Patent Publication Number: US-10761767-B2

Title: Computer system and method for controlling storage apparatus that has replication direction from first logical device (in first storage) to second logical device (in second storage) and from said second logical device to third logical device (in said second storage), wherein said replication direction is reversed when second computer takes over for first computer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage entry of PCT Application No: PCT/JP2016/070545 filed Jul. 12, 2016, the contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a computer system and a method for controlling a storage apparatus. 
     BACKGROUND ART 
     Along with the progress of virtualization techniques, it becomes possible to run a plurality of virtual machines on one physical host computer, and to perform failover in the event of a system failure, by causing the processing that has been executed by a virtual machine to be taken over by another virtual machine on the remote host computer. 
     Virtual machine information such as images and use data of the virtual machines can be stored in a logical device of a storage apparatus. In such a configuration, along with execution of failover of the virtual machine, failover is performed from a logical device of a storage apparatus of a primary site where the virtual machine information has been stored to a logical device of a storage apparatus of a secondary site such as a remote site, thereby interchanging the primary and secondary logical devices. Thus, the unit of the logical device to be associated with the virtual machine becomes important. 
     PTL 1 discloses a method of dividing one logical device of a storage apparatus into a plurality of virtual volumes on a host computer and storing data used by a virtual machine for each virtual volume. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP 2012-79245 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     A conglomerate LUN structure has been proposed as a scheme that allocates logical devices to virtual machines. In this scheme, a plurality of the logical devices of a storage apparatus is grouped into a plurality of LUN conglomerates, a logical path is set to an administrative logical unit (ALU) playing a role of a gateway in the logical conglomerate, an input/output (I/O) command from a host computer side is issued while designating an identifier of a subsidiary logical unit (SLU) other than the ALU in the logical conglomerate, and the storage apparatus distributes I/O processing to the SLU designated by the received command. As a result, one or a plurality of the SLUs is allocated to one virtual server on the host computer so that it is possible to set the logical devices of the storage apparatus in units of virtual servers, and it is possible to perform failover in units of the SLUs. 
     Examples of the failover include an official failover that is automatically performed with occurrence of an actual failure or the like as a trigger, and a test failover that is executed systematically for the purpose of verification of failover or the like. 
     In the test failover, a snapshot acquired from a logical device of a remote copy destination is used in some cases so as not to affect work in production running or a remote copy configuration. Further, there is a case where the production work operation is continued in a virtual machine in the middle of executing the test failover in order to use snapshot data at a predetermined point in time. For example, it is a case where a failure occurs in a virtual machine of a primary site in the middle of executing the test failover by a virtual machine of a secondary site using a snapshot. 
     At this time, the snapshot of the secondary site connected to the virtual machine in the middle of executing the test failover is set to be handled as the latest data. Further, the snapshot set to be handled as the latest data has no remote copy configuration with the logical device of the primary site, and thus, resumption of remote copy in a reverse direction from the snapshot of the secondary site as a failover destination to the logical device of the primary site is requested in order to maintain the remote copy configuration. 
     There is a related art in which data of logical devices are synchronized in a reverse direction from a secondary site to a primary site with respect to a pair of the logical devices which has performed remote copy from the primary site to the secondary site. However, a remote copy pair is not configured between a snapshot of the secondary site and the logical device of the primary site, and it is necessary to newly constitute the remote copy pair. 
     When constituting a new remote copy pair, it is necessary to copy the data of the entire volume area from the secondary site to the primary site, so that there occurs a problem that it takes time to reconfigure the remote copy. 
     An object of the present invention is to perform remote copy in a reverse direction from a snapshot of a secondary site to a logical device of a primary site, which do not constitute a remote copy pair, at high speed without generating the entire area copy. 
     Solution to Problem 
     The present invention relates to a computer system that includes a management computer, a first storage apparatus, and a second storage apparatus. A first logical device of the first storage apparatus and a second logical device of the second storage apparatus constitute a remote copy pair. The second logical device and a third logical device of the second storage apparatus constitute a copy pair. The second logical device and the third logical device have virtual IDs to be recognized by an issuer of an I/O request. The second storage apparatus interchanges the virtual IDs of the third logical device and the second logical device with reception of a predetermined command from the management computer as a trigger during processing of the I/O request from the issuer of the I/O request to the third logical device, thereby switching an access destination of the issuer of the I/O request from the third logical device to the second logical device. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to speed up the resumption of remote copy in the reverse direction with the snapshot (third logical device) of the remote copy destination volume (second logical device) as a copy source. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating a first embodiment and a second embodiment of the present invention and illustrating an example of a physical configuration of a computer system. 
         FIG. 2  is a block diagram illustrating the first embodiment of the present invention and illustrating an example of a logical configuration of the computer system. 
         FIG. 3  is a diagram illustrating the first embodiment of the present invention and illustrating an example of I/O processing at the time of execution of test failover. 
         FIG. 4  is a diagram illustrating the first embodiment of the present invention and illustrating an example of I/O processing during remote copy reconfiguration. 
         FIG. 5  is a diagram illustrating the first embodiment and the second embodiment of the present invention and illustrating an example of a hierarchical structure of a storage area of a storage apparatus. 
         FIG. 6  is a diagram illustrating the first embodiment of the present invention and illustrating examples of programs and tables in the storage apparatus. 
         FIG. 7  is a table illustrating the first embodiment of the present invention and illustrating an example of an SLU management table. 
         FIG. 8  is a table illustrating the first embodiment of the present invention and illustrating an example of an LDEV management table. 
         FIG. 9  is a table illustrating the first embodiment and the second embodiment of the present invention and illustrating an example of a snapshot pair management table. 
         FIG. 10  is a table illustrating the first embodiment and the second embodiment of the present invention and illustrating an example of a remote copy pair management table. 
         FIG. 11  illustrates the first embodiment of the present invention and illustrates an example of a flowchart of an I/O request processing program. 
         FIG. 12  illustrates the first embodiment of the present invention and illustrates an example of a flowchart of a remote copy resumption preparation program. 
         FIG. 13  illustrates the first embodiment of the present invention and illustrates an example of a flowchart of a remote copy resumption program. 
         FIG. 14  is a block diagram illustrating the second embodiment of the present invention and illustrating an example of a logical configuration of the computer system. 
         FIG. 15  is a diagram illustrating the second embodiment of the present invention and illustrating an example of I/O processing during remote copy reconfiguration. 
         FIG. 16  is a diagram illustrating the second embodiment of the present invention and illustrating an example of a virtual LDEV management table. 
         FIG. 17  is a diagram illustrating the second embodiment of the present invention and illustrating an example of a virtual LDEV-actual LDEV management table. 
         FIG. 18  illustrates the second embodiment of the present invention and illustrates an example of a flowchart of a remote copy resumption preparation program. 
         FIG. 19  is a sequence diagram illustrating the first embodiment of the present invention and illustrating an example of a process from the test failover to the remote copy resumption. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same reference signs will be attached to the same parts. However, the present invention is not limited by the embodiments, and various application examples conforming to an idea of the present invention are included in a technical scope of the present invention. In addition, each component may be plural or singular unless specifically limited. 
     Incidentally, various kinds of information will be sometimes described with an expression, “xxx table” in the following description, but the various kinds of information may be expressed with a data structure other than the table. In order to indicate that the information is not dependent on the data structure “xxx table” can be called “xxx information”. 
     In addition, there is a case where processing is described with a “program” as a subject in the following description, but the subject of the processing may be a processor since the program is executed by the processor (for example, a central processing unit (CPU)) to perform the prescribed processing appropriately using a storage resource (for example, a memory) and a communication interface device (for example, a communication port). The processor may have dedicated hardware in addition to the CPU. The computer program may be installed in each computer from a program source. For example, the program source may be a program distribution server or a storage medium. 
     In addition, each element can be identified based on an ID, a number, or the like, but other kinds of identification information such as a name may be used as long as the information is identifiable. 
     First Embodiment 
     A first embodiment of the present invention will be described with reference to  FIGS. 1 to 13 .  FIG. 1  is a block diagram illustrating a physical configuration of a computer system according to the first embodiment and a second embodiment. 
     For example, this computer system is configured to include one or a plurality of host computers  110 , one or a plurality of first storage apparatuses  120 , one or a plurality of second storage apparatuses  130 , and one or a plurality of management computers  140 . 
     The host computer  110 , the first storage apparatus  120 , and the second storage apparatus  130  are connected by communication lines  151 ,  152 , and  153  via, for example, a storage area network (SAN)  150  (shown in  FIG. 2 ). 
     The host computer  110 , the first storage apparatus  120 , the second storage apparatus  130 , and the management computer  140  are connected by communication lines  161 ,  162 ,  163 , and  164 , for example, via a management network  160 . 
     The first storage apparatus  120  and the second storage apparatus  130  are connected by communication lines  172  and  173 , for example, via a wide area network (WAN)  170 . 
     Incidentally, the above-described communication lines  151 ,  152 ,  153 ,  161 ,  162 ,  163 ,  164 ,  172 , and  173  are configured as wired lines such as metal cables and optical fiber cables, for example, but the respective elements may be wirelessly connected. In such a case, these communication lines are omitted. In addition, each of these communication lines is not limited to one but may be plural. 
     In addition, the SAN  150 , the management network  160 , and the WAN  170  may be a common network. These networks are communication networks, and can be configured using, for example, a SAN, a WAN, a local area network (LAN), or the like. 
     The host computer  110  is, for example, a computer device configured to include a CPU  111 , a memory  112 , a storage device  113 , an input device  114 , an output device  115 , a host bus adapter (HBA)  116 , and an interface control unit  117 , and is constituted by, for example, a personal computer, a work station, a main frame, and the like. 
     The CPU  111  is a processor that controls the entire host computer  110 , and reads various programs stored in the storage device  113  on the memory  112  to execute the read programs. 
     The memory  112  is not only used to store the various programs read from the storage device  113  by the CPU  111  at the time of activating of the host computer  110  but also used as a work memory of the CPU  111 . 
     The storage device  113  is configured using, for example, a hard disk drive (HDD) or a solid state drive (SSD), and is used to store and hold various programs and control data. 
     The input device  114  is configured using, for example, a keyboard switch, a pointing device, a microphone, or the like. The output device  115  is configured using, for example, a liquid crystal display or the like. 
     The host bus adapter  116  performs protocol control at the time of communication with the storage apparatuses  120  and  130 . As the HBA  116  executes such a protocol control function, data and a command are transmitted and received between the host computer  110  and the storage apparatuses  120  and  130  and between the first storage apparatus  120  and the second storage apparatus  130 . 
     The interface control unit  117  is an adapter configured to connect the host computer  110  to the management network  160 . 
     A virtualization program  118  is a program configured to virtualize resources of the CPU  111 , the memory  112 , the storage device  113 , the input device  114 , the output device  115 , the HBA  116 , and the interface control unit  117  of the host computer  110  and allocate and manage the virtualized resources in units of virtual machines, and is executed by the CPU  111  by being read from the storage device  113  to the memory  112 . 
     Since the first storage apparatus  120  and the second storage apparatus  130  have the same configuration in the present embodiment, the description regarding the second storage apparatus  130  will be omitted. 
     The first storage apparatus  120  includes a plurality of storage devices  121  and a control unit  122  which controls input and output of data with respect to the storage device  121 . 
     The storage device  121  is configured using an expensive disk such as a SCSI disk formed using an HDD or an SSD, an inexpensive disk such as a serial at attachment (SATA) disk and an optical disk, or the like. The plurality of storage devices  121  constitutes one redundant-array-of-inexpensive-disks (RAID) group, and one or a plurality of logical units is set on a physical storage area provided by one or a plurality of the RAID groups. Then, data from the host computer  110  is stored in the logical unit in units of blocks each having a predetermined size. 
     The control unit  122  is configured to include a CPU  123 , a main memory  124 , a nonvolatile memory  125 , a cache memory  126 , a plurality of host-side ports  127 , a plurality of storage-device-side ports  128 , and an interface control unit  129 . 
     The CPU  123  is a processor that controls the entire first storage apparatus  120 , and reads various programs stored in the storage device  121  on the main memory  124  to execute the read programs. 
     The main memory  124  is not only used to store various programs read from the nonvolatile memory  125  by the CPU  123  at the time of activating of the first storage apparatus  120  but also used as a work memory of the CPU  123 . 
     The nonvolatile memory  125  is used to store and hold various programs and control data. The cache memory  126  is mainly used as a storage area of a queue and the like which temporarily stores data transmitted and received between the host computer  110  and the storage device  121 . 
     The host-side port  127  is an adapter configured to connect the first storage apparatus  120  to the SAN  150  or the WAN  170 . The storage-device-side port  128  is an adapter configured to connect the control unit  122  to the storage device  121 . The interface control unit  129  is an adapter configured to connect the first storage apparatus  120  to the management network  160 . 
     The management computer  140  is a computer device configured to manage the host computer  110 , the first storage apparatus  120 , and the second storage apparatus  130 , and is configured to include, for example, a CPU  141 , a memory  142 , a storage device  143 , an input device  144 , an output device  145 , and an interface control unit  147 . 
     The CPU  141  is a processor that controls the entire management computer  140 , and reads various programs stored in the storage device  143  on the memory  142  to execute the read programs. The memory  142  is not only used to store the various programs read from the storage device  143  by the CPU  141  at the time of activating of the management computer  140  but also used as a work memory of the CPU  141 . 
     The storage device  143  is configured using, for example, an HDD or an SSD, and is used to store and hold various programs and control data. The input device  144  is configured using, for example, a keyboard switch, a pointing device, a microphone, or the like. The output device  145  is configured using, for example, a liquid crystal display or the like. 
     The interface control unit  147  is an adapter configured to connect the management computer  140  to the management network  160 . A storage management program  148  can transmit an operation request of a logical device to the control unit  122  of the first storage apparatus  120 , and control unit  132  of the second storage apparatus  130 , via the management network  160 . The storage management program  148  is read from the storage device  143  to the memory  142  by the CPU  141  and executed. 
       FIG. 2  is a block diagram illustrating a logical configuration of the computer system according to the first embodiment. A storage apparatus in the present embodiment is not limited to either the first storage apparatus  120  or the second storage apparatus  130 , and thus, is described as the storage apparatus  120  or  130 . 
     A virtual machine  210  is a virtual computer which is virtualized by the virtualization program  118  and to which some of computer resources of the host computer  110  are allocated. 
     A virtual volume (VVOL)  212  is a logical device provided to the virtual machine  210  by the virtualization program  118 , and is the unit in which the host computer  110  recognizes the SLU  217  (to be described later) of the storage apparatuses  120  and  130  as the logical device. 
     The virtualization program  118  reads an I/O request (read, write, or the like) from the virtual machine  210  to the VVOL  212  and issues an I/O command to the storage apparatuses  120  and  130 . The VVOL  212  and the SLU  217  are associated with each other via an LU  214  and an ALU  215  which will be described later. 
     The logical unit (LU)  214  is a unit obtained by dividing or aggregating storage areas provided by the storage device  121  in logical units. 
     The ALU  215  is a logical device which is recognized as a representative from the host computer  110  among the logical devices of the storage apparatuses  120  and  130 . The ALU  215  is managed in association with the SLU  217  of the storage apparatus  130 . 
     The SLU  217  is a logical device managed by an SLU ID that is an ID recognized by the host by virtualizing the logical devices of the storage apparatuses  120  and  130 , and is managed in association with the ALU  215 . The I/O command from the host computer  110  to the storage apparatuses  120  and  130  is issued while designating an identifier of the SLU  217 . 
       FIG. 3  is a schematic diagram illustrating an example of I/O processing during execution of test failover according to the first embodiment. 
     Incidentally, those attached with “-A” and “-B” in the drawing are the same as those described without being attached with “-A” and “-B” in  FIG. 2 , but are described to be distinguished for the sake of the description. 
     An I/O path  310  represents an example of processing an I/O request issued from a virtual machine  210 -A. The I/O request issued from the virtual machine  210 -A of a first host computer  110 -A to a VVOL  212 -A is transmitted to the first storage apparatus  120  via the SAN  150 . 
     At this time, the first storage apparatus  120  in which a LU 1 ( 214 -A) associated with the VVOL  212 -A of the first host computer  110 -A is defined receives this I/O request, and performs I/O processing on an SLU 1 ( 320 ) which is an SLU associated with an ALU 1 ( 215 -A), associated with the LU 1 ( 214 -A), and is associated with the VVOL  212 -A. 
     An attribute of this SLU 1 ( 320 ) is a remote copy primary volume (RC PVOL). 
     A remote copy path  311  represents an example of remote copy to copy data of the SLU 1 ( 320 ) of the first storage apparatus  120  to an SLU 2 ( 321 ) of the second storage apparatus  130 . 
     An attribute of the SLU 2 ( 321 ) of the second storage apparatus  130  is a remote copy secondary volume (RC SVOL). 
     An update content of the SLU 1 ( 320 ) of the first storage apparatus  120  is transferred from the first storage apparatus  120  to the second storage apparatus  130 , and is reflected on the SLU 2 ( 321 ) of the second storage apparatus  130 . 
     A snapshot creation path  312  is an example of copying data of the SLU 2 ( 321 ) of the second storage apparatus  130  to a snapshot volume (SS VOL)  322  which is another SLU in the second storage apparatus  130 . 
     The data of the SLU 2 ( 321 ) of the second storage apparatus  130  is copied to the SS VOL  322  at a preset timing such as every fixed time. At this time, it is possible to designate a different snapshot VOL for each copy. 
     Here, there is a case where test failover of the virtual machine  210 -A is performed using data of the SS VOL  322  without stopping the processing of the I/O path  310  and the remote copy path  311  from the virtual machine  210 -A under production running to the SLU 1 ( 320 ). 
     As a configuration example for implementing such a method, a description will be given with a configuration in which a virtual machine  210 -B of a second host computer  110 -B is designated as a failover destination, and the SS VOL  322  of the second storage apparatus  130  associated with a VVOL  212 -B is provided to the virtual machine  210 -B. 
     An I/O path  313  is an I/O path generated with reception of a “test failover execution command” instructing start of test failover by the second host computer  110 -B from the management computer  140 , as a trigger, and represents an example of processing an I/O request issued from the virtual machine  210 -B. 
     The I/O request issued from the virtual machine  210 -B of the second host computer  110 -B to the VVOL  212 -B is transmitted to the second storage apparatus  130  via the SAN  150 . 
     At this time, the second storage apparatus  130  in which a LU 2 ( 214 -B) associated with the VVOL  212 -B of the second host computer  110 -B is defined receives this I/O request, and performs I/O processing on the SS VOL  322  which is the SLU associated with an ALU 2 ( 215 -B), associated with the LU 2 ( 214 -B), and associated with the VVOL  212 -B. 
       FIG. 4  is a schematic diagram of I/O processing at the time of switching a remote copy direction according to the first embodiment. 
     There is a case where it is desired to operate the I/O path  313  as a positive site instead of the I/O path  310  during execution of the test failover as exemplified in  FIG. 3 . For example, it corresponds to a case where a failure occurs in the first host computer  110 -A. At this time, redundancy by remote copy from the second storage apparatus  130  to the first storage apparatus  120  is required instead of the remote copy path  311 . 
     A process in which the second storage apparatus  130  changes an I/O path and a remote copy path according to an instruction from the management computer  140  will be described. A combined path of an I/O path  410  and an I/O path  411  represents the same path as the I/O path  313  of  FIG. 3 . 
     A snapshot restoration path  412  represents a process executed with reception of a “remote copy resumption preparation command” instructing transition to an official failover state by the second storage apparatus  130  from the management computer  140  as a trigger, the process of copying the data of the SS VOL  322  created from the SLU 2 ( 321 ) of the second storage apparatus  130  to the SLU 2 ( 321 ) again. 
     Here, for example, when there is an updated area in the SS VOL  322  according to the I/O request issued from the virtual machine  210 -B, it is possible to shorten a copy time by copying only the area where the update has occurred to the SLU 2 ( 321 ). 
     An I/O path  413  represents a process at the time of changing the SLU that processes the I/O request from the virtual machine  210 -B from the SS VOL  322  to the SLU 2 ( 321 ). The change from the I/O path  411  to the I/O path  413  is performed by changing an ID of the SLU 2 ( 321 ) from  2000  to  3000  and changing an ID of the SS VOL  322  from  3000  to  2000  (details will be described later with reference to  FIG. 12 ). 
     A remote copy path  414  is a copy path of data set with reception of a “remote copy reconfiguration command” instructing resumption of remote copy in the reverse direction by the second storage apparatus  130  from the management computer  140  as a trigger, and represents an example of a remote copy process of copying the data of the SLU 2 ( 321 ) after restoring the snapshot to the SLU 1 ( 320 ) of the first storage apparatus  120 . 
     This resumption of remote copy is performed after changing the attribute of the SLU 2 ( 321 ) from the RC SVOL to the RC PVOL and changing the attribute of the SLU 1 ( 320 ) from the RC PVOL to the RC SVOL (details will be described later with reference to  FIG. 13 ). 
     After changing the attribute of the volume, an update content of the SLU 2 ( 321 ) is transferred from the second storage apparatus  130  to the first storage apparatus  120  and reflected on the SLU 1 ( 320 ). 
       FIG. 5  is an explanatory diagram illustrating a hierarchical structure of storage areas of the first storage apparatus  120  and the second storage apparatus  130  according to the first embodiment and the second embodiment. Although the first storage apparatus  120  will be described hereinafter, the second storage apparatus  130  also has the same hierarchical structure, and thus, will not be described. 
     The first storage apparatus  120  provides a storage area provided by the storage device  121  as a logical unit (LU)  530  to the host computer  110 . 
     In this case, a plurality of intermediate storage tiers, configured to associate the storage device  121  with the logical unit  530 , is provided between the storage device  121  and the logical unit  530 . The intermediate storage tier can include, for example, a RAID group  510  and a logical device (LDEV)  520 . 
     The RAID group  510  is an intermediate storage tier that connects the storage device  121  which is a lower storage tier and the logical device  520  which is an upper storage tier, and is defined on a storage area provided by each of the storage devices  121  constituting the RAID group. 
     The logical device  520  is an intermediate storage tier that connects the RAID group  510 , which is a lower storage tier, and the logical unit  530  that is an upper storage tier, and is a storage area configured by aggregating all or some of storage areas of one or a plurality of the RAID groups  510  or a storage area configured by extracting some of storage areas of the RAID group  510 . 
     The logical device  520  can have attributes of the ALU  215  and the SLU  217 . 
       FIG. 6  is an explanatory diagram illustrating program and table configurations in the nonvolatile memories  125  and  135  of the storage apparatuses  120  and  130  according to the first embodiment. 
     Since the first storage apparatus  120  and the second storage apparatus  130  have the same configuration, the description regarding the second storage apparatus  130  will not be given. 
     In  FIG. 6 , an SLU management table  601 , an LDEV management table  602 , a snapshot pair management table  603 , a remote copy pair management table  604 , an I/O request processing program  611 , a remote copy resumption preparation program  612 , and a remote copy resumption program  613  are stored in the nonvolatile memory  125 . The respective tables  601  to  604  and the respective programs  611  to  613  are transferred from the nonvolatile memory  125  to the main memory  124  and are executed by the CPU  123 . Incidentally, the respective tables  601  to  604  are set in advance by the management computer  140 . 
     In addition, the first storage apparatus  120  and the second storage apparatus  130  communicate with each other at a predetermined timing to update the remote copy pair management table  604 . For example, when the first storage apparatus  120  updates the remote copy pair management table  604 , the second storage apparatus  130  is notified of the update content. Alternatively, the management computer  140  may update the remote copy pair management table  604  at a predetermined timing. 
     The SLU management table  601  is a table configured to allow the CPU  123  of the first storage apparatus  120 , for example, to store a logical unit number (LUN), an ALU ID, an SLU ID, and an I/O queuing flag corresponding to a port for each of ports of the own storage apparatus. Details of this table will be described with reference to  FIG. 7 . 
     The LDEV management table  602  is a table configured to allow the CPU  123  of the first storage apparatus  120 , for example, to store an LDEV ID, an LDEV start address, and an LDEV end address for each of the SLUs defined in the own storage apparatus. Details of this table will be described with reference to  FIG. 8 . 
     The snapshot pair management table  603  is a table configured to allow the CPU  123  of the first storage apparatus  120 , for example, to store an LDEV ID of a snapshot creation source, an LDEV ID of a snapshot volume, and a pair state for each of snapshot pairs defined in the own storage apparatus. Details of this table will be described with reference to  FIG. 9 . 
     The remote copy pair management table  604  is a table configured to allow the CPU  123  of the first storage apparatus  120 , for example, to store an LDEV ID, a volume attribute, an LDEV ID of a partner forming a remote copy pair, and a storage apparatus ID of a partner forming a remote copy pair for each of remote copy pairs defined in the own storage apparatus. Details of this table will be described with reference to  FIG. 10 . 
     The I/O request processing program  611  is a program configured to cause the CPU  123  of the first storage apparatus  120  to process a command that requests I/O processing of data received from the host computer  110  (a read command, a write command, or the like). Details of this program will be described with reference to  FIG. 11 . 
     The remote copy resumption preparation program  612  is a program configured to cause the CPU  123  of the first storage apparatus  120  to process a command requesting remote copy resumption preparation for a snapshot volume received from the management computer  140 . Details of this program will be described with reference to  FIG. 12 . 
     The remote copy resumption program  613  is a program configured to cause the CPU  123  of the first storage apparatus  120  to copy data of an SLU of the own storage apparatus to an SLU in a different storage apparatus. Details of this program will be described with reference to  FIG. 13 . 
     Hereinafter, the respective tables stored in a nonvolatile memory  146  of the second storage apparatus  130  of the present invention will be described with reference to  FIGS. 7 to 10 . 
       FIG. 7  is a table illustrating an example of the SLU management table  601  according to the first embodiment. 
     The SLU management table  601  manages, for example, a port ID column  701 , a LUN column  702 , an ALU ID column  703 , an SLU ID column  704 , and an I/O queuing flag column  705  in association with each other. 
     In the port ID column  701 , identification information of the ports  128  and  138  defined in the own storage apparatus is stored. In the LUN column  702 , a LUN which is identification information of the LU  214  is stored. 
     In the ALU ID column  703 , identification information of the ALU  215  is stored. In the SLU ID column  704 , identification information (virtual ID) of the SLU  217  defined for each ALU is stored. 
     In the I/O queuing flag column  705 , information indicating whether or not to take I/O for the SLU out of a queue is stored. Queuing continues without taking the I/O out of the queue if a queuing flag is ON. If the queuing flag is OFF, it indicates that the I/O can be taken out of the queue. Incidentally, the queue is set in advance in predetermined areas of the cache memories  126  and  136 . 
     For example, a row  711  indicates that an SLU ID “1000” is associated with an ALU ID “000”, a LUN “00”, and a port ID “00”, and the I/O queuing flag of the SLU is “OFF”. 
       FIG. 8  is a table illustrating an example of the LDEV management table  602  according to the first embodiment. 
     The LDEV management table  602  manages, for example, an SLU ID column  801 , an LDEV ID column  802 , an LDEV start address column  803  column, and an LDEV end address column  804  in association with each other. 
     In the SLU ID column  801 , identification information (virtual ID) of an SLU defined in the own storage apparatus is stored. In the LDEV ID column  802 , identification information of an LDEV associated with the SLU is stored. 
     In the LDEV start address column  803 , start address information of an area of the LDEV associated with the SLU is stored. In the LDEV end address column  804 , end address information of the area of the LDEV associated with the SLU is stored. 
     For example, a row  811  indicates that an LDEV ID associated with an SLU ID “2000” is “2222”, a start address and an end address of an area of the LDEV are “020000” and “020999”, respectively. 
       FIG. 9  is a table illustrating an example of the snapshot pair management table  603  according to the first embodiment and the second embodiment. 
     The snapshot pair management table  603 , for example, manages a pair ID column  901 , a snapshot creation source LDEV ID column  902 , a snapshot volume LDEV ID column  903 , and a pair state column  904  in association with each other. 
     In the pair ID column  901 , identification information of a snapshot pair defined in the own storage apparatus is stored. In the snapshot creation source LDEV ID column  902 , identification information of an LDEV of a volume serving as a snapshot creation source of the snapshot pair is stored. 
     In the snapshot volume LDEV ID column  903 , identification information of an LDEV of a snapshot volume forming a pair relationship with the snapshot creation source LDEV is stored. In the pair state column  904 , information on a copy pair state (PAIR (duplication), Suspend (division), or the like) of the snapshot pair is stored. 
     For example, a row  911  indicates that a snapshot creation source LDEV ID of a snapshot pair ID “1-1” is “2222”, an LDEV ID of a snapshot volume is “3333”, and a pair state is “Suspend (division)”. 
     In a different example of the drawing, it is indicated that the SLU 2 (LDEV ID 902=2222) and the SS VOL  322  (LDEV ID 902=3333) of the second storage apparatus  130  in  FIG. 3  are in a relationship of a copy pair. Incidentally, the copy pair defines a relationship of replication between different logical devices. 
       FIG. 10  is a table illustrating an example of the remote copy pair management table  604  according to the first embodiment and the second embodiment. 
     The remote copy pair management table  604  manages, for example, a pair ID column  1001 , an LDEV ID column  1002 , an pair attribute column  1003 , a pair partner LDEV ID column  1004 , and a pair partner storage apparatus ID column  1005  in association with each other. 
     In the pair ID column  1001 , identification information of a remote copy pair defined in the own storage apparatus is stored. In the LDEV ID column  1002 , identification information of an LDEV of the own storage apparatus side of the remote copy pair is stored. 
     In the pair attribute column  1003 , information on a remote copy pair attribute (PVOL or SVOL) of the LDEV is stored. In the pair partner LDEV ID column  1004 , identification information of an LDEV of a remote copy partner of the LDEV is stored. 
     In the pair partner storage apparatus ID column  1005 , identification information of a storage apparatus of the remote copy partner of the LDEV is stored. 
     For example, a row  1011  indicates that an LDEV ID of the own storage apparatus side of a remote copy pair ID “1” is “2222”, a pair attribute of the LDEV is “SVOL”, and an LDEV ID of a remote copy partner of the LDEV is “1111”, and a storage apparatus ID of the remote copy partner is “ST01”. 
     Incidentally, the remote copy pair defines a relationship of replication of a logical device between different storage apparatuses (the first storage apparatus  120  and the second storage apparatus  130 ). 
     Hereinafter, various kinds of processing performed in the first embodiment will be described in detail with reference to  FIGS. 11 to 13 . Each flowchart illustrates an outline of each processing within a range necessary for understanding and implementing the present invention, but the order of processes may be not necessarily limited to the illustrated order. 
       FIG. 11  is a flowchart illustrating processing performed by the I/O request processing program  611  according to the first embodiment. 
     This processing is started with reception of write request by the first storage apparatus  120  and the second storage apparatus  130  from the host computer  110  as a trigger. 
     Hereinafter, an example in which the first storage apparatus  120  receives the write request will be described. In Step S 1101 , the I/O request processing program  611  analyzes an SCSI command, issued from the host computer  110  and stored in the queue, and acquires a port ID, a LUN, an ALU ID, and an SLU ID which are designated as I/O destinations. 
     In Step S 1102 , the I/O request processing program  611  searches the “SLU ID” column  704  in the SLU management table  601  for the SLU ID acquired in Step S 1101 , and acquires a value of the corresponding “I/O queuing flag” column  705 . 
     In Step S 1103 , the I/O request processing program  611  ends the processing when the value of the “I/O queuing flag” column  705  acquired in Step S 1102  is ON (S 1103 : YES), and the processing transitions to Step S 1104  when the value is OFF (S 1103 : NO). 
     In Step S 1104 , when it is determined as NO in Step S 1103 , the I/O request processing program  611  acquires a request from the queued host computer  110  and performs write processing to the SLU 1 ( 320 ). 
     When the remote copy from the SLU 1 ( 320 ) to the SLU 2 ( 321 ) of the second storage apparatus  130  is asynchronous remote copy, the I/O request processing program  611  writes update data, as a journal, to a journal volume after completing the writing processing to the SLU 1 ( 320 ), and transitions to Step S 1105 . 
     Even after the transition to Step S 1105 , the journal written in the journal volume of the first storage apparatus  120  is asynchronously copied to a journal volume of the second storage apparatus  130  via the WAN  170  and the copied journal is reflected on the SLU 2 ( 321 ). 
     When the remote copy from the SLU 1 ( 320 ) to the SLU 2 ( 321 ) of the second storage apparatus  130  is synchronous remote copy, the I/O request processing program  611  transfers update data from the SLU 1 ( 320 ) to the SLU 2 ( 321 ) after completion of the write processing to the SLU 1 ( 320 ), and transitions to Step S 1105  after receiving a response indicating that the transferred update data has been reflected on the SLU 2 ( 321 ). 
     In Step S 1105 , the I/O request processing program  611  makes a response with respect to the SCSI command, which is the request from the host computer  110  taken out of the queue, to indicate that the write processing has been completed. 
     In Step S 1106 , the I/O request processing program  611  transitions to Step S 1104  and repeats the above-described processes if it is a state where the request from the host computer  110  is queued in the first storage apparatus  120  (S 1106 : YES), and ends the processing if there is no queued request. 
     Although the example of controlling the extraction from the stored queue when receiving the I/O request based on the value (ON/OFF) of the “I/O queuing flag” column  705  of the SLU management table  601  has been illustrated in the present embodiment, another queue storing an I/O request may be used when the value of the “I/O queuing flag” column  705  is ON, or other queue management methods may be used. 
       FIG. 12  is a flowchart illustrating processing performed by the remote copy resumption preparation program  612  according to the first embodiment. 
     In the first embodiment, this processing is performed with reception of the “remote copy resumption preparation command” for the SS VOL  322  by the second storage apparatus  130  from the management computer  140  as a trigger. 
     In Step S 1201 , the remote copy resumption preparation program  612  receives the remote copy resumption preparation command from the management computer  140 . 
     In Step S 1202 , the remote copy resumption preparation program  612  acquires an SLU ID of the SS VOL  322  which is a snapshot VOL from the remote copy resumption preparation command received from the management computer  140 . 
     In Step S 1203 , the remote copy resumption preparation program  612  searches the “SLU ID” column  801  of the LDEV management table  602  for the SLU ID of the SS VOL  322  acquired in S 1202 , and acquires a value of the “LDEV ID” column  802  corresponding to a search result. 
     In Step S 1204 , the remote copy resumption preparation program  612  searches the “snapshot VOL LDEV ID” column  903  of the snapshot pair management table  603  for the LDEV ID of the SS VOL  322  acquired in S 1203 , and acquires a value of the “snapshot creation source LDEV ID” column  902  corresponding to a search result as an LDEV ID of the SLU 2 ( 321 ). 
     In addition, the remote copy resumption preparation program  612  searches the “LDEV ID” column  802  of the LDEV management table  602  for the LDEV ID of the SLU 2 ( 321 ) acquired as above, and acquires a value of the “SLU ID” column  801  corresponding to a search result. This value is used in Step S 1209 . 
     In Step S 1205 , the remote copy resumption preparation program  612  searches the “LDEV ID” column  1002  of the remote copy pair management table  604  for the LDEV ID of the SLU 2 ( 321 ) acquired in Step S 1204 , and verifies that the corresponding row exists (that is, the SLU 2 ( 321 ) has already configured a remote copy pair). Incidentally, the processing is ended when the SLU ( 321 ) has not configured a remote copy pair. 
     In Step S 1206 , the remote copy resumption preparation program  612  searches the “SLU ID” column  704  of the SLU management table  601  for the SLU ID of the SS VOL  322  specified in Step S 1202 , and changes a value of the “I/O queuing flag” column  705  corresponding to a search result to ON. 
     In Step S 1207 , the remote copy resumption preparation program  612  kicks off a snapshot restoration process from the SS VOL  322  specified in Step S 1202  to the SLU 2 ( 321 ) specified in Step S 1204 , and transitions to Step S 1208 . In the snapshot restoration process performed in the background with the kick-off as a trigger, only differential data between the SS VOL  322  and the SLU 2 ( 321 ) is copied. 
     In Step S 1208 , the remote copy resumption preparation program  612  updates one whose value is the SLU ID of the SS VOL  322  to the SLU ID of the SLU 2 ( 321 ) and updates one whose value is the SLU ID of the SLU 2 ( 321 ) to the SLU ID of the SS VOL  322  for the “SLU ID” column  801  of the LDEV management table  602 , thereby interchanging the values. 
     Due to this change of the SLU ID column  801 , the I/O request of the virtual machine  210 -B illustrated in  FIG. 4  is changed from the I/O path  411  to the I/O path  413  and transmitted to the SLU 2 ( 321 ). 
     In Step S 1209 , the remote copy resumption preparation program  612  searches the “SLU ID” column  704  of the SLU management table  601  for the SLU ID of the SS VOL  322  specified in Step S 1202  (the SLU ID of the SLU 2 ( 321 ) after interchanging the SLU IDs), and changes a value of the “I/O queuing flag” column  705  corresponding to a search result to OFF. 
     In Step S 1210 , the remote copy resumption preparation program  612  notifies the management computer  140  of a response indicating that the processing of the remote copy resumption preparation command has been completed, and ends the processing. 
     As a result of the above processing, in the second storage apparatus  130 , the remote copy resumption preparation program  612  changes the value of the I/O queuing flag column  705  of the SS VOL  322  being accessed by the virtual machine  210 -B to ON, and interchanges the SLU IDs of the SS VOL  322  and the SLU 2 ( 321 ) after stopping the issuance of the I/O request, whereby the I/O path  411  is switched to the I/O path  413 . 
     Then, the remote copy resumption preparation program  612  kicks off the snapshot restoration process after the start of queuing to execute the process in the background. As a result, only the differential data is copied from the SS VOL  322  to the SLU 2 ( 321 ), and the snapshot restoration process is executed. 
     Thereafter, the remote copy resumption preparation program  612  changes the value of the I/O queuing flag column  705  of the SLU 2 ( 321 ) to OFF, thereby transferring the I/O request issued by the virtual machine  210 -B to the SLU 2 ( 321 ). As a result, the logical volume to be read or written by the virtual machine  210 -B is switched from the SS VOL  322  to the SLU 2 ( 321 ). Incidentally, there is a case where the snapshot restoration process is continued even after the end of queuing. 
       FIG. 13  is a flowchart illustrating processing performed by the remote copy resumption program  613  in the first embodiment. 
     In the first embodiment, this processing is performed with reception of a “remote copy resumption (reverse direction) command” by the remote copy resumption program  613  of the second storage apparatus  130  from the management computer  140  as a trigger. 
     In Step S 1301 , the remote copy resumption program  613  receives the remote copy resumption (reverse direction) command from the management computer  140 . 
     In Step S 1302 , the remote copy resumption program  613  acquires the SLU ID of the SLU 2 ( 321 ), which is the RC SVOL, from the remote copy resumption (reverse direction) command received from the management computer  140 . 
     Here, the SLU ID included in the remote copy resumption (reverse direction) command received from the management computer  140  by the remote copy resumption program  613  in Step S 1301  and the SLU ID included in the remote copy resumption preparation command received from the management computer  140  by the remote copy resumption preparation program  612  in Step S 1201  of  FIG. 12  are the same values. However, since the IDs of the SLU 2 ( 321 ) and SS VOL ( 322 ) are interchanged in Step S 1207  of  FIG. 12 , the SLU indicated by this SLU ID is the value changed from SS VOL  322  to the SLU 2 ( 321 ). 
     In Step S 1303 , the remote copy resumption program  613  searches the “SLU ID column”  801  of the LDEV management table  602  for the SLU ID of the SLU 2 ( 321 ) acquired in Step S 1302 , and acquires the value of the “LDEV ID” column  802  corresponding to a search result. 
     In Step S 1304 , the remote copy resumption program  613  searches the “LDEV ID” column  1002  of the remote copy pair management table  604  possessed by the second storage apparatus  130  for an LDEV ID corresponding to the SLU 2 ( 321 ) acquired in S 1303 , and changes a value of the “pair attribute” column  1003  corresponding to a search result from SVOL to PVOL. 
     In addition, the remote copy resumption program  613  instructs the first storage apparatus  120  to change the value of the “pair attribute” column  1003  of the row having the same pair ID in the remote copy pair management table  604  from PVOL to SVOL. 
     In Step S 1305 , the remote copy resumption program  613  executes differential copy from the SLU 2 ( 321 ) to the SLU 1 ( 320 ). Specifically, the remote copy from the SLU 1 ( 320 ) to the SLU 2 ( 321 ) is divided, and then, processing is performed to copy only the data of an area where update has occurred in the SLU 2 ( 321 ) from the SLU 2 ( 321 ) to the SLU 1 ( 320 ). 
     In Step S 1306 , the remote copy resumption program  613  notifies the management computer  140  of a response indicating the completion of resumption of the remote copy, and ends the process. Incidentally, the processing in this step may be performed at a predetermined timing, for example, after the end of S 1304  and before the start of S 1305 . 
     Through the above processing, the relationship between the copy pair of the first storage apparatus  120  and the second storage apparatus  130  is reversed, and remote copy is performed from the SLU 2 ( 321 ) of the second storage apparatus  130  to the SLU 1 ( 320 ) of the first storage apparatus  120 . 
       FIG. 19  is a sequence diagram illustrating an example of processing performed in the entire computer system from the test failover to the remote copy resumption. 
     In the first host computer  110 -A, the virtual machine  210 -A operates on the primary site (active system). When the virtual machine  210 -A performs write to the first storage apparatus  120  (S 1 ), the data written in the SLU 1 ( 320 ) is remotely copied to the SLU 2 ( 321 ) of the second storage apparatus  130  which is a remote copy pair (S 2 ). 
     Next, the management program  148  of the management computer  140  transmits an instruction for a test failover to the virtual machine  210 -B of the second host computer  110 -B (S 3 ). The virtual machine  210 -B operating on the secondary site (standby system) causes the second storage apparatus  130  to generate the snapshot volume (SS VOL  322 ) of the SLU 2 (S 4 ), and performs a failover test using the SS VOL  322  (S 5 ). 
     Incidentally, when generating the SS VOL  322 , the second storage apparatus  130  sets a virtual ID (SLU ID) of the corresponding logical device, and causes the virtual machine  210 -B issuing the I/O request to recognize the virtual ID. 
     In the virtual machine  210 -B, a failure occurs in the virtual machine  210 -A of the primary site during execution of the test failover (S 6 ). When detecting that the failure has occurred in the virtual machine  210 -A, the management computer  140  transmits an instruction to switch from the test failover to an official failover to the virtual machine  210 -B of the secondary site (S 7 ). Then, the management computer  140  transmits a resumption preparation command for remote copy to the second storage apparatus  130  constituting the standby system (S 8 ). 
     The second storage apparatus  130  starts queuing of the SS VOL  322  to inhibit the SS VOL  322  from being updated (S 9 ), and then, the second storage apparatus  130  interchanges the SLU IDs of the SS VOL  322  and the SLU 2 ( 321 ) to switch the SLU to be accessed by the virtual machine  210 -B to the SLU 2 ( 321 ) of the copy pair S-VOL (S 10 ). In addition, the snapshot restoration process is executed in the background (S 11 ), and the differential data between the SS VOL  322  and the SLU 2 ( 321 ) is copied to the SLU 2 ( 321 ). 
     Next, the second storage apparatus  130  ends the queuing and permits an access to the SLU 2 ( 321 ) of the virtual machine  210 -B (S 12 ). The second storage apparatus  130  notifies the management computer  140  of the completion of preparation for resuming the remote copy (S 13 ). Incidentally, there is a case where the snapshot restoration process continues even after the queuing ends as described above. 
     When receiving the completion of preparation for resuming the remote copy, the management program  148  of the management computer  140  transmits the remote copy resumption command to the second storage apparatus  130  (S 14 ). 
     The remote copy resumption program  613  of the second storage apparatus  130  changes the pair attribute column  1003  of the SLU 2 ( 322 ) from SVOL to PVOL in the remote copy pair management table  604  (S 15 ). Next, the remote copy resumption program  613  instructs the first storage apparatus  120  to change the pair attribute of the SLU 1 ( 320 ), which is a copy pair of the SLU 2 ( 322 ), from PVOL to SVOL (S 16 ). 
     Then, the remote copy resumption program  613  copies a differential between SLU 2 ( 322 ) and SLU 1 ( 320 ) to the SLU 1 ( 320 ) (S 17 ). When the differential copy has been completed, the remote copy resumption program  613  notifies the management computer  140  that the resumption of the remote copy has been completed (S 18 ). Thereafter, when receiving write from the virtual machine  210 -B, the second storage apparatus  130  performs remote copy of the data written in the SLU 2 ( 322 ) to the SLU 1 ( 320 ). 
     As described above, when the failure occurs during the test failover in the first embodiment, the second storage apparatus  130  stops the I/O request to the snapshot (SS VOL), which has been used by the standby virtual machine  210 -B, writes the differential from the snapshot to the SLU 2 ( 322 ) which is the SVOL of the remote copy, and then, interchanges IDs of the snapshot and the SLU 2 to switch a path of a volume to be written by the virtual machine  210 -B. 
     Next, the second storage apparatus  130  permits the I/O request from the virtual machine  210 -B to the SLU 2, switches the relationship between the PVOL and the SVOL of the SLU 1 ( 320 ) of the first storage apparatus  120  in the relationship of the copy pair with the SLU 2 of the second storage apparatus  130 , and then, performs the differential copy to restore the SLU 1. 
     In the first embodiment, it is unnecessary to perform full copy from the SS VOL, which has been used in the test failover, to the PVOL of the first storage apparatus  120  as in the above-described related art, and it is sufficient if the differential copy and the switching of the SLU IDs, and the switching of the remote copy direction are performed, and thus, it is possible to shorten the time required for the failover. In other words, it is possible to implement the remote copy in the reverse direction from the snapshot of the secondary site to the logical device of the primary site, which does not constitute the remote copy pair, at high speed without performing the entire area copy. 
     Second Embodiment 
     A second embodiment of the present invention will be described with reference to  FIGS. 14 to 18 . 
       FIG. 14  is a block diagram illustrating an example of a logical configuration of the computer system in the second embodiment. A physical configuration is the same as that of the first embodiment of  FIG. 1 . The host computer  110 , the HBA  116 , the port  127 , the storage apparatuses  120  and  130 , the SAN  150 , the virtual machine  210 , and the LU  214  in the second embodiment are the same as those in  FIGS. 1 and 2  of the first embodiment, and thus, the description thereof will not be given. 
     The virtual logical device  1410  is a unit in which the host computer  110  recognizes the LU  214  of the storage apparatuses  120  and  130 . In the second embodiment, a plurality of the virtual machines  210  in the same host computer  110  can share a virtual logical device  1410 . 
     An I/O request (read, write, or the like) from the virtual machine  210  to the virtual logical device  1410  is issued as an I/O command to the storage apparatuses  120  and  130 . 
     LDEVs  1420  of the first storage apparatus  120  and the second storage apparatus  130  are logical devices of the storage apparatuses  120  and  130 . The LDEV  1420  is managed using an LDEV ID recognized by the host computer  110  or a virtual LDEV ID which is a virtual ID, and an example where the LDEV  1420  is managed using the virtual LDEV ID is illustrated in the second embodiment. The LDEV  1420  is managed in association with the LU  214  by (to be described later) a virtual LDEV management table  1600 . 
       FIG. 15  is a conceptual diagram of processing performed in I/O processing at the time of switching a remote copy direction according to the second embodiment. A description will be given focusing on a difference from  FIG. 4  which is the schematic diagram of the I/O processing at the time of switching the remote copy direction according to the first embodiment. 
     An I/O request issued from the virtual machine  210 -B of the second host computer  110 -B to a virtual logical device  1420 -B is transmitted to the second storage apparatus  130  via the SAN  150 . 
     At this time, the second storage apparatus  130  having a SS VOL  1522  associated with a virtual logical device  1420 -B receives this I/O request and performs I/O processing with respect to the SS VOL  1522 . 
     The second storage apparatus  130  changes an I/O path from an I/O path  1512  to an I/O path  1513  according to an instruction from the management computer  140 . Specifically, it is performed after changing an ID of the LDEV 2 ( 1521 ) from  2000  to  3000  and changing an ID of the SS VOL  1522  from  3000  to  2000  (details will be described later with reference to  FIG. 18 ). 
     The processing and execution triggers of a snapshot restoration path  1514  and a remote copy path  1515  are the same as those of the snapshot restoration path  412  and the remote copy path  414  of  FIG. 4 . The processing and execution triggers will not be described since the description can be made by replacing the SLU 1 ( 320 ) and the SLU 2 ( 321 ) of  FIG. 4  with the LDEV 1 ( 1520 ) and the LDEV 2 ( 1521 ). 
       FIG. 16  is a table illustrating an example of the virtual LDEV management table  1600  according to the second embodiment. 
     The virtual LDEV management table  1600  manages, for example, a port ID column  1601 , a LUN column  1602 , a virtual LDEV ID column  1603 , and an I/O queuing flag column  1604  in association with each other. 
     In the virtual LDEV ID column  1603 , identification information (virtual ID) of an LDEV virtually assigned to an LDEV defined in the own storage apparatus is stored. 
     In addition, the port ID column  1601 , the LUN column  1602 , and the I/O queuing flag column  1604  are the same as the port ID column  701 , the LUN column  702 , and the I/O queuing flag column  705  of  FIG. 7  of the first embodiment, and thus, will not be described. 
     For example, in a row  1611 , a virtual LDEV ID “1000” is associated with a LUN “00” and a port ID “00”, and it is indicated that the I/O queuing flag of the LDEV is “OFF”. 
       FIG. 17  is a table illustrating an example of a virtual LDEV-actual LDEV management table  1700  according to the second embodiment. 
     The virtual LDEV-actual LDEV management table  1700  manages, for example, a virtual LDEV ID  1701  column, an LDEV ID column  1702 , an LDEV start address column  1703  column, and an LDEV end address column  1704  in association with each other. 
     In the virtual LDEV ID column  1701 , identification information (virtual ID) of the LDEV virtually assigned to the LDEV defined in the own storage apparatus is stored. 
     In addition, the LDEV ID column  1702 , the LDEV start address column  1703  column, and the LDEV end address column  1704  are the same as the LDEV ID column  802 , the LDEV start address column  803 , and the LDEV end address column  804  in  FIG. 8 , and thus, will not be described. 
     For example, a row  1711  indicates that an LDEV ID associated with a virtual LDEV ID “2000” is “2222”, a start address and an end address of an area of the LDEV are “020000” and “020999”, respectively. 
       FIG. 18  is a flowchart illustrating an example of processing performed by a remote copy resumption preparation program  1800  according to the second embodiment. 
     In the second embodiment, this processing is performed with reception of a “remote copy resumption preparation command” for the SS VOL  1522  by the second storage apparatus  130  from the management computer  140  as a trigger. 
     In Step S 1801 , the remote copy resumption preparation program  1800  receives the remote copy resumption preparation command from the management computer  140 . In Step S 1802 , the remote copy resumption preparation program  1800  acquires an LDEV ID of the SS VOL  1522  which is a snapshot VOL from the remote copy resumption preparation command received from the management computer  140 . 
     In Step S 1803 , the remote copy resumption preparation program  1800  searches the “virtual LDEV ID” column  1701  of the virtual LDEV-actual LDEV management table  1700  for the LDEV ID of the SS VOL  1522  acquired in Step S 1802 , and acquires a value of the “LDEV ID” column  1702  corresponding to a search result. 
     In Step S 1804 , the remote copy resumption preparation program  1800  searches the “snapshot VOL LDEV ID” column  903  of the snapshot pair management table  603  for the LDEV ID of the SS VOL  1522  acquired in Step S 1803 , and acquires a value of the “snapshot creation source LDEV ID” column  902  corresponding to a search result as an LDEV ID of the LDEV 2 ( 1521 ). 
     In addition, the remote copy resumption preparation program  1800  searches the “virtual LDEV ID” column  1701  of the virtual LDEV-actual LDEV management table  1700  for the LDEV ID of the LDEV 2 ( 1521 ) acquired as above, and acquires a value of the “LDEV ID” column  1702  corresponding to a search result. This value is used in Step S 1809 . 
     In Step S 1805 , the remote copy resumption preparation program  1800  searches the “LDEV ID” column  1002  of the remote copy pair management table  604  for the LDEV ID of LDEV 2 ( 1521 ) acquired in Step S 1804 , and verifies that the corresponding row exists (that is, the LDEV 2 ( 1521 ) has already configured a remote copy pair). 
     In Step S 1806 , the remote copy resumption preparation program  1800  searches the “virtual LDEV ID” column  1603  of the virtual LDEV management table  1600  for the LDEV ID of the SS VOL  1522  specified in Step S 1802 , and changes a value of the corresponding “I/O queuing flag” column  1604  to ON. 
     In Step S 1807 , the remote copy resumption preparation program  1800  kicks off a snapshot restoration process from the SS VOL  1522  specified in Step S 1802  to the LDEV 2 ( 1521 ) specified in Step S 1804 , and transitions to Step S 1808 . In the snapshot restoration process performed in the background with the kick-off as a trigger, only differential data between the SS VOL  1522  and the LDEV 2 ( 1521 ) is copied. 
     In Step S 1808 , the remote copy resumption preparation program  1800  updates one whose value is the LDEV ID of SS VOL  1522  to the LDEV ID of LDEV 2 ( 1521 ) and updates one whose value is LDEV 2 ( 1521 ) to the LDEV ID of the SS VOL  1522  for the “virtual LDEV ID” column  1701  of the virtual LDEV-actual LDEV management table  1700 , thereby interchanging the IDs. As a result, the I/O path is switched from the I/O path  1512  to the I/O path  1513 . 
     In Step S 1809 , the remote copy resumption preparation program  1800  searches the “virtual LDEV ID” column  1603  of the virtual LDEV management table  1600  for the LDEV ID of the SS VOL  1522  specified in S 1802  (the LDEV ID of LDEV 2 ( 1521 ) after interchanging of the LDEV IDs), and changes a value of the “I/O queuing flag” column  1604  corresponding to a search result to OFF. 
     In Step S 1810 , the remote copy resumption preparation program  1800  notifies the management computer  140  of a response indicating that the the processing of the remote copy resumption preparation command has been completed, and ends the processing. 
     As described above, when a failure occurs during a test failover in the second embodiment, the write to the snapshot (SS VOL) that has been used by the standby virtual machine  210 -B is stopped, and the virtual IDs (virtual LDEV IDs) of the snapshot and the LDEV 2 are interchanged to switch a path of a volume to be written by the virtual machine  210 -B. In addition, the snapshot restoration process is executed in the background, and a differential from snapshot (SS VOL) is written to the LDEV 2 ( 1521 ) which is the SVOL of the remote copy. Next, the I/O request from the virtual machine  210 -B to the LDEV 2 is permitted, the relationship between the PVOL and SVOL of the LDEV 1 of the first storage apparatus  120  having the relationship of the copy pair with the LDEV 2 of the second storage apparatus  130  is switched, and then, differential copy is performed to restore the LDEV 1. Incidentally, there is a case where the snapshot restoration process is continued even after the end of queuing. 
     In the second embodiment, it is also unnecessary to perform full copy from the SS VOL, which has been used in the test failover, to the PVOL of the first storage apparatus  120  as in the above-described related art, and it is sufficient if the differential copy and the switching of the IDs of the LDEV 2, and the switching of the remote copy direction are performed, and thus, it is possible to shorten the time required for recovery from the failover even when the virtual LDEV is adopted as the logical device. 
     Although the embodiments of the present invention have been described as above, the present invention is not limited to these embodiments, and, of course, can be modified in various ways within a scope not departing from a gist thereof. For example, in the first or second embodiment, the remote copy resumption program  613  may be executed continuously after executing the remote copy resumption preparation program  612  except for the completion response in S 1210  with reception of one command, which is a combination of information of two commands of the remote copy pair resumption preparation command and the remote copy pair resumption (reverse direction) by the second storage apparatus  130  from the management computer  140  as a trigger. 
     In addition, in the first or second embodiment, each step of the remote copy resumption preparation program  612  and the remote copy resumption program  613  may be executed respectively with reception of different commands from the management computer  140  as a trigger. For example, a response may be made to the management computer  140  after executing S 1202  to S 1205  and the processes of S 1206 , S 1207 , S 1208 , and S 1209  may be executed with reception of mutually different commands in the remote copy resumption preparation program  612 , and a response may be made to the management computer  140  after executing S 1302  to S 1304  and the process of S 1305  may be executed with reception of a different command in the remote copy resumption program  613 . 
     In addition, in the first or second embodiment, it is possible to consider a configuration, as one of modifications, in which a part or the whole of the storage apparatus is not included since a virtual machine in a server in a host computer serves a role as a host computer, and each program and each table of the first storage apparatus  120  and the second storage apparatus  130  operate in the host computer. 
     Incidentally, the present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail in order to describe the present invention in an easily understandable manner, and are not necessarily limited to those including the entire configuration that has been described above. In addition, some configurations of a certain embodiment can be substituted by configurations of another embodiment, and further, a configuration of another embodiment can be also added to a configuration of a certain embodiment. In addition, addition, deletion, or replacement of other configurations can be applied alone or in combination for a part of the configuration of each embodiment. 
     In addition, a part or all of each of the above-described configurations, functions, processing units, processing means, and the like may be realized, for example, by hardware by designing with an integrated circuit and the like. In addition, each of the above-described configurations, functions, and the like may also be realized by software by causing a processor to interpret and execute a program for realizing each of the functions. Information such as programs, tables, and files that realize the respective functions can be installed in a recording device such as a memory, a hard disk, and a solid state drive (SSD), or a recording medium such as an IC card, an SD card, and a DVD. 
     In addition, only control lines and information lines considered to be necessary for the description have been illustrated, and all of the control lines and information lines required as a product are not necessarily illustrated. It may be considered that most of configurations are practically connected to each other.