the LDEVs  181  configuring the LUs) in the first storage apparatus  10  is managed. As shown in  FIG. 4 , the LU management table  430  has one or more records each including items of a LUN  431  and an own real LDEV number  432 . 
         [0136]    Among the items, in the LUN  431 , a LUN of a LU provided to the host computer  3  is set. In the own real LDEV number  432 , a real LDEV number of the LDEV  181  in the first storage device  10  configuring the LU is set. 
         [0137]    In the remote pair management table  440  shown in  FIG. 4 , correspondence between the LDEV  181  configuring the primary LU in the primary apparatus (the first storage apparatus  10 ) and the LDEV  181  configuring the secondary LU in the secondary apparatus (the second storage apparatus  10 ) is managed. 
         [0138]    As shown in  FIG. 4 , the remote pair management table  440  has one or more records each including items of own real LDEV number  441 , PVOL/SVOL  442 , partner real serial number  443 , partner real LDEV number  444 , partner real port ID  445 , control state  446 , and quorum drive ID  447 . 
         [0139]    Among the items, in the own real LDEV number  441 , a real LDEV number of a certain LDEV  181  in the first storage apparatus  10  is set. 
         [0140]    In the PVOL/SVOL  442 , information indicating whether the certain LDEV  181  configures the primary LU or the secondary LU is set. If the certain LDEV  181  configures the primary LU, “PVOL” is set, while if the certain LDEV  181  configures the secondary LU, “SVOL” is set. 
         [0141]    In the partner real serial number  443 , a real serial number of the second storage apparatus  10  is set, the second storage apparatus  10  having a LDEV  181  forming a remote pair with the certain LDEV  181 . 
         [0142]    In the partner real LDEV number  444 , a real LDEV number of the LDEV  181  in the second storage apparatus  10  which is forming a remote pair with the certain LDEV  181  is set. 
         [0143]    In the partner real port ID  445 , a real port ID of the network port  111  for accessing the partner LDEV  181  forming the remote pair with the certain LDEV  181  is set, the network port  111  provided in the second storage apparatus  10  in which the partner LDEV  181  is present. 
         [0144]    In the control state  446 , information indicating the current control state of the above-described remote pair is set. If the remote pair is in a pair state, “Pair” is set, if in a split state, any one of “Split (PSUS)”, “Split (SSWS)”, and “Split (PSUE)” is set, and if in a re-sync state, “Re-sync” is set. 
         [0145]    Which one is set among the states of “Split (PSUS)”, “Split (SSWS)”, and “Split (PSUE)” is determined in accordance with the data in the primary LU or the secondary LU configured of the certain LDEV  181 . 
         [0146]    For example, if the latest data is reflected in only the primary LU, “Split (PSUE)” is set in the control state of the LDEV  181  configuring the primary LU and “Split (PSUE)” is similarly set in the control state of the LDEV  181  configuring the secondary LU. On the other hand, if the latest data is reflected in only the secondary LU, “Split (PSUS)” is set in the control state of the LDEV  181  configuring the primary LU and “Split (SSWS)” is set in the control state of the LDEV  181  configuring the secondary LU. 
         [0147]    In the quorum drive ID  447 , an identifier (hereinafter, referred to as quorum drive ID) of a quorum drive set for the above-described remote pair is set. Here, the quorum drive is a storage apparatus configured using the LDEVs  181  in the fourth storage apparatus  10  different from the primary apparatus (the first storage apparatus  10 ) and the secondary apparatus (the second storage apparatus  10 ). The first storage apparatus  10  and the second storage apparatus  10  manage a quorum drive (the LDEVs  181  with the real LDEV numbers “#80:00” and “#90:00” in  FIG. 2 ) configured using (by mounting) the LDEVs  181  in the fourth storage apparatus  10 , in the same manner as the normal LDEVs  181 . 
         [0148]    In the quorum drive, for example, information (for example, information indicating which data is in the latest state) required to ensure consistency between the data in the primary LU and the data in the secondary LU is managed. For example, when an error occurs in the primary apparatus, the unique information virtualization function switches the path for the primary LU to the path for the secondary LU, and starts accepting (receiving) the data I/O request from the host computer  3 . If the switch is performed, for example, before completion of duplication processing for maintaining the pair state between the primary LU and the secondary LU in the remote copy function, the data in the primary LU and the data in the secondary LU may not be the same (correspond). Accordingly, in order to prevent such inconsistency from occurring, information indicating whether or not the duplication processing is completed is managed in a storage apparatus  10  (for example, the fourth storage apparatus  10  shown in  FIG. 2 ) different from the primary apparatus and the secondary apparatus, and update of the secondary LU is suspended until the duplication processing is completed. 
         [0149]    In the quorum drive management table  450  shown in  FIG. 4 , information related to the quorum drive is managed. The quorum drive management table  450  has one or more records each including items of quorum drive ID  451 , partner real serial number  452 , own virtual serial number  453 , and real LDEV number  454 . 
         [0150]    Among the items, quorum drive IDs are set in the quorum drive ID  451 . 
         [0151]    In the partner real serial number  452 , a real serial number of the second storage apparatus  10  (the partner storage apparatus  10  which accesses the quorum drive) being the partner in the remote copy function is set. 
         [0152]    In the own virtual serial number  453 , a virtual serial number which the first storage apparatus  10  is showing to the host computer  3  in the unique information virtualization function is set. 
         [0153]    In the real LDEV number  454 , a real LDEV number of the quorum drive in the first storage apparatus  10  (a LDEV number of the LDEV  181  present in the fourth storage apparatus  10 ) is set. 
         [0154]    In the serial number management table  460  shown in  FIG. 4 , virtual serial numbers selectable as a virtual serial number which the first storage apparatus  10  shows to the host computer  3  is managed. As shown in  FIG. 4 , the serial number management table  460  has one or more records each including items of own real serial number  461  and own virtual serial number  462 . 
         [0155]    Among the items, in own real serial number  461 , a real serial number of the first storage apparatus  10  is set. In own virtual serial number  462 , a virtual serial number which the first storage apparatus  10  can use is set. 
         [0156]    As shown in  FIG. 4 , in the unique information conversion table  470 , a correspondence between the real unique information and the virtual unique information is managed. The first storage apparatus  10  refers to the unique information conversion table  470  as needed when processing related to a data I/O request or an inquiry received from the host computer  3  is performed. 
         [0157]    As shown in  FIG. 4 , the unique information conversion table  470  has one or more records each including items of own real port ID  471 , own real LDEV number  472 , own real serial number  473 , own virtual port ID  474 , own virtual LDEV number  475 , and own virtual serial number  476 . The own real port ID  471 , the own real LDEV number  472 , and the own real serial number  473  are items in which real unique information is set. The own virtual port ID  474 , the own virtual LDEV number  475 , and the own virtual serial number  476  are items in which virtual unique information is set. 
         [0158]    Among the items, in own real port ID  471 , a real port ID of the network port  111  in the first storage apparatus  10  is set. In own real LDEV number  472 , a real LDEV number of the LDEV  181  in the first storage apparatus  10  is set. In own real serial number  473 , a real serial number of the first storage apparatus  10  is set. 
         [0159]    In own virtual port ID  474 , a virtual port ID set for the real port ID set in the own real port ID  471  is set. In own virtual LDEV number  475 , a virtual LDEV number set for the real LDEV number set in the own real LDEV number  472  is set. In own virtual serial number  476 , a virtual serial number set for the real serial number of the first storage apparatus  10  is set. 
         [0160]    &lt;Table in Second Storage Apparatus&gt; 
         [0161]      FIG. 5  shows various tables managed in the second storage apparatus  10 . As shown in  FIG. 5 , the second storage apparatus  10  manages own virtual port management table  510 , partner virtual port management table  520 , LU management table  530 , remote pair management table  540 , quorum drive management table  550 , serial number management table  560 , and unique information conversion table  570 . These tables are stored in the shared memory (the SM  14 ) in the storage apparatus  10 , for example. An operator manipulates the management apparatus  4  to set contents of the tables, for example. 
         [0162]    As shown in  FIG. 5 , the own virtual port management table  510  has one or more records each including items of own real port ID  511 , own virtual port ID  512 , and enabled/disabled  513 . 
         [0163]    Among the items, in the own real port ID  511 , a real port ID of a certain network port  111  in the second storage apparatus  10  is set. In the own virtual port ID  512 , a virtual port ID set for the real port ID is set. 
         [0164]    In the enabled/disabled  513 , information indicating whether or not the certain network port  111  is currently available is set. If the certain network port  111  is available, “Enabled” is set, while if the certain network port  111  is not available, “Disabled” is set. For example, when an operator has manipulated the management apparatus  4  to disable the certain network port  111 , “Disabled” is set in the enabled/disabled  513 . Furthermore, when there is an error in the communication function of the first communication network  5  or the second storage apparatus  10 , “Disabled” is also set in the enabled/disabled  513 . 
         [0165]    As shown in  FIG. 5 , the partner virtual port management table  520  has one or more records each including items of partner serial number  521 , partner real port ID  522 , partner virtual port ID  523 , and enabled/disabled  524 . 
         [0166]    Among the items, in partner serial number  521 , a serial number of the first storage device  10  is set, the first storage device  10  being the primary device which is the partner of this second storage device  10  being the secondary device in the remote copy function. 
         [0167]    In partner real port ID  522 , a real port ID of a certain network port  111  of the first storage device  10  being the primary device is set. In partner virtual port ID  523 , a virtual port ID set for the real port ID is set. 
         [0168]    In enabled/disabled  524 , information indicating whether or not the certain network port  111  is currently available is set. If the certain network port  111  is available, “Enabled” is set, while if the certain network port  111  is not available, “Disabled” is set. For example, when an operator has manipulated the management apparatus  4  to disable the certain network port  111 , “Disabled” is set in enabled/disabled  524 . Furthermore, when there is an error in the first communication network  5  or the storage apparatus  10  (the first storage apparatus  10  or the second storage apparatus  10 ), “Disabled” is also set in enabled/disabled  524 . 
         [0169]    In LU management table  530  shown in  FIG. 5 , correspondence between the LUs and the LDEVs  181  (the LDEVs  181  configuring the LUs) in the second storage apparatus  10  is managed. As shown in  FIG. 5 , LU management table  530  has one or more records each including items of a LUN  531  and an own real LDEV number  532 . 
         [0170]    Among the items, in LUN  531 , a LUN of a LU provided to the host computer  3  is set. In own real LDEV number  532 , a real LDEV number of the LDEV  181  in the second storage device  10  configuring the LU is set. 
         [0171]    In remote pair management table  540  shown in  FIG. 5 , correspondence between the LDEV  181  configuring the secondary LU in the secondary apparatus (the second storage apparatus  10 ) and the LDEV  181  configuring the primary LU in the primary apparatus (the first storage apparatus  10 ) is managed. 
         [0172]    As shown in  FIG. 5 , remote pair management table  540  has one or more records each including items of own real LDEV number  541 , PVOL/SVOL  542 , partner real serial number  543 , partner real LDEV number  544 , partner real port ID  545 , control state  546 , and quorum drive ID  547 . 
         [0173]    Among the items, in own real LDEV number  541 , a real LDEV number of a certain LDEV  181  in the second storage apparatus  10  is set. 
         [0174]    In PVOL/SVOL  542 , information indicating whether the certain LDEV  181  configures the primary LU or the secondary LU is set. If the certain LDEV  181  configures the primary LU, “PVOL” is set, while if the certain LDEV  181  configures the secondary LU, “SVOL” is set. 
         [0175]    In partner real serial number  543 , a real serial number of the first storage apparatus  10  is set, the first storage apparatus  10  having a LDEV  181  forming a remote pair with the certain LDEV  181 . 
         [0176]    In partner real LDEV number  544 , a real LDEV number of the LDEV  181  in the first storage apparatus  10  forming a remote pair with the certain LDEV  181  is set. 
         [0177]    In partner real port ID  545 , a real port ID of the network port  111  for accessing the partner LDEV  181  forming the remote pair with the certain LDEV  181  is set, the network port  111  provided in the first storage apparatus  10  in which the partner LDEV  181  is present. 
         [0178]    In control state  546 , information indicating a current control state of the above-described remote pair is set. If the remote pair is in a pair state, “Pair” is set, if in a split state, any one of “Split (PSUS)”, “Split (SSWS)” and “Split (PSUE)” is set, and if in a re-sync state, “Re-sync” is set. 
         [0179]    In quorum drive ID  547 , a quorum drive ID of a quorum drive set for the above-described remote pair is set. 
         [0180]    In quorum drive management table  550  shown in  FIG. 5 , information related to the quorum drive is managed. The quorum drive management table  550  has one or more records each including items of quorum drive ID  551 , partner real serial number  552 , own virtual serial number  553 , and real LDEV number  554 . 
         [0181]    Among the items, a quorum drive ID is set in quorum drive ID  551 . 
         [0182]    In partner real serial number  552 , a real serial number of the first storage apparatus  10  (the partner storage apparatus  10  which accesses the quorum drive) being the partner in the remote copy function is set. 
         [0183]    In own virtual serial number  553 , a virtual serial number which the second storage apparatus  10  is showing to the host computer  3  in the unique information virtualization function is set. 
         [0184]    In real LDEV number  554 , a real LDEV number of the quorum drive in the second storage apparatus  10  (a LDEV number of the LDEV  181  present in the fourth storage apparatus  10 ) is set. 
         [0185]    In serial number management table  560  shown in  FIG. 5 , virtual serial numbers selectable as a virtual serial number which the second storage apparatus  10  shows to the host computer  3  is managed. As shown in  FIG. 5 , the serial number management table  560  has one or more records each including items of own real serial number  561  and own virtual serial number  562 . 
         [0186]    Among the items, in own real serial number  561 , a real serial number of the second storage apparatus  10  is set. In own virtual serial number  562 , a virtual serial number which the second storage apparatus  10  can use is set. Note that, in the unique information virtualization function, the first storage apparatus  10  and the second storage apparatus  10  select the same virtual serial number from the serial number management table  460  and the serial number management table  560 , respectively, to show to the host computer  3 . 
         [0187]    In the unique information conversion table  570  shown in  FIG. 5 , correspondence between the real unique information and the virtual unique information is managed. The second storage apparatus  10  refers to the unique information conversion table  570  as needed when processing related to a data I/O request or an inquiry received from the host computer  3  is performed. 
         [0188]    As shown in  FIG. 5 , the unique information conversion table  570  has one or more records each including items of own real port ID  571 , own real LDEV number  572 , own real serial number  573 , own virtual port ID  574 , own virtual LDEV number  575 , and own virtual serial number  576 . The own real port ID  571 , the own real LDEV number  572 , and the own real serial number  573  are items in which the real unique information is set. The own virtual port ID  574 , the own virtual LDEV number  575 , and the own virtual serial number  576  are items in which the virtual unique information is set. 
         [0189]    Among the items, in the own real port ID  571 , a real port ID of the network port  111  in the second storage apparatus  10  is set. In the own real LDEV number  572 , a real LDEV number of the LDEV  181  in the second storage apparatus  10  is set. In the own real serial number  573 , a real serial number of the second storage apparatus  10  is set. 
         [0190]    In own virtual port ID  574 , a virtual port ID set for the real port ID set in the own real port ID  571  is set. In own virtual LDEV number  575 , a virtual LDEV number set for the real LDEV number set in the own real LDEV number  572  is set. In own virtual serial number  576 , a virtual serial number set for the real serial number of the second storage apparatus  10  is set. 
         [0191]    =Overview of Processing when Error Occurs= 
         [0192]    Next, a description will be given of processing to be performed when an error occurs in the first storage apparatus  10  in the storage system  1  where the unique information virtualization function is achieved. 
         [0193]      FIG. 6  is a diagram explaining an overview of processing performed in the storage system  1  in chronological order when an error occurs in the first storage apparatus  10 . Furthermore,  FIG. 7  is a diagram schematically showing the operations of the respective stages in  FIG. 6 . The processing will be described below with reference to the drawings. 
         [0194]    &lt;First Stage&gt; 
         [0195]    Among the stages shown in  FIGS. 6 and 7 , the first stage corresponds to a normal operation state before occurrence of an error, where operation of the unique information virtualization function is performed for the first storage apparatus  10  and the second storage apparatus  10 . In the first stage, the host computer  3  sends an data I/O request only to the first storage apparatus  10 . Furthermore, one or more paths from the host computer  3  to the second storage apparatus  10  are in an available state (online) although not used yet. 
         [0196]    Furthermore, in the first stage, a LU in the first storage apparatus  10  and a LU in the second storage apparatus  10  form a remote pair. Thus, when data in the LU in the first storage apparatus  10  is updated, the same data is automatically reflected in the LU in the partner second storage apparatus  10 . Accordingly, duplication of data or management of difference information is performed to make the data in the LU in the first storage apparatus  10  and the data in the LU in the second storage apparatus  10  equal to each other. Furthermore, in the first stage, both of the first storage apparatus  10  and the second storage apparatus  10  show the same virtual unique information (the virtual serial number and the virtual LDEV number) to the host computer  3 . 
         [0197]    Note that, contents set in the path management table  300  shown in  FIG. 3  correspond to the first stage. As shown in  FIG. 3 , in the path management table  300 , “1” is set in currently-used flag  318  only for the owner paths which have path IDs “1” and “2” and which lead to LUs with LUNs “0” and “1”, respectively. Furthermore, “Online” is set in path state  317  for the non-owner paths which have path IDs “5” and “6” and which lead to LUs with LUNs “0” and “1”, respectively. 
         [0198]    Therefore, in the state corresponding to this path management table  300 , the host computer  3  can see unique information (LDEV numbers “#10:00” and “#10:01” and serial number “FFF0”) of the owner paths with the path IDs “1” and “2”, and can also see port IDs “1A” and “2A” which lead to LUs with LUNs “0” and “1”, respectively. In this manner, in the first stage, the host computer  3  sees as if there is one storage apparatus  10 , LUs (the LDEVs  181  configuring the LUs) which are present in the storage apparatus  10 , and a plurality of paths to the LUs, are present. 
         [0199]    &lt;Second Stage&gt; 
         [0200]    The second stage corresponds to a circumstance where an error occurs in the first storage apparatus  10  and a failover from the first storage apparatus  10  to the second storage apparatus  10  is performed. 
         [0201]    Upon detecting an occurrence of an error in the first storage apparatus  10 , the host computer  3  switches the path, and starts to send the data I/O request to the second storage apparatus  10  (hereinafter, the second storage apparatus  10  continues to receive the data I/O request from the host computer  3 ). 
         [0202]    Note that, the host computer  3  detects the occurrence of an error in the first storage apparatus  10  on the basis of, for example, an error response for the data I/O request sent to the first storage apparatus  10 , timeout of the data I/O request, blockage of a path from the host computer  3  to the first storage apparatus  10 , or the like. 
         [0203]    The switching of path described above is performed by suspending the use of a currently used path to the first storage apparatus  10 , and by starting to use a path seen by the host computer  3  in the first stage that leads to the second storage apparatus  10 . 
         [0204]    In the second stage, the second storage apparatus  10  shows to the host computer  3  the same virtual unique information as the virtual unique information which the first storage apparatus  10  has showed to the host computer  3 . Note that, the redundant management for the remote pair is no longer performed because an error has occurred in the first storage apparatus  10  being the primary apparatus. 
         [0205]    To be specific, for example, in a case where the first stage is in the state of the path management table  300  shown in  FIG. 3 , the following setting is performed when an error occurs in the first storage apparatus  10 . As shown in  FIG. 8 , “Offline” is set in path state  317  and “0” is set in the currently-used flag  318  for each of the owner paths with path IDs “1” and “2”, and “1” is set in the currently-used flag  318  for the non-owner paths with path IDs “5” and “6”. Therefore, the host computer  3  can see port ID “2A” leading to each of the LUs with LUNs “0” and “1”. Furthermore, the host computer  3  can also see virtual unique information (LDEV numbers “#10:00” and “#10:01” and serial number “FFF0”) of the non-owner paths with path IDs “5” and “6”. 
         [0206]      FIG. 9  shows an example of the remote pair management table  540  in the second storage apparatus  10  after the path is switched and the reception of a data I/O request sent from the host computer  3  is started. 
         [0207]    As shown in  FIG. 9 , “Split (SSWS)” is set in the control state  546  for each of secondary LUs in the second storage apparatus  10 . Note that, “SSWS” in parentheses indicates that the secondary LU is subjected to an update which is not reflected in the primary LU, as described above. 
         [0208]    Note that, after the failover is performed, the second storage apparatus  10  shows to the host computer  3  the same virtual unique information as the virtual unique information which the first storage apparatus  10  has showed to the host computer  3 . Accordingly, the host computer  3  does not have to change settings of the unique information when a path is switched. 
         [0209]    &lt;Third Stage&gt; 
         [0210]    In the third stage, in order to resume the redundant management for the remote pair of the second storage apparatus  10  as the primary apparatus and the third storage apparatus  10  as the secondary apparatus, the second storage apparatus  10  starts duplication of data to a LU newly set as a primary LU (hereinafter, referred to as new primary LU) while using, as a source, the secondary LU (hereinafter, referred to as old secondary LU) of the remote pair stopped being used in the redundant management. This duplication is performed by using the local copy function. Details of the third stage will be described later. 
         [0211]    &lt;Fourth Stage&gt; 
         [0212]    In the fourth stage, in order to form a new remote pair (hereinafter, referred to as new remote pair) of the new primary LU in the second storage apparatus  10  and a new secondary LU (hereinafter, referred to as new secondary LU) in the third storage apparatus  10 , the second storage apparatus  10  and the third storage apparatus  10  each perform necessary settings of the tables and start duplication of data from the new primary LU to the new secondary LU. Note that, this duplication is performed using the remote copy function. Details of the fourth stage will be described later. 
         [0213]    &lt;Fifth Stage&gt; 
         [0214]    At the fifth stage, after duplication of data from the old secondary LU to the new primary LU by the local copy function is completed, a path from the host computer  3  to the third storage apparatus  10  is set, and operation of the unique information virtualization function for the new remote pair is started. Details of the fifth stage will be described later. 
         [0215]    =Detailed Explanations= 
         [0216]    &lt;Details of Third Stage&gt; 
         [0217]      FIG. 10  is a diagram for explaining the third stage, and is a diagram showing a state where the second storage apparatus  10  uses the local copy function to perform duplication of data to the new primary LU while using, as a source, the secondary LU of the remote pair stopped being used in the redundant management. 
         [0218]    In this example, data of the LDEV  181  which has configured the old secondary LU and which has the real LDEV number “#21:00” is duplicated to the LDEV  181  which configures the new primary LU, which is coupled to the network port  111  with a real port ID “3A”, and which has a real LDEV number “#22:00”. Similarly data of the LDEV  181  which has configured the old secondary LU and which has the real LDEV number “#21:01” is duplicated to the LDEV  181  which configures the new primary LU, which is coupled to the network port  111  of the real port ID “3A”, and which has a real LDEV number “#22:01”. 
         [0219]      FIG. 11  is a flowchart for explaining processing (hereinafter, referred to as local copy start command processing S 100 ) mainly performed by the management apparatus  4  when duplication using the local copy function is started. Note that, in the local copy start command processing S 1100 , the management apparatus  4  accesses the various tables stored in the shared memory (the SM  14 ) in the second storage apparatus  10  as needed via the second communication network  6 . 
         [0220]    As shown in  FIG. 11 , firstly, the management apparatus  4  receives, from a user, designation of a source LU and a target LU (or the LDEVs  181  configuring these LUs) (S 1111 ). 
         [0221]    Next, the management apparatus  4  judges whether or not the target LU (the LDEV  181  configuring the target LU) is normally operating (for example, whether or not the target LU has an error in functions such as write and read) (S 1112 ). This judgment is made, for example, based on the error information managed in the shared memory (the SM  14 ) in the second storage apparatus  10 . If the target LU is normally operating (S 1112 : YES), the processing proceeds to S 1113 , while if the target LU is not normally operating (S 1112 : NO), the processing proceeds to S 1121 . 
         [0222]    In S 1113 , the management apparatus  4  judges whether or not the target LU is already used for other purposes (for example, local copy function, remote copy function, and the like). This judgment is made, for example, based on the information managed in the shared memory (the SM  14 ) in the second storage apparatus  10 . If the target LU is not used for other purposes (S 1113 : YES), the processing proceeds to S 1114 , while if the target LU is already used for other purposes (S 1113 : NO), the processing proceeds to S 1121 . 
         [0223]    In S 1114 , the management apparatus  4  judges whether or not data in the source LDEV  181  is in the latest state. This judgment is made, for example, by referring to the contents of the control state  546  of the remote pair management table  540  managed in the shared memory (the SM  14 ) in the second storage apparatus  10 . Specifically, if “Pair” or “Split (SSWS)” is set in the control state  546 , the management apparatus  4  judges that the data in the source LDEV  181  is in the latest state. If the data in the source LDEV  181  is in the latest state (S 1114 : YES), the processing proceeds to S 1115 , while if the data is not in the latest state (S 1114 : NO), the processing proceeds to S 1121 . 
         [0224]    In S 1115 , the management apparatus  4  sends the second storage apparatus  10  a command to start the operation of the local copy function for the local pair of the source LU and the target LU accepted in S 1111 . Meanwhile, in S 1121 , the management apparatus  4  outputs an error message to the UI  46  in the management apparatus  4 . 
         [0225]      FIG. 12  is a flowchart for explaining processing (hereinafter, referred to as local copy start processing S 1200 ) performed in the second storage apparatus  10  when the management apparatus  4  sends a command to start operation of the local copy function. The processing will be described below with reference to  FIG. 12 . 
         [0226]    Upon receiving the command from the management apparatus  4  (S 1211 ), the second storage apparatus  10  creates a table (hereinafter, referred to as local pair management table  1300 ) to be used in the operation of the local copy function, and stores the table in the shared memory (the SM  14 ) (S 1212 ). 
         [0227]      FIG. 13  shows an example of the local pair management table  1300 . As shown in  FIG. 13 , the local pair management table  1300  has one or more records each including items of own real LDEV number  1311 , source/target  1312 , partner real LDEV number  1313 , and control state  1314 . 
         [0228]    Among the items, in the own real LDEV number  1311 , a real LDEV number of a certain LDEV  181  in the second storage apparatus  10  is set. 
         [0229]    In source/target  1312 , information indicating whether the certain LDEV  181  configures the source LU or the target LU in the local copy function is set. If the certain LDEV  181  configures the source LU, “Source” is set, while if the certain LDEV  181  configures the target LU, “Target” is set. 
         [0230]    In partner real LDEV number  1313 , a real LDEV number of a LDEV  181  in the second storage apparatus  10  forming a local pair with the certain LDEV  181  is set. 
         [0231]    In control state  1314 , information indicating a current control state of the local pair is set. If the local pair is in a pair state, “Pair” is set, if in a split state, “Split” is set, and if in a re-sync state, “Re-sync” is set. 
         [0232]    Referring back to  FIG. 12 , next, the second storage apparatus  10  starts the operation of the local copy function for the local pair of the source LU and the target LU, after having created the local pair management table  1300  (S 1213 ). After the operation is started, duplication of data and management of difference information is performed between the source LU and the target LU to make the data in the source LU and the data in the target LU equal to each other. 
         [0233]    &lt;Details of Fourth Stage&gt; 
         [0234]      FIG. 14  is a diagram for explaining the fourth stage, and is a diagram showing a state where the new primary LU in the second storage apparatus  10  and the new secondary LU in the third storage apparatus  10  form a new remote pair, and duplication of data from the new primary LU to the new secondary LU is performed by using the remote copy function. 
         [0235]    In this example, data of the LDEV  181  which configures the new primary LU in the second storage apparatus  10  and which has the real LDEV number “#22:00” is duplicated to the LDEV  181  which configures the new secondary LU, which is coupled to the network port  111  with real port ID “4A” in the third storage apparatus  10 , and which has a real LDEV number “#30:00”. Similarly data of the LDEV  181  which configures the new primary LU and which has the real LDEV number “#22:01” is duplicated to the LDEV  181  which configures the new secondary LU, which is coupled to the network port  111  with the real port ID “4A” in the third storage apparatus  10 , and which has a real LDEV number “#30:01”. 
         [0236]    Furthermore, as shown in  FIG. 14 , the second storage apparatus  10  is provided with a quorum drive (the LDEV  181  with a real LDEV number “#A0:00”) based on the LDEV  181  in the fourth storage apparatus  10 , as a quorum drive to ensure consistency between data in the new primary LU and data in the new secondary LU. Furthermore, the third storage apparatus  10  is provided with a quorum drive (LDEV  181  with a real LDEV number “#B0:00”) based on the LDEV  181  in the fourth storage apparatus  10 . 
         [0237]      FIG. 15  shows the quorum drive management table  550  in the second storage apparatus  10  and the quorum drive management table  650  in the third storage apparatus  10 , after information related to the quorum drives is added. Note that, the quorum drive management table  650  in the third storage apparatus  10  is stored in the shared memory (the SM  14 ) in the third storage apparatus  10 . 
         [0238]    As shown in  FIG. 15 , to the quorum drive management table  550  in the second storage apparatus  10  a records is added where the items are set as follows: “E” is set in the quorum drive ID  551 ; “3333”, which is a real serial number of the third storage apparatus  10 , is set in the partner real serial number  552 ; “FFF0”, which is the virtual serial number shown to the host computer  3 , is set in the own virtual serial number  553 ; and “A0:00”, which is the real LDEV number of the quorum drive, is set in the real LDEV number  554 . 
         [0239]    Furthermore, in the quorum drive management table  650  in the third storage apparatus  10 , a record is registered where the items are set as follows: “E” is set in quorum drive ID  651 ; “2222”, which is the real serial number of the second storage apparatus  10 , is set in partner real serial number  652 ; “FFF0”, which is the virtual serial number shown to the host computer  3  by the third storage apparatus  10 , is set in own virtual serial number  653 ; and “B0:00”, which is the real LDEV number of the quorum drive, is set in real LDEV number  654 . 
         [0240]      FIG. 16  is a flowchart for explaining processing (hereinafter, referred to as remote copy start command processing S 1600 ) mainly performed by the management apparatus  4  when data is duplicated from the new primary LU to the new secondary LU by using the remote copy function. Note that, in the remote copy start command processing S 1600 , the management apparatus  4  accesses the various tables stored in the shared memory (SM  14 ) in the second storage apparatus  10  and the third storage apparatus  10  via the second communication network  6  as needed. 
         [0241]    As shown in  FIG. 16 , firstly, the management apparatus  4  receives, from a user, designation of a new primary LU and a new secondary LU (or the LDEVs  181  configuring these LUs) (S 1611 ). 
         [0242]    Next, the management apparatus  4  judges whether or not the new secondary LU (the LDEV  181  configuring the new secondary LU) is normally operating (for example, whether or not the new secondary LU has an error in functions such as write and read) (S 1612 ). This judgment is made, for example, based on the error information managed in the shared memory (the SM  14 ) in the third storage apparatus  10 . If the new secondary LU is normally operating (S 1612 : YES), the processing proceeds to S 1613 , while if the new secondary LU is not normally operating (S 1612 : NO), the processing proceeds to S 1621 . 
         [0243]    In S 1613 , the management apparatus  4  judges whether or not the new secondary LU (the LDEV  181  configuring the secondary LU) is already used for other purposes (for example, the local copy function, the remote copy function, and the like). This judgment is made, for example, based on information managed in the shared memory (the SM  14 ) in the third storage apparatus  10 . If the new secondary LU is not used for other purposes (S 1613 : YES), the processing proceeds to S 1614 , while if the new secondary LU is already used for other purposes (S 1613 : NO), the processing proceeds to S 1621 . 
         [0244]    In S 1614 , the management apparatus  4  sends a command to start the operation of the remote copy function for the remote pair of the new primary LU and the new secondary LU accepted in S 1611 . Meanwhile, in S 1621 , the management apparatus  4  outputs an error message to the UI  46  in the management apparatus  4 . 
         [0245]    For example, in the above command, the management apparatus  4 , sets as the new primary LU of the remote pair, network port  111  with real port ID “3A” and LDEV  181  with LDEV number “#22:00”, sets as the new secondary LU, network port  111  with real port ID “4A” and LDEV  181  with LDEV number “#30:00”, and sets the quorum drive with quorum ID “E” for the remote pair. 
         [0246]    Similarly, in the above command, the management apparatus  4 , sets as the new primary LU of the remote pair, network port  111  with real port ID “3A” and LDEV 181  with LDEV number “#22:01”, sets as the new secondary LU of the remote pair, network port  111  with real port ID “4A” and LDEV 181  with LDEV number “#30:01”, and sets the quorum drive with quorum ID “E” for the remote pair. 
         [0247]      FIG. 17  is a flowchart for explaining processing (hereinafter, referred to as remote copy start processing S 1700 ) performed in the second storage apparatus  10  when the management apparatus  4  sends a command to start the operation of the remote copy function. 
         [0248]    As shown in  FIG. 17 , upon receiving the command from the management apparatus  4  (S 1711 ), the second storage apparatus  10  acquires information related to the new primary LU specified in the command, from the local pair management table  1300  and the remote pair management table  540  (S 1712 ). Then, the second storage apparatus  10  compares the acquired information and the quorum drive management table  550 , and acquires a virtual serial number which the second storage apparatus  10  is currently showing to the host computer  3  (S 1713 ). 
         [0249]    For example, when the tables in the second storage apparatus  10  have the contents shown in  FIG. 5 , the second storage apparatus  10 , acquires from the local pair management table  1300  real LDEV numbers “#21:00” and “21:01” of the source of the local pair on the basis of LDEV numbers “#22:00” and “#22:01” of the new primary LU designated (set) by the management apparatus  4 . Then, the second storage apparatus  10  acquires “F”, which is a quorum drive ID corresponding to the real LDEV numbers, from the remote pair management table  540  (S 1712 ). Subsequently, the second storage apparatus  10  acquires “FFF0” as a virtual serial number (a content of the own virtual serial number  553 ) corresponding to the acquired quorum drive ID “F”, from the quorum drive management table  550  (S 1713 ). 
         [0250]    Next, the second storage apparatus  10  acquires, from the partner virtual port management table  520 , the virtual port ID set for the network port  111  to which a primary LU (hereinafter, referred to as old primary LU) of a remote pair (hereinafter, referred to as old remote pair) formed before occurrence of the error in the first storage apparatus  10  is coupled (S 1714 ). 
         [0251]    For example, when the tables in the second storage apparatus  10  have the contents shown in  FIG. 5 , the second storage apparatus  10  acquires “1A” and “1X” set in the partner virtual port ID  523  of the partner virtual port management table  520  (S 1714 ). 
         [0252]    Next, the second storage apparatus  10  adds a record related to the new remote pair to the own virtual port management table  510  (S 1715 ).  FIG. 18  shows a state where a record related to the new remote pair is added to the own virtual port management table  510  when the own virtual port management table  510  in the second storage apparatus  10  has the contents shown in  FIG. 5 . As shown in  FIG. 18 , a record in which “3A” is set in the own real port ID  511 , “1X” is set in the own virtual port ID  512 , and “Enabled” is set in the enabled/disabled  513  is added to the own virtual port management table  510  as a record related to the new remote pair. Note that, the setting contents of the record are notified as needed, for example, from the management apparatus  4  or the third storage apparatus  10  to the second storage apparatus  10 . 
         [0253]    Next, the second storage apparatus  10  adds a record related to the new remote pair to the partner virtual port management table  520  (S 1716 ).  FIG. 18  shows a state where a record related to the new remote pair is added to the partner virtual port management table  520  when the partner virtual port management table  520  in the second storage apparatus  10  has the contents shown in  FIG. 5 . As shown in  FIG. 18 , a record with “3333” set in the partner real serial number  521 , “4A” set in the partner real port ID  522 , “2X” set in the partner virtual port ID  523 , and “Enabled” set in the enabled/disabled  524  is added to the partner virtual port management table  520  as a record related to the new remote pair. Note that, the setting contents of the record are notified as needed, for example, from the management apparatus  4  or the third storage apparatus  10  to the second storage apparatus  10 . 
         [0254]    Next, the second storage apparatus  10  adds a record related to the new remote pair to the remote pair management table  540  (S 1717 ).  FIG. 19  shows a state where a record related to the new remote pair is added to the remote pair management table  540  when the remote pair management table  540  in the second storage apparatus  10  has the contents shown in  FIG. 5 . As shown in  FIG. 19 , a record with “#22:00” set in the own real LDEV number  541 , “PVOL” set in the PVOL/SVOL  542 , “3333” set in the partner real serial number  543 , “#30:00” set in the partner real LDEV number  544 , “4A” set in the partner real port ID  545 , “Pair” set in the control state  546 , and “E” set in the quorum drive ID  547  is added to the remote pair management table  540  as a record related to the new remote pair. 
         [0255]    Moreover, a record with “#22:01” set in the own real LDEV number  541 , “PVOL” set in the PVOL/SVOL  542 , “3333” set in the partner real serial number  543 , “#30:01” set in the partner real LDEV number  544 , “4A” set in the partner real port ID  545 , “Pair” set in the control state  546 , and “E” set in the quorum drive ID  547  is added to the remote pair management table  540  as a record related to the new remote pair. Note that, the setting contents of the record are notified as needed, for example, from the management apparatus  4  or the third storage apparatus  10  to the second storage apparatus  10 . 
         [0256]    Next, the second storage apparatus  10  adds a record related to the new remote pair to the unique information conversion table  570  (S 1718 ).  FIG. 19  shows a state where a record related to the new remote pair is added to the unique information conversion table  570  when the unique information conversion table  570  in the second storage apparatus  10  has the contents shown in  FIG. 5 . As shown in  FIG. 19 , a record with “3A” set in the own real port ID  571 , “#22:00” set in the own real LDEV number  572 , “2222” set in the own real serial number  573 , “1X” set in the own virtual port ID  574 , “#10:00” set in the own virtual LDEV number  575 , and “FFF0” set in the own virtual serial number  576  is added to the unique information conversion table  570  as a record related to the new remote pair. 
         [0257]    Moreover, a record with “3A” set in the own real port ID  571 , “#22:01” set in the own real LDEV number  572 , “2222” set in the own real serial number  573 , “1X” set in the own virtual port ID  574 , “#10:01” set in the own virtual LDEV number  575 , and “FFF0” set in the own virtual serial number  576  is added to the unique information conversion table  570  as a record related to the new remote pair. Note that, the setting contents of the records are notified as needed, for example, from the management apparatus  4  or the third storage apparatus  10  to the second storage apparatus  10 . 
         [0258]    Next, the second storage apparatus  10  sends to the third storage apparatus  10  a setting command for the tables related to the new remote pair (S 1720 ), and waits to receive setting completion notification of the tables which is sent from the third storage apparatus  10  (S 1721 ). Subsequently, upon receiving the setting completion notification from the third storage apparatus  10  (S 1721 : YES), the second storage apparatus  10  starts the operation of the remote copy function for the new remote pair (S 1722 ). Note that, if the setting completion notification cannot be received within a predetermined period of time from the third storage apparatus  10  (S 1721 : NO), the second storage apparatus  10  notifies the management apparatus  4  of a timeout error (S 1731 ). 
         [0259]      FIG. 20  is a flowchart for explaining processing (hereinafter, referred to as remote copy start preparation processing S 2000 ) performed by the third storage apparatus  10  when the second storage apparatus  10  sends the setting command for the tables related to the new remote pair. The processing will be described below with reference to  FIG. 20 . 
         [0260]    Upon receiving the command from the management apparatus  4  (S 2011 ), the third storage apparatus  10  creates an own virtual port management table  610  shown in  FIG. 21 , to which a record related to the new remote pair is registered (S 2012 ). As shown in  FIG. 21 , a record with “4A” set in own real port ID  611 , “2X” set in own virtual port ID  612 , and “Enabled” to enabled/disabled  613  is registered to the own virtual port management table  610  as a record related to the new remote pair. Note that, the setting contents of the record are notified as needed, for example, from the management apparatus  4  or the second storage apparatus  10  to the third storage apparatus  10 . 
         [0261]    Next, the third storage apparatus  10  creates a partner virtual port management table  620  shown in  FIG. 21 , to which a record related to the new remote pair is registered (S 2013 ). As shown in  FIG. 21 , a record with “2222” set in the partner real serial number  621 , “3A” set in the partner real port ID  622 , “1X” set in the partner virtual port ID  623 , and “Enabled” set in the enabled/disabled  624  is registered to the partner virtual port management table  620  as a record related to the new remote pair. Note that, the setting contents of the record are notified as needed, for example, from the management apparatus  4  or the second storage apparatus  10  to the third storage apparatus  10 . 
         [0262]    Next, the third storage apparatus  10  creates a remote pair management table  640  shown in  FIG. 21 , to which a record related to the new remote pair is registered (S 2014 ). As shown in  FIG. 21 , a record with “#30:00” set in a own real LDEV number  641 , “SVOL” set in a PVOL/SVOL  642 , “2222” set in a partner real serial number  643 , “#22:00” set in a partner real LDEV number  644 , “3A” set in an partner real port ID  645 , “Pair” set in a control state  646 , and “E” set in a quorum drive ID  647  is registered to the remote pair management table  640  as a record related to the new remote pair. 
         [0263]    Moreover, a record with “#30:01” set in the own real LDEV number  641 , “SVOL” set in the PVOL/SVOL  642 , “2222” set in the partner real serial number  643 , “#22:01” set in the partner real LDEV number  644 , “3A” set in the partner real port ID  645 , “Pair” set in the control state  646 , and “E” set in the quorum drive ID  647  is registered as a record related to the new remote pair. Note that, the setting contents of the records are notified as needed, for example, from the management apparatus  4  or the second storage apparatus  10  to the third storage apparatus  10 . 
         [0264]    Next, the third storage apparatus  10  creates a unique information conversion table  670  shown in  FIG. 21 , to which a record related to the new remote pair is registered (S 2015 ). As shown in  FIG. 21 , a record with “4A” set in own real port ID  671 , “#30:00” set in own real LDEV number  672 , “3333” set in own real serial number  673 , “2X” set in own virtual port ID  674 , “#10:00” set in own virtual LDEV number  675 , and “FFF0” set in own virtual serial number  676  is registered to the unique information conversion table  670  as a record related to the new remote pair. 
         [0265]    Moreover, a record with “4A” set in the own real port ID  671 , “#30:01” set in the own real LDEV number  672 , “3333” set in the own real serial number  673 , “2X” set in the own virtual port ID  674 , “#10:01” set in the own virtual LDEV number  675 , and “FFF0” set in the own virtual serial number  676  is registered as a record related to the new remote pair. Note that, the setting contents of the records are notified as needed, for example, from the management apparatus  4  or the second storage apparatus  10  to the third storage apparatus  10 . 
         [0266]    Referring back to  FIG. 20 , when the creation of the tables described above is completed, the third storage apparatus  10  sends the second storage apparatus  10  notification notifying that setting of the tables related to the new remote pair is completed (S 2016 ). 
         [0267]    &lt;Details of Fifth Stage&gt; 
         [0268]      FIG. 22  is a diagram for explaining the fifth stage, and is a diagram showing a state where operation of the unique information virtualization function is started, the unique information virtualization function for the new remote pair formed of the new primary LU in the second storage apparatus  10  and the new secondary LU in the third storage apparatus  10 . 
         [0269]    As shown in  FIG. 22 , when the operation of the unique information virtualization function for the new remote pair is started, paths are set from the host computer  3  in way that: the network port  111  (the network port  111  with real port ID “3A” and virtual port ID “1X”) coupled to the new primary LU (the LDEVs  181  with respective real LDEV numbers “#22:00” and “#22:01”) in the second storage apparatus  10  is coupled to the host computer  3 ; and that the network port  111  (the network port  111  with real port ID “4A” and virtual port ID “2X”) coupled to the new secondary LU (the LDEVs  181  with respective real LDEV numbers “#30:00” and “#30:01”) in the third storage apparatus  10  is coupled to the host computer  3 . Note that, at the time when the paths are set, the network port  111  with real port ID “2A” continues to receive an data I/O request from the host computer  3 . Therefore, in the second storage apparatus  10 , both of the old secondary LU and the new primary LU are capable of being updated by the data I/O request sent from the host computer  3 . 
         [0270]    In the unique information conversion table  570  in the second storage apparatus  10 , a virtual LDEV number same as the virtual LDEV number set for the LDEVs  181  (the LDEVs  181  with respective real LDEV numbers “#10:00” and “#10:01”) having configured the old primary LU is set for the LDEVs  181  (the LDEVs  181  with respective real LDEV numbers “#22:00” and “#22:01”) configuring the new primary LU. Furthermore, virtual port ID “1X”, which is set for the network port  111  coupled to the old primary LU, is set for the network port  111  with real port ID “3A”. 
         [0271]    Accordingly, by setting the paths in the above-described way, the host computer  3  sees as if a plurality of paths (path (second path) including the network port  111  with real port ID “2A”, a path (hereinafter, referred to as third path) including the network port  111  with real port ID “3A”, and a path (hereinafter, referred to as fourth path) including the network port  111  with real port ID “4A”) exist for each of the LDEVs  181  with the LDEV numbers “#10:00” and “#10:01”. 
         [0272]    After the paths are set, the second storage apparatus  10  monitors whether or not the new primary LU is updated by the data I/O request received via the network port  111  with real port ID “3A”. When detecting that the new primary LU has been updated, the second storage apparatus  10  inhibits an access from the host computer  3  to the old secondary LU (closes the old secondary LU). When the new primary LU is updated in this way, the old secondary LU is closed to prevent the host computer  3  from accessing old data. 
         [0273]      FIG. 23  shows a state of the path management table  300  managed by the host computer  3  after the paths are set in the way described above. As shown in  FIG. 23 , each of the paths including the network ports  111  with port IDs “1X”, “2A”, and “2X”, respectively (paths (third path) with respective path IDs “3” and “4”, paths (second path) with respective path IDs “5” and “6”, and paths (fourth path) with respective path IDs “7” and “8”) is seen to be in an online state from the host computer  3 . Furthermore, because the network port  111  with port ID “1X” is an owner path, this network port  111  is preferentially used and “1” is set in the currently-used flag  318  of this network port  111 . 
         [0274]      FIG. 24  is a flowchart for explaining processing (hereinafter, referred to as data I/O processing (second storage apparatus) S 2400 ) performed in the second storage apparatus  10  when the second storage apparatus  10  receives the data I/O request from the host computer  3  after the paths are set in the way described above. 
         [0275]    As shown in  FIG. 24 , upon receiving the data I/O request sent from the host computer  3  (S 2411 : YES), the second storage apparatus  10  refers to the local pair management table  1300 , and judges whether or not a LU (hereinafter, referred to as I/O target LU) being a target of the data I/O request is any one of the old secondary LU and the new primary LU (in other words, judges whether or not the LDEV  181  (hereinafter, referred to as I/O target LDEV) configuring the I/O target LU is registered in the local pair management table  1300 ) (S 2412 ). If the I/O target LU is any one of the old secondary LU and the new primary LU (S 2412 : YES), the processing proceeds to S 2421 , while if the I/O target LU is neither the old secondary LU nor the new primary LU (S 2412 : NO), the processing proceeds to S 2431 . 
         [0276]    In S 2421 , the second storage apparatus  10  refers to the local pair management table  1300  and the remote pair management table  540 , and judges whether the LU being the target of the data I/O request is the old secondary LU (a source of the local pair) or the new primary LU (a target of the local pair). If the I/O target LU is the old secondary LU (S 2421 : old secondary LU), the processing proceeds to S 2422 , while if the I/O target LU is the new primary LU (S 2421 : new primary LU), the processing proceeds to S 2423 . 
         [0277]    In S 2422 , the second storage apparatus  10  executes normal I/O processing on the old secondary LU. In addition, the second storage apparatus  10  reflects (duplicates) the update difference of the old secondary LU in the new primary LU by using the local copy function in order to ensure consistency between the local pair. Then, the processing proceeds to S 2431 . 
         [0278]    In S 2423 , the second storage apparatus  10  executes normal I/O processing on the new primary LU, and closes the old secondary LU. Then, processing proceeds to S 2431 . 
         [0279]    In S 2431 , the second storage apparatus  10  refers to the remote pair management table  540 , and judges whether the LU being the target of the data I/O request is the new primary LU. If the I/O target LU is the new primary LU (S 2431 : YES), processing proceeds to S 2432 , while if the I/O target LU is not the new primary LU (S 2431 : NO), processing proceeds to S 2433 . 
         [0280]    In S 2432 , the second storage apparatus  10  executes normal I/O processing on the new primary LU. In addition, the second storage apparatus  10  reflects (duplicates) the updated data of the new primary LU in the new secondary LU by using the remote copy function in order to ensure consistency between the remote pair. 
         [0281]    In S 2433 , the second storage apparatus  10  executes normal I/O processing on the I/O target LU. Then, the processing returns to S 2411 . 
         [0282]      FIG. 25  is a flowchart for explaining processing (hereinafter, referred to as data I/O processing (third storage apparatus) S 2500 ) performed in the third storage apparatus  10  when the third storage apparatus  10  receives the data I/O request from the host computer  3  after the paths are set in the way described above. 
         [0283]    Upon receiving the data I/O request sent from the host computer  3  (S 2511 : YES), the third storage apparatus  10  refers to the remote pair management table  640 , and judges whether or not a LU (hereinafter, referred to as I/O target LU) being a target of the data I/O request is the new secondary LU (in other words, judges whether or not the LDEV  181  (hereinafter, referred to as I/O target LDEV) configuring the I/O target LU is registered in the remote pair management table  640 ) (S 2512 ). If the I/O target LU is the new secondary LU (S 2512 : YES), processing proceeds to S 2513 , while if the I/O target LU is not the new secondary LU (S 2512 : NO), processing proceeds to S 2514 . 
         [0284]    In S 2515 , the third storage apparatus  10  sets “Split (SSWS)” in the control state  646  of the LDEV  181  configuring the I/O target LU in the remote pair management table  640 , and transitions the state of the remote pair including the I/O target LU to a split state. Note that, in this case, the transition to the split state is also notified to the second storage apparatus  10 . In response to this notification, the second storage apparatus  10  sets “Split (PSUS)” in the control state  546  of a corresponding LDEV  181  in the remote pair management table  540  thereof. After that, the processing returns to S 2511 . 
         [0285]    In S 2514 , normal I/O processing on the I/O target LU is performed. After that, the processing returns to S 2511 . 
         [0286]    As described above, in the storage system  1  according to this embodiment, the first storage apparatus  10  and the second storage apparatus  10  each provide a common virtual serial number (virtual apparatus ID) as an identifier thereof to the host computer  3 . Moreover, the first storage apparatus  10  and the second storage apparatus  10  each provide a common virtual LDEV number (virtual volume ID) as an identifier of the LDEV  181  (storage volume) therein to the host computer  3 . Furthermore, a remote copy function is employed for the remote pairs respectively including the old primary LU and the new primary LU. 
         [0287]    Furthermore, when an error occurs in the first storage apparatus  10 , the second storage apparatus  10  starts to receive an data I/O request from the host computer  3  via the second path, and uses the local copy function for the local pair of the old secondary LU (second storage volume) and the new primary LU (third storage volume). Moreover, the second storage apparatus  10  and the third storage apparatus  10  start operation of the remote copy function for the remote pair of the new primary LU (third storage volume) and the new secondary LU (fourth storage volume). Then, the third storage apparatus  10  starts to receive the data I/O request from the host computer  3  via the fourth path, and starts data I/O to and from the fourth storage volume. 
         [0288]    Here, at any of the stages described above, all of the storage apparatuses  10  provide a common virtual serial number and a common virtual LDEV number to the host computer  3 . As described above, the storage system  1  according to the present embodiment performs processing to recover the storage system to a high-availability operational status by using the local copy function and the remote copy function provided in the storage apparatus  10 , and at the same time always provides the host computer  3  with the common virtual serial number and the common virtual LDEV number in the time before and after the occurrence of an error and from the time after the occurrence of the error to the time when the storage system recovers to the high-availability operational status. Accordingly, the storage system  1  can continuously provide service during a period after the occurrence of the error in the first storage apparatus  10  until the storage system  1  recovers to a high-availability operational status, without causing the host computer  3  to change settings for the serial number and the LDEV. 
         [0289]    Therefore, according to the storage system  1  of the present embodiment, even when an error occurs in the first storage apparatus  10 , the storage system  1  can smoothly recover to a high-availability operational status without affecting the host computer  3 . 
         [0290]    Furthermore, during the recovering period described above, both the data I/O request to the old secondary LU via the second path and the data I/O request to the new primary LU via the third path can be received because the old secondary LU (second storage volume) and the new primary LU (third storage volume) are managed by the local copy function to make the data therein equal to each other. Accordingly, the reception of the data I/O request to the new primary LU via the third path can be smoothly started while the reception of the data I/O request to the old secondary LU via the second path is continuously performed. 
         [0291]    Furthermore, the second storage apparatus  10 , monitors whether or not the new primary LU is updated by the data I/O request after starting the reception of the data I/O request from the host computer  3  via the third path. When detecting that the new primary LU has been updated, the second storage apparatus  10  stops receiving the data I/O request from the host computer  3  via the second path. Accordingly, a path from the second path to the third path or the fourth path can be smoothly switched using the update of the new primary LU as a trigger, while the reception of the data I/O request to the old secondary LU with non-latest data is stopped. 
         [0292]    Furthermore, as shown in the path management table  300  in each of  FIG. 3  and  FIG. 23 , in the first stage before the error occurs in the first storage apparatus  10 , the first storage apparatus  10  provides to the host computer  3 , as a first virtual port ID, a virtual port ID (third virtual port ID) to be used as the third path, and provides to the host computer  3 , as a second virtual port ID, a virtual port ID (fourth virtual port ID) to be used as the fourth path. Accordingly, in a failover (switching from the first path to the second path) from the first storage apparatus  10  to the second storage apparatus  10  or in switching from the second path to the third path or the fourth path, the host computer  3  does not have to change settings for a new path or be rebooted. Thus, the path can be switched without affecting the service of the host computer  3 . 
         [0293]    Although an embodiment has been described above, the embodiment is provided to facilitate the understanding of the present invention, and is not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit of the present invention, and includes equivalents thereof.