Abstract:
Disclosed herein is a method for controlling a storage device controller connected to a storage device provided with a plurality of storage volumes for storing data respectively and an information processing apparatus for requesting an input/output of data so as to receive an input/output request from the information processing apparatus and execute an input/output processing of the data for each of the plurality of storage volumes. The method brings one (primary) of the plurality of storage volumes into correspondence with another (secondary) in which a copy of data is to be written when the data is written in the primary volume so as to form a pair group consisting of a plurality of pairs, each having such a primary volume and such a secondary volume. Upon receiving an input/output request from the information processing apparatus, the method starts resetting of the correspondence between storage volumes of each pair included in the pair group to decide whether or not it is after resetting of the correspondence is started that the request has been issued and executes an input/output processing after resetting the correspondence if the request is issued after resetting of the correspondence is started.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims priority upon Japanese Patent Application No. 2002-366374 filed on Dec. 18, 2002, which is herein incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a method for controlling a storage device controller, a storage device controller, and a program.  
         [0004]     2. Description of the Related Arts  
         [0005]     There is a well-known copy management function used in a storage system that includes an information processing apparatus and a disk array unit connected to each other for communications. The function manages primary volume data in duplicate by copying data from a primary volume to a secondary volume in real time. The primary (master) volume that is a source of copy and the secondary (sub) volume that is a destination of copy are paired.  
         [0006]     In such a storage system, however, data often overflows one primary volume into other primary volumes during communications between the information processing apparatus and the disk array unit. If an attempt is made to back up the data in such an occasion, a plurality of pairs (of primary and secondary volumes) must be reset from the paired state. If data in a primary volume for which the pair is already reset is updated during sequential resetting of paired states, the data is not updated in its corresponding secondary volume while data in a primary volume of which pair state is not reset is updated in its corresponding secondary volume sometimes.  
       SUMMARY OF THE INVENTION  
       [0007]     Under such circumstances, it is an object of the present invention to provide a method for controlling a storage device controller, a storage device controller, and a program capable of managing copies of data while keeping the consistency among the data stored in a plurality of storage volumes.  
         [0008]     One aspect of the present invention resides in the storage device controlling method that controls the storage device controller connected to a storage device provided with a plurality of storage volumes for storing data and an information processing apparatus for requesting the input/output of the data and used to input/output the data to/from the storage volumes. The method comprises a step of bringing one (source) of the storage volumes into correspondence with another (destination) in which a copy of data is to be written when the data is written in the source storage volume so as to form a pair group consisting of a plurality of such source and destination storage volumes; a step of resetting the correspondence between source and destination storage volumes of each pair in the pair group; a step of deciding whether or not it is after the correspondence is reset that an input/output request has been issued from the information processing apparatus; and a step of inputting/outputting data after the correspondence is reset when it is after the correspondence is reset that the input/output request has been issued from the information processing apparatus.  
         [0009]     The storage device and the storage device controller are included in the disk array unit. The information processing apparatus and the disk array unit are included in the storage system.  
         [0010]     Storage volumes are storage resources provided in the disk array unit or storage device and they are divided into physical volumes and logical volumes. A physical volume is a physical storage area provided in a disk drive of the disk array unit or storage device and a logical volume is a storage area allocated logically in a physical volume.  
         [0011]     The “paired” means a state in which two storage volumes are brought into correspondence with each other as described above.  
         [0012]     That is why the present invention can provide a method for controlling a storage device controller, a storage device controller, and a program capable of managing copies of data while keeping the consistency among data stored in a plurality of storage volumes as described above. 
     
    
     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 an overall block diagram of a storage system in an embodiment of the present invention;  
         [0015]      FIG. 2  is a block diagram of an information processing apparatus in the embodiment of the present invention;  
         [0016]      FIG. 3  is a block diagram of a channel adapter provided in a storage device controller in the embodiment of the present invention;  
         [0017]      FIG. 4  is a table stored in a shared storage provided in the storage device controller in the embodiment of the present invention;  
         [0018]      FIG. 5  is pairs of storage volumes in the embodiment of the present invention;  
         [0019]      FIG. 6  is a flowchart of the processings of the storage device controller for splitting a pair in the embodiment of the present invention;  
         [0020]      FIG. 7  is a flowchart of the processings of the storage device controller for splitting a pair and inputting/outputting the split pair data items in the embodiment of the present invention;  
         [0021]      FIG. 8  is a table stored in the shared storage provided in the storage device controller in the embodiment of the present invention; and  
         [0022]      FIG. 9  is a flowchart of the processings of the storage device controller for splitting a pair. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     Hereunder, the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.  
         [0000]     ===Overall Configuration=== 
         [0024]     At first, the storage system in an embodiment of the present invention will be described with reference to the block diagram shown in  FIG. 1 .  
         [0025]     An information processing apparatus  100  is a computer provided with a CPU (Central Processing Unit), a memory, etc. The CPU of the information processing apparatus  100  executes various types of programs to realize various functions of the apparatus  100 . The information processing apparatus  100  is used, for example, as a core computer in an automatic teller machine in a bank, a flight ticket reservation system, or the like.  
         [0026]     The information processing apparatus  100  is connected to a storage device controller  200  to communicate with the controller  200 . The information processing apparatus  100  issues data input/output commands (requests) to the storage-device controller  200  to read/write data from/to the storage devices  300 . The information processing apparatus  100  also sends/receives various commands to/from the storage device controller  200  to manage the storage devices  300 . For example, the commands are used for managing copies of data stored in the storage volumes provided in the storage devices  300 .  
         [0027]      FIG. 2  shows a block diagram of the information processing apparatus  100 .  
         [0028]     The information processing apparatus  100  is configured by a CPU  110 , a memory  120 , a port  130 , a media reader  140 , an input device  150 , and an output device  160 .  
         [0029]     The CPU  110  controls the whole information processing apparatus  100  and executes the programs stored in the memory  120  to realize various functions of the apparatus  100 . The media reader  140  reads programs and data recorded on the recording medium  170 . The memory  120  stores the programs and data read by the reader  140 . Consequently, the media reader  170  can be used to read a storage device management program  121  and an application program  122  recorded in the medium  170  and store them in the memory  120 . The recording medium  170  may be any of flexible disks, CD-ROM disks, semiconductor memories, etc. The media reader  140  may also be built in the information processing apparatus  100  or provided as an external device. The input device  150  is used by the operator to input data addressed to the information processing apparatus  100 . The input device  150  may be any of keyboards, mice, etc. The output device  160  outputs information to external. The output device  160  may be any of displays, printers, etc. The port  130  is used to communicate with the storage device controller  200 . In that connection, the storage device management program  121  and the application program  122  may be received from another information processing apparatus  100  through the port  130  and stored in the memory  120 .  
         [0030]     The storage device management program  121  manages copies of data stored in the storage volumes provided in the storage devices  300 . The storage device controller  200  manages copies of data with use of various copy management commands received from the information processing apparatus  100 .  
         [0031]     The application program  122  realizes the functions of the information processing apparatus  100 . For example, the program  122  realizes functions of an automatic teller machine of a bank and functions of a flight ticket reservation system as described above.  
         [0032]     Next, the storage device controller  200  will be described with reference to  FIG. 1  again. The storage device controller  200  controls the storage devices  300  according to the commands received from the information processing apparatus  100 . For example, when receiving a data input/output request from the information processing apparatus  100 , the storage device controller  200  inputs/outputs data to/from a storage volume provided in a storage device  300 .  
         [0033]     The storage device controller  200  is configured by a channel adapter  210 , a cache memory  220 , a shared storage  230 , a disk adapter  240 , a management terminal (SVP: SerVice Processor)  260 , and a connection unit  250 .  
         [0034]     The channel adapter  210  provided with a communication interface with the information processing apparatus  100  exchanges data input/output commands, etc. with the information processing apparatus  100 .  
         [0035]      FIG. 3  shows a block diagram of the channel adapter  210 .  
         [0036]     The channel adapter  210  is configured by a CPU  211 , a cache memory  212 , a control memory  213 , a port  215 , and a bus  216 .  
         [0037]     The CPU  211  controls the whole channel adapter  210  by executing a control program  214  stored in the control memory  213 . The control program  214  stored in the control memory  213  thus enables data copies to be managed in this embodiment. The cache memory  212  stores data, commands, etc. to be exchanged with the information processing apparatus  100  temporarily. The port  215  is a communication interface used for the communication with the information processing apparatus  100  and other devices provided in the storage device controller  200 . The bus  216  enables the mutual connection among those devices.  
         [0038]     Return to  FIG. 1  again. The cache memory  220  stores data to be exchanged between the channel adapter  210  and the disk adapter  240  temporarily. In other words, if the channel adapter  210  receives a write command as a data input/output command from the information processing apparatus  100 , the channel adapter  210  writes the command in the shared storage  230  and the target data received from the information processing apparatus  100  in the cache memory  220  respectively. The disk adapter  240  then reads the target data from the cache memory  220  according to the write command written in the shared storage and writes the read data in a storage device  300 .  
         [0039]     The management terminal  260  is a kind of information processing apparatus used for the maintenance/management of the storage device controller  200  and the storage devices  300 . For example, the management terminal  260  changes the control program  214  executed in the channel adapter  210  to another. The management terminal  260  may be built in the storage device controller  200  or may be separated. The management terminal  260  may also be dedicated to the maintenance/management of the storage device controller  200  and the storage devices  300  or may be configured as a general information processing apparatus for maintenance/management. The configuration of the management terminal  260  is the same as that of the information processing apparatus  100  shown in  FIG. 2 . Concretely, the management terminal  260  is configured by a CPU  110 , a memory  120 , a port  130 , a recording media reader  140 , an input device  150 , and an output device  160 . Consequently, the control program to be executed in the channel adapter  210  may be read from the recording medium  170  through the media reader  140  of the management terminal  260  or received from the information processing apparatus  100  connected thereto through the port  130  of the management terminal  260 .  
         [0040]     The disk adapter  240  controls the storage devices  300  according to the commands received from the channel adapter  210 .  
         [0041]     Each of the storage devices  300  is provided with a storage volume to be used by the information processing apparatus  100 . Storage volumes are storage resources provided in the storage devices  300  and divided into physical volumes that are physical storage areas provided in disk drives of the storage devices  300  and logical volumes that are storage areas allocated logically in those physical volumes. The disk drives may be any of, for example, hard disk drives, flexible disk drives, semiconductor storage devices, etc. The disk adapter  240  and each of the storage devices  300  may be connected to each other directly as shown in  FIG. 1  or through a network. The storage devices  300  may also be united with the storage device controller  200  into one.  
         [0042]     The shared storage  230  can be accessed from both of the channel adapter  210  and the disk adapter  240 . The shared storage is used to receive/send data input/output requests/commands and store management information, etc. of the storage device controller  200  and the storage devices  300 . In this embodiment, the shared storage  230  stores a consistency group management table  231  and a pair management table  232  as shown in  FIG. 4 .  
         [0000]     ===Pair Management Table=== 
         [0043]     The pair management table  232  is used to manage copies of data stored in the storage devices  300 . The table  232  has columns of “pair”, “primary volume”, “sub volume”, “pair state”, and “consistency group”.  
         [0044]     The “pair” column holds pair names. A pair means a combination of two storage volumes.  FIG. 5  shows an example of paired storage volumes. In  FIG. 5 , two pairs, that is, pairs A and B are denoted. One of paired volumes and the other of the paired volumes are managed as a primary volume and a secondary volume. In  FIG. 5 , a primary volume is described as a master volume and a secondary volume is described as a sub volume. A plurality of secondary volumes can be combined with one primary volume.  
         [0045]     Return to the pair management table  232  shown in  FIG. 4 . The “primary” column describes primary volumes paired with secondary volumes while the “secondary” column describes secondary volumes paired with primary volumes.  
         [0046]     The “pair state” column describes the state of each pair of volumes. The “pair state” is classified into “paired”, “split”, and “re-sync”.  
         [0047]     The “paired” denotes that data in a secondary volume is updated with the data in its corresponding primary volume written by the information processing apparatus  100 . The consistency of the data stored in a pair of primary and secondary volumes is assured with such correspondence set between those primary and secondary volumes.  
         [0048]     The “split” denotes that data in a secondary volume is not updated with the data in its corresponding primary volume written by the information processing apparatus  100 . Concretely, while primary and secondary volumes are in such a “split” state, the correspondence between those volumes is reset. Consequently, the data consistency is not assured between those primary and secondary volumes. However, because data in any secondary volume that is in the “split” state is not updated, the data in secondary volumes can be backed up during the while; for example, data stored in secondary volumes can be saved in a magnetic tape or the like. This makes it possible to back up data while the data in primary volumes is used continuously during the backup operation for a job that has been executed by the information processing apparatus  100 .  
         [0049]     The “re-sync” denotes a transition state of a pair of volumes, for example, from “split” to paired”. More concretely, the “re-sync” means a state in which data in a secondary volume is being updated with the data written in its corresponding primary volume while the pair is in the “split” state. When the data in the secondary volume is updated, the state of the pair is changed to “paired”.  
         [0050]     To form a pair of storage volumes or to change the state of the pair from “paired”/“split” to “split”/“paired”, the operator instructs the information processing apparatus  100  in which the storage device management program  121  is executed through the input device  150 . A command from the operator is then sent to the channel adapter  210  of the storage device controller  200 . After that, the channel adapter  210  executes the control program  214  to form a pair of storage volumes or change the state of the pair according to the command. According to the state of the formed pair of storage volumes, the channel adapter  210  controls the object storage volumes, for example, updating a secondary volume with a copy of data updated in its corresponding primary volume when those volumes are “paired”.  
         [0051]     As described above, the channel adapter  210  changes the states of pairs one by one sequentially. This is because one primary volume can be paired with a plurality of secondary volumes as described above and if the states of a plurality of pairs are changed simultaneously, the management of primary volumes comes to become complicated.  
         [0052]     Forming a pair of volumes and changing the state of each pair of volumes can also be made automatically at a predetermined time or according to a command received from another information processing apparatus  100  connected through the port  130  independently of instructions from the operator.  
         [0000]     ===Consistency Group=== 
         [0053]     The “consistency group” column describes the number of each consistency group (pair group) consisting of pairs of volumes. A consistency group means a group of a plurality of storage volume pairs to be controlled so that the states of those pairs are changed to the “split” together. Concretely, a plurality of pairs in a consistency group are controlled so that their states are changed to the “split” simultaneously (hereinafter, this processing will be referred to as the synchronism among the state changes to the “split”) while the states of a plurality of paired volumes are changed one by one sequentially as described above.  
         [0054]     For example, assume now that the information processing apparatus  100  writes data in a storage volume while the pair states of a plurality of paired volumes in a consistency group are changed sequentially from “paired” to “split”. If no consistency group is formed and the data is written in a paired primary volume after the pair state is changed to the “split”, the data is not written in its corresponding secondary volume. If the data is written in a paired primary volume of which state is not changed to the “split” yet, the data is also written in the secondary volume. If the paired primary volume belongs to a consistency group at that time, however, the data is not written in its corresponding secondary volume regardless of the pair state of the primary volume (whether it is in the “split” or not). This is because the data is written in the primary volume after pair splitting (resetting of the correspondence between primary and secondary volumes) is started in the consistency group.  
         [0055]     Forming a consistency group with a plurality of pairs such way is effective for a case in which data is to be stored in a plurality of storage volumes, for example, when write data is too large to be stored in one storage volume and when it is controlled so that one file data is stored in a plurality of storage volumes.  
         [0056]     Such assured synchronism of the pair state changes of volumes to the “split” in a consistency group is also effective for writing/reading of data in/from secondary volumes requested from the information processing apparatus  100 .  
         [0057]     Concretely, if no consistency group is already formed, data can be written/read in/from any paired secondary volume after the pair state is changed to the “split” while it is inhibited to write/read data in/from any secondary volume of which pair state is not changed to the “split”.  
         [0058]     In this embodiment, a batch split receiving flag (ID information) of the consistency group management table  231  is used to assure the synchronism of such pair state changes of volumes to the “split” in the above consistency group. Next, the processings for assuring such synchronism will be described with reference to the flowchart shown in  FIG. 6 .  
         [0059]     Processing Flow  
         [0060]     The following processings are executed by the CPU  211  provided in the channel adapter  210  with use of the control program  214  (program) consisting of codes for realizing various operations in this embodiment.  
         [0061]     At first, the channel adapter  210  receives a pair splitting request (split command) addressed to a consistency group from the information processing apparatus  100 (S 1000 ). The channel adapter  210  then turns on the batch split receiving flag in the consistency group management table  231  stored in the shared storage  230  (S 1001 ). After that, the channel adapter  210  begins to change the pair state of a not-split pair of volumes in the consistency group to the “split” (S 1003 ). Concretely, the channel adapter  210  resets the correspondence between the primary volume and the secondary volume in the pair and stops updating of the data in the secondary volume with the data written in the primary volume. The channel adapter  210  then changes the description for the pair in the “paired” column in the pair management table  232  to “split” (S 1004 ). Those processings are repeated for each pair in the consistency group. When the states of all the pairs in the consistency group are changed to the “split” (S 1005 ), the channel adapter  210  turns off the batch split flag, then exits the processing.  
         [0062]     If the channel adapter  210  receives a read/write request from the information processing apparatus  100  during the above processing, the adapter  210  checks whether or not the request is addressed to a not-split storage volume, that is, a “paired” storage volume (for which the correspondence to its secondary volume is not reset)(S 1006 ). If the check result is YES (addressed), the adapter  210  changes the pair state of the volume to the “split” (S 1007 ). The adapter  210  then changes the description of the pair in the pair state column in the pair management table  232  to the “split” (S 1008 ) and executes the data read/write processing (input/output processing)(S 1009 ).  
         [0063]     On the other hand, if the check result in (S 1006 ) is NO (not addressed), this means that the command is addressed to a “split” volume. The adapter  210  thus executes the read/write processing for the storage volume (S 1009 ) immediately.  
         [0064]     Consequently, the synchronism of the pair state changes of “paired” volumes to the “split” in a consistency group is assured.  
         [0065]     In the flowchart shown in  FIG. 6 , if the channel adapter  210  receives a read/write request from the information processing apparatus  100  while splitting paired volumes in a consistency group sequentially, the adapter  210  checks whether or not the request is addressed to a not-split pair of volumes (S 1006 ) to execute the read/write processing (S 1009 ). However, it is also possible for the adapter  210  to suppress the execution of the read/write processing requested from the information processing apparatus  100  while the adapter  210  splits paired volumes in a consistency sequentially. In that connection, the adapter  210  can execute the read/write processing after the adapter  210  completes splitting of all the paired volumes in the consistency group and turns off the batch split flag.  
         [0066]      FIG. 7  shows a flowchart for those processings by the channel adapter  210  in detail.  
         [0067]     At first, the channel adapter  210  forms a consistency group for both pairs A and B according to a command received from the information processing apparatus  100 (S 2000  to S 2002 ). The command is inputted, for example, by the operator through the input device  150  of the information processing apparatus  100 . The command inputted to the information processing apparatus  100  is sent to the channel adapter  210  by the storage device management program  121 . The “paircreate-g GRP0” shown in  FIG. 7  is such a command. Receiving the command, the channel adapter  210  forms a consistency group, then records predetermined data in the pair management table  232  and the consistency group management table  231  stored in the shared storage  230  respectively.  FIG. 4  shows how the predetermined data is recorded in those tables  231  and  232 . However, although the state of the pair A is described as “split” in the pair state column in the pair management table  232  shown in  FIG. 4 , the state of the pair A at that time is actually “paired”. Similarly, although “ON” is described in the batch split receiving flag column for the consistency group  0  in the consistency group management table  231 , the actual state at that time is actually “OFF”.  
         [0068]     The channel adapter  210 , when receiving a read/write request (R/W 1 ) for the storage volume  1  in the pair A from the information processing apparatus  100 (S 2008 ), executes the read/write processing as usually (S 2009 ). This is because “OFF” is described in the batch split receiving flag column for the consistency group  0  in the consistency group management table  231 .  
         [0069]     After that, the information processing apparatus  100  instructs the channel adapter  210  to split the pair B in the consistency group  0  with a command (S 2003 ). The “pairsplit-g GRP0” shown in  FIG. 7  is an example of the command issued at that time. This command may also be inputted by the operator through the input device  150  of the information processing apparatus  100 .  
         [0070]     The channel adapter  210  then turns on the batch split receiving flag for the consistency group  0  in the consistency group management table  231  stored in the shared storage  230  (S 2004 ) to start splitting of each pair sequentially (S 2005 , S 2006 ).  FIG. 4  shows the pair management table  232  in which the pair A is split. Completing splitting of all the target pairs, the channel adapter  210  turns OFF the batch split receiving flag and exits the processing (S 2007 ).  
         [0071]     If the channel adapter  210  receives a read/write request (R/W 2 ) addressed to the storage volume  3  of the pair B from the information processing apparatus  100  (S 2010 ) while the channel adapter  210  turns ON the batch split receiving flag (S 2004 ) after receiving a split command addressed to the consistency group  0  from the information processing apparatus  100 , the channel adapter  210  executes the read/write processing as usually (S 2011 ). This is because “OFF” is still set in the batch split receiving column for the consistency group  0  in the consistency group management table  231 .  
         [0072]     However, if the channel adapter  210  receives a read/write request (R/W 3 ) addressed to the storage volume  3  of the pair B from the information processing apparatus  100  (S 2012 ) after turning ON the batch split receiving flag (S 2004 ), the channel adapter  210  splits the pair B (S 2013 ), then executes the read/write processing (S 2014 ).  
         [0073]     As described above, the channel adapter  210 , when receiving a read/write request from the information processing apparatus  100 , refers to the batch split receiving flag to check whether or not it is after resetting of the pair state of each pair in the consistency group is started that the read/write command has been issued.  
         [0074]     If the channel adapter  210  receives the read/write request (R/W 4 ) after completing splitting of the pair A in (S 2005 ), the channel adapter  210  executes the read/write processing (S 2016 ). This is because “split” is set for the pair A in the pairing column in the pair management table  232  and the channel adapter  210  knows that “split” denotes that the pair A is split.  
         [0075]     In that connection, no splitting processing is done for the pair B in (S 2005 ), since the pair B is already split during the read/write processing in (S 2013 ).  
         [0076]     In this embodiment, because the batch split receiving flag is provided as described above, the synchronism among the pair state changes of all the pairs in a consistency group to the “split” is assured.  
         [0000]     ===Consistency Group Management Table=== 
         [0077]     Next, a description will be made for another embodiment of the present invention with respect to the management information in the consistency group management table  231 .  
         [0078]     In this embodiment, each split starting time is recorded in the consistency group management table  231  as shown in  FIG. 8 . In the example shown in  FIG. 8 , splitting of pairs in the consistency group  0  is started at 12:00. When splitting of all the pairs in the consistency group  0  is completed, the description in the split starting time column is changed to “-”.  
         [0079]     A split starting time is specified with a command received from the information processing apparatus  100 . Such split starting may also be specified so as to be started immediately with a command; no concrete time is specified in such an occasion. In that connection, the current time is recorded in the split starting time column.  
         [0080]     In this embodiment, the channel adapter  210 , when receiving a read/write command from the information processing apparatus  100 , compares the read/write command issued time recorded in the read/write command (request) with the time described in the split starting time column of the consistency group management table  231 . If the command issued time is later, the channel adapter  210  executes the read/write processing after the end of the splitting.  
         [0081]     This is why it is possible to assure the synchronism among the state changes of pairs in a consistency group to the “split”.  
         [0000]     ===Processing Flow=== 
         [0082]     Next, how the above processings are executed will be described in detail with reference to the flowchart shown in  FIG. 9 .  
         [0083]     The processings are executed by the CPU  211  of the channel adapter  210  with use of the control program  214  consisting of codes for realizing various operations in this embodiment.  
         [0084]     At first, the channel adapter  210  receives a pair splitting request (split command) addressed to a consistency group from the information processing apparatus  100  (S 3000 ). The channel adapter  210  then records the split starting time recorded in the split command in the split starting time column of the consistency group management table  231  stored in the shared storage  230  (S 3001 ). After that, the channel adapter  210  compares the split starting time with the current time to check whether or not the split starting time is passed (S 3003 ). If the check result is YES (passed), the channel adapter  210  begins the state change of a not-split pair in the consistency group to the “split” (S 3004 ). Concretely, the channel adapter  210  resets the correspondence between primary and secondary volumes of the pair and suppresses updating of the data in the secondary volume with the data written in the primary volume. The channel adapter  210  then changes the description for the pair in the pair state column in the pair management table  232  to “split” (S 3005 ). The above processings are repeated for all of the pairs in the consistency group. When the states of all the pairs in the consistency group are changed to “split” (S 3006 ), the channel adapter  210  changes the description for the pair in the split starting time column to “-” and exits the processing (S 3007 ).  
         [0085]     If the channel adapter  210  receives a read/write request from the information processing apparatus  100  during the above processing, the channel adapter  210  checks whether or not the request is addressed to a not-split pair, that is, a “paired” storage volume (the correspondence is not reset)(S 3008 ). If the check result is YES (addressed), the channel adapter  210  compares the command issued time recorded in the command with the split starting time (S 3010 ). If the command issued time is later, the channel adapter  210  changes the pair state to the “split” (S 3011 ), then changes the description for the pair in the pair state column in the pair management table  232  to “split” (S 3012 ). After that, the channel adapter  210  executes the read/write processing (input/output processing) (S 3013 ).  
         [0086]     On the other hand, if the read/write command is addressed to a split pair in (S 3008 ), that is, a “split” storage volume or the command issued time recorded in the request is earlier than the split starting time, the channel adapter  210  reads/writes data from/in the storage volume (S 3009 ).  
         [0087]     This is why it is possible to assure the synchronism among the state changes of the pairs in a consistency group to the “split”.  
         [0088]     In the flowchart shown in  FIG. 9 , if the channel adapter  210  receives a read/write request from the information processing apparatus  100  while splitting pairs in a consistency group sequentially, the channel adapter  210  checks whether or not the request is addressed to a not-split storage volume (S 3008 ) and executes the read/write processing (S 3009 , S 3013 ). However, the channel adapter  210  can also suppress execution of the read/write processing even when receiving a read/write request from the information processing apparatus  100  while splitting pairs in a consistency group sequentially as described above. In that occasion, the channel adapter  210  executes the read/write processing after completing splitting of all the pairs in the consistency group and changing the description for the pair in the split starting time column to “-”.  
         [0089]     In this embodiment, consistency groups are formed by storage devices  300  connected to the same storage device controller respectively. However, the present invention is not limited only to that embodiment. In this embodiment, consistency groups should preferably be formed by storage devices  300  connected to a plurality of storage device controllers respectively. In that connection, a consistency group may be formed over a plurality of storage device controllers  200  that come to communicate with each another to create the consistency group management table  231  and the pair management table  232 . The consistency group management table  231  and the pair management table  232  may be managed by one of the storage device controllers  200  and shared with other storage device controllers  200  or each of those storage device controllers manages the same table. Furthermore, volumes controlled by a plurality of storage device controllers  200  should preferably be paired in this embodiment. In that connection, a pair might be formed over a plurality of storage device controllers  200  and those storage device controllers  200  come to communicate with each another to create the consistency group management table  231  and the pair management table  232 . In that connection, the consistency group management table  231  and the pair management table  232  may be managed by one of the storage device controllers  200  and shared with other storage device controllers  200  or those storage device controllers manages the same table respectively.  
         [0090]     While the embodiments of the present invention have been described, the description is just for illustrative purposes, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.