Abstract:
A data processing system includes a first storage system that is connected to a host device and sends and receives data to and from the host device; a second storage system that is connected to the first storage system and receives data from the first storage system; and a third storage system that is connected to the first storage system and receives data from the first storage system. The first storage system, the second storage system and the third storage system are arranged to be changeable between a first status including first and second copy pairs and a second status including a third copy pair in response to a predetermined condition at the first storage system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation application of U.S. Ser. No. 12/246,527, filed Oct. 7, 2008, which is a continuation application of U.S. Ser. No. 11/581,413, filed Oct. 17, 2006 (now U.S. Pat. No. 7,447,855), which is a continuation application of application Ser. No. 11/334,511, filed Jan. 19, 2006 (now U.S. Pat. No. 7,143,254), which is a divisional application of application Ser. No. 10/784,356, filed Feb. 23, 2004, (now U.S. Pat. No. 7,130,975) and claim the benefit of foreign priority of Japanese Application No. 2003-316183, filed Sep. 9, 2003, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to storage systems, and more particularly, to data replication among a plurality of storage systems and resuming data replication processing when failures occur in the storage systems. 
       RELATED BACKGROUND ART 
       [0003]    In recent years, in order to provide continuous service to clients at all times, technologies concerning data replication among storage systems have become important to make it possible for a data processing system to provide services even when a failure occurs in a first storage system. There have been technologies for replicating information stored in the first storage system on second and third storage systems. 
         [0004]    For example, according to one of the known technologies, a first storage system stores data in a first storage system, and transfers data stored in the first storage system to a second storage system, as well as to a third storage system. A computer and the first storage system are connected by a communications link, the first storage system and the second storage system are connected by a communications link, and the first storage system and the third storage system are also connected by a communications link. The first storage system has a first logical volume that is the subject of replication. The second storage system has a second logical volume that is a replication of the first logical volume. The third storage system has a third logical volume that is a replication of the first logical volume. The first storage system, when updating the first logical volume, performs a data replication processing on the second logical volume, and stores in management information a difference between the first logical volume data and the third logical volume data for every data size of a predetermined size. Subsequently, the first storage system uses the management information to perform a data replication processing on the third logical volume. 
         [0005]    The conventional technology described manages the difference in data between the first logical volume and the third logical volume for every data size of a predetermined size. The management information that manages such differences entails a problem of growing larger in proportion to the amount of data that is the subject of replication. Furthermore, due to the fact that the third logical volume is updated based on the management information and in an order unrelated to the order of data update, data integrity cannot be maintained in the third logical volume. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention relates to a data processing system that performs a data replication processing from a first storage system to a third storage system, while maintaining data integrity in the third storage system. Furthermore, the present invention relates to reducing the amount of management information used in data replication. 
         [0007]    The present invention also relates to a data processing system that maintains data integrity in the third storage system even while data in the third storage system is updated to the latest data in the event the first storage system fails. Moreover, a data processing system in accordance with the present invention shortens the amount of time required to update data to the latest data. 
         [0008]    In accordance with an embodiment of the present invention, a first storage system stores as journal information concerning update of data stored in the first storage system. Each journal is formed from a copy of data used for update, and update information such as a write command for update, an update number that indicates a data update order, etc. Furthermore, a third storage system obtains the journal via a communications line between the first storage system and the third storage system and stores the journal in a storage area dedicated to journals. The third storage system has a replication of data that the first storage system has, and uses the journal to update data that corresponds to data in the first storage system in the order of the data update in the first storage system. 
         [0009]    Furthermore, a second storage system has a replication of data that the first storage system has, and the first storage system updates data stored in the second storage system via a communications line between the second storage system and the first storage system when data stored in the first storage system is updated. A data update command on this occasion includes an update number or an update time that was used when the first storage system created the journal. When the data is updated, the second storage system creates update information using the update number or the update time it received from the first storage system and stores the update information as a journal in a storage area dedicated to journals. 
         [0010]    In the event the first storage system fails, the third storage system obtains via a communications line between the second storage system and the third storage system only those journals that the third storage system does not have and updates data that correspond to data in the first storage system in the order of data update in the first storage system. 
         [0011]    According to the present invention, the amount of management information required for data replication can be reduced while maintaining data integrity among a plurality of storage systems. Furthermore, according to the present invention, in the event a storage system or a host computer that comprises a data processing system fails, data replication can be continued at high speed and efficiently while maintaining data integrity. 
         [0012]    Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings that illustrate, by way of example, various features of embodiments of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Preferred embodiments of the present invention will now be described in conjunction with the accompanying drawings, in which: 
           [0014]      FIG. 1  is a block diagram of a logical configuration of one embodiment of the present invention. 
           [0015]      FIG. 2  is a block diagram of a storage system in accordance with one embodiment of the present invention. 
           [0016]      FIG. 3  is a diagram illustrating the relationship between update information and write data according to one embodiment of the present invention. 
           [0017]      FIG. 4  is a diagram illustrating an example of volume information according to one embodiment of the present invention. 
           [0018]      FIG. 5  is a diagram illustrating an example of pair information according to one embodiment of the present invention. 
           [0019]      FIG. 6  is a diagram illustrating an example of group information according to one embodiment of the present invention. 
           [0020]      FIG. 7  is a diagram illustrating an example of pointer information according to one embodiment of the present invention. 
           [0021]      FIG. 8  is a diagram illustrating the structure of a journal logical volume according to one embodiment of the present invention. 
           [0022]      FIG. 9  is a flowchart illustrating the procedure for initiating data replication according to one embodiment of the present invention. 
           [0023]      FIG. 10  is a flowchart illustrating an initial copy processing according to one embodiment of the present invention. 
           [0024]      FIG. 11  is a diagram illustrating a command reception processing according to one embodiment of the present invention. 
           [0025]      FIG. 12  is a flowchart of the command reception processing according to one embodiment of the present invention. 
           [0026]      FIG. 13  is a flowchart of a journal creation processing according to one embodiment of the present invention. 
           [0027]      FIG. 14  is a diagram illustrating a journal read reception processing according to one embodiment of the present invention. 
           [0028]      FIG. 15  is a flowchart of the journal read reception processing according to one embodiment of the present invention. 
           [0029]      FIG. 16  is a diagram illustrating a journal read processing according to one embodiment of the present invention. 
           [0030]      FIG. 17  is a flowchart of the journal read processing according to one embodiment of the present invention. 
           [0031]      FIG. 18  is a flowchart of a journal store processing according to one embodiment of the present invention. 
           [0032]      FIG. 19  is a diagram illustrating a restore processing according to one embodiment of the present invention. 
           [0033]      FIG. 20  is a flowchart of the restore processing according to one embodiment of the present invention. 
           [0034]      FIG. 21  is a diagram illustrating an example of update information according to one embodiment of the present invention. 
           [0035]      FIG. 22  is a diagram illustrating an example of update information when a journal creation processing takes place according to one embodiment of the present invention. 
           [0036]      FIG. 23  is a flowchart of a remote write command reception processing according to one embodiment of the present invention. 
           [0037]      FIG. 24  is a flowchart of a journal replication processing according to one embodiment of the present invention. 
           [0038]      FIG. 25  is a flowchart illustrating the procedure for resuming data replication among storage systems in the event a primary storage system  100 A fails according to one embodiment of the present invention. 
           [0039]      FIG. 26  is a diagram illustrating an example of volume information according to one embodiment of the present invention. 
           [0040]      FIG. 27  is a diagram illustrating an example of pair information according to one embodiment of the present invention. 
           [0041]      FIG. 28  is a diagram illustrating an example of group information according to one embodiment of the present invention. 
           [0042]      FIG. 29  is a diagram illustrating an example of pointer information according to one embodiment of the present invention. 
           [0043]      FIG. 30  is a diagram illustrating the structure of a journal logical volume according to one embodiment of the present invention. 
           [0044]      FIG. 31  is a diagram illustrating an example of volume information according to one embodiment of the present invention. 
           [0045]      FIG. 32  is a diagram illustrating an example of pair information according to one embodiment of the present invention. 
           [0046]      FIG. 33  is a diagram illustrating an example of group information according to one embodiment of the present invention. 
           [0047]      FIG. 34  is a diagram illustrating an example of pointer information according to one embodiment of the present invention. 
           [0048]      FIG. 35  is a diagram illustrating the structure of a journal logical volume according to one embodiment of the present invention. 
           [0049]      FIG. 36  is a diagram illustrating an example of pair information according to one embodiment of the present invention. 
           [0050]      FIG. 37  is a diagram illustrating an example of group information according to one embodiment of the present invention. 
           [0051]      FIG. 38  is a diagram illustrating an example of volume information according to one embodiment of the present invention. 
           [0052]      FIG. 39  is a diagram illustrating an example of pair information according to one embodiment of the present invention. 
           [0053]      FIG. 40  is a diagram illustrating an example of group information according to one embodiment of the present invention. 
           [0054]      FIG. 41  is a diagram illustrating an example of pointer information according to one embodiment of the present invention. 
           [0055]      FIG. 42  is a block diagram illustrating the operation that takes place in the event the primary storage system  100 A fails according to one embodiment of the present invention. 
           [0056]      FIG. 43  is a diagram illustrating an example of pair information according to one embodiment of the present invention. 
           [0057]      FIG. 44  is a diagram illustrating an example of group information according to one embodiment of the present invention. 
           [0058]      FIG. 45  is a diagram illustrating an example of volume information according to one embodiment of the present invention. 
           [0059]      FIG. 46  is a diagram illustrating an example of pair information according to one embodiment of the present invention. 
           [0060]      FIG. 47  is a diagram illustrating an example of group information according to one embodiment of the present invention. 
           [0061]      FIG. 48  is a block diagram illustrating the operation that takes place in the event a host computer  180  fails according to one embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0062]    A data processing system in accordance with an embodiment of the present invention will now be described with reference to the accompanying drawings. 
         [0063]      FIG. 1  is a block diagram of a logical configuration of one embodiment of the present invention. 
         [0064]    According to the present embodiment, a host computer  180  and a storage system  100 A are connected by a connection path  190 , and the storage system  100 A is connected to a storage system  100 B and a storage system  100 C, which have replications of data stored in the storage system  100 A, by connection paths  200 . Furthermore, the storage system  100 B and the storage system  100 C are connected by the connection path  200 . In the following description, in order to readily differentiate the storage system  100  having data that is the subject of replication and the storage systems  100  that have replicated data, the storage system  100  having the data that is the subject of replication shall be called a primary storage system  100 A, while storage systems  100  that have the replicated data shall be called a secondary storage system  100 B and a secondary storage system  100 C. Storage areas within each storage system are managed in divided areas, and each divided storage area is called a logical volume. 
         [0065]    The capacity and the physical storage position (a physical address) of each logical volume  230  within each storage system  100  can be designated using a maintenance terminal, such as a computer, or the host computer  180  connected to the storage system  100 . The physical address of each logical volume  230  is stored in volume information  400 , described later. A physical address is, for example, a number (a storage device number) that identifies a storage device  150  (see  FIG. 2 ) within the storage system  100  and a numerical value that uniquely identifies a storage area within the storage device  150 , such as a position from the head of a storage area in the storage device  150 . In the following description, a physical address shall be a combination of a storage device number and a position from the head of a storage area within a storage device. Although a logical volume is a storage area of one storage device in the following description, one logical volume can be correlated to storage areas of a plurality of storage devices by converting logical addresses and physical addresses. 
         [0066]    Data stored in each storage system  100  can be uniquely designated for referencing and updating purposes by using a number (a logical volume number) that identifies a logical volume and a numerical value that uniquely identifies a storage area, such as a position from the head of a storage area of a logical volume; a combination of a logical volume number and a position from the head of a storage area in the logical volume (a position within logical address) shall hereinafter be called a logical address. 
         [0067]    In the following description, in order to readily differentiate data that is the subject of replication from replicated data, the logical volume  230  with data that is the subject of replication shall be called a primary logical volume, while the logical volumes  230  with replicated data shall be called secondary logical volumes. A primary logical volume and a corresponding secondary logical volume shall be called a pair. The state and relationship between a primary logical volume and a secondary logical volume are stored in pair information  500 , described later. 
         [0068]    A management unit called a group is provided in order to maintain the order of data update between logical volumes. For example, let us assume that the host computer  180  updates data  1  in a primary logical volume  1 , and subsequently reads data  1  and uses numerical values of the data  1  to perform a processing to update data  2  in a primary logical volume  2 . When a data replication processing from the primary logical volume  1  to a secondary logical volume  1 , and a data replication processing from the primary logical volume  2  to a secondary logical volume  2 , take place independently, the replication processing of data  2  to the secondary logical volume  2  may take place before the replication processing of data  1  to the secondary logical volume  1 . If the replication processing of data  1  to the secondary logical volume  1  is halted due to a failure that occurs between the replication processing of data  2  to the secondary logical volume  2  and the replication processing of data  1  to the secondary logical volume  1 , the data integrity between the secondary logical volume  1  and the secondary logical volume  2  is lost. In order to maintain data integrity between the secondary logical volume  1  and the secondary logical volume  2  even in such instances, logical volumes whose data update order must be maintained are registered in the same group, so that an update number from group information  600 , described later, is allocated to each logical volume within one group, and a replication processing to the secondary logical volumes is performed in the order of update numbers. Update times may be used in place of update numbers. For example, in  FIG. 1 , a logical volume (DATA  1 ) and a logical volume (DATA  2 ) form a group  1  in the primary storage system  100 A. Furthermore, a logical volume (data  1 ), which is a replication of the logical volume (DATA  1 ), and a logical volume (data  2 ), which is a replication of the logical volume (DATA  2 ), form a group  1  in the secondary storage system  100 C. Similarly, a logical volume (COPY  1 ), which is a replication of the logical volume (DATA  1 ), and a logical volume (COPY  2 ), which is a replication of the logical volume (DATA  2 ), form a group  1  in the secondary storage system  100 B. 
         [0069]    When updating data of the primary logical volumes (DATA  1 , DATA  2 ) that are the subject of replication, the primary storage system  100 A creates journals, described later, and stores them in a logical volume of the primary storage system  100 A in order to update data of the secondary logical volumes (COPY  1 , COPY  2 ). In the description of the present embodiment example, a logical volume that stores journals only (hereinafter called a “journal logical volume”) is allocated to each group. In  FIG. 1 , the journal logical volume for group  1  is a logical volume (JNL  1 ). 
         [0070]    Similarly, when updating data in the secondary logical volumes (data  1 , data  2 ) of the secondary storage system  100 C, the secondary storage system  100 C creates journals, described later, and stores them in a journal logical volume within the secondary storage system  100 C. In  FIG. 1 , the journal logical volume for group  1  is a logical volume (jnl  1 ). 
         [0071]    A journal logical volume is allocated to each group within the secondary storage system  100 B as well. Each journal logical volume is used to store journals that are transferred from the primary storage system  100 A to the secondary storage system  100 B. When there is a high load on the secondary storage system  100 B, instead of updating data of the secondary logical volumes (COPY  1 , COPY  2 ) when the journals are received, the data of the secondary logical volumes (COPY  1 , COPY  2 ) can be updated later when the load on the secondary storage system  100 B is low, for example, by storing journals in the journal logical volume. Furthermore, if there is a plurality of connection paths  200 , the transfer of journals from the primary storage system  100 A to the secondary storage system  100 B can be performed in a multiplex manner to make effective use of the transfer capability of the connection paths  200 . Numerous journals may accumulate in the secondary storage system  100 B due to update order, but this does not pose any problem since journals that cannot be used immediately for data updating of the secondary logical volumes can be stored in the journal logical volume. In  FIG. 1 , the journal logical volume for group  1  is a logical volume (JNL  2 ). 
         [0072]    Each journal is comprised of write data and update information. The update information is information for managing write data, and comprises of the time at which a write command was received (update time), a group number, an update number in the group information  600  described later, a logical address of the write command, the size of the write data, and the logical address in the journal logical volume where the write data is stored. The update information may have only either the time at which the write command was received or the update number. If the time at which the write command was created is in the write command from the host computer  180 , the time at which the write command was created can be used instead of the time at which the write command was received. Using  FIGS. 3 and 21 , an example of update information of a journal will be described. Update information  310  stores a write command that was received at 22:20:10 on Mar. 17, 1999. The write command is a command to store write data at position  700  from the head of a storage area of a logical volume number  1 , and the data size is  300 . The write data in the journal is stored beginning at position  1500  from the head of a storage area in a logical volume number  4  (the journal logical volume). From this, it can be seen that the logical volume whose logical volume number is  1  belongs to group  1  and that this is the fourth data update since data replication of group  1  began. 
         [0073]    As shown in  FIG. 3 , each journal logical volume is divided into a storage area for storing update information (an update information area) and a storage area for storing write data (a write data area), for example. In the update information area, update information is stored from the head of the update information area in the order of update numbers; when the update information reaches the end of the update information area, the update information is stored from the head of the update information area again. In the write data area, write data are stored from the head of the write data area; when the write data reach the end of the write data area, the write data are stored from the head of the write data area again. The ratio of the update information area to the write data area can be a fixed value or set through a maintenance terminal or the host computer  180 . Such information is stored in pointer information  700 , described later. In the following description, each journal logical volume is divided into areas for update information and write data; however, a method in which journals, i.e., update information and corresponding write data, are consecutively stored from the head of a logical volume can also be used. 
         [0074]    Referring to  FIG. 1 , an operation for reflecting data update made to the primary logical volume (DATA  1 ) of the primary storage system  100 A on the secondary logical volume (data  1 ) of the secondary storage system  100 C and the secondary logical volume (COPY  1 ) of the secondary storage system  100 B will be generally described. 
         [0075]    (1) Upon receiving a write command for data in the primary logical volume (DATA  1 ) from the host computer  180 , the primary storage system  100 A updates data in the primary logical volume (DATA  1 ), stores journals in the journal logical volume (JNL  1 ), and issues a command to the secondary system  100 C to update the corresponding data in the secondary logical volume (data  1 ) in the secondary system  100 C (a remote write command), through a command reception processing  210  and a read/write processing  220  described later ( 270  in  FIG. 1 ). 
         [0076]    (2) Upon receiving the remote write command from the primary storage system  100 A, the secondary storage system  100 C updates corresponding data in the secondary logical volume (data  1 ) and stores the journals in the journal logical volume (jnl  1 ) through the command reception processing  210  and the read/write processing  220 , described later ( 270  in  FIG. 1 ). 
         [0077]    (3) After receiving a response to the remote write command, the primary storage system  100 A reports the end of the write command to the host computer  180 . As a result, data in the primary logical volume (DATA  1 ) in the primary storage system  100 A and data in the secondary logical volume (data  1 ) in the secondary storage system  100 C match completely. Such data replication is called synchronous data replication. 
         [0078]    (4) The secondary storage system  100 B reads the journals from the primary storage system  100 A through a journal read processing  240 , described later, and stores the journals in the journal logical volume (JNL  2 ) through the read/write processing  220  ( 280  in  FIG. 1 ). 
         [0079]    (5) Upon receiving a journal read command from the secondary storage system  100 B, the primary storage system  100 A reads the journals from the journal logical volume (JNL  1 ) and sends the journals to the secondary storage system  100 B through the command reception processing  210  and the read/write processing  220 , described later ( 280  in  FIG. 1 ). 
         [0080]    (6) The secondary storage system  100 B uses the pointer information  700  through a restore processing  250  and the read/write processing  220 , described later, to read the journals from the journal logical volume (JNL  2 ) in ascending order of update numbers and updates data in the secondary logical volume (COPY  1 ) ( 290  in  FIG. 1 ). As a result, data in the primary logical volume (DATA  1 ) in the primary storage system  100 A and data in the secondary logical volume (COPY  1 ) in the secondary storage system  100 B match completely some time after the update of the primary logical volume (DATA  1 ). Such data replication is called asynchronous data replication. 
         [0081]    The internal configuration of the storage system  100  is shown in  FIG. 2 . Each storage system  100  is comprised of one or more host adapters  110 , one or more disk adapters  120 , one or more cache memories  130 , one or more shared memories  140 , one or more storage devices  150 , one or more common paths  160 , and one or more connection lines  170 . The host adapters  110 , the disk adapters  120 , the cache memories  130  and the shared memories  140  are mutually connected by the common paths  160 . The common paths  160  may be redundant in case of a failure of one of the common paths  160 . The disk adapters  120  and the storage devices  150  are connected by the connection lines  170 . In addition, although not shown, a maintenance terminal for setting, monitoring and maintaining the storage system  100  is connected to every host adapter  110  and every disk adapter  120  by a dedicated line. 
         [0082]    Each host adapter  110  controls data transfer between the host computer  180  and the cache memories  130 . Each host adapter  110  is connected to the host computer  180  or another storage system  100  via a connection line  190  and the connection path  200 , respectively. Each disk adapter  120  controls data transfer between the cache memories  130  and the storage devices  150 . The cache memories  130  are memories for temporarily storing data received from the host computer  180  or data read from the storage devices  150 . The shared memories  140  are memories shared by all host adapters  110  and disk adapters  120  within the same storage system  100 . 
         [0083]    The volume information  400  is information for managing logical volumes and includes volume state, format, capacity, synchronous pair number, asynchronous pair number, and physical address.  FIG. 4  shows an example of the volume information  400 . The volume information  400  is stored in a memory, such as the shared memories  140 , that can be referred to by the host adapters  110  and the disk adapters  120 . The volume state is one of “normal,” “primary,” “secondary,” “abnormal,” and “blank.” The logical volume  230  whose volume state is “normal” or “primary” indicates that the logical volume  230  can be accessed normally from the host computer  180 . The logical volume  230  whose volume state is “secondary” can allow access from the host computer  180 . The logical volume  230  whose volume state is “primary” indicates that it is the logical volume  230  from which data is being replicated. The logical volume  230  whose volume state is “secondary” indicates that it is the logical volume  230  on which replication is made. The logical volume  230  whose volume state is “abnormal” indicates that it is the logical volume  230  that cannot be accessed normally due to a failure. A failure may be a malfunction of the storage device  150  that has the logical volume  230 , for example. The logical volume  230  whose volume state is “blank” indicates that it is not in use. Synchronous pair numbers and asynchronous pair numbers are valid if the corresponding volume state is “primary” or “secondary,” and each stores a pair number for specifying the pair information  500 , described later. If there is no pair number to be stored, an invalid value (for example, “0”) is set. In the example shown in  FIG. 4 , a logical volume  1  has OPEN  3  as format, a capacity of 3 GB, its data stored from the head of a storage area of the storage device  150  whose storage device number is  1 , is accessible, and is a subject of data replication. 
         [0084]    The pair information  500  is information for managing pairs and includes a pair state, a primary storage system number, a primary logical volume number, a secondary storage system number, a secondary logical volume number, a group number, and a copy complete address (i.e., copied address).  FIG. 5  shows an example of the pair information  500 . The pair information  500  is stored in a memory, such as the shared memories  140 , that can be referred to by the host adapters  110  and the disk adapters  120 . The pair state is one of “normal,” “abnormal,” “blank,” “not copied” and “copying.” If the pair state is “normal,” it indicates that data of the primary logical volume  230  is replicated normally. If the pair state is “abnormal,” it indicates that data in the primary logical volume  230  cannot be replicated due to a failure. A failure can be a disconnection of the connection path  200 , for example. If the pair state is “blank,” it indicates that the corresponding pair number information is invalid. If the pair state is “copying,” it indicates that an initial copy processing, described later, is in progress. If the pair state is “not copied,” it indicates that the initial copy processing, described later, has not yet taken place. The primary storage system number is a number that specifies the primary storage system  100 A that has the primary logical volume  230 . The secondary storage system number is a number that specifies the secondary storage system  100 B that has the secondary logical volume  230 . The group number is a group number to which the primary logical volume belongs to, if the storage system is the primary storage system. The group number is a group number to which the secondary logical volume belongs to, if the storage system is a secondary storage system. The copy complete address will be described when the initial copy processing is described later. Pair information  1  in  FIG. 5  indicates that the subject of data replication is the primary logical volume  1  in the primary storage system A, that the data replication destination is the secondary logical volume  1  in the secondary storage system B, and that the data replication processing has taken place. 
         [0085]    The group information  600  includes a group state, a pair set, a journal logical volume number, an update number, a replication type, a partner storage system number, and a partner group number.  FIG. 6  shows an example of the group information  600 . The group information  600  is stored in a memory, such as the shared memories  140 , that can be referred to by the host adapters  110  and the disk adapters  120 . The group state is one of “normal,” “abnormal,” “blank,” “halted,” and “in preparation.” If the group state is “normal,” it indicates that at least one pair state in the corresponding pair sets is in the “normal” state. If the group state is “abnormal,” it indicates that all pair states in the corresponding pair sets are in the “abnormal” state. If the group state is “blank,” it indicates that corresponding group number information is invalid. If the storage system is the primary storage system, the “halted” group state indicates that journals will not be created temporarily. The state is used when the group state is “normal” and journal creation is to be halted temporarily. If the storage system is a secondary storage system, the “halted” group state indicates that the journal read processing will not be carried out temporarily. The state is used when the group state is “normal” and reading journals from the primary storage system is to be temporarily halted. If the group state is “in preparation,” it indicates that a data replication initiation processing, described later, is in progress. If the storage system is the primary storage system, each pair set includes pair numbers of all primary logical volumes that belong to the group indicated by the corresponding group number. If the storage system is a secondary storage system, each pair set includes pair numbers of all secondary logical volumes that belong to the group indicated by the corresponding group number. The journal logical volume number indicates the journal logical volume number that belongs to the group with the corresponding group number. If there is no journal logical volume that belongs to the group with the corresponding group number, an invalid value (for example, “0”) is set. The update number has an initial value of 1 and changes whenever a journal is created. The update number is stored in the update information of journals and used by the secondary storage system  100 B to maintain the order of data update. The replication type is either “synchronous” or “asynchronous.” If the replication type is “synchronous,” the primary logical volume and the secondary logical volume are updated simultaneously. As a result, data in the primary logical volume and data in the secondary logical volume match completely. If the replication type is “asynchronous,” the secondary logical volume is updated after the primary logical volume is updated. As a result, data in the primary logical volume and data in the secondary logical volume sometimes do not match (i.e., data in the secondary logical volume is old data of the primary logical volume), but data in the secondary logical volume completely matches data in the primary logical volume after some time. If the storage system is the primary storage system, the partner storage system number is the secondary storage system number that has the paired secondary logical volume that belongs to the corresponding group. If the storage system is a secondary storage system, the partner storage system number is the primary storage system number that has the paired primary logical volume that belongs to the corresponding group. If the storage system is the primary storage system, the partner group number is the group number to which the paired secondary logical volume of the corresponding group belongs. If the storage system is a secondary storage system, the partner group number is the group number to which the paired primary logical volume of the corresponding group belongs. For example, group information  1  in  FIG. 6  is comprised of primary logical volumes  1 ,  2  based on pair information  1 ,  2 , and of a journal logical volume  4 , and indicates that data replication processing (asynchronous) has taken place normally. 
         [0086]    The pointer information  700  is stored for each group and is information for managing the journal logical volume for the corresponding group; it includes an update information area head address, a write data area head address, an update information latest address, an update information oldest address, a write data latest address, a write data oldest address, a read initiation address, and a retry initiation address.  FIGS. 7 and 8  show an example of the pointer information  700 . The update information area head address is the logical address at the head of the storage area for storing update information in the journal logical volume (update information area). The write data area head address is the logical address at the head of the storage area for storing write data in the journal logical volume (write data area). The update information latest address is the head logical address to be used for storing update information when a journal is stored next. The update information oldest address is the head logical address that stores update information of the oldest (i.e., having the lowest update number) journal. The write data latest address is the head logical address to be used for storing write data when a journal is stored next. The write data oldest address is the head logical address that stores write data of the oldest (i.e., the having the lowest update number) journal. The read initiation address and the retry initiation address are used only in the primary storage system  100 A in the journal read reception processing, described later. In the example of the pointer information  700  shown in  FIGS. 7 and 8 , the area for storing journal update information (the update information area) spans from the head of the storage areas to position  699  of the logical volume  4 , while the area for storing journal write data (the write data area) spans from position  700  to position  2699  of the storage areas of the logical volume  4 . The journal update information is stored from position  200  to position  499  of the storage areas of the logical volume  4 , and the next journal update information will be stored beginning at position  500  of the storage areas of the logical volume  4 . The journal write data is stored from position  1300  to position  2199  of the storage areas of the logical volume  4 , and the next journal write data will be stored beginning at position.  2200  of the storage areas of the logical volume  4 . 
         [0087]    Although a mode in which one journal logical volume is allocated to each group is described below, a plurality of journal logical volumes may be allocated to each group. For example, two journal logical volumes can be allocated to one group, and the pointer information  700  can be provided for each journal logical volume, so that journals can be stored in the two journal logical volumes alternately. By doing this, writing the journals to the storage device  150  can be distributed, which can improve performance. Furthermore, this can also improve the journal read performance. Another example would be one in which two journal logical volumes are allocated to one group, but only one journal logical volume is normally used. The other journal logical volume is used when the performance of the journal logical volume that is normally used declines or the journal logical volume that is normally used fails and cannot be used. An example of the declining performance of the logical volume that is normally used is a case in which a journal logical volume is comprised of a plurality of storage devices  150 , where data are stored in RAID method, and at least one storage device  150  that comprises the RAID fails. 
         [0088]    It is preferable for the volume information  400 , the pair information  500 , the group information  600  and the pointer information  700  to be stored in the shared memories  140 . However, the present embodiment example is not limited to this and the information can be stored together or dispersed among the cache memories  130 , the host adapters  110 , the disk adapters  120 , and/or storage devices  150 . 
         [0089]    Next, a procedure for initiating data replication (a data replication initiation processing) from the primary storage system  100 A to the secondary storage system  100 B and the secondary storage system  100 C will be described using  FIGS. 9 and 10 . 
         [0090]    (1) Group creation (step  900 ) will be described. Using a maintenance terminal or the host computer  180 , a user refers to the group information  600  for the primary storage system  100 A and obtains a group number A, whose group state is “blank.” Similarly, the user obtains a group number B of the secondary storage system  100 B (or of the secondary storage system  100 C). Using the maintenance terminal or the host computer  180 , the user gives a group creation instruction to the primary storage system  100 A. The group creation instruction is comprised of the group number A that is the subject of the instruction, a partner storage system number B, a partner group number B, and a replication type. 
         [0091]    Upon receiving the group creation instruction, the primary storage system  100 A makes changes to the group information  600 . Specifically, the primary storage system  100 A sets the group state for the group number A that is the subject of instruction to “in preparation” in the group information  600 ; the partner storage system number to the partner storage system number B instructed; the partner group number to the partner group number B instructed; and the replication type to the replication type instructed. The primary storage system  100 A sets the update number of the group information  600  to 1 (initial value). Furthermore, the primary storage system  100 A gives a group creation instruction to the storage system having the partner storage system number B. In the group creation instruction, the group number that is the subject of the instruction is the partner group number B, the partner storage system number is the storage system number of the primary storage system  100 A, the partner group number is the group number A that is the subject of the original instruction, and the replication type is the replication type instructed. 
         [0092]    (2) Next, pair registration (step  910 ) will now be described. Using the maintenance terminal or the host computer  180 , the user designates information that indicates the subject of data replication and information that indicates the data replication destination and gives a pair registration instruction to the primary storage system  100 A. The information that indicates the subject of data replication is the group number A and the primary logical volume number A that are the subject of data replication. The information that indicates the data replication destination is the secondary logical volume number B in the secondary storage system  100 B for storing the replication data. 
         [0093]    Upon receiving the pair registration instruction, the primary storage system  100 A obtains a pair number whose pair state is “blank” from the pair information  500  and sets “not copied” as the pair state; the primary storage system number A that indicates the primary storage system  100 A as the primary storage system number; the primary logical volume number A instructed as the primary logical volume number; the partner storage system number of the group number A in the group information  600  as the secondary storage system number; the secondary logical volume number B instructed as the secondary logical volume number; and the group number A instructed as the group number. The primary storage system  100 A adds the pair number obtained for the group number A instructed to the pair set in the group information  600 , and changes the volume state of the primary logical volume number A to “primary.” 
         [0094]    The primary storage system  100 A notifies the partner storage system for the group number A instructed in the group information  600  of the primary storage system number A indicating the primary storage system  100 A, the partner group number B for the group number A in the group information  600 , the primary logical volume number A, and the secondary logical volume number B, and commands a pair registration. The secondary storage system  100 B obtains a blank pair number whose pair state is “blank” from the pair information  500  and sets “not copied” as the pair state; the primary storage system number A notified as the primary storage system number; the primary logical volume number A notified as the primary logical volume number; the secondary storage system number B as the secondary storage system number; the secondary logical volume number B notified as the secondary logical volume number; and the group number B notified as the group number. Additionally, the secondary storage system  100 B adds the pair number obtained to the pair set for the group number B instructed in the group information  600 , and changes the volume state of the secondary volume number B to “secondary.” 
         [0095]    The above operation is performed on all pairs that are the subject of data replication. 
         [0096]    Although registering logical volumes with a group and setting logical volume pairs are performed simultaneously according to the processing, they can be done individually. 
         [0097]    (3) Next, journal logical volume registration (step  920 ) will be described. Using the maintenance terminal or the host computer  180 , the user gives the primary storage system  100 A an instruction to register the logical volume to be used for storing journals (a journal logical volume) with a group (a journal logical volume registration instruction). The journal logical volume registration instruction is comprised of a group number and a logical volume number. 
         [0098]    The primary storage system  100 A registers the logical volume number instructed as the journal logical volume number for the group number instructed in the group information  600 . In addition, the primary storage system  100 A sets the volume state of the logical volume to “normal” in the volume information  400 . 
         [0099]    Similarly, using the maintenance terminal or the host computer  180 , the user refers to the volume information  400  for the secondary storage system  100 B, designates the secondary storage system  100 B, the group number B, and the logical volume number to be used as the journal logical volume, and gives a journal logical volume registration instruction to the primary storage system  100 A. The primary storage system  100 A transfers the journal logical volume registration instruction to the secondary storage system  100 B. The secondary storage system  100 B registers the logical volume number instructed as the journal logical volume number for the group number B instructed in the group information  600 . In addition, the secondary storage system  100 B sets the volume state for the corresponding logical volume to “normal” in the volume information  400 . 
         [0100]    Alternatively, using the maintenance terminal of the secondary storage system  100 B or the host computer  180  connected to the secondary storage system  100 B, the user may designate the group number and the logical volume number to be used as the journal logical volume and give a journal logical volume registration instruction to the secondary storage system  100 B. The user would then do the same with the secondary storage system  100 C. 
         [0101]    The operations described are performed on all logical volumes that are to be used as journal logical volumes. However, step  910  and step  920  may be reversed in order. 
         [0102]    (4) Next, data replication processing initiation (step  930 ) will be described. Using the maintenance terminal or the host computer  180 , the user designates a group number C, whose replication type is synchronous, and the group number B, whose replication type is asynchronous, for initiating the data replication processing, and instructs the primary storage system  100 A to initiate the data replication processing. The primary storage system  100 A sets all copy complete addresses in the pair information  500  that belong to the group B to 0. 
         [0103]    The primary storage system  100 A instructs the partner storage system  100 B for the group number B in the group information  600  to change the group state of the partner group number of the group number B in the group information  600  to “normal” and to initiate the journal read processing and the restore processing, described later. The primary storage system  100 A instructs the partner storage system  100 C for the group number C in the group information  600  to change the group state of the partner group number of the group number C to “normal” in the group information  600 . 
         [0104]    The primary storage system  100 A changes the group state of the group number C and of the group number B to “normal” and initiates the initial copy processing, described later. 
         [0105]    Although the synchronous data replication processing initiation and the asynchronous data replication processing initiation are instructed simultaneously according to the description, they can be performed individually. 
         [0106]    (5) Next, an initial copy processing end (step  940 ) will be described. 
         [0107]    When the initial copying is completed, the primary storage system  100 A notifies the end of the initial copy processing to the secondary storage system  100 B and the secondary storage system  100 C. The secondary storage system  100 B and the secondary storage system  100 C change the pair state of every secondary logical volume that belongs to either the group B or the group C to “normal.” 
         [0108]      FIG. 10  is a flowchart of the initial copy processing. In the initial copy processing, using copy complete addresses in the pair information  500 , a journal is created per unit size in sequence from the head of storage areas for all storage areas of the primary logical volume that is the subject of data replication. Copy complete addresses have an initial value of 0, and the amount of data created is added each time a journal is created. The storage areas from the head of the storage areas of each logical volume to one position prior to the copy complete addresses represent storage areas for which journals have been created through the initial copy processing. By performing the initial copy processing, data in the primary logical volume that have not been updated can be transferred to the secondary logical volume. A host adapter A within the primary storage system  100 A performs the processing according to the following description, but the processing may be performed by the disk adapters  120 . 
         [0109]    (1) The host adapter A within the primary storage system  100 A obtains a primary logical volume A that is part of a pair that belongs to the asynchronous replication type group B, which is the subject of processing, and whose pair state is “not copied”; the host adapter A changes the pair state to “copying” and repeats the following processing (steps  1010 ,  1020 ). If there is no primary logical volume A, the host adapter A terminates the processing (step  1030 ). 
         [0110]    (2) If the primary logical volume A is found in step  1020  to exist, the host adapter A creates a journal per data unit size (for example, 1 MB data). The journal creation processing is described later (step  1040 ). 
         [0111]    (3) To update data in the secondary logical volume that forms a synchronous pair with the primary logical volume A, the host adapter A sends a remote write command to the secondary storage system C, which has the secondary logical volume that is part of the synchronous pair. The remote write command includes a write command, a logical address (where the logical volume is the secondary logical volume C of the synchronous pair number, and the position within the logical volume is the copy complete address), data amount (unit size), and the update number used in step  1040 . Instead of the update number, the time at which the journal was created may be used (step  1045 ). The operation of the secondary storage system C when it receives the remote write command will be described in a command reception processing  210 , described later. 
         [0112]    (4) Upon receiving a response to the remote write command, the host adapter A adds to the copy complete address the data size of the journal created (step  1050 ). 
         [0113]    (5) The above processing is repeated until the copy complete addresses reach the capacity of the primary logical volume A (step  1060 ). When the copy complete addresses become equal to the capacity of the primary logical volume A, which indicates that journals have been created for all storage areas of the primary logical volume A, the host adapter A updates the pair state to “normal” and initiates the processing of another primary logical volume (step  1070 ). 
         [0114]    Although logical volumes are described as the subject of copying one at a time according to the flowchart, a plurality of logical volumes can be processed simultaneously. 
         [0115]      FIG. 11  is a diagram illustrating the processing of the command reception processing  210 ;  FIG. 12  is a flowchart of the command reception processing  210 ;  FIG. 13  is a flowchart of a journal creation processing;  FIG. 23  is a flowchart of a remote write command reception processing; and  FIG. 24  is a flowchart of a journal replication processing. Next, by referring to these drawings, a description will be made as to an operation that takes place when the primary storage system  100 A receives a write command from the host computer  180  to write to the logical volume  230  that is the subject of data replication. 
         [0116]    (1) The host adapter A within the primary storage system  100 A receives an access command from the host computer  180 . The access command includes a command such as a read, write or journal read command, described later, as well as a logical address that is the subject of the command, and data amount. Hereinafter, the logical address shall be called a logical address A, the logical volume number a logical volume A, the position within the logical volume a position A within the logical volume, and the data amount a data amount A, in the access command (step  1200 ). 
         [0117]    (2) The host adapter A checks the access command (steps  1210 ,  1215 ,  1228 ). If the access command is found through checking in step  1215  to be a journal read command, the host adapter A performs the journal read reception processing described later (step  1220 ). If the access command is found to be a remote write command, the host adapter A performs a remote write command reception processing described later (step  2300 ). If the access command is found to be a command other than these, such as a read command, the host adapter A performs a read processing according to conventional technologies (step  1230 ). 
         [0118]    (3) If the access command is found through checking in step  1210  to be a write command, the host adapter A refers to the logical volume A in the volume information  400  and checks the volume state (step  1240 ). If the volume state of the logical volume A is found through checking in step  1240  to be other than “normal” or “primary,” which indicates that the logical volume A cannot be accessed, the host adapter A reports to the host computer  180  that the processing ended abnormally (step  1245 ). 
         [0119]    (4) If the volume state of the logical volume A is found through checking in step  1240  to be either “normal” or “primary,” the host adapter A reserves at least one cache memory  130  and notifies the host computer  180  that the primary storage system  100 A is ready to receive data. Upon receiving the notice, the host computer  180  sends write data to the primary storage system  100 A. The host adapter A receives the write data and stores it in the cache memory  130  (step  1250 ;  1100  in  FIG. 11 ). (5) The host adapter A refers to the volume information, pair information and group information of the logical volume A and checks whether the logical volume A is the subject of asynchronous replication (step  1260 ). If through checking in step  1260  the volume state of the logical volume A is found to be “primary,” the pair state of the pair with the asynchronous pair number that the logical volume A belongs to is “normal,” and the group state of the group that the pair belongs to is “normal,” these indicate that the logical volume A is the subject of asynchronous replication; consequently, the host adapter A performs the journal creation processing described later (step  1265 ). 
         [0120]    (6) The host adapter A refers to the volume information, pair information and group information of the logical volume A and checks whether the logical volume A is the subject of synchronous replication (step  1267 ). If through checking in step  1267  the volume state of the logical volume A is found to be “primary,” the pair state of the pair with the synchronous pair number that the logical volume A belongs to is “normal,” and the group state of the group that the pair belongs to is “normal,” these indicate that the logical volume A is the subject of synchronous replication; consequently, the host adapter A sends to the secondary storage system C having the logical volume that forms the pair with the synchronous pair number a remote write command to store the write data received from the host computer  180  ( 1185  in  FIG. 11 ). The remote write command includes a write command, a logical address (where the logical volume is the secondary logical volume C that forms the pair with the synchronous pair number, and the position within the logical volume is the position A within the logical volume), data amount A, and the update number used in step  1265 . Instead of the update number, the time at which the write command was received from the host computer  180  may be used. If the logical volume is found through checking in step  1267  not to be the logical volume that is the subject of synchronous replication, or if the journal creation processing in step  1265  is not successful, the host adapter A sets the numerical value “0,” which indicates invalidity, as the update number. 
         [0121]    (7). Upon receiving a response to step  1267  or to the remote write command in step  1268 , the host adapter A commands the disk adapter  120  to write the write data to the storage area of the storage device  150  that corresponds to the logical address A ( 1160  in  FIG. 11 ), and reports to the host computer  180  that the processing ended (steps  1270 ,  1280 ). Subsequently, the disk adapter  120  stores the write data in the storage area through the read/write processing ( 1170  in  FIG. 11 ). 
         [0122]    Next, the journal creation processing will be described. 
         [0123]    (1) The host adapter A checks the volume state of the journal logical volume (step  1310 ). If the volume state of the journal logical volume is found through checking in step  1310  to be “abnormal,” journals cannot be stored in the journal logical volume; consequently, the host adapter A changes the group state to “abnormal” and terminates the processing (step  1315 ). In such a case, the host adapter A converts the journal logical volume to a normal logical volume. 
         [0124]    (2) If the journal logical volume is found through checking in step  1310  to be in the “normal” state, the host adapter A continues the journal creation processing. The journal creation processing entails different processing depending on whether the processing is part of an initial copy processing or a part of a command reception processing (step  1320 ). If the journal creation processing is a part of a command reception processing, the host adapter A performs the processing that begins with step  1330 . If the journal creation processing is a part of an initial copy processing, the host adapter A performs the processing that begins with step  1370 . 
         [0125]    (3) If the journal creation processing is a part of a command reception processing, the host adapter A checks whether the logical address A that is the subject of writing is set as the subject of initial copy processing (step  1330 ). If the pair state of the logical volume A is “not copied,” the host adapter A terminates the processing without creating any journals, since a journal creation processing will be performed later as part of an initial copy processing (step  1335 ). If the pair state of the logical volume A is “copying,” and if the copy complete address is equal to or less than the position A within the logical address, the host adapter A terminates the processing without creating any journals, since a journal creation processing will be performed later as part of an initial copy processing (step  1335 ). Otherwise, i.e., if the pair state of the logical volume A is “copying” and if the copy complete address is greater than the position A within the logical address, or if the pair state of the logical volume A is “normal,” the initial copy processing is already completed, and the host adapter A continues the journal creation processing. 
         [0126]    (4) Next, the host adapter A checks whether a journal can be stored in the journal logical volume. The host adapter A uses the pointer information  700  to check whether there are any blank areas in the update information area (step  1340 ). If the update information latest address and the update information oldest address in the pointer information  700  are equal, which indicates that there are no blank areas in the update information area, the host adapter A terminates the processing due to a failure to create a journal (step  1390 ). 
         [0127]    If a blank area is found in the update information area through checking in step  1340 , the host adapter A uses the pointer information  700  to check whether the write data can be stored in the write data area (step  1345 ). If the write data oldest address falls within a range of the write data latest address and a numerical value resulting from adding the data amount A to the write data latest address, which indicates that the write data cannot be stored in the write data area, the host adapter A terminates the processing due to a failure to create a journal (step  1390 ). 
         [0128]    (5) If the journal can be stored, the host adapter A obtains a logical address for storing the update number and update information, as well as a logical address for storing write data, and creates update information in at least one cache memory  130 . The update number set in the group information  600  is a numerical value resulting from adding 1 to the update number of the subject group obtained from the group information  600 . The logical address for storing the update information is the update information latest address in the pointer information  700 , and a numerical value resulting from adding the size of the update information to the update information latest address is set as the new update information latest address in the pointer information  700 . The logical address for storing the write data is the write data latest address in the pointer information  700 , and a numerical value resulting from adding the data amount A to the write data latest address is set as the new write data latest address in the pointer information  700 . 
         [0129]    The host adapter A sets as the update information the numerical values obtained, the group number, the time at which the write command was received, the logical address A within the write command, and the data amount A (step  1350 ;  1120  in  FIG. 11 ). For example, if a write command to write a data size of 100 beginning at position  800  from the head of the storage area of the primary logical volume  1  that belongs to group  1  in the state of the group information  600  shown in  FIG. 6  and the pointer information  700  shown in  FIG. 7  is received, the update information shown in  FIG. 22  is created. The update number for the group information is 6, the update information latest address in the pointer information is  600  (the update information size is 100), and the write data latest address is  2300 . 
         [0130]    (6) The host adapter A commands the disk adapter  120  to write the update information and write data of the journal on the storage device  150  and ends the processing normally (step  1360 ;  1130 ,  1140  and  1150  in  FIG. 11 ). 
         [0131]    (7) If the journal creation processing is a part of an initial copy processing, the host adapter A performs the processing that begins with step  1370 . The host adapter A checks whether a journal can be created. The host adapter A uses the pointer information  700  to check whether there are any blank areas in the update information area (step  1370 ). If the update information latest address and the update information oldest address in the pointer information  700  are equal, which indicates that there are no blank areas in the update information area, the host adapter A terminates the processing due to a failure to create a journal (step  1390 ). Since the write data of journals is read from the primary logical volume and no write data areas are used in the initial copy processing described in the present embodiment example, there is no need to check whether there are any blank areas in the write data area. 
         [0132]    (8) If it is found through checking in step  1370  that a journal can be created, the host adapter A creates update information in at least one cache memory  130 . The time the update number was obtained is set as the time the write command for the update information was received. The group number that a pair with an asynchronous pair number of the logical volume belongs to is set as the group number. The update number set in the group information  600  is a numerical value resulting from adding 1 to the update number obtained from the group information  600 . The logical address that is the subject of the initial copy processing (copy complete address in the pair information) is set as the logical address of the write command and the logical address of the journal logical volume storing the write data. The unit size of the initial copy processing is set as the data size of the write data. The logical address for storing update information is the position of the update information latest address in the pointer information  700 , and a numerical value resulting from adding the size of the update information to the update information latest address is set as the new update information latest address in the pointer information  700  (step  1380 ;  1120  in  FIG. 11 ). 
         [0133]    (9) The host adapter A commands the disk adapter  120  to write the update information to the storage device  150  and ends the processing normally (step  1385 ;  1140  and  1150  in  FIG. 11 ). 
         [0134]    Although the update information is described to be in at least one cache memory  130  according to the description above, the update information may be stored in at least one shared memory  140 . 
         [0135]    Write data does not have to be written to the storage device  150  asynchronously, i.e., immediately after step  1360  or step  1385 . However, if the host computer  180  issues another command to write in the logical address A, the write data in the journal will be overwritten; for this reason, the write data in the journal must be written to the storage device  150  that corresponds to the logical address of the journal logical volume in the update information before the subsequent write data is received from the host computer  180 . Alternatively, the write data can be saved in a different cache memory and later written to the storage device  150  that corresponds to the logical address of the journal logical volume in the update information. 
         [0136]    Although journals are stored in the storage devices  150  according to the journal creation processing described, the cache memory  130  having a predetermined amount of memory for journals can be prepared in advance and the cache memory  130  can be used fully before the journals are stored in the storage device  150 . The amount of cache memory for journals can be designated through the maintenance terminal, for example. 
         [0137]    Next, a description will be made as to a processing that takes place when a host adapter C of the secondary storage system  100 C receives a remote write command from the primary storage system  100 A (a remote write command reception processing). A remote write command includes a write command, a logical address (a secondary logical volume C, a position A within the logical volume), a data amount A, and an update number. 
         [0138]    (1) The host adapter C in the secondary system  100 C refers to the volume information  400  for the logical volume C and checks the volume state of the secondary logical volume C (step  2310 ). If the volume state of the logical volume C is found through checking in step  2310  to be other than “secondary,” which indicates that the logical volume C cannot be accessed, the host adapter C reports to the primary storage system  100 A that the processing ended abnormally (step  2315 ). 
         [0139]    (2) If the volume state of the logical volume C is found through checking in step  2310  to be “secondary,” the host adapter C reserves at least one cache memory  130  and notifies the primary storage system  100 A of its readiness to receive data. Upon receiving the notice, the primary storage system  100 A sends write data to the secondary storage system  100 C. The host adapter C receives the write data and stores it in the cache memory  130  (step  2320 ). 
         [0140]    (3) The host adapter C checks the update number included in the remote write command and if the update number is the invalid value “0,”which indicates that journals were not created in the primary storage system  100 A, the host adapter C does not perform the journal replication processing in step  2400  (step  2330 ). 
         [0141]    (4) The host adapter C checks the update number included in the remote write command and if the update number is a valid value (a value other than “0”), the host adapter C checks the volume state of the journal logical volume. If the volume state of the journal logical volume is “abnormal,” which indicates that journals cannot be stored in the journal logical volume, the host adapter C does not perform the journal replication processing in step  2400  (step  2340 ). 
         [0142]    (5) If the volume state of the journal logical volume is found through checking in step  2340  to be “normal,” the host adapter C performs the journal replication processing  2400  described later. 
         [0143]    (6) The host adapter C commands one of the disk adapters  120  to write the write data in the storage area of the storage device  150  that corresponds to the logical address in the remote write command, and reports to the primary storage system A that the processing has ended (steps  2360 ,  2370 ). Subsequently, the disk adapter  120  stores the write data in the storage area through the read/write processing. 
         [0144]    Next, the journal replication processing  2400  will be described. 
         [0145]    (1) The host adapter C checks whether a journal can be stored in the journal logical volume. The host adapter C uses the pointer information  700  to check whether there are any blank areas in the update information area (step  2410 ). If the update information latest address and the update information oldest address in the pointer information  700  are equal, which indicates that there are no blank areas in the update information area, the host adapter C frees the storage area of the oldest journal and reserves an update information area (step  2415 ). Next, the host adapter C uses the pointer information  700  to check whether the write data can be stored in the write data area (step  2420 ). If the write data oldest address is within a range of the write data latest address and a numerical value resulting from adding the data amount A to the write data latest address, which indicates that the write data cannot be stored in the write data area, the host adapter C frees the journal storage area of the oldest journal and makes it possible to store the write data (step  2425 ). 
         [0146]    (2) The host adapter C creates update information in at least one cache memory  130 . The update time in the remote write command is set as the time the write command for the update information was received. The group number that a pair with a synchronous pair number in the logical volume C belongs to is set as the group number. The update number in the remote write command is set as the update number. The logical address in the remote write command is set as the logical address of the write command. The data size A in the remote write command is set as the data size of the write data. The logical address of the journal logical volume for storing write data is the write data latest address in the pointer information  700 , and a numerical value resulting from adding the size of the write data to the write data latest address is set as the write data latest address in the pointer information  700 . The logical address for storing the update information is the update information latest address in the pointer information  700 , and a numerical value resulting from adding the size of the update information to the update information latest address is set as the update information latest address in the pointer information  700  (step  2430 ). 
         [0147]    (3) The host adapter C commands one of the disk adapters  120  to write the update information and write data to at least one storage device  150 , and ends the processing as a successful journal creation (step  2440 ). Subsequently, the disk adapter  120  writes the update information and the write data to the storage device  150  through the read/write processing and frees the cache memory  130 . 
         [0148]    In this way, the secondary storage system C frees storage areas of old journals and constantly maintains a plurality of new journals. 
         [0149]    The read/write processing  220  is a processing that the disk adapters  120  implement upon receiving a command from the host adapters  110  or the disk adapters  120 . The processing implemented are a processing to write data in the designated cache memory  130  to a storage area in the storage device  150  that corresponds to the designated logical address, and a processing to read data to the designated cache memory  130  from a storage area in the storage device  150  that corresponds to the designated logical address. 
         [0150]      FIG. 14  is a diagram illustrating the operation (a journal read reception processing) by a host adapter A of the primary storage system  100 A upon receiving a journal read command, and  FIG. 15  is a flowchart of the operation. Below, these drawings are used to describe the operation that takes place when the primary storage system  100 A receives a journal read command from the secondary storage system  100 B. 
         [0151]    (1) The host adapter A in the primary storage system  100 A receives an access command from the secondary system  100 B. The access command includes an identifier indicating that the command is a journal read command, a group number that is the subject of the command, and whether there is a retry instruction. In the following, the group number within the access command shall be called a group number A (step  1220 ;  1410  in  FIG. 14 ). 
         [0152]    (2) The host adapter A checks whether the group state of the group number A is “normal” (step  1510 ). If the group state is found through checking in step  1510  to be other than “normal,” such as “abnormal,” the host adapter A notifies the secondary storage system  100 B of the group state and terminates the processing. The secondary storage system  100 B performs processing according to the group state received. For example, if the group state is “abnormal,” the secondary storage system  100 B terminates the journal read processing (step  1515 ). 
         [0153]    (3) If the group state of the group number A is found through checking in step  1510  to be “normal,” the host adapter A checks the state of the journal logical volume (step  1520 ). If the volume state of the journal logical volume is found through checking in step  1520  not to be “normal,” such as “abnormal,” the host adapter A changes the group state to “abnormal,” notifies the secondary storage system  100 B of the group state, and terminates the processing. The secondary storage system  100 B performs processing according to the group state received. For example, if the group state is “abnormal,” the secondary storage system  100 B terminates the journal read processing (step  1525 ). 
         [0154]    (4) If the volume state of the journal logical volume is found through checking in step  1520  to be “normal,” the host adapter A checks whether the journal read command is a retry instruction (step  1530 ). 
         [0155]    (5) If the journal read command is found through checking in step  1530  to be a retry instruction, the host adapter A re-sends to the secondary storage system  100 B the journal it had sent previously. The host adapter A reserves at least one cache memory  130  and commands one of the disk adapters  120  to read to the cache memory  130  information concerning the size of update information beginning at the retry head address in the pointer information  700  ( 1420  in  FIG. 14 ). 
         [0156]    In the read/write processing, the disk adapter  120  reads the update information from at least one storage device  150 , stores the update information in the cache memory  130 , and notifies of it to the host adapter A ( 1430  in  FIG. 14 ). 
         [0157]    The host adapter A receives the notice of the end of the update information reading, obtains the write data logical address and write data size from the update information, reserves at least one cache memory  130 , and commands the disk adapter  120  to read the write data to the cache memory  130  (step  1540 ;  1440  in  FIG. 14 ). 
         [0158]    In the read/write processing, the disk adapter  120  reads the write data from the storage device  150 , stores the write data in the cache memory  130 , and notifies of it to the host adapter A ( 1450  in  FIG. 14 ). 
         [0159]    The host adapter A receives the notice of the end of write data reading, sends the update information and write data to the secondary storage system  100 B, frees the cache memory  130  that has the journal, and terminates the processing (step  1545 ;  1460  in  FIG. 14 ). 
         [0160]    (6) If the journal read command is found through checking in step  1530  not to be a retry instruction, the host adapter A checks whether there is any journal that has not been sent; if there is such a journal, the host adapter A sends the journal to the secondary storage system  100 B. The host adapter A compares the read head address to the update information latest address in the pointer information  700  (step  1550 ). 
         [0161]    If the read head address and the update information latest address are equal, which indicates that all journals have been sent to the secondary storage system  100 B, the host adapter A sends “no journals” to the secondary storage system  100 B (step  1560 ) and frees the storage area of the journal that was sent to the secondary storage system  100 B when the previous journal read command was processed (step  1590 ). 
         [0162]    In the freeing processing of the journal storage area, a retry head address is set as the update information oldest address in the pointer information  700 . If the update information oldest address becomes the write data area head address, the update information oldest address is set to 0. The write data oldest address in the pointer information  700  is changed to a numerical value resulting from adding to the write data oldest address the size of the write data sent in response to the previous journal read command. If the write data oldest address becomes a logical address in excess of the capacity of the journal logical volume, the write data area head address is assigned a lower position and corrected. 
         [0163]    (7) If an unsent journal is found through checking in step  1550 , the host adapter A reserves at least one cache memory  130  and commands one of the disk adapters  120  to read to the cache memory  130  information concerning the size of update information beginning at the read head address in the pointer information  700  ( 1420  in  FIG. 14 ). 
         [0164]    In the read/write processing, the disk adapter  120  reads the update information from at least one storage device  150 , stores the update information in the cache memory  130 , and notifies of it to the host adapter A ( 1430  in  FIG. 14 ). 
         [0165]    The host adapter A receives the notice of the end of the update information reading, obtains the write data logical address and write data size from the update information, reserves at least one cache memory  130 , and commands the disk adapter  120  to read the write data to the cache memory  130  (step  1570 ;  1440  in  FIG. 14 ). 
         [0166]    In the read/write processing, the disk adapter  120  reads the write data from the storage device  150 , stores the write data in the cache memory  130 , and notifies of it to the host adapter A ( 1450  in  FIG. 14 ). 
         [0167]    The host adapter A receives the notice of the end of the write data reading, sends the update information and write data to the secondary storage system  100 B (step  1580 ) and frees the cache memory  130  that has the journal ( 1460  in  FIG. 14 ). The host adapter A then sets the read head address as the retry head address, and a numerical value resulting from adding the update information size of the journal sent to the read head address as the new read head address, in the pointer information  700 . 
         [0168]    (8) The host adapter A frees the storage area of the journal that was sent to the secondary storage system  100 B when the previous journal read command was processed (step  1590 ). 
         [0169]    Although the primary storage system  100 A sends journals one at a time to the secondary storage system  100 B according to the journal read reception processing described, a plurality of journals may be sent simultaneously to the secondary storage system  100 B. The number of journals to be sent in one journal read command can be designated in the journal read command by the secondary storage system  100 B, or the user can designate the number in the primary storage system  100 A or the secondary storage system  100 B when registering groups. Furthermore, the number of journals to be sent in one journal read command can be dynamically varied according to the transfer capability of or load on the connection paths  200  between the primary storage system  100 A and the secondary storage system  100 B. Moreover, instead of designating the number of journals to be sent, the amount of journals to be transferred may be designated upon taking into consideration the size of journal write data. 
         [0170]    Although journals are read from at least one storage device  150  to at least one cache memory  130  according to the journal read reception processing described, this processing is unnecessary if the journals are already in the cache memory  130 . 
         [0171]    Although the freeing processing of journal storage area in the journal read reception processing described is to take place during the processing of the next journal read command, the storage area can be freed immediately after the journal is sent to the secondary storage system  100 B. Alternatively, the secondary storage system  100 B can set in the journal read command an update number that may be freed, and the primary storage system  100 A can free the journal storage area according to the instruction. 
         [0172]      FIG. 16  is a diagram illustrating the journal read processing  240 ,  FIG. 17  is the flowchart of it, and FIG,  18  is a flowchart of a journal store processing. Below, an operation by a host adapter B of the secondary storage system  100 B to read journals from the primary storage system  100 A and store the journals in a journal logical volume is described below using these drawings. 
         [0173]    (1) If the group state is “normal” and the replication type is asynchronous, the host adapter B in the secondary storage system  100 B reserves at least one cache memory  130  for storing a journal, and sends to the primary storage system  100 A an access command that includes an identifier indicating that the command is a journal read command, a group number of the primary storage system  100 A that is the subject of the command, and whether there is a retry instruction. Hereinafter, the group number in the access command shall be called a group number A (step  1700 ,  1610  in  FIG. 16 ). 
         [0174]    (2) The host adapter B receives a response and a journal from the primary storage system  100 A ( 1620  in  FIG. 16 ). 
         [0175]    (3) The host adapter B checks the response; if the response from the primary storage system  100 A is “no journals,” which indicates that there are no journals that belong to the designated group in the primary storage system  100 A, the host adapter B sends a journal read command to the primary storage system  100 A after a predetermined amount of time (steps  1720 ,  1725 ). 
         [0176]    (4) If the response from the primary storage system  100 A is “the group state is abnormal” or “the group state is blank,” the host adapter B changes the group state of the secondary storage system  100 B to the state received and terminates the journal read processing (steps  1730 ,  1735 ). 
         [0177]    (5) If the response from the primary storage system  100 A is other than those described above, i.e., if the response is that the group state is “normal,” the host adapter B checks the volume state of the corresponding journal logical volume (step  1740 ). If the volume state of the journal logical volume is “abnormal,” which indicates that journals cannot be stored in the journal logical volume, the host adapter B changes the group state to “abnormal” and terminates the processing (step  1745 ). In this case, the host adapter B converts the journal logical volume to a normal logical volume and returns the group state to normal. 
         [0178]    (6) If the volume state of the journal logical volume is found through checking in step  1740  to be “normal,” the host adapter B performs a journal store processing  1800  described later. If the journal store processing  1800  ends normally, the host adapter B sends the next journal read command. Alternatively, the host adapter B can send the next journal read command after a predetermined amount of time has passed (step  1700 ). The timing for sending the next journal command can be a periodic transmission based on a predetermined interval, or it can be determined based on the number of journals received, the communication traffic volume on the connection paths  200 , the storage capacity for journals that the secondary storage system  100 B has, or on the load on the secondary storage system  100 B. The timing can also be determined based on the storage capacity for journals that the primary storage system  100 A has or on a numerical value in the pointer information  700  of the primary storage system  100 A as read from the secondary storage system  100 B. The transfer of the information can be done through a dedicated command or as part of a response to a journal read command. The subsequent processing is the same as the processing that follows step  1700 . 
         [0179]    (7) If the journal store processing in step  1800  does not end normally, which indicates that there are insufficient blank areas in the journal logical volume, the host adapter B cancels the journal received and sends a journal read command in a retry instruction after a predetermined amount of time (step  1755 ). Alternatively, the host adapter B can retain the journal in the cache memory  130  and perform the journal store processing again after a predetermined amount of time. This is due to the fact that there is a possibility that there would be more blank areas in the journal logical volume after a predetermined amount of time as a result of a restore processing  250 , described later. If this method is used, it is unnecessary to indicate whether there is a retry instruction in the journal read command. 
         [0180]    Next, the journal store processing  1800  shown in  FIG. 18  will be described. 
         [0181]    (1) The host adapter B checks whether a journal can be stored in the journal logical volume. The host adapter B uses the pointer information  700  to check whether there are any blank areas in the update information area (step  1810 ). If the update information latest address and the update information oldest address in the pointer information  700  are equal, which indicates that there are no blank areas in the update information area, the host adapter B terminates the processing due to a failure to create a journal (step  1820 ). 
         [0182]    (2) If blank areas are found in the update information area through checking in step  1810 , the host adapter B uses the pointer information  700  to check whether the write data can be stored in the write data area (step  1830 ). If the write data oldest address falls within a range of the write data latest address and a numerical value resulting from adding the data amount A to the write data latest address, the write data cannot be stored in the write data area; consequently, the host adapter B terminates the processing due to a failure to create a journal (step  1820 ). 
         [0183]    (3) If the journal can be stored, the host adapter B changes the group number and the logical address of the journal logical volume for storing write data of the update information received. The group number is changed to the group, number of the secondary storage system  100 B, and the logical address of the journal logical volume is changed to the write data latest address in the pointer information  700 . Furthermore, the host adapter B changes the update information latest address to a numerical value resulting from adding the size of the update information to the update information latest address, and the write data latest address to a numerical value resulting from adding the size of the write data to the write data latest address, in the pointer information  700 . Moreover, the host adapter B changes the update number in the group information  600  to the update number of the update information received (step  1840 ). 
         [0184]    (4) The host adapter B commands one of the disk adapters  120  to write the update information and write data to at least one storage device  150 , and ends the processing as a successful journal creation (step  1850 ;  1630  in  FIG. 16 ). Subsequently, the disk adapter  120  writes the update information and the write data to the storage device  150  through the read/write processing and frees the cache memory  130  ( 1640  in  FIG. 16 ). 
         [0185]    Although the journals are stored in the storage devices  150  according to the journal creation processing described, the cache memory  130  having a predetermined amount of memory for journals can be prepared in advance and the cache memory  130  can be used fully before the journals are stored in the storage device  150 . The amount of cache memory for journals can be designated through the maintenance terminal, for example. 
         [0186]      FIG. 19  is a diagram illustrating the restore processing  250 , and  FIG. 20  is a flowchart of it. Below, an operation by the host adapter B of the secondary storage system  100 B to utilize journals in order to update data is described below using these drawings. The restore processing  250  can be performed by one of the disk adapters  120  of the secondary storage system  100 B. 
         [0187]    (1) The host adapter B checks if the group state of the group number B is “normal” or “halted” (step  2010 ). If the group state is found through checking in step  2010  to be other than “normal” or “halted,” such as “abnormal,” the host adapter B terminates the restore processing (step  2015 ). 
         [0188]    (2) If the group state is found through checking in step  2010  to be “normal” or “halted,” the host adapter B checks the volume state of the corresponding journal logical volume (step  2020 ). If the volume state of the journal logical volume is found through checking in step  2020  to be “abnormal,” which indicates that the journal logical volume cannot be accessed, the host adapter B changes the group state to “abnormal” and terminates the processing (step  2025 ). 
         [0189]    (3) If the volume state of the journal logical volume is found to be “normal” through checking in step  2020 , the host adapter B checks whether there is any journal that is the subject of restore. The host adapter B obtains the update information oldest address and the update information latest address in the pointer information  700 . If the update information oldest address and the update information latest address are equal, there are no journals that are the subject of restore; consequently, the host adapter B terminates the restore processing for the time being and resumes the restore processing after a predetermined amount of time (step  2030 ). 
         [0190]    (4) If a journal that is the subject of restore is found through checking in step  2030 , the host adapter B performs the following processing on the journal with the oldest (i.e., smallest) update number. The update information for the journal with the oldest (smallest) update number is stored beginning at the update information oldest address in the pointer information  700 . The host adapter B reserves at least one cache memory  130  and commands one of the disk adapters  120  to read to the cache memory  130  information concerning the size of update information from the update information oldest address ( 1910  in  FIG. 19 ). 
         [0191]    In the read/write processing, the disk adapter  120  reads the update information from at least one storage device  150 , stores the update information in the cache memory  130 , and notifies of it to the host adapter B ( 1920  in  FIG. 19 ). 
         [0192]    The host adapter B receives the notice of the end of the update information reading, obtains the write data logical address and write data size from the update information, reserves at least one cache memory  130 , and commands the disk adapter  120  to read the write data to the cache memory  130  ( 1930  in  FIG. 19 ). 
         [0193]    In the read/write processing, the disk adapter  120  reads the write data from the storage device  150 , stores the write data in the cache memory  130 , and notifies of it to the host adapter B (step  2040 ;  1940  in  FIG. 19 ). 
         [0194]    (5) The host adapter B finds from the update information the logical address of the secondary logical volume to be updated, and commands one of the disk adapters  120  to write the write data to the secondary logical volume (step  2050 ;  1950  in  FIG. 19 ). In the read/write processing, the disk adapter  120  writes the data to the storage device  150  that corresponds to the logical address of the secondary logical volume, frees the cache memory  130 , and notifies of it to the host adapter B ( 1960  in  FIG. 19 ). 
         [0195]    (6) The host adapter B receives the notice of write processing completion from the disk adapter  120  and frees the storage area for the journal. In the freeing processing of the journal storage area, the update information oldest address in the pointer information  700  is changed to a numerical value resulting from adding the size of the update information thereto. If the update information oldest address becomes the write data area head address, the update information oldest address is set to 0. The write data oldest address in the pointer information  700  is changed to a numerical value resulting from adding the size of the write data to the write data oldest address. If the write data oldest address becomes a logical address in excess of the capacity of the journal logical volume, the write data area head address is assigned a lower position and corrected. The host adapter B then begins the next restore processing (step  2060 ). 
         [0196]    Although journals are read from at least one storage device  150  to at least one cache memory  130  in the restore processing  250 , this processing is unnecessary if the journals are already in the cache memories  130 . 
         [0197]    Although the primary storage system  100 A determines which journals to send based on the pointer information  700  in the journal read reception processing and the journal read processing  240  described, the journals to be sent may instead be determined by the secondary storage system  100 B. For example, an update number can be added to the journal read command. In this case, in order to find the logical address of the update information with the update number designated by the secondary storage system  100 B in the journal read reception processing, a table or a search method for finding a logical address storing the update information based on the update number can be provided in the shared memories  140  of the primary storage system  100 A. 
         [0198]    Although the journal read command is used in the journal read reception processing and the journal read processing  240  described, a normal read command may be used instead. For example, the group information  600  and the pointer information  700  for the primary storage system  100 A can be transferred to the secondary storage system  100 B in advance, and the secondary storage system  100 B can read data in the journal logical volume (i.e., journals) of the primary storage system  100 A. 
         [0199]    Although journals have been described as being sent from the primary storage system  100 A to the secondary storage system  100 B in the order of update numbers in the journal read reception processing, the journals do not have to be sent in the order of update numbers. Furthermore, a plurality of journal read commands may be sent from the primary storage system  100 A to the secondary storage system  100 B. In this case, in order to process journals in the order of update numbers in the restore processing, a table or a search method for finding a logical address storing update information based on each update number is provided in the secondary storage system  100 B. 
         [0200]    In the data processing system according to the present invention described, the storage system A stores information concerning data update as journals. The storage system B has a replication of data that the storage system A has; the storage system B obtains journals from the storage system A in an autonomic manner and uses the journals to update its data that correspond to data of the storage system A in the order of data update in the storage system A. Through this, the storage system B can replicate data of the storage system A, while maintaining data integrity. Furthermore, management information for managing journals does not rely on the capacity of data that is the subject of replication. 
         [0201]    The procedure for using a host computer  180 C and the storage system  100 C to resume the information processing performed by the host computer  180  and to resume data replication on the storage system  100 B in the event the primary storage system  100 A fails is shown in  FIG. 25 ; a block diagram of the logical configuration of the procedure is shown in  FIG. 42 . The host computer  180  and the host computer  180 C may be the same computer. 
         [0202]    In the following description,  FIG. 4  shows the volume information,  FIG. 5  shows the pair information,  FIG. 6  shows the group information,  FIG. 7  shows the pointer information, and  FIG. 8  shows a diagram illustrating the pointer information of the primary storage system  100 A before it fails.  FIG. 26  shows the volume information,  FIG. 27  shows the pair information,  FIG. 28  shows the group information,  FIG. 29  shows the pointer information, and  FIG. 30  shows a diagram illustrating the pointer information of the secondary storage system  100 B (asynchronous replication) before the primary storage system  100 A fails. Since the secondary storage system  100 B performs asynchronous data replication, it may not have all the journals that the primary storage system  100 A has (update numbers  3 - 5 ). In the present example, the secondary storage system  100 B does not have the journal for the update number  5 .  FIG. 31  shows the volume information,  FIG. 32  shows the pair information,  FIG. 33  shows the group information,  FIG. 34  shows the pointer information, and  FIG. 35  shows a diagram illustrating the pointer information of the secondary storage system  100 C (synchronous replication) before the primary storage system  100 A fails. Since the secondary storage system  100 C performs synchronous data replication, it has all the journals (update numbers  3 - 5 ) that the primary storage system  100 A has. 
         [0203]    (1) A failure occurs in the primary storage system  100 A and the primary logical volumes (DATA  1 , DATA  2 ) become unusable (step  2500 ). 
         [0204]    (2) Using the maintenance terminal of the storage system  100 C or the host computer  180 C, the user instructs the storage system  100 C to change the asynchronous replication source. The asynchronous replication source change command is a command to change the source of asynchronous data replication (i.e., the primary logical volume) on a group-by-group basis and includes replication source information (a storage system number C and a group number C that have the secondary logical volumes (data  1 , data  2 ) in synchronous data replication) and replication destination information (a storage system number B and a group number B that have the secondary storage volumes (COPY  1 , COPY  2 ) in asynchronous data replication) (step  2510 ). 
         [0205]    (3) Upon receiving the asynchronous replication source change command, the storage system  100 C refers to the volume information, pair information and group information of the storage system  100 B and the storage system  100 C; obtains a group number D whose group state is “blank” in the storage system  100 C; and makes changes to the volume information, pair information and group information of the storage system  100 C so that asynchronous data replication pairs would be formed with the logical volumes C (data  1 , data  2 ) that belong to the group C in the storage system  100 C as primary logical volumes and the logical volumes B (COPY  1 , COPY  2 ) that belong to the group B in the storage system  100 B as secondary logical volumes. However, the combinations of the logical volumes C and the logical volumes B are to be consistent with the pairs that are each formed with the logical volume A in the primary storage system  100 A. Furthermore, the secondary storage system  100 C changes group information such that the journal logical volume that used to belong to the group C would be continued to be used in the group D. More specifically, the storage system  100 C changes the update number for the group D to the update number for the group C and the journal logical volume number for the group D to the journal logical volume number for the group C, and makes all items in the pointer information for the group D same as the pointer information for the group C. Through the asynchronous replication source change command, the storage system  100 C changes the pair information for the storage system  100 C shown in  FIG. 32  to the pair information shown in  FIG. 39 , the group information for the storage system  100 C shown in  FIG. 33  to the group information shown in  FIG. 40 , and the volume information for the storage system  100 C shown in  FIG. 31  to the volume information shown in  FIG. 38 . 
         [0206]    The storage system  100 C commands the storage system  100 B to change its pair information and group information so that asynchronous data replication pairs would be formed with the logical volumes C (data  1 , data  2 ) that belong to the group C in the storage system  100 C as primary logical volumes and the logical volumes B (COPY  1 , COPY  2 ) that belong to the group B in the storage system  100 B as secondary logical volumes. However, the combinations of the logical volumes C and the logical volumes B are to be consistent with the pairs that are each formed with the logical volume A in the primary storage system  100 A. 
         [0207]    The storage system  100 B refers to the volume information, pair information and group information of the storage system  100 B and the storage system  100 C and makes changes to the pair information and group information of the storage system  100 B. By changing the pair information for the group B shown in  FIG. 27  to the pair information shown in  FIG. 36 , the group information shown in  FIG. 28  to the group information shown in  FIG. 37 , and the state of the group information for the group B to “halted,” the storage system  100 B halts the journal read processing to the storage system  100 A (steps  2530 ,  2540 ). 
         [0208]    (4) The storage system  100 C sends a response to the asynchronous replication source change command to either the host computer  180 C or the maintenance terminal. The user recognizes the end of the asynchronous replication source change processing through the host computer  180 C or the maintenance terminal and begins using the storage system  100 C (steps  2550 ,  2560 ). 
         [0209]    (5) The storage system  100 B sends a journal read position designation command to the storage system  100 C (step  2570 ). The journal read position designation command is a command to change the pointer information of the group D of the storage system  100 C and to designate a journal that is sent based on a journal read command from the storage system  100 B; the journal read position designation command includes a partner group number D and an update number B. The partner group number D designates the partner group number for the group number B. The update number designates a numerical value resulting from adding 1 to the update number in the group information for the group number B. In the example shown in  FIG. 37 , the partner group number  2  and the update number  5  are designated. 
         [0210]    (6) Upon receiving the journal read position designation command, the storage system  100 C refers to the pointer information  700  and checks whether there is a journal for the update number B. The storage system  100 C reads the update information of the update information oldest address in the pointer information from at least one storage device  150  and obtains the oldest (smallest) update number C. 
         [0211]    If the update number C is equal to or less than the update number B in the journal read position designation command, which indicates that the storage system  100 C has the journal for the update number B, the storage system  100 B can continue with the asynchronous data replication. In this case, the storage system  100 C frees storage areas for journals that precede the update number B, changes the read head address and the retry head address to addresses for storing the update information for the update number B, and sends “resumption possible” to the storage system  100 B. Through this, the pointer information shown in  FIG. 34  is changed to the pointer information shown in  FIG. 41  (step  2580 ). 
         [0212]    On the other hand, if the update number C is greater than the update number B in the journal read position designation command, which indicates that the storage system  100 B does not have the journal required by the storage system  100 C, the storage system  100 B cannot continue the asynchronous data replication. In this case, data replication must be initiated based on the procedures described using  FIGS. 9 and 10  from the primary storage system  100 C to the secondary storage system  100 B. 
         [0213]    (7) Upon receiving the “resumption possible” response, the storage system  100 B resumes a journal read processing to the storage system  100 C by changing the state of the group information for the group B to “normal” (step  2590 ). 
         [0214]    The storage system  100 B does not have to issue a journal read position designation command. In this case, the storage system  100 B initiates a journal read processing and receives the oldest journal from the storage system  100 C. If the update number C of the journal received is greater than a numerical value resulting from adding 1 to the update number in the group information for the group number B (the update number B), which indicates that the storage system  100 C does not have the journal required by the storage system  100 B, the storage system  100 B halts the data replication process. If the update number C of the journal received is less than the update number B, which indicates that the storage system  100 B already has the journal, the storage system B cancels the journal and continues the journal read processing. If the update number C of the journal received is equal to the update number B, the storage system B stores the journal received in the journal logical volume and continues the journal read processing. 
         [0215]    An operation to reflect data update to the primary logical volume (data  1 ) of the primary storage system  100 C on the secondary logical volume (COPY  1 ) of the secondary storage system  100 B after the host computer  180 C begins to use the storage system  100 C is generally described using  FIG. 42 . 
         [0216]    (1) Upon receiving a write command from the host computer  180 C for data in the primary logical volume (data  1 ), the primary storage system  100 C updates data in the primary logical volume (data  1 ) and stores journals in the journal logical volume (jnl  1 ) through the command reception processing  210  and the read/write processing  220 , and reports the end of the write command to the host computer  180 C ( 4200  in  FIG. 42 ). 
         [0217]    (2) The secondary storage system  100 B reads journals from the primary storage system  100 C through the journal read processing  240  and stores the journals in the journal logical volume (JNL  2 ) through the read/write processing  220  ( 4210  in  FIG. 42 ). 
         [0218]    (3) Upon receiving a journal read command from the secondary storage system  100 B, the primary storage system  100 C reads the journals from the journal logical volume (jnl  1 ) and sends the journals to the secondary storage system  100 B through the command reception processing  210  and the read/write processing  220  ( 4210  in  FIG. 42 ). 
         [0219]    (4) The secondary storage system  100 B uses the pointer information  700  through the restore processing  250  and the read/write processing  220  to read the journals from the journal logical volume (JNL  2 ) in ascending order of update numbers and updates data in the secondary logical volume (COPY  1 ) ( 4220  in  FIG. 42 ). As a result, data in the primary logical volume (data  1 ) in the primary storage system  100 C and data in the secondary logical volume (COPY  1 ) in the secondary storage system  100 B match completely some time after the update of the primary logical volume. 
         [0220]    In the data processing system according to the present invention described above, the storage system C uses update numbers and update times from the storage system A to create journals. If the storage system A, which is the subject of data replication, fails and information processing is continued using the storage system C, the storage system B changes the journal acquisition source from the storage system A to the storage system C. As a result, the storage system B can continue to replicate data of the storage system A, while maintaining data integrity. Furthermore, management information for managing journals does not rely on the capacity of data that is the subject of replication. 
         [0221]    A description will be made as to the procedure for using the host computer  180 C and the storage system  100 C to resume the information processing performed by the host computer  180  and to resume data replication on the storage system  100 B in the event the host computer  180  fails. A block diagram of the logical configuration of the procedure is shown in  FIG. 48 . The difference between this situation and the situation in which the primary storage system  100 A fails is that since the storage system  100 A can be used, synchronous data replication is performed by the storage system  100 A, in addition to the asynchronous data replication on the storage system  100 B. 
         [0222]    In the following description,  FIG. 4  shows the volume information,  FIG. 5  shows the pair information,  FIG. 6  shows the group information,  FIG. 7  shows the pointer information, and  FIG. 8  shows a diagram illustrating the pointer information of the primary storage system  100 A before the host computer  180  fails.  FIG. 26  shows the volume information,  FIG. 27  shows the pair information,  FIG. 28  shows the group information,  FIG. 29  shows the pointer information, and  FIG. 30  shows a diagram illustrating the pointer information of the secondary storage system  100 B (asynchronous replication) before the host computer  180  fails. Since the secondary storage system  100 B performs asynchronous data replication, it may not have all the journals that the primary storage system  100 A has (update numbers  3 - 5 ). In the present example, the secondary storage system  100 B does not have the journal for the update number  5 .  FIG. 31  shows the volume information,  FIG. 32  shows the pair information,  FIG. 33  shows the group information,  FIG. 34  shows the pointer information, and  FIG. 35  shows a diagram illustrating the pointer information of the secondary storage system  100 C (synchronous replication) before the host computer  180  fails. Since the secondary storage system  100 C performs synchronous data replication, it has all the journals (update numbers  3 - 5 ) that the primary storage system  100 A has. 
         [0223]    (1) A failure occurs in the host computer  180 . 
         [0224]    (2) Using the maintenance terminal of the storage system  100 C or the host computer  180 C, the user issues the asynchronous replication source change command, described earlier, and a synchronous replication exchange command to the storage system  100 C. The synchronous replication exchange command is a command to reverse the relationship between the primary logical volume and the secondary logical volume in synchronous data replication on a group-by-group basis, and includes replication source information (a storage system number A and a group number A that have the primary logical volumes (DATA  1 , DATA  2 ) in synchronous data replication) and replication destination information (a storage system number C and a group number C that have the secondary storage volumes (COPY  1 , COPY  2 ) in synchronous data replication). 
         [0225]    (3) Upon receiving the synchronous replication exchange command, the storage system  100 C refers to the volume information, pair information and group information of the storage system  1000 , and makes changes to the volume information, pair information and group information of the storage system  100 C so that synchronous data replication pairs would be formed with the logical volumes A (DATA  1 , DATA  2 ) that belong to the group A in the storage system  100 A as secondary logical volumes and the logical volumes C (COPY  1 , COPY  2 ) that belong to the group C in the storage system  100 C as primary logical volumes. However, the combinations of the logical volumes A and the logical volumes C must be logical volumes that already formed pairs in synchronous data replication. 
         [0226]    The storage system  100 C commands the storage system  100 A to change its volume information, pair information and group information so that synchronous data replication pairs would be formed with the logical volumes A (DATA  1 , DATA  2 ) that belong to the group A in the storage system  100 A as secondary logical volumes and the logical volumes C (COPY  1 , COPY  2 ) that belong to the group C in the storage system  100 C as primary logical volumes. However, the combinations of the logical volumes A and the logical volumes C must be logical volumes that already formed pairs in synchronous data replication. Furthermore, the storage system  100 C commands the storage system  100 A to create a journal whenever data in a secondary logical volume in a synchronous data replication pair is updated. In the storage system  100 A, the journal logical volume for storing journals is, for example, the journal logical volume (JNL  1 ) that was used for asynchronous data replication in the storage system  100 A before the host computer  180  failed. 
         [0227]    The storage system  100 A refers to the volume information, pair information and group information of the storage system  100 A and makes changes to the volume information, the pair information and group information of the storage system  100 A. After making changes to information for the storage system  100 A and the storage system  100 C is completed, the storage system  100 C sends a response to the synchronous replication exchange command to the host computer  180 C or the maintenance terminal. 
         [0228]    Through the asynchronous replication source change command and the synchronous replication exchange command, the storage system  100 C changes the pair information for the storage system  100 C shown in  FIG. 32  to the pair information shown in  FIG. 43 , the group information for the storage system  100 C shown in  FIG. 33  to the group information shown in  FIG. 44 , and the volume information for the storage system  100 C shown in  FIG. 31  to the volume information shown in  FIG. 38 . 
         [0229]    Through the asynchronous replication source change command, the storage system  100 B changes the pair information for the storage system  100 B shown in  FIG. 27  to the pair information shown in  FIG. 36  and the group information for the storage system  100 B shown in  FIG. 28  to the group information shown in  FIG. 37 . 
         [0230]    Through the synchronous replication exchange command, the storage system  100 A changes the pair information for the storage system  100 A shown in  FIG. 5  to the pair information shown in  FIG. 46 , the group information for the storage system  100 A shown in  FIG. 6  to the group information shown in  FIG. 47 , and the volume information for the storage system  100 A shown in  FIG. 4  to the volume information shown in  FIG. 45 . 
         [0231]    The user recognizes the end of the asynchronous replication source change and the synchronous replication exchange processing through the host computer  180 C or the maintenance terminal and begins using the storage system  100 C. The subsequent processing is the same as the processing that begins with step  2570 . 
         [0232]    In the data processing system according to the present invention, the storage system C uses update numbers and update times from the storage system A to create journals. If the host computer fails and another host computer continues information processing using the storage system C, the storage system B changes the journal acquisition source from the storage system A to the storage system C. As a result, the storage system B can continue to replicate data of the storage system A while maintaining data integrity. Furthermore, by changing settings so that the storage system A can synchronously replicate data of the storage system C, both the synchronous and asynchronous data replication can be performed as before the host computer failed. 
         [0233]    While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention. 
         [0234]    Japanese patent application No. 2003-183734 filed in Japan on Jun. 27, 2003, Japanese patent application No. 2003-050244 filed in Japan on Feb. 27, 2003, and U.S. patent application Ser. No. 10/603,076 filed in the U.S. on Jun. 23, 2003, which are technology of remote copy, are incorporated herein. 
         [0235]    The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.