Abstract:
Provided is a copy pair monitoring method which is for a storage system having at least one host computer, at least one storage subsystem, and a management computer, the storage subsystem including volumes storing data requested by the host computer to be written, the management computer being accessible to the host computer and the storage subsystem. The copy pair monitoring method is characterized by including the steps of: obtaining every piece of copy pair definition information that is stored in the host computer; removing duplicate copy pair definition information from the whole copy pair definition information obtained; and collecting the copy pair status based on the obtained copy pair definition information from which duplicate copy pair definition information has been removed.

Description:
CLAIM OF PRIORITY 
       [0001]    The present application claims priority from Japanese patent application 2006-239929 filed on Sep. 5, 2006, the content of which is hereby incorporated by reference into this application. 
       BACKGROUND 
       [0002]    This invention relates to a storage system composed of a host computer, a storage subsystem and a management computer and, more specifically, a technique of monitoring copy pairs. 
         [0003]    The development of information-oriented society has resulted in the introduction of computer systems everywhere, and the amount of data processed by individual computer systems is growing at an explosive rate. Another result of the advance of information-oriented society is the enhanced importance given to data that is handled by computer systems and data stored in computer systems is demanded to be high in reliability. Data stored in computer systems has to be protected against all kinds of disaster, and it is a responsibility to society to prevent the loss of data stored in computer systems. 
         [0004]    Such the computer systems ensure data reliability by storing the same data in multiple volumes. Data outputted from a host computer which executes processing is not only stored in a volume within a storage subsystem that is connected directly to the host computer but also copied to another volume to be duplicated. 
         [0005]    Copy between a source volume and a target volume that are in the same storage subsystem is commonly called local copy, whereas copy between a source volume and a target volume that are in different storage subsystems is called remote copy. Local copy and remote copy are employed in computer systems that are required to have high reliability. 
         [0006]    Local copy and remote copy are collectively called replication. Replication enables a computer system to continue operating when a failure in one volume renders this volume inoperative with the use of data stored in the other volume. 
         [0007]    Two volumes associated with each other by replication, that is, a source volume and a target volume, are called a copy pair. The host computer stores definition information of volumes forming a copy pair to operate the copy pair and obtains information on the status of the copy pair based on the definition information. 
         [0008]    For example, US 2005/114467 A discloses techniques which allow a host computer to obtain replication status information of a remote site storage subsystem that is not directly connected to the host computer. 
       SUMMARY 
       [0009]    Monitoring of the copy pair status is important in order for the host computer to check whether replication operation is running properly. 
         [0010]    For instance, an application administrator such as a data base management system (DBMS) monitors copy pairs formed from volumes that are used by the application he/she manages. A storage administrator monitors copy pairs constituted of volumes in storage subsystems he/she manages. 
         [0011]    It is common in this case that some copy pairs are monitored by the application administrator and the storage administrator both. Accordingly, monitoring one storage system separately by an application administrator and a storage administrator results in an unnecessary workload on storage subsystems. 
         [0012]    There are two types of copy pair monitoring method, one in which information of every copy pair in a storage subsystem is obtained and one in which copy pair information is obtained according to copy pair definitions stored in the host computer or the like. 
         [0013]    The former monitoring method puts unnecessary workload on storage subsystems since information of every copy pair in a storage subsystem is collected even when only a limited count of copy pairs need monitoring. 
         [0014]    This invention has been made in view of the above, and it is therefore an object of this invention to avoid an overlap in monitoring of copy pairs that are monitored by various administrators from different points of view. 
         [0015]    According to a representative aspect of this invention, there is provided a storage system including: at least one host computer having a first processor for performing processing, a first memory unit, which is connected to the first processor, a first interface connected to the first processor, and a first interface connected to the first processor; at least one storage subsystem having a second processor for performing processing, a disk device, which contains volumes storing data requested by the host computer to be written, and a second interface connected to the second processor; and a management computer having a third processor for performing processing, a third memory unit connected to the third processor, and a third interface connected to the third processor. The storage system being characterized in that: a primary volume from which data is copied (i.e., a source volume) and a secondary volume to which data is copied (i.e., a target volume) create a copy pair; the first memory unit of each host computer stores definition information of the copy pair which indicates an association between the primary volume and the secondary volume creating the copy pair; and the third processor obtains every piece of copy pair definition information stored in the first memory unit, removes duplicate copy pair definition information from the whole copy pair definition information obtained from the first memory unit, collects the copy pair status based on the copy pair definition information from which the duplication copy pair definition information has been removed. 
         [0016]    According to an aspect of this invention, an overlap in monitoring of copy pairs is avoided and the monitoring workload on a storage system is thus lessened. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The present invention can be appreciated by the description which follows in conjunction with the following figures, wherein: 
           [0018]      FIG. 1  is a block diagram showing the configuration of a storage system according to a first embodiment of this invention; 
           [0019]      FIG. 2  is a diagram showing the configuration of a copy pair definition table which is stored in a local disk in a storage subsystem according to the first embodiment of this invention; 
           [0020]      FIG. 3  is a diagram showing the relation of copy groups which are managed by host computers according to the first embodiment of this invention; 
           [0021]      FIG. 4  is a diagram showing the configuration of a copy group definition table that is stored in a host computer A according to the first embodiment of this invention; 
           [0022]      FIG. 5  is a diagram showing the configuration of another copy group definition table that is stored in a host computer A according to the first embodiment of this invention; 
           [0023]      FIG. 6  is a diagram showing the configuration of a copy group definition table that is stored in a host computer B according to the first embodiment of this invention; 
           [0024]      FIG. 7  is a diagram showing the configuration of a copy group definition table that is stored in a host computer C according to the first embodiment of this invention; 
           [0025]      FIG. 8  is a diagram showing the configuration of an information obtaining definition table which is created in a memory in a management computer according to the first embodiment of this invention; 
           [0026]      FIG. 9  is a diagram showing the configuration of a copy pair monitoring table which is created in the memory in the management computer according to the first embodiment of this invention; 
           [0027]      FIG. 10  is a diagram illustrating a host computer selecting screen according to the first embodiment of this invention; 
           [0028]      FIG. 11  is a diagram illustrating a copy group selecting screen according to the first embodiment of this invention; 
           [0029]      FIG. 12  is a diagram illustrating a copy pair information displaying screen according to the first embodiment of this invention; 
           [0030]      FIG. 13  is a flow chart for processing that is executed by a management program according to the first embodiment of this invention to create the information obtaining definition table; 
           [0031]      FIG. 14  is a flow chart for processing that is executed by the management program according to the first embodiment of this invention to create the copy pair monitoring table; 
           [0032]      FIG. 15  is a diagram showing the configuration of a definition count table according to a second embodiment of this invention; 
           [0033]      FIG. 16  is a flow chart for processing that is executed by a management program according to the second embodiment of this invention to choose which copy group definition table is referred to in fetching the copy pair status; 
           [0034]      FIG. 17  is a diagram illustrating a copy group priority determining screen according to a third embodiment of this invention; 
           [0035]      FIG. 18  is a diagram showing the configuration of a copy group priority table according to the third embodiment of this invention; and 
           [0036]      FIG. 19  is a diagram showing the configuration of a copy group priority determining rule table according to a fourth embodiment of this invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       [0037]    A first embodiment of this invention will be described with reference to  FIG. 1  to  FIG. 14 . It should be noted that this invention is not limited to the first and other embodiments described below. 
         [0038]      FIG. 1  is a block diagram showing the configuration of a storage system according to the first embodiment of this invention. 
         [0039]    This storage system has a storage subsystem  1000 , a host computer  1100 , and a management computer  1200 . 
         [0040]    The storage subsystem  1000  and the host computer  1100  are interconnected via a data network  1300 . The data network  1300  is a network for data communications, in this embodiment, a storage area network (SAN). The data network  1300  can be other data communication networks than SANs, for example, an IP network. 
         [0041]    The storage subsystem  1000  and the host computer  1100  are connected to the management computer  1200  via a management network  1400 . The management network  1400  is a network for data communications, in this embodiment, an IP network. The management network  1400  can be other data communication networks than IP networks, for example, a storage area network (SAN). 
         [0042]    The data network  1300  and the management network  1400  may be one same network. One computer may serve as the management computer  1200  and the host computer  1100  both. 
         [0043]      FIG. 1  shows one storage subsystem  1000 , one host computer  1100 , and one management computer  1200  for convenience of explanation, but the storage system can have more than one storage subsystem  1000 , host computer  1100 , and management computer  1200 . 
         [0044]    The storage subsystem  1000  has a disk device  1010  and a disk controller  1020 . The disk device  1010  stores data requested by the host computer  1100  to be written. The disk controller  1020  controls processing of the storage subsystem  1000 . 
         [0045]    The disk device  1010  has plural volumes, here, volumes  1011 A,  1011 B,  1011 C, and  1011 D. The volumes  1011 A,  1011 B,  1011 C, and  1011 D in the disk device  1010  are collectively and generically referred to as volume  1011 . 
         [0046]    The volumes  1011  in this invention are not limited to a particular volume type and can be a hard disk drive (HDD), which is a physical storage area, or a logical device, which is a logical storage area. For convenience of explanation,  FIG. 1  shows four volumes  1011  but the storage system can have as many volumes  1011  as necessary. 
         [0047]    The volumes  1011  can form copy pairs. A copy pair includes one source volume  1011  and one target volume  1011  which stores a copy of data stored in the source volume  1011 . 
         [0048]    The disk controller  1020  has a host I/F  1022 , a management I/F  1026 , a disk I/F  1025 , a main memory  1021 , a CPU  1023 , and a local disk  1027 . 
         [0049]    The local disk  1027  is a disk device such as a hard disk that is connected to the disk controller  1020 . The local disk  1027  stores a storage microprogram  1028  and a copy pair definition table  1029 . 
         [0050]    The local disk  1027  may instead be a flash memory connected to the disk controller  1020 . 
         [0051]    The storage microprogram  1028  is loaded onto the main memory  1021  of the disk controller  1020  and executed by the CPU  1023 . The storage microprogram  1028  controls copy pairs and collects the copy pair status as requested by the host computer  1100 . 
         [0052]    Copy pair control exerted by the storage microprogram  1028  includes, for example, “create”, “synchronization”, and “suspend”. In “create”, the storage microprogram  1028  creates a new copy pair. In “synchronization”, the primary volume  1011  and the secondary volume  1011  are in sync with each other and data in the primary volume  1011  matches data in the secondary volume  1011 . In “suspend”, the synchronization between the primary volume  1011  and the secondary volume  1011  is suspended. “Create”, “synchronization” and “suspend” are terms used to indicate the status of a copy pair formed from the volumes  1011 , and the copy pair status is fetched by the storage microprogram  1028 . 
         [0053]    The copy pair definition table  1029  stores information on some of the volumes  1011  in the storage subsystem  1000  that form copy pairs. Details of the copy pair definition table  1029  will be described with reference to  FIG. 2 . 
         [0054]    The storage microprogram  1028  and the copy pair definition table  1029  are stored in the local disk  1027  of the disk controller  1020  in this embodiment, but this invention is not limited thereto. The storage microprogram  1028  and the copy pair definition table  1029  may be stored in, for example, a flash memory connected to the disk controller  1020 , or the volumes  1011  in the disk device  1010 . 
         [0055]    The host I/F  1022  is a network interface that connects the storage subsystem  1000  to the data network  1300 . The host I/F  1022  exchanges data and control commands with the host computer  1100  through the data network  1300 . 
         [0056]    The management I/F  1026  is a network interface that connects the storage subsystem  1000  to the management network  1400 . The management I/F  1026  exchanges data and control commands with the host computer  1100  and with the management computer  1200  through the management network  1400 . 
         [0057]    The disk I/F  1025  is an interface that connects the disk controller  1020  to the disk device  1010 . 
         [0058]    The host computer  1100  has a storage I/F  1110 , a display device  1120 , a CPU  1130 , an input device  1140  such as a keyboard and a mouse, a management I/F  1150 , a memory  1160 , and a local disk  1170 . The storage I/F  1110 , the display device  1120 , the CPU  1130 , the input device  1140 , the management I/F  1150 , the memory  1160 , and the local disk  1170  are connected to one another. 
         [0059]    The storage I/F  1110  is a network interface that connects the host computer  1100  to the data network  1300 . The storage I/F  1110  exchanges data and control commands with the storage subsystem  1000  through the data network  1300 . 
         [0060]    The management I/F  1150  is a network interface that connects the host computer  1100  to the management network  1400 . The management I/F  1150  exchanges data and control commands with the storage subsystem  1000  and with the management computer  1200  through the management network  1400 . 
         [0061]    The local disk  1170  is a disk device such as a hard disk. The local disk  1170  stores an information collecting agent  1161 , a recovery manager  1162 , an application  1163 , and a copy group definition table  1171 . 
         [0062]    The copy group definition table  1171  shows information that defines a copy group obtained by grouping plural copy pairs together. The copy group will be described in detail with reference to  FIG. 3 . 
         [0063]    One of reasons for defining copy group information in the host computer  1100  is security. In the case where plural corporations or the like use the storage subsystem  1000  in one storage system (of, for example, an SSP: Storage Service Provider) and each corporation is allocated particular volumes  1011 , the storage system unnecessarily collects information of copy pairs constituted of volumes that are used by other corporations when only copy pairs formed from the respectively allocated volumes  1011  need to be monitored. This poses a security problem. 
         [0064]    It is therefore a common practice to define copy pair definition information in the host computer  1100 , so that definition information of a copy pair to be monitored is retrieved from the host computer  1100  having this definition information and information on the copy pair is obtained based on the retrieved definition information. In this case, when there is a change in copy pair configuration, definition information is retrieved from the host computer  1100  and copy pairs are monitored periodically based on the retrieved definition information. A copy pair configuration change is, for example, an addition of a copy pair or a removal of a copy pair. 
         [0065]    The information collecting agent  1161 , the recovery manager  1162 , and the application  1163  are loaded onto the memory  1160  in the host computer  1100 , and executed by the CPU  1130 . 
         [0066]    The application  1163  reads and writes data in the volumes  1011  in the storage subsystem  1000 . The application  1163  is, for example, a data base management system (DBMS) or a file system. 
         [0067]    The recovery manager  1162  sends a request to the storage microprogram  1028  to control a copy pair or to collect the copy pair status. The function of the recovery manager  1162  to send requests to the storage microprogram  1028  to control a copy pair and to collect the copy pair status is provided by a command line interface, an application programming interface, or the like in order to allow an administrator or another program to execute the function. 
         [0068]    The information collecting agent  1161  sends, in response to a request made by a management program  1265 , which is stored in the management computer  1200 , information in the copy group definition table  1171  stored in the local disk  1170  to the management program  1265 . 
         [0069]      FIG. 1  shows one application  1163  for convenience of explanation, but the local disk  1170  in this embodiment can store more than one application  1163 . 
         [0070]    The management computer  1200  has a management I/F  1210 , a display device  1220 , a CPU  1230 , an input device  1240  such as a keyboard and a mouse, a memory  1250 , and a local disk  1260 . The management I/F  1210 , the display device  1220 , the CPU  1230 , the input device  1240 , the memory  1250 , and the local disk  1260  are connected to one another. 
         [0071]    The management I/F  1210  is a network interface that connects the management computer  1200  to the management network  1400 . The management I/F  1210  exchanges data and control commands with the storage subsystem  1000  and with the host computer  1100  through the management network  1400  in order to manage the storage subsystem  1000 . 
         [0072]    The local disk  1260  is a disk device such as a hard disk connected to the management computer  1200 . The local disk  1260  stores a copy group definition table  1264  and the management program  1265 . 
         [0073]    The copy group definition table  1264  is obtained from the host computer  1100  and is the same as the copy group definition table  1171  stored in the host computer  1100 . The copy group definition table  1264  may be stored in the memory  1250  of the management computer  1200  instead of the local disk  1260 . 
         [0074]    The management program  1265  is loaded onto the memory  1250  in the management computer  1200 , and executed by the CPU  1230 . 
         [0075]    The management program  1265  obtains the copy group definition table  1171  from the host computer  1100 . The management program  1265  has a function of creating an information obtaining definition table  1263 , a function of creating a copy group monitoring table  1266 , and a function of displaying the status of a copy pair. 
         [0076]    With the function of creating the information obtaining definition table  1263 , the management program  1265  creates the information obtaining definition table  1263  in the memory  1250  from definition information of copy pairs that belong to a copy group registered in the obtained copy group definition table  1171 . With the function of creating the copy group monitoring table  1266 , the management program  1265  creates the copy pair monitoring table  1266  in the memory  1250  based on the created information obtaining definition table  1263 . With the function of displaying the status of a copy pair, the management program  1265  makes a graphical user interface (GUI) display the copy pair status to the administrator based on the created copy pair monitoring table  1266 . 
         [0077]    The memory  1250  stores the information obtaining definition table  1263  and the copy pair monitoring table  1266 . 
         [0078]    The information obtaining definition table  1263  registers definition information of copy pairs that do not overlap and are registered in the copy group definition table  1264 . Details of the information obtaining definition table  1263  will be described with reference to  FIG. 8 . The management program  1265  fetches the status of a copy pair whose definition information is found in the information obtaining definition table  1263 . 
         [0079]    The copy pair monitoring table  1266  registers the copy pair status collected by the management program  1265 . Details of the copy pair monitoring table  1266  will be described with reference to  FIG. 9 . 
         [0080]      FIG. 2  is a diagram showing the configuration of the copy pair definition table  1029  which is stored in the local disk  1027  in the storage subsystem  1000  according to the first embodiment of this invention. 
         [0081]    The copy pair definition table  1029  shows definition information of some of the volumes  1011  in the storage subsystem  1000  that form copy pairs. A copy pair includes one primary volume  1011  which is a source volume and one secondary volume  1011  which is a target volume  1011 , and data stored in the primary volume  1011  is copied to the secondary volume  1011 . 
         [0082]    The copy pair definition table  1029  contains, in each row, a volume ID  2110 , a consistency group (CTG) ID  2120 , a type  2130 , a copy pair name  2140 , a paired storage ID  2150 , and a paired volume ID  2160 . 
         [0083]    Registered as the volume ID  2110  is an identifier that is assigned to each volume  1011  in the storage subsystem  1000 . The identifier of each volume  1011  is unique throughout the storage subsystem  1000  where that particular volume  1011  is located. 
         [0084]    Registered as the CTG ID  2120  is an identifier unique to each copy pair group in which data consistency has to be maintained. The storage subsystem  1000  assigns the same consistency group identifier to copy pairs that are not allowed to lose consistency through operation as members of the same group. 
         [0085]    In this way, when, for instance, a request to operate a copy pair belonging to a certain consistency group is sent from the host computer  1100  to the storage subsystem  1000 , all other copy pairs included in this consistency group receive the same operation along with the copy pair that is designated by the received request. When a copy pair does not need to maintain consistency with other copy pairs, nothing is registered as the CTG ID  2120 . 
         [0086]    A copy group is similar to a consistency group in that copy pairs are grouped together. However, copy pairs are grouped into a copy group by a unit that is specified by the administrator (for example, on a service application basis, or on an operation basis such as a backup operation basis). 
         [0087]    On the other hand, copy pairs are grouped into a consistency group in order for the storage subsystem  1000  to operate copy pairs while maintaining the consistency among the copy pairs. 
         [0088]    Consistency groups are created in the disk controller  1020  with the use of definition information registered in the copy group definition table  1171 , which is stored in the host computer  1100 , when the administrator defines the copy group definition table  1171 . Alternatively, the creation of consistency groups may not be related to the defining of the copy group definition table  1171 . 
         [0089]    Registered as the type  2130  is information that indicates whether the volume  1011  identified by the registered volume ID  2110  is the primary volume  1011  or the secondary volume  1011 . 
         [0090]    Registered as the copy pair name  2140  is a name that is assigned to each copy pair. A copy pair is uniquely identified from the primary volume  1011 , the storage subsystem  1000  that has this primary volume  1011 , the secondary volume  1011  that constitutes this copy pair, and the storage subsystem  1000  that has this secondary volume  1011 . However, it is difficult for an administrator to manage a copy pair by its primary and secondary volumes  1011  and the storage subsystem  1000  having the primary and secondary volumes  1011 . It is therefore common for an administrator to assign a name to a copy pair and manage the copy pair by the assigned name. 
         [0091]    In the case where the administrator manages copy pairs using the copy group definition table  1171 , which is stored in the host computer  1100 , there is no need for the administrator to refer to the copy pair definition table  1029  stored in the storage subsystem  1000  himself/herself. Then, copy pairs are not assigned names and the copy pair definition table  1029  does not contain the copy pair name  2140 . 
         [0092]    Registered as the paired storage ID  2150  is an identifier unique to the storage subsystem  1000  having the volume  1011  that is identified by the registered paired volume ID  2160 . 
         [0093]    Registered as the paired volume ID  2160  is an identifier unique to the volume  1011  that forms a copy pair with the volume  1011  identified by the registered volume ID  2110 . 
         [0094]    Rows  2210  and  2220  of the copy pair definition table  1029  show copy pair definitions. In the case where the volume  1011  that is identified by the registered volume ID  2110  has plural paired volumes  1011 , in other words, when one volume  1011  is paired with plural volumes  1011  forming plural copy pairs, definitions of the copy pairs constituted of the one volume  1011  are registered in plural rows of the copy pair definition table  1029 . 
         [0095]      FIG. 3  is a diagram showing the relation of copy pairs which are managed by the host computer  1100  according to the first embodiment of this invention. 
         [0096]    The storage system shown in  FIG. 3  has a two data center configuration which places data centers Site A  3310  and Site B  3320  in different sites. At least one storage subsystem  1000  is installed in each of the data centers. 
         [0097]    For instance, if a normal business operation or service is to be carried out in New York while data of the business operation is to be kept in New York and California, a data center has to be placed in New York and California each. 
         [0098]    In the data center Site A  3310 , a storage subsystem  1000 A (hereinafter referred to as SUB 1 ) and a storage subsystem  1000 B (hereinafter referred to as SUB 2 ) are installed. Set in the data center Site B  3320  are a storage subsystem  1000 C (hereinafter referred to as SUB 3 ) and a storage subsystem  1000 D (hereinafter referred to as SUB 4 ). 
         [0099]    The SUB 1 , SUB 2 , SUB 3 , and SUB 4  have the volumes  1011 . For example, the SUB 1  has a volume  1011 E and a volume  1011 F whereas the SUB 3  has a volume  1011 G. 
         [0100]    The volumes  1011  can form copy pairs. For instance, the volume  1011 F in the SUB 1  and the volume  1011 E in the SUB 1  form a copy pair P 1 . The volume  1101  F in the SUB 1  and the volume  1011 G in the SUB 3  form a copy pair P 5 . 
         [0101]    When a copy pair is formed from two volumes  1011  that are in the same storage subsystem  1000 , data copy between these volumes  1011  forming the copy pair is called local copy. In the example of  FIG. 3 , copy pairs between which local copy is executed are the copy pair P 1 , a copy pair P 2 , a copy pair P 3 , a copy pair P 4 , a copy pair P 9 , a copy pair P 10 , a copy pair P 11 , and a copy pair P 12 . 
         [0102]    When a copy pair is formed from two volumes  1011  that are in different storage subsystems  1000 , data copy between these volumes  1011  forming the copy pair is called remote copy. In the example of  FIG. 3 , copy pairs between which remote copy is executed are the copy pair P 5 , a copy pair P 6 , a copy pair P 7 , and a copy pair P 8 . 
         [0103]    Copy pairs are grouped into groups by, for example, service type in order to make them easier for the administrator to manage. Copy pairs grouped together because of having the same service type belong to the same copy group. 
         [0104]    In  FIG. 3 , a host computer  1100 A manages a copy group A  3111  and a copy group B  3121 . A host computer  1100 B manages a copy group C  3131 . A host computer  1100 C manages a copy group D  3141 . 
         [0105]    The copy group A  3111  is constituted of the copy pair P 1 , the copy pair P 2 , and the copy pair P 3 . The copy group B  3121  is constituted of the copy pair P 1 , the copy pair P 2 , the copy pair P 5 , the copy pair P 6 , the copy pair P 9 , and the copy pair P 10 . The copy group C  3131  is constituted of the copy pair P 9 , the copy pair P 10 , the copy pair P 11 , and the copy pair P 12 . The copy group D  3141  is constituted of the copy pair P 2 , the copy pair P 3 , the copy pair P 4 , the copy pair P 6 , the copy pair P 7 , the copy pair P 8 , the copy pair P 10 , the copy pair P 11 , and the copy pair P 12 . 
         [0106]    Each host computer  1100  stores for each copy group the copy group definition table  1171  which is definition information of copy pairs belonging to a copy group it manages. 
         [0107]    Described next with reference to  FIG. 4  to  FIG. 7  are the copy group definition tables  1171  respectively stored in the host computer  1100 A, the host computer  1100 B, and the host computer  1100 C in  FIG. 3 . The copy group definition tables  1171  shown in  FIG. 4  to  FIG. 7  have the same configuration, and the following description therefore takes the copy group definition table  1171  of  FIG. 4  as an example. 
         [0108]      FIG. 4  is a diagram showing the configuration of the copy group definition table  1171  that is stored in the host computer  1100 A according to the first embodiment of this invention. 
         [0109]    The copy group definition table  1171  contains, in each row, a host computer name  4110 , a copy group name  4120 , a copy pair name  4130 , a primary storage subsystem name  4140 , a primary volume ID  4150 , a secondary storage subsystem name  4160  and a secondary volume ID  4170 . 
         [0110]    Registered as the host computer name  4110  is the name of the host computer  1100  that stores the copy group definition table  1171 . 
         [0111]    The name of a copy group is registered as the copy group name  4120 . Registered as the copy pair name  4130  is the name of a copy pair belonging to the copy group that is identified by the registered copy group name  4120 . The copy pair name  4130  may be omitted since each copy pair is uniquely identified from the primary storage subsystem name  4140 , the primary volume ID  4150 , the secondary storage subsystem name  4160 , and the secondary volume ID  4170 . The copy pair name  4130  is contained in the copy group definition table  1171  commonly because it facilitates copy pair management for the administrator. 
         [0112]    Registered as the primary storage subsystem name  4140  is the name of the storage subsystem  1000  having the volume  1011  that serves as the primary volume of the copy pair. Registered as the primary volume ID  4150  is the identifier of the volume  1011  that serves as the primary volume of the copy pair. Each volume  1011  is assigned an identifier unique throughout the storage subsystem  1000  that has the volume  1011  in question. 
         [0113]    Registered as the secondary storage subsystem name  4160  is the name of the storage subsystem  1000  having the volume  1011  that serves as the secondary volume of the copy pair. Registered as the secondary volume ID  4170  is the identifier of the volume  1011  that serves as the secondary volume of the copy pair. Each volume  1011  is assigned an identifier unique throughout the storage subsystem  1000  that has the volume  1011  in question. 
         [0114]    A row  4210  in the copy group definition table  1171  holds information that defines the copy pair P 1  shown in  FIG. 3 , a row  4220  holds information that defines the copy pair P 2  shown in  FIG. 3 , and a row  4230  holds information that defines the copy pair P 3  shown in  FIG. 3 . 
         [0115]    The copy group definition table  1171  of  FIG. 4  defines that the host computer  1100 A manages the copy group A  3111  constituted of the copy pair P 1 , the copy pair P 2 , and the copy pair P 3 . 
         [0116]    The copy group definition table  1171  that is shown in  FIG. 5  and stored in the host computer  1100 A defines that the host computer  1100 A manages the copy group B  3121  constituted of the copy pair P 1 , the copy pair P 2 , the copy pair P 5 , the copy pair P 6 , the copy pair P 9 , and the copy pair P 10 . 
         [0117]    The copy group definition table  1171  that is shown in  FIG. 6  and stored in the host computer  1100 B defines that the host computer  1100 B manages the copy group C  3131  constituted of the copy pair P 9 , the copy pair P 10 , the copy pair P 11 , and the copy pair P 12 . 
         [0118]    The copy group definition table  1171  that is shown in  FIG. 7  and stored in the host computer  1100 C defines that the host computer  1100 C manages the copy group D  3141  constituted of the copy pair P 2 , the copy pair P 3 , the copy pair P 4 , the copy pair P 6 , the copy pair P 7 , the copy pair P 8 , the copy pair P 10 , the copy pair P 11 , and the copy pair P 12 . 
         [0119]    In this embodiment, definition information of one copy group is registered in one copy group definition table  1171 . Alternatively, one copy group definition table  1171  may register definition information of copy pairs in all copy groups that are managed by the host computer  1100  that stores this copy group definition table  1171 . 
         [0120]      FIG. 8  is a diagram showing the configuration of the information obtaining definition table  1263 , which is created in the memory  1250  of the management computer  1200  according to the first embodiment of this invention. 
         [0121]    The management program  1265  executes operation sequence shown in  FIG. 13  to create the information obtaining definition table  1263 , and thereby deletes overlapping copy pairs from the copy group definition tables  1264  obtained from the respective host computers  1100 . The management program  1265  thus creates the information obtaining definition table  1263  in the memory  1250  of the management computer  1200 . When the management computer  1200  sends a request to collect the copy pair status to the host computers  1100 , it is the status of copy pairs defined in the information obtaining definition table  1263  that is requested to be collected. 
         [0122]    The information obtaining definition table  1263  contains, in each row, a host computer name  8110 , a copy pair name  8120 , a primary storage subsystem name  8130 , a primary volume ID  8140 , a secondary storage subsystem name  8150 , and a secondary volume ID  8160 . 
         [0123]    Registered as the host computer name  8110  is the name of the host computer  1100  that sends to the storage subsystem  1000  a request to fetch the status of a copy pair identified by the registered copy pair name  8120 . 
         [0124]    The copy pair name  8120 , the primary storage subsystem name  8130 , the primary volume ID  8140 , the secondary storage subsystem name  8150 , and the secondary volume ID  8160  indicate the same names or IDs as in the copy group definition table  1171 , and their descriptions will therefore be omitted. 
         [0125]      FIG. 9  is a diagram showing the configuration of the copy pair monitoring table  1266 , which is created in the memory  1250  of the management computer  1200  according to the first embodiment of this invention. 
         [0126]    The management program  1265  executes processing shown in  FIG. 14  to create the copy pair monitoring table  1266 , and thereby creates the copy pair monitoring table  1266  in the memory  1250  of the management computer  1200 . 
         [0127]    The copy pair monitoring table  1266  contains, in each row, a primary storage subsystem name  9100 , a primary volume ID  9200 , a secondary storage subsystem name  9300 , a secondary volume ID  9400 , and copy pair status  9500 . 
         [0128]    The primary storage subsystem name  9100 , the primary volume ID  9200 , the secondary storage subsystem name  9300 , and the secondary volume ID  9400  indicate the same names or IDs as in the copy group definition table  1171 , and their descriptions will therefore be omitted. 
         [0129]    Registered as the copy pair status  9500  is the status of a copy pair that is uniquely identified from the primary storage subsystem name  9100 , the primary volume ID  9200 , the secondary storage subsystem name  9300 , and the secondary volume ID  9400 . For example, “PAIR”, “SUSPEND”, or the like is registered as the copy pair status  9500 . “PAIR” indicates that the primary volume  1011  and the secondary volume  1011  are in sync with each other, and that data in the primary volume  1011  matches data in the secondary volume  1011 . “SUSPEND” indicates that the synchronization between the primary volume  1011  and the secondary volume  1011  is in a suspended state. 
         [0130]    The copy pair monitoring table  1266  in this embodiment contains the copy pair status  9500 , but may hold other kinds of information such as the data matching ratio of volumes forming a copy pair. 
         [0131]    Next, a description will be given with reference to  FIG. 10  to  FIG. 12  on management screens used by the administrator to monitor copy pairs. 
         [0132]      FIG. 10  is a diagram illustrating a host computer selecting screen  10000  according to the first embodiment of this invention. 
         [0133]    The host computer selecting screen  10000  is displayed on the display device  1220  of the management computer  1200  when the management program  1265  in the management computer  1200  is loaded onto the memory  1250  and executed by the CPU  1230 . 
         [0134]    The host computer selecting screen  10000  contains checkboxes  10010 , host computer name fields  10020 , an “execute” button (i.e., OK button)  10100  and a cancel button  10200 . 
         [0135]    The host computer selecting screen  10000  shows as many checkboxes  10010  and host computer name fields  10020  as the number of host computers  1100  registered in the copy group definition table  1264  by the host name  4110 . 
         [0136]    When the host computer selecting screen  10000  is first displayed on the display device  1220 , none of the checkboxes  10010  is checked. The administrator can check one or more checkboxes  10010 . 
         [0137]    The “execute” button  10100  is enabled when the administrator checks one or more checkboxes  10010 . When enabled, the “execute” button can be selected, by the administrator. As the “execute” button is operated, a copy group selecting screen  11000  shown in  FIG. 11  is displayed. 
         [0138]    The cancel button  10200  is operated to close the host computer selecting screen  10000 . 
         [0139]      FIG. 11  is a diagram illustrating the copy group selecting screen  11000  according to the first embodiment of this invention. 
         [0140]    The copy group selecting screen  11000  is displayed on the display device  1220  when the management program  1265  stored in the management computer  1200  is loaded onto the memory  1250  and executed by the CPU  1230 . 
         [0141]    The copy group selecting screen  11000  contains checkboxes  11010 , host computer name fields  11020 , copy group name fields  11030 , an “execute” button (i.e., OK button)  11100 , and a cancel button  11200 . 
         [0142]    The copy group selecting screen  11000  shows as many checkboxes  11010 , host computer name fields  11020 , and copy group name fields  11030  as the number of copy groups that are registered in the copy group definition table  1264  by the copy group name  4120  and that are managed by the host computer  1100  chosen in the host computer selecting screen  10000 . 
         [0143]    When the copy group selecting screen  11000  is first displayed on the display device  1220 , none of the checkboxes  11010  is checked. The administrator can check one or more checkboxes  11010 . 
         [0144]    The “execute” button  11100  is enabled when the administrator checks one or more checkboxes  11010 . When enabled, the “execute” button can be operated (clicked on) by the administrator. As the “execute” button is operated, a copy pair information displaying screen  12000  shown in  FIG. 12  is displayed. 
         [0145]    The cancel button  11200  is operated to close the copy group selecting screen  11000 . 
         [0146]      FIG. 12  is a diagram illustrating the copy pair information displaying screen  12000  according to the first embodiment of this invention. 
         [0147]    The copy pair information displaying screen  12000  is displayed on the display device  1220  when the management program  1265  stored in the management computer  1200  is loaded onto the memory  1250  and executed by the CPU  1230 . 
         [0148]    The copy pair information displaying screen  12000  contains a host computer name field  12210 , a copy group name field  12220 , a copy pair name field  12230 , and a copy pair information field  12240 . 
         [0149]    The copy pair information displaying screen  12000  displays the status of copy pairs that constitute a copy group chosen in the copy group selecting screen  11000 . 
         [0150]    The copy pair information displaying screen  12000  in  FIG. 12  displays the status of copy pairs belonging to one copy group. When plural copy groups are chosen in the copy group selecting screen  11000 , the copy pair information displaying screen  12000  displays the status of all copy pairs in the chosen copy groups. 
         [0151]    Also, the example of the copy pair information displaying screen  12000  shown in  FIG. 12  is of when only one host computer  1100  is chosen. When plural host computers  1100  are chosen, on the other hand, the copy pair information displaying screen  12000  displays the status of all copy pairs in copy groups that are managed by the chosen host computers  1100 . 
         [0152]    The host computer name field  12210  displays the name of the host computer  1100  chosen in the host computer selecting screen  10000 . The host computer  1100  displayed in the host computer name field  12210  stores one or more copy group definition tables  1171 . 
         [0153]    Displayed in the copy group name field  12220  is the name of the copy group chosen in the copy group selecting screen  11000 . 
         [0154]    The copy pair name field  12230  displays the name of a copy pair belonging to a copy group that is displayed in the copy group name field  12220 . 
         [0155]    Displayed in the copy pair information field  12240  is the status of a copy pair that is displayed in the copy pair name field  12230 . 
         [0156]    The following description is about processing executed in the management computer  1200  from when the host computer selecting screen  10000  shown in  FIG. 10  is displayed until when the copy pair information displaying screen  12000  shown in  FIG. 12  is displayed. 
         [0157]    As the host computer  1100  is chosen in the host computer selecting screen  10000 , the management program  1265  refers to every copy group definition table  1264  to obtain the name of a copy group that is managed by the host computer  1100  chosen. 
         [0158]    Specifically, the management program  1265  selects from among all copy group definition tables  1264  ones whose host name  4110  matches the name of the chosen host computer  1100 . The management program  1265  next obtains the copy group name  4120  from each copy group definition table  1264  selected. 
         [0159]    The management program  1265  displays the name of the chosen host computer  1100  in the host computer name field  11020  and displays each obtained copy group name (i.e., copy group name  4120 ) in the copy group name field  11030 . 
         [0160]    As copy groups are selected in the copy group selecting screen  11000 , the management program  1265  obtains, from the copy group definition table  1264 , the copy pair name  4130  and copy pair definition information (i.e., the primary storage subsystem name  4140 , the primary volume ID  4150 , the secondary storage subsystem name  4160 , the secondary volume ID  4170 ) that are associated with each copy group selected. 
         [0161]    Specifically, the management program  1265  selects from among all of the selected copy group definition tables  1264  ones whose copy group name  4120  matches the name of any one of the chosen copy groups. The management program  1265  next obtains, from each copy group definition table  1264  selected, the copy pair name  4130 , the primary storage subsystem name  4140 , the primary volume ID  4150 , the secondary storage subsystem name  4160 , and the secondary volume ID  4170 . 
         [0162]    The management program  1265  then chooses from the copy pair monitoring table  1266  every entry whose copy pair definition information matches the obtained copy pair definition information. From every chosen entry, the management program  1265  extracts the copy pair status  9500 . 
         [0163]    The management program  1265  displays the obtained copy pair name  4130  in the copy pair name field  12230 , and displays the extracted copy pair status  9500  in the copy pair information field  12240 . 
         [0164]    The display screens of  FIG. 10  to  FIG. 12  are, in this embodiment, displayed on the display device  1220  of the management computer  1200 , but may be displayed on display devices of other computers. For instance, the display device  1120  of the host computer  1100  may display the display screens shown in  FIG. 10  to  FIG. 12 . 
         [0165]    The host computer selecting screen  10000  in this embodiment allows the administrator to choose one or more host computers  1100  out of all the host computers  1100 . Alternatively, only a limited number of host computers  1100  may be chosen in the host computer selecting screen  10000 . 
         [0166]    How to limit the host computers  1100  that can be chosen by the administrator will be described next. 
         [0167]    The administrator first accesses the management computer  1200  through one of the host computers  1100  in the storage system. 
         [0168]    The assumption here is that the management computer  1200  stores a host computer IP address table which registers the IP addresses of the host computers  1100 . 
         [0169]    When accessed by the host computer  1100 , the management computer  1200  refers to the host computer IP address table to identify through which host computer  1100  the access has been made. The management computer  1200  then skips displaying the host computer selecting screen  10000  shown in  FIG. 10 , and displays the names of copy groups managed by the host computer  1100  through which the access has been made in the copy group selecting screen  11000  shown in  FIG. 11 . The management computer  1200  next displays, in the copy pair information displaying screen  12000  shown in  FIG. 12 , the status of copy pairs belonging to copy groups that are selected in the copy group selecting screen  11000 . 
         [0170]    The copy pair information displaying screen  12000  thus displays only the status of copy pairs belonging to copy groups that are managed by the host computer  1100  through which the access has been made. Since configuration information of these copy pairs and the copy pair status are not disclosed to the administrators of other host computers  1100  illicitly, the security of the storage system is improved. 
         [0171]    Instead of skipping displaying the host computer selecting screen  10000  of  FIG. 10 , the management computer  1200  may fix the host computer selecting screen  10000  such that the administrator can only choose the host computer  1100  through which the access has been made. 
         [0172]    The description given next is about processing in which the management computer  1200  obtains copy pair information. 
         [0173]    The processing of obtaining copy pair information includes processing of creating the information obtaining definition table  1263  and processing of creating the copy pair monitoring table  1266 . 
         [0174]    The processing in which the management computer  1200  creates the information obtaining definition table  1263  will be described in detail with reference to  FIG. 13 . The processing in which the management computer  1200  updates the copy pair monitoring table  1266  will be described in detail with reference to  FIG. 14 . 
         [0175]    Processing in which the management computer  1200  creates the information obtaining definition table  1263  is described first. 
         [0176]    The information collecting agent  1161  run in the host computer  1100  monitors the copy group definition table  1171  for a change. When there is a change in the copy group definition table  1171 , the information collecting agent  1161  notifies the management program  1265 , which is run in the management computer  1200 , of the change in the copy group definition table  1171 . 
         [0177]    Notified of the change in the copy group definition table  1171 , the management program  1265  executes the processing of creating the information obtaining definition table  1263 . The processing of creating the information obtaining definition table  1263  may be executed upon instruction from the administrator to create the information obtaining definition table  1263 , instead of upon notification from the information collecting agent  1161 . 
         [0178]      FIG. 13  is a flow chart for the processing through which the information obtaining definition table  1263  is created by the management program  1265  according to the first embodiment of this invention. 
         [0179]    First, when notified of a change in the copy group definition table  1171  from the information collecting agent  1161 , the management program  1265  collects the copy group definition table  1171  from every host computer  1100 . The management program  1265  stores each collected copy group definition table  1171  in the local disk  1260  (Step  13010 ). Instead of sending a notification of a change in the copy group definition table  1171  to the management program  1265 , the information collecting agent  1161  may send the changed copy group definition table  1171  to the management program  1265 . The management program  1265  stores the received copy group definition table  1171  in the local disk  1260 . 
         [0180]    Next, the management program  1265  deletes information that has been registered in the information obtaining definition table  1263  stored in the memory  1250 , thereby initializing the information obtaining definition table  1263  (Step  13020 ). 
         [0181]    The management program  1265  then loads onto the memory  1250  every copy group definition table  1264  that has been stored in the local disk  1260  in the processing of Step  13010  (Step  13030 ) For each copy group definition table  1264  loaded onto the memory  1250 , the management program  1265  judges whether or not the table holds copy pair definition information (i.e., the primary storage subsystem name  4140 , the primary volume ID  4150 , the secondary storage subsystem name  4160 , and the secondary volume ID  4170 ) (Step  13040 ). Judging that the copy group definition table  1264  loaded onto the memory  1250  holds copy pair definition information, the management program  1265  proceeds to processing of Step  13050 . On the other hand, when it is judged that the copy group definition table  1264  loaded onto the memory  1250  does not hold copy pair definition information, the processing of creating the information obtaining definition table  1263  is terminated. 
         [0182]    In other words, the management program  1265  executes the processing of Steps  13050  to  13080  as long as copy pair definition information is left in the copy group definition table  1264  loaded onto the memory  1250 . 
         [0183]    When copy pair definition information is found in the copy group definition table  1264  loaded onto the memory  1250 , the management program  1265  picks up definition information of one copy pair out of copy pair definition information that is held in the copy group definition table  1264  loaded onto the memory  1250 , and deletes the picked up copy pair definition information from the copy group definition table  1264  (Step  13050 ). 
         [0184]    The management program  1265  next creates a new entry in the information obtaining definition table  1263 . The management program  1265  registers the picked up copy pair definition information in the newly created entry (Step  13060 ). 
         [0185]    Next, the management program  1265  judges whether or not the same information as the copy pair definition information picked up through the processing of Step  13050  is held in other copy group definition tables  1264  than the one from which this copy pair definition information has been picked up (Step  13070 ). Judging that other copy group definition tables  1264  do not hold this copy pair definition information, the management program  1265  returns to the processing of Step  13040 . 
         [0186]    Judging that other copy group definition tables  1264  hold this copy pair definition information, the management program  1265  deletes the copy pair information from those other copy group definition tables  1264  (Step  13080 ). 
         [0187]    Copy pairs that have identical values in all of the primary storage subsystem name, primary volume ID, secondary storage subsystem name, and secondary volume ID fields are deemed as the same copy pair irrespective of whether their copy pair names are the same or different. 
         [0188]    The management program  1265  repeats the processing of Steps  13040  to  13080  until no copy pair definition information is left in the copy group definition table  1264  loaded onto the memory  1250 . When there is no more copy pair definition information left in the copy group definition table  1264  loaded onto the memory  1250 , the management program  1265  ends the processing of creating the information obtaining definition table  1263 . 
         [0189]    After the creation of the information obtaining definition table  1263  is completed, the management program  1265  executes the processing of creating the copy pair monitoring table  1266  based on the created information obtaining definition table  1263  until a change occurs in the copy group definition table  1171  stored in the host computer  1100 . 
         [0190]    The information obtaining definition table  1263  avoids registering information of the same copy pair more than once, thereby preventing the management program  1265  from obtaining status information of the same copy pair twice or more in one round, or cycle, of information collecting. This makes it possible to provide a storage system that collects the copy pair status without burdening the storage subsystem  1000  with an excess load. 
         [0191]    The processing in which the management computer  1200  updates the copy pair monitoring table  1266  is now described. 
         [0192]      FIG. 14  is a flow chart for the processing through which the copy pair monitoring table  1266  is created by the management program  1265  according to the first embodiment of this invention. 
         [0193]    The processing of creating the copy pair monitoring table  1266  is processing in which the management program  1265  periodically collects the status of copy pairs registered in the information obtaining definition table  1263 , and registers the collected copy pair status in the copy pair monitoring table  1266 . The cycle in which the management program  1265  collects the status of copy pairs registered in the information obtaining definition table  1263  may be set in the management program  1265  in advance, or may be set by the administrator. 
         [0194]    As the first step of this processing, the management program  1265  secures an area in the memory  1250  to store a counter, and initializes the counter to 0 (Step  14010 ). The counter is provided by a timer function of the management program  1265 . 
         [0195]    Next, the management program  1265  judges whether or not an instruction to end copy pair monitoring has been given from the administrator (Step  14020 ). Judging that the administrator has given an instruction to end copy pair monitoring, the management program  1265  terminates the processing of creating the copy pair monitoring table  1266 . 
         [0196]    On the other hand, when it is judged that the administrator has not given an instruction to end copy pair monitoring, the management program  1265  judges whether or not the counter has counted up the cycle for collecting the copy pair status (Step  14030 ). Judging that the counter has not finished counting up the cycle for collecting the copy pair status, the management program  1265  returns to the processing of Step  14020 . In the processing of Step S 14020 , the management program  1265  terminates the processing of creating the copy pair monitoring table  1266  when an instruction to end copy pair monitoring is given from the administrator within the cycle for collecting the copy pair status. 
         [0197]    On the other hand, when it is judged that the counter has counted up the cycle for collecting the copy pair status, the management program  1265  collects the status of copy pairs registered in the information obtaining definition table  1263  (Step  14040 ). 
         [0198]    Specifically, the management program  1265  sends a request to collect the copy pair status to each host computer  1100  registered in the information obtaining definition table  1263  by the host computer name  8110 . This request contains copy pair definition information (i.e., the primary storage subsystem name  8130 , the primary volume ID  8140 , the secondary storage subsystem name  8150 , and the secondary volume ID  8160 ). 
         [0199]    Receiving the request, the host computer  1100  implements the recovery manager  1162 . The recovery manager  1162  sends a request to collect the copy pair status to the storage subsystem  1000  that is specified in the request by the primary storage subsystem name  8130  and to the storage subsystem  1000  that is specified in the request by the secondary storage subsystem name  8150 . 
         [0200]    Receiving the request, the primary and secondary storage subsystems  1000  each execute their own storage microprograms  1028 . The storage microprogram  1028  that is executed in the primary storage subsystem  1000  fetches the status of the volume  1011  that is identified by the primary volume ID  4150  contained in the request. The storage microprogram  1028  that is executed in the secondary storage subsystem  1000  fetches the status of the volume  1011  that is identified by the secondary volume ID  4170  contained in the request. 
         [0201]    The storage microprograms  1028  executed in the primary and secondary storage subsystems  1000  send the fetched status of the volumes  1011  to the host computer  1100  that has made the request. Receiving the status of the volumes  1011 , the host computer  1100  identifies from the received status of the volumes  1011  the copy pair status of the copy pair definition information contained in the request. The host computer  1100  sends the identified copy pair status to the management computer  1200 . 
         [0202]    The management computer  1200  thus collects the status of copy pairs registered in the information obtaining definition table  1263 . 
         [0203]    The management program  1265  then makes the collected copy pair status reflected in the copy pair monitoring table  1266  (Step  14050 ), and returns to Step  14010 . 
         [0204]    A description will be given next with reference to  FIG. 10  to  FIG. 12  on a procedure that is employed by the administrator to monitor the copy pair status. 
         [0205]    The description takes as an example a procedure in which the administrator of the application  1163  that is stored in the host computer  1100 A monitors copy pairs to be managed. 
         [0206]    First, the administrator calls up a monitoring function of the management program  1265 . The administrator can call up the monitoring function of the management program  1265  through, for example, the management computer  1200 . 
         [0207]    As the monitoring function of the management program  1265  is called up, the host computer selecting screen  10000  shown in  FIG. 10  is displayed. The administrator checks one or some of the checkboxes  10010  displayed on the host computer selecting screen  10000  that correspond to the host computers  1100  to be monitored (in this example, Host A), and operates, or clicks on, the “execute” button (i.e., OK button)  10100 . As the “execute” button is operated, the copy group selecting screen  11000  is displayed. 
         [0208]    The administrator checks one or some of the checkboxes  11010  displayed on the copy group selecting screen  11000  that correspond to copy groups to be monitored (in this example, CG. A), and operates the “execute” button  11100 . As the “execute” button  11100  is operated, the management program  1265  collects from the copy pair monitoring table  1266  the status of copy pairs that belong to the selected copy groups, and causes the copy pair information displaying screen  12000  to be displayed. 
         [0209]    The copy pair information displaying screen  12000  displays the collected copy pair status. The administrator operates a “close” button  12100  to close the copy pair information displaying screen  12000 . 
         [0210]    The copy pair information displaying screen  12000  in this embodiment displays the copy pair status only once and the displayed copy status information is not updated. However, an “update” button may be added to the copy pair information displaying screen  12000  so that, when the administrator operates the “update” button, the management program  1265  again fetches the copy pair status from the copy pair monitoring table  1266  and makes the copy pair information displaying screen  12000  display the fetched copy pair status again. 
         [0211]    Alternatively, the management program  1265  may automatically update the copy pair information displaying screen  12000  at the intervals in which the copy pair monitoring table  1266  is created. 
         [0212]    In this embodiment, one host computer  1100  is chosen in the host computer selecting screen  10000  and one copy group is chosen in the copy group selecting screen  11000 . Alternatively, plural host computers and copy groups may be chosen in the screens  10000  and  11000 , respectively. 
       Second Embodiment 
       [0213]    The information obtaining definition table  1263  is created in the first embodiment by deleting duplicate definition information of the same copy pair among copy pair definition information registered in the copy group definition tables  1264 . No two pieces of copy pair status information obtained from the thus created information obtaining definition table  1263  overlap. 
         [0214]    In a second embodiment of this invention, when every piece of copy pair definition information registered in one copy group definition table  1264  is found in any one of other copy group definition tables  1264 , this copy group definition table  1264 , whose every piece of copy pair definition information has a duplicate, is deleted. Then the management program  1265  collects the status of copy pairs that are registered in the remaining copy group definition tables  1264 . 
         [0215]    The second embodiment will be described with reference to  FIG. 15  and  FIG. 16 . In the second embodiment, descriptions on the same components as those in the first embodiment will be omitted. 
         [0216]    The configuration of a storage system according to the second embodiment of this invention is described with reference to  FIG. 1 . 
         [0217]    The memory  1250  of the management computer  1200  in the second embodiment does not store the information obtaining definition table  1263 . The memory  1250  stores the copy group definition table  1264  and a definition count table  15000  instead. 
         [0218]      FIG. 15  is a diagram showing the configuration of the definition count table  15000  according to the second embodiment of this invention. 
         [0219]    The definition count table  15000  contains, in each row, a primary storage subsystem name  15100 , a primary volume ID  15200 , a secondary storage subsystem name  15300 , a secondary volume ID  15400 , and a definition count  15500 . 
         [0220]    The primary storage subsystem name  15100 , the primary volume ID  15200 , the secondary storage subsystem name  15300 , and the secondary volume ID  15400  indicate the same names or IDs as in the copy group definition tables  1171  of  FIG. 4  to  FIG. 7 , and their descriptions will therefore be omitted. 
         [0221]    Registered as the definition count  15500  is the number of times a copy pair is defined in the copy group definition tables  1264 . Specifically, in the case where the same copy pair definition information is found in plural copy group definition tables  1264  loaded onto the memory  1250 , a number indicating how many copy pairs have the identical copy pair information is registered as the definition count  15500 . 
         [0222]    Processing in which the management computer  1200  obtains copy pair information consists of, when every piece of copy pair definition information registered in one copy group definition table  1264  is found in any other copy group definition tables  1264 , processing of deleting this copy group definition table  1264  and processing of updating the copy pair monitoring table  1266 . 
         [0223]    The processing of updating the copy pair monitoring table  1266  in the second embodiment is the same as in the first embodiment, and a description thereof will be omitted. Described here is processing that is employed by the management program  1265  to choose which copy group definition table  1264  is to be referred to in collecting the copy pair status. 
         [0224]    The management program  1265  obtains the copy group definition table  1171  stored in the host computer  1100 , and stores the obtained copy group definition table  1171  in the local disk  1260 . Stored in the memory  1250  of the management computer  1200  is a subset of the copy group definition tables  1264  after the management program  1265  executes processing shown in  FIG. 16  to choose which copy group definition table  1264  is to be referred to in collecting the copy pair status. 
         [0225]      FIG. 16  is a flow chart for the processing that is employed by the management program  1265  according to the second embodiment of this invention to choose which copy group definition table  1264  is to be referred to in collecting the copy pair status. 
         [0226]    The management program  1265  first collects the copy group definition tables  1171  from the host computers  1100  through the information collecting agent  1161 , and stores the obtained copy group definition tables  1171  in the local disk  1260  (Step  16010 ). 
         [0227]    Next, the management program  1265  deletes information that has been registered in the definition count table  15000  stored in the memory  1250  of the management computer  1250 , thereby initializing the definition count table  15000  (Step  16020 ). 
         [0228]    The management program  1265  then loads onto the memory  1250  every copy group definition table  1264  stored in the local disk  1260  (Step  16030 ) 
         [0229]    The management program  1265  executes a processing of Step  16050  for every copy group definition table  1264  loaded onto the memory  1250  (Steps  16040  and  16050 ). After completion of the processing of Step  16050  for all copy group definition tables  1264 , the management program  1265  proceeds to processing of Step  16060  (Step  16040 ). 
         [0230]    The management program  1265  picks up copy pair definition information held in the copy group definition table  1264  loaded onto the memory  1250 , and makes the picked up copy pair definition information reflected in the definition count table  15000  (Step  16050 ). 
         [0231]    Specifically, when the picked up copy pair information matches copy pair definition information registered in the definition count table  15000 , the management program  1265  increments a value registered as the definition count  15050  in the definition count table  15000 . In the case where the picked up copy pair definition information matches none of the copy pair definition information registered in the definition count table  15000 , the management program  1265  adds a new entry to the definition count table  15000 . The management program  1265  registers “1” as the definition count  15050  of the added entry, and stores the picked up copy pair definition information in the added entry. 
         [0232]    Through the processing of Steps  16040  to  16050 , the management program  1265  creates the definition count table  15000 . The definition count table  15000  shows, about each piece of copy pair definition information, how many times in total the copy pair definition information in question has been defined in the copy group definition tables  1264  loaded onto the memory  1250 . 
         [0233]    The management program  1265  next executes processing of Steps  16060  to  16090  to select from among the copy group definition tables  1264  loaded onto the memory  1250  ones that are necessary in collecting the copy pair status, and to delete the copy group definition tables  1264  that are deemed unnecessary from the memory  1250 . 
         [0234]    The management program  1265  executes the processing of Steps  16060  to  16090  for every copy group definition table  1264  loaded onto the memory  1250  (Steps  16060  to  16090 ). After completion of the processing of Steps  16060  to  16090  for all copy group definition tables  1264 , the management program  1265  terminates the processing. 
         [0235]    The management program  1265  chooses every entry of the definition count table  15000  that holds copy pair definition information identical with any piece of copy pair information registered in the picked up copy group definition table  1264 . From each chosen entry, the management program  1265  extracts the definition count  15500 . The management program  1265  then judges whether or not the extracted definition count  15500  is equal to or larger than “2” (Step  16070 ). 
         [0236]    Judging that the definition count  15500  is smaller than “2” (i.e., when the definition count  15500  is “1”), the management program  1265  returns to the processing of Step  16060 . 
         [0237]    Judging that the definition count  15500  is “2” or larger, the management program  1265  decrements the extracted definition count  15500  (Step  16080 ). 
         [0238]    The management program  1265  then deletes the picked up copy group definition table  1264  from the memory  1250  (Step  16090 ). 
         [0239]    The duplicate copy group definition table  1264  is deleted from the memory  1250  by executing the processing of Steps  16060  to  16090 . 
         [0240]    Thus, the memory  1250  now stores a subset of the copy pair monitoring tables  1264  stored in the local disk  1260 . The management program  1265  collects the copy pair status based on copy pair definition information that is registered in the subset of the copy group definition tables  1264  stored in the memory  1250 . This enables the management program  1265  to collect the copy pair status without missing any copy pair. Further, this causes the management program  1265  to generate less load while monitoring the storage subsystem  1000  than in the case where the copy pair status is collected with the use of every copy group definition table  1264 . 
       Third Embodiment 
       [0241]    The storage systems according to the first embodiment and the second embodiment lessen the load on the storage subsystem  1000  by avoiding monitoring the same copy pair twice or more in one round of monitoring. However, the storage systems according to the first embodiment and the second embodiment do not deal with a matter about which host computer  1100  is to be engaged in monitoring a copy pair when the copy pair is managed by more than one host computer  1100 . 
         [0242]    In addition, copy pair monitoring through the host computer  1100  burdens the host computer  1100  with the load of monitoring copy pairs. For instance, when a copy pair is managed by the host computer  1100  where an application of a service is run and by the backup host computer  1100 , the load of copy pair monitoring affects the service less if it is the backup host computer  1100  that collects the copy pair status. 
         [0243]    In a third embodiment of this invention, the administrator of the storage system sets an order of priority to the host computers  1100 . When the host computer  1100  that is given a high priority level and the host computer  1100  that is given a low priority level manage the same copy pair, the host computer  1100  of low priority obtains copy pair information. A service is thus affected less by copy pair monitoring. 
         [0244]    The third embodiment will be described with reference to  FIG. 17  and  FIG. 18 . In the third embodiment, descriptions on the same components as those in the first embodiment will be omitted. 
         [0245]    The memory  1250  of the management computer  1200  in a storage system according to the third embodiment of this invention stores a copy group priority table  18000 . The rest of the storage system according to the third embodiment is the same as the storage system according to the first embodiment of this invention, and repetition of the same descriptions will be avoided. 
         [0246]      FIG. 17  is a diagram illustrating a copy group priority determining screen  17000  according to the third embodiment of this invention. 
         [0247]    The copy group priority determining screen  17000  is a graphical user interface (GUI) called up by the administrator. 
         [0248]    The copy group priority determining screen  17000  contains a priority level input field  17100 , a host computer name field  17200 , a copy group name field  17300 , an “execute” button (i.e., OK button)  17400  and a cancel button  17500 . 
         [0249]    The priority level of a copy group is entered in the priority level input field  17100 . The priority level of a copy group is set by the administrator. For instance, the administrator assigns a high priority level to a copy group that is used to provide a service, and a low priority level to a copy group for uses that are not directly relevant to the service. The administrator may set a high priority level to a copy group to which only a few resources are available, and a low priority level to a copy group to which a lot of resources are available. A larger value entered in the priority level input field  17100  means a lower priority level for the copy group whereas a smaller value entered in the priority level input field  17100  means a higher priority level for the copy group. 
         [0250]    The priority level is entered on a copy group basis in the copy group priority determining screen  17000  shown in  FIG. 17 . Alternatively, the priority level may be determined for each host computer  1100  so that copy groups that are managed by the same host computer  1100  are all given the same priority level. 
         [0251]    The name of the host computer  1100  is entered in the host computer name field  17200 . The name of a copy group is entered in the copy group name field  17300 . 
         [0252]    As the “execute” button is operated, or clicked on, the copy group priority table  18000  shown in  FIG. 18  is updated according to a priority level set in the copy group priority determining screen  17000 . 
         [0253]    The cancel button  17500  is operated to close the copy group priority determining screen  17000 . 
         [0254]      FIG. 18  is a diagram showing the configuration of the copy group priority table  18000  according to the third embodiment of this invention. 
         [0255]    The copy group priority table  18000  is stored in the memory  1250  of the management computer  1200 . 
         [0256]    The copy group priority table  18000  contains a priority level  18100 , a copy group name  18200  and a host computer name  18300  in each row. 
         [0257]    A priority level is registered as the priority level  18100 . The name of a copy group is registered as the copy group name  18200 . Registered as the host computer name  18300  is the name of the host computer  1100  that manages the copy group identified by the registered copy group name  18200 . A larger value registered as the priority level  18100  means a lower priority level for the copy group whereas a smaller value registered as the priority level  18100  means a higher priority level for the copy group. 
         [0258]    Processing of collecting the copy pair status according to the third embodiment consists of processing in which the management program  1265  creates the information obtaining definition table  1263  and processing in which the management program  1265  updates the copy pair monitoring table  1266 . The processing in which the management program  1265  updates the copy pair monitoring table  1266  is the same as in the first embodiment, and a description thereof will be omitted. 
         [0259]    Described here is a difference between the processing in which the management program  1265  creates the information obtaining definition table  1263  according to the third embodiment and the corresponding processing of the first embodiment. 
         [0260]    The administrator calls up the copy group priority determining screen  17000  to set an order of priority to copy groups in advance. Once an order of priority is set to copy groups, the copy group priority table  18000  is created in the memory  1250 . 
         [0261]    Thereafter, through the processing of Step  13030  in the processing of creating the information obtaining definition table  1263  shown in  FIG. 13 , the management program  1265  loads the copy group definition tables  1264  onto the memory  1250  in descending order of values registered as the priority  18100  in the copy group priority table  18000 . In the case where the copy group priority table  18000  is as shown in  FIG. 18 , the copy group definition table  1264  that is loaded onto the memory  1250  by the management program  1265  first is the copy group definition table  1264  that is associated with the copy group CG.  04 , which is given a priority level “4”. 
         [0262]    Next, through the processing of Step  13050 , the management program  1265  chooses the copy group definition tables  1264  one by one in an order in which the copy group definition tables  1264  have been loaded onto the memory  1250 . The management program  1265  repeatedly performs the following processing on the chosen copy group definition tables  1264 . From each chosen copy group definition table  1264 , the management program  1265  extracts the host computer name  4110 , the copy pair name  4130 , and copy pair definition information. 
         [0263]    The management program  1265  then creates a new entry in the information obtaining definition table  1263  through the processing of Step  13060 . The management program  1265  registers the extracted host computer name  4110 , copy pair name  4130 , and copy pair definition information in the newly created entry. 
         [0264]    In this manner, when a copy pair is managed by plural host computers  1100 , definition information of copy pairs belonging to a low priority copy group is registered in the information obtaining definition table  1263 . 
         [0265]    Accordingly, when a copy pair is managed by plural host computers  1100 , the host computer  1100  that manages a low priority copy group collects the copy pair status. A service application run in the host computer  1100  of high priority is thus less affected by copy pair monitoring. 
       Fourth Embodiment 
       [0266]    While the administrator sets an order of priority to copy groups in the third embodiment, a fourth embodiment of this invention has the management computer  1200  set an order of priority to copy groups according to a priority determining rule which is laid down in advance. 
         [0267]    Described below is the difference between the fourth embodiment and the third embodiment. 
         [0268]      FIG. 19  is a diagram showing the configuration of a copy group priority determining rule table  19000  according to the fourth embodiment of this invention. 
         [0269]    The copy group priority determining rule table  19000  contains a priority level “high” field  19100  and a priority level “low” field  19200 . 
         [0270]    A rule for setting a high priority level is registered in the priority level “high” field  19100 . A rule for setting a low priority level is registered in the priority level “low” field  19200 . 
         [0271]    A row  19300  and a row  19400  hold rules for setting a priority level. 
         [0272]    The row  19300  holds a rule in which the priority level is determined by whether the volume  1011  constituting a copy pair is in the upstream or the downstream. Generally speaking, an upstream volume is a source volume from which data is copied and a downstream volume is a target volume to which data is copied. 
         [0273]    To give an example, a volume A and a volume B form a copy pair with the volume A as the primary volume and the volume B as the secondary volume. The volume B is also paired with a volume C, and the volume B serves as the primary volume of this copy pair while the volume C serves as the secondary volume. 
         [0274]    In this case, the volume A is an upstream volume to the volume B and the volume C. The volume B is a downstream volume to the volume A and an upstream volume to the volume C. The volume C is a downstream volume to the volume A and the volume B. 
         [0275]    The most upstream volume (the volume A) is more often than not the volume  1011  that is directly related to a service application executed in the host computer  1100 . Accordingly, when two volumes  1011  form a copy pair and have an upstream/downstream relation, the upstream volume  1011  is given a high priority level whereas a low priority level is assigned to the downstream volume  1011 . 
         [0276]    The row  19400  holds a rule in which the priority level of a copy group constituted of copy pairs where remote copy is executed is set higher than that of a copy group constituted of copy pairs where local copy is executed. 
         [0277]    In general, a copy pair between which remote copy is executed is more likely to be affected by a failure than a copy pair between which local copy is executed. It is for this reason that the priority level of a copy group constituted of copy pairs where remote copy is executed is set higher than that of a copy group constituted of copy pairs where local copy is executed. 
         [0278]    The rule held in the row  19400  may be modified such that the administrator sets the priority level of a copy group constituted of copy pairs where local copy is executed higher than that of a copy group constituted of copy pairs where remote copy is executed, depending on the environment, operation characteristics, and other characteristics of the storage system. 
         [0279]    The administrator can add an entry to the copy group priority determining rule table  19000 . The administrator can also remove an entry from the copy group priority determining rule table  19000 . This enables the administrator to add or delete a rule for determining the priority level to and from the copy group priority determining rule table  19000 . 
         [0280]    In the processing of Step  13030  shown in  FIG. 13 , when loading the copy group definition tables  1264  onto the memory  1250 , the management program  1265  creates the copy group priority table  18000  according to the copy group priority determining rule table  19000 . Specifically, the management program  1265  determines the priority level of a copy group according to rules registered in the copy group priority determining rule table  19000 . 
         [0281]    The procedure of determining the priority level will be described taking as an example a case in which the copy group definition tables  1171  shown in  FIG. 4  to  FIG. 7  are respectively stored in the host computers  1100  of the storage system shown in  FIG. 3 . In the description, A&gt;B indicates that the priority level of A is higher than that of B. 
         [0282]    According to the rule of the row  19300 , the priority levels of the copy pairs in  FIG. 3  are: P 5 &gt;P 9 ; P 6 &gt;P 10 ; P 7 &gt;P 11 ; and P 8 &gt;P 12 . 
         [0283]    According to the rule of the row  19400 , copy pairs where remote copy is executed (i.e., P 5 , P 6 , P 7 , and P 8 ) are assigned higher priority levels than those of copy pairs where local copy is executed (i.e., P 1 , P 2 , P 3 , P 4 , P 9 , P 10 , P 11 , and P 12 ). 
         [0284]    In the case of the storage system shown in  FIG. 3 , not all of the copy groups are uniquely assigned a priority level by the rules held in the rows  1930  and  1940 . However, copy pairs where remote copy is executed and that are the most upstream pairs (P 5 , P 6 , P 7 , and P 8 ) are given the highest priority level. Copy pairs where local copy is executed and that are the most upstream pairs (P 1 , P 2 , P 3 , and P 4 ) are given the second highest priority level. Copy pairs where local copy is executed and that are the most downstream pairs (P 9 , P 10 , P 11 , and P 12 ) are given the lowest priority level. 
         [0285]    It is thus determined that the copy group  3111  constituted of the copy pairs P 1 , P 2 , and P 3  is to have a higher priority level than that of the copy group  3131  constituted of the copy pairs P 9 , P 10 , P 11 , and P 12 . 
         [0286]    In the manner described above, only definitions of copy pairs that would affect a service relatively little are registered in the information obtaining definition table  1263  without needing the administrator to set a priority level to each copy group. This means that, when a copy pair is managed by plural host computers  1100 , the host computer  1100  that manages a copy group of low priority collects the copy pair status. A service application run in the host computer  1100  that manages a copy group of high priority level is thus affected less by copy pair monitoring. 
         [0287]    While the present invention has been described in detail and pictorially in the accompanying drawings, the present invention is not limited to such detail but covers various obvious modifications and equivalent arrangements, which fall within the purview of the appended claims.