Abstract:
A disk volume access controlling method includes the steps of, setting a threshold number of times of accesses from a computer to a predetermined disk volume per time unit, acquiring a number of times of accesses to the predetermined disk volume per time unit, seeking whether or not the number of times of accesses acquired exceeds the threshold number of times, creating a mirror volume for the predetermined disk volume in case that the number of times of accesses acquired exceeds the threshold number of times, and changing an access pass between the computer and the predetermined disk volume to another access pass between the computer and the mirror volume created. It then becomes possible to distribute accesses to a certain disk volume, and further to make the accesses to a plurality of volumes even.

Description:
INCORPORATION BY REFERENCE  
       [0001]     The present application claims priority from Japanese application JP2004-152730 filed on May 24, 2004, the content of which is hereby incorporated by reference into this application.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to disk access control techniques which are intended to distribute a load associated with disk accesses when a plurality of service programs are to access a disk storage device.  
         [0003]     JP-A-11-149350 discloses techniques related to a distribution of a disk access load caused by a plurality of read requests made to a disk storage device.  
         [0004]     Specifically, JP-A-11-149350 discloses a disk storage system which comprises a controller having a plurality of external connection pointers, a storage device group comprised of a plurality of storage devices such that write data is written into each of the storage devices, and a plurality of paths connected to the storage device group and controller. The controller reads stored data based on a first read request and a second read request issued from a processor to the storage device group from any of the storage devices in the group which is left empty, and transfers read data to the processor through an external connection point, thereby successfully distributing input/output processing between the processor and disk device group to improve the parallelism of the input/output processing executable by the controller.  
       SUMMARY OF THE INVENTION  
       [0005]     It is preferable for a method of controlling accesses to the disk storage devices not to involve manually replicating predetermined volumes beforehand for distributing a disk access load through the replication. It then is unnecessary for a user to be imposed to execute the processing involved in the replication of disks when the disk access load suddenly fluctuates or when no increase was predicted in the disk access load, thus it becomes possible to make it easy to immediately execute the access control.  
         [0006]     Thus, it is preferable for a disk access control method using replicated volumes to make an improvements in terms of dynamic execution of access control.  
         [0007]     It is therefore an object of the present invention to limit the number of times of accesses to a predetermined volume in a disk storage device per unit time to a certain value without the need for previous manual replication of volumes or modifications to a program. Specifically, a particular monitoring unit detects that the number of times of accesses to a volume per unit time exceeds an upper limit value, and requests a controller of the disk storage device to replicate the volume, such that a management program for the disk storage device distributes accesses to the original volume and replicated volume.  
         [0008]     The object of the present invention is achieved by a system which includes a disk storage device having a volume replication function in a SAN (Storage Area Network), a computer A for executing a program which accesses the disk storage device, and a management computer B for executing a management program B for managing the disk storage device.  
         [0009]     To achieve the object, the following steps are executed: 
        (1) setting an upper limit value for the number of times of accesses per unit time;     (2) monitoring disk accesses by a particular monitoring unit;     (3) requesting replication of a predetermined volume, and replicating the volume; and     (4) switching an access path.        
 
         [0014]     Items set in (1) are classified into three patterns by conditions under which a replication request is made from a disk access situation at a current time. The conditions for making the replication request are listed below: 
        (a) when the number of times of accesses to a predetermined volume per unit time at the current time exceeds the upper limit value;     (b) when a predicted number of times of accesses in T minutes later from the current time exceeds the upper limit value; and     (c) when the current time matches with the value calculated by subtracting a time required for replication from a previously set replication time in a replication management schedule which indicates the number of replicas of a predetermined volume over time.        
 
         [0018]     Items set in case (a) include a predetermined volume, and the number of times of accesses to the volume per unit time, wherein an upper limit value management table is created from the set items at step (1).  
         [0019]     Items set in case (b) include a time period T between a time at which a predicted number of times of accesses per unit time is calculated and the current time, and the number of data N used for calculating the predicted number of times of accesses per unit time in addition to a predetermined volume, and the number of times of accesses to the volume per unit time. Similar to-case (a), the upper limit value management table is created from the set items at step (1).  
         [0020]     In case (c), a replication management table is created at step (1) for indicating the number of replicas at a time at which a volume is replicated or a replicated volume is deleted. Next, at step (2), three patterns are available depending on where disk accesses are monitored.  
         [0021]     Components responsible for the monitoring of disk accesses are listed below. 
        (d) a processing program on the computer A;     (e) the controller of the disk storage device; and     (f) a management program B on the management computer B for managing the disk storage device.        
 
         [0025]     Any of the components (d)-(f) monitors disk accesses, and the same component as that responsible for the monitoring of disk accesses manages the upper limit value management table created from the items set at step (1), and the replication management table.  
         [0026]     In case (d), disk accesses to a predetermined volume is monitored by acquiring the number of times of accesses per unit time from an access monitoring unit of a management program A on the same computer A responsible for the system management.  
         [0027]     In case (e), disk accesses to a predetermined volume is monitored by acquiring data from an access monitoring unit in the controller of the disk storage device.  
         [0028]     In case (f), disk accesses to a predetermined volume is monitored by acquiring data from an access monitoring unit of the management program B for managing the disk storage device.  
         [0029]     At step (3), it is determined whether or not a replication request should be made under any of the conditions (a)-(c) shown at step (1). This determination is made by any of the components (d)-(f) shown at step (2). When the result of the determination indicates that the replication is necessary, a request for replicating the predetermined volume is made to the controller of the disk storage device, so that the controller of the disk storage device responsively replicates the predetermined volume.  
         [0030]     At step (4), the completion of the replication of the predetermined volume is followed by an update to the contents of an access destination management table of each program previously contained in the management program B for managing the disk storage device to switch the access path, such that a program additionally attempting to access the original volume is directed to access the replicated volume.  
         [0031]     By following the foregoing steps, even if a plurality of programs simultaneously access one and the same volume, the number of times of accesses to each volume in the disk storage device per unit time is limited to a certain value or less, thus improving the disk access performance.  
         [0032]     As described above, according to the present invention, the volume access load can be distributed by creating a replica of the predetermined volume, and distributing accesses to the original volume to the original volume and replicated volume. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]      FIG. 1  is a block diagram illustrating the principles of a system according to the present invention;  
         [0034]      FIG. 2  is a block diagram illustrating the configuration of a system according in a first, a fourth, and a seventh embodiment;  
         [0035]      FIG. 3  is a flow chart generally illustrating a sequence of processing steps in the first embodiment;  
         [0036]      FIG. 4  shows an upper limit management table used in the first to third embodiments;  
         [0037]      FIG. 5  shows an access destination management table;  
         [0038]      FIG. 6  is a block diagram illustrating the configuration of a system according to a second, a fifth, and an eighth embodiment;  
         [0039]      FIG. 7  is a flow chart generally illustrating a sequence of processing steps in the second embodiment;  
         [0040]      FIG. 8  is a block diagram illustrating the configuration of a system according to a third, a sixth, and a ninth embodiment;  
         [0041]      FIG. 9  is a flow chart generally illustrating a sequence of processing steps in the third embodiment;  
         [0042]      FIG. 10  is a flow chart generally illustrating a sequence of processing steps in the fourth embodiment;  
         [0043]      FIG. 11  shows an upper limit value management table used in the fourth to sixth embodiments;  
         [0044]      FIG. 12  is a flow chart generally illustrating a sequence of processing steps in the fifth embodiment;  
         [0045]      FIG. 13  is a flow chart generally illustrating a sequence of processing steps in the sixth embodiment;  
         [0046]      FIG. 14  is a flow chart generally illustrating a sequence of processing steps in the seventh embodiment;  
         [0047]      FIG. 15  is a graph representing a replication management schedule;  
         [0048]      FIG. 16  shows a replication management table;  
         [0049]      FIG. 17  is a flow chart generally illustrating a sequence of processing steps in the eighth embodiment;  
         [0050]      FIG. 18  is a flow chart generally illustrating a sequence of processing steps in the ninth embodiment;  
         [0051]      FIG. 19A  is a diagram representing a determination made in the fourth, fifth, and sixth embodiments as to whether a predicted number of times of accesses exceeds to an upper limit value when a target volume is replicated;  
         [0052]      FIG. 19B  is a diagram representing a determination made in the fourth, fifth, and sixth embodiments as to whether a predicted number of times of accesses exceeds to an upper limit value when the target volume is not replicated; and  
         [0053]      FIG. 20  is a diagram showing the principles of distributing a load by re-configuring volumes. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0054]     In the following, some embodiments of a disk access control method according to the present invention will be described with reference to the accompanying drawings which illustrate such embodiments.  
       First Embodiment  
       [0055]      FIG. 1  shows a conceptual block diagram of a system as a first embodiment according to the present invention, and  FIG. 2  is a block diagram illustrating the configuration of a system according to a first embodiment. The illustrated system according to the first embodiment comprises a disk storage device  11  having a volume replication function; a computer A 1  which executes a processing program  4  for accessing the disk storage device  11 ; and a management computer B 8  which executes a management program B 9  for managing the disk storage device  11 . A service program A 5  running on the processing program  4  generates an input/output request to a certain volume in the disk storage device  11 . In response to the request, a controller  12  of the disk storage device  11  performs an input/output operation for the volume associated with the request. The disk storage device  11  is systematically managed by the management program B 9  which runs on the management computer B 8 . Such configured systems are, as shown below, capable of dynamically distributing accesses concentrated on a predetermined volume from a plurality of service programs, such as when the service program A 5 , a service program B 6 , and a service program C 7  access to a logical volume P 13 .  FIG. 3  is a flow chart generally illustrating a sequence of processing steps in the first embodiment. The processing flow is outlined below.  
         [0056]     At step  101 , the processing program  4  receives an upper limit value set by the user for the number of times of accesses to a predetermined volume per unit time.  
         [0057]     At step  102 , the processing program  4  creates an upper limit value management table  15 .  
         [0058]     At step  103 , the processing program  4  acquires data on the number of times of accesses per unit time at the current time from the management program A 2 .  
         [0059]     At step  104 , the processing program  4  determines whether or not the acquired data exceeds the upper limit value.  
         [0060]     At step  105 , the controller  12  of the disk storage device  11  replicates the predetermined volume.  
         [0061]     At step  106 , the management program B 9  creates an access destination management table  18 .  
         [0062]     At step  107 , the management program B 9  switches the volume to be accessed from the original volume to the replicated volume.  
         [0063]     At step  108 , the processing program  4  determines whether or not the access distribution processing is valid.  
         [0064]     Next, detailed description will be made below on the steps in  FIG. 3  when the user controls accesses to the logical volume P 13 .  
         [0065]     At step  101 , the user sets an upper limit value for the number of times of accesses to the logical volume P 13  per unit time for the processing program  4 .  
         [0066]     At step  102 , the processing program  4  creates the upper limit value management table  15  comprised of a volume name  16  and an upper limit value  17 , as shown in  FIG. 4 , sets an upper limit value of 1000 [times/min] for the logical volume P 13 , and enters the logical volume P 13  and the set upper limit value into the upper limit value management table  15 .  
         [0067]     At step  103 , the processing program  4  receives data on the number of times of accesses to the logical volume P 13  per unit time from an access monitoring unit  3  of the management program A 2 . Upon receipt of the data, the processing program  4  references the upper limit value management table  15  to retrieve the upper limit value of 1000 [times/min] for the logical volume P 13 .  
         [0068]     At step  104 , the processing program  4  determines whether or not the data acquired from the access monitoring unit  3  of the management program A 2  at step  103  exceeds the upper limit value of 1000 [times/min] retrieved from the upper limit value management table  15  at step  103 . When the upper limit value of 1000 [times/min] is not exceeded, the processing flow proceeds to step  108 . Conversely, when the upper limit value of 1000 [times/min] is exceeded, the processing flow proceeds to step  104 .  
         [0069]     At step  105 , the processing program  4  requests the controller  12  of the disk storage device  11  to replicate the logical volume P 13 . Upon receipt of the replication request, the controller  12  of the disk storage device  11  creates a logical volume R 14  which is a mirror volume of the replication requested volume P 13 .  
         [0070]     At step  106 , after the mirror volume has been completely created at step  105 , the controller  12  of the disk storage device  11  notifies the management program B 9  running on the management computer B 8  of the completion of replication. Upon receipt of the notification of the completed replication, an access controller  10  of the management program B 9  creates the access destination management table  18  comprised of a program name  19 , an access requested volume name  20 , and an accessed volume name  21 , as shown in  FIG. 5 . The access requested volume name  20  indicates the name of a volume which is requested for an access by each service program that requests an access to the logical volume P 13 , while the accessed volume name  21  indicates the name of a volume which is actually accessed by the service program. When the service programs A 5  and B 6  are to access the logical volume P 13  at the time of step  106 , the controller  12  enters the names of the access requesting programs, i.e., service programs A 5 , B 6  into the access destination management table  18 .  
         [0071]     At step  107 , when the service program C 7  additionally requests an access to the logical volume P 13  after step  106 , the management program B 9  enters data into the access destination management table  18  such that the service program C 7  is forced to access the logical volume R 14 . In other words, the volume accessed by the service program C 7  is changed from the logical volume P 13  to the logical volume R 14 . When an access is requested to the logical volume P 13  from a service program which has been previously registered in the access destination management table  18 , the management program B 9  references the access destination management table  18  to retrieve the accessed volume name  21 . The management program B 9  notifies the controller  12  of the disk storage device  11  of the accessed volume from the accessed volume name  21  retrieved from the access destination management table  18 . Upon receipt of the notification, the controller  12  of the disk storage device  11  performs an input/output operation to the volume notified from the management program B 9 .  
         [0072]     At step  108 , the processing program  4  determines the validity of the access control processing for distributing the accesses to the logical volume P 13 . When determined as valid, the processing flow jumps back to step  103 . When not determined as valid, the processing flow is terminated.  
         [0073]     By executing steps  101  to  108  described above, the system internally carries out the replication of the logical volume P 13  and the switching of the accessed volume from the logical volume P 13  to the replicated volume R 14 , which are involved in the distribution of disk accesses to the logical volume P 13  specified by the user, thereby advantageously limiting the number of times of disk accesses to the logical volume P 13  to a certain value or less.  
       Second Embodiment  
       [0074]      FIG. 6  is a block diagram illustrating the configuration of a system according to a second embodiment. The illustrated system according to the second embodiment comprises a disk storage device  11  having a volume replication function; a computer A 1  which executes a processing program  4  that accesses the disk storage device  11 ; and a management computer B 8  which executes a management program B 9  for managing the disk storage device  11 . A service program A 5  running on the processing program  4  generates an input/output request to a certain volume in the disk storage device  11 , and a controller  12  of the disk storage device  11 , upon receipt of the request, performs an input/output operation for the requested volume. The disk storage device  11  is systematically managed by the management program B 9  which runs on the management computer B 8 . Such configured systems are, as shown below, capable of dynamically distributing accesses concentrated on a predetermined volume from a plurality of service programs, such as when the service program A 5 , a service program B 6 , and a service program C 7  access to a logical volume P 13 . The second embodiment differs from the first embodiment in that the controller  12  of the disk storage device  11  is responsible for the creation of the upper limit value management table  15 , the monitoring of the number of times of accesses, and the comparison of the monitored number of times with the upper limit value.  FIG. 7  is a flow chart generally illustrating a sequence of processing steps in the second embodiment. The processing flow is outlined below.  
         [0075]     At step  109 , the controller  12  of the disk storage device  11  receives an upper limit value set by the user for the number of times of accesses to a predetermined volume per unit time.  
         [0076]     At step  110 , the controller  12  of the disk storage device  11  creates the upper limit value management table  15 .  
         [0077]     At step  111 , the controller  12  of the disk storage device  11  acquires data on the number of times of accesses per unit time at the current time from the management program A 2 .  
         [0078]     At step  112 , the controller  12  of the disk storage device  11  determines whether or not the acquired data exceeds the upper limit value.  
         [0079]     At step  113 , the controller  12  of the disk storage device  11  replicates the predetermined volume.  
         [0080]     At step  114 , the management program B 9  creates the access destination management table  18 .  
         [0081]     At step  115 , the management program B 9  switches the volume to be accessed from the original volume to the replicated volume.  
         [0082]     At step  116 , the controller  12  determines whether or not the access distribution processing is valid.  
         [0083]     Next, detailed description will be made below on the steps in  FIG. 7  when the user controls accesses to the logical volume P 13 .  
         [0084]     At step  109 , the user sets an upper limit value for the number of times of accesses to the logical volume P 13  per unit time for the controller  12  of the disk storage device  11 .  
         [0085]     At step  110 , the controller  12  of the disk storage device  11  creates the upper limit value management table  15  comprised of the volume name  16  and upper limit value  17 , as shown in  FIG. 4 , sets an upper limit value of 1000 [times/min] for the logical volume P 13 , and enters the logical volume P 13  and the set upper limit value into the upper limit value management table  15 .  
         [0086]     At step  111 , the controller  12  of the disk storage device  11  receives data on the number of times of accesses to the logical volume P 13  per unit time from an access monitoring unit  3  of the in the disk storage device  11 . Upon receipt of the data, the controller  12  of the disk storage device  11  references the upper limit value management table  15  to retrieve the upper limit value of 1000 [times/min] for the logical volume P 13 .  
         [0087]     At step  112 , the controller  12  of the disk storage device  11  determines whether or not the data acquired from the access monitoring unit  3  of the management program A 2  at step  111  exceeds the upper limit value of 1000 [times/min] retrieved from the upper limit value management table  15  at step  111 . When the upper limit value of 1000 [times/min] is not exceeded, the processing flow proceeds to step  116 . Conversely, when the upper limit value of 1000 [times/min] is exceeded, the processing flow proceeds to step  113 . At step  113 , the controller  12  of the disk storage device  11  creates a logical volume R 14  which is a mirror volume of the replication requested volume P 13 .  
         [0088]     At step  114 , after the mirror volume has been completely created at step  113 , the controller  12  of the disk storage device  11  notifies the management program B 9  running on the management computer B 8  of the completion of replication. Upon receipt of the notification of the completed replication, an access controller  10  of the management program B 9  creates the access destination management table  18  comprised of the program name  19 , access requested volume name  20 , and accessed volume name  21 , as shown in  FIG. 5 . The access requested volume name  20  indicates the name of a volume which is requested for an access by each service program that requests an access to the logical volume P 13 , while the accessed volume name  21  indicates the name of a volume which is actually accessed by the service program. When the service programs A 5  and B 6  are to access the logical volume P 13  at the time of step  114 , the management program B 9  enters the names of the access requesting programs, i.e., the service programs A 5 , B 6  into the access destination management table  18 .  
         [0089]     At step  115 , when the service program C 7  additionally requests an access to the logical volume P 13  after step  114 , the management program B 9  enters data into the access destination management table  18  such that the service program C 7  is forced to access the logical volume R 14 . In other words, the volume accessed by the service program C 7  is changed from the logical volume P 13  to the logical volume R 14 . When an access is requested to the logical volume P 13  from a service program which has been previously registered in the access destination management table  18 , the management program B 9  references the access destination management table  18  to retrieve the accessed volume name  21 . The management program B 9  notifies the controller  12  of the disk storage device  11  of the accessed volume from the accessed volume name  21  retrieved from the access destination management table  18 . Upon receipt of the notification, the controller  12  of the disk storage device  11  performs an input/output operation to the volume notified from the management program B 9 .  
         [0090]     At step  116 , the controller  12  of the disk storage device  11  determines the validity of the access control processing for distributing the accesses to the logical volume P 13 . When determined as valid, the processing flow jumps back to step  111 . When not determined as valid, the processing flow is terminated.  
         [0091]     By executing steps  109  to  116  described above, the system internally carries out the replication of the logical volume P 13  and the switching of the accessed volume from the logical volume P 13  to the replicated volume R 14 , which are involved in the distribution of disk accesses to the logical volume P 13  specified by the user, thereby advantageously limiting the number of times of disk accesses to the logical volume P 13  to a certain value or less.  
       Third Embodiment  
       [0092]      FIG. 8  is a block diagram illustrating the configuration of a system according to a third embodiment. The illustrated system according to the third embodiment comprises a disk storage device  11  having a volume replication function; a computer A 1  which executes a processing program  4  that accesses the disk storage device  11 ; and a management computer B 8  which executes a management program B 9  for managing the disk storage device  11 . A service program A 5  running on the processing program  4  generates an input/output request to a certain volume in the disk storage device  11 , and a controller  12  of the disk storage device  11 , upon receipt of the request, performs an input/output operation for the requested volume. The disk storage device  11  is systematically managed by the management program B 9  which runs on the management computer B 8 . Such configured systems are, as shown below, capable of dynamically distributing accesses concentrated on a predetermined volume from a plurality of service programs, such as when the service program A 5 , a service program B 6 , and a service program C 7  access to a logical volume P 13 . The third embodiment differs from the second embodiment in that the management program B 9  associated with the disk storage device  11  is responsible for the creation of the upper limit value management table  15 , monitoring of the number of times of accesses, and the comparison of the monitored number of times with the upper limit value.  FIG. 9  is a flow chart generally illustrating a sequence of processing steps in the third embodiment. The processing flow is outlined below.  
         [0093]     At step  117 , the management program B 9  receives an upper limit value set by the user for the number of times of accesses to a predetermined volume per unit time.  
         [0094]     At step  118 , the management program B 9  creates the upper limit value management table  15 .  
         [0095]     At step  119 , the management program B 9  acquires data on the number of times of accesses per unit time at the current time from the management program A 2 .  
         [0096]     At step  120 , the management program B 9  determines whether or not the acquired data exceeds the upper limit value.  
         [0097]     At step  121 , the controller  12  of the disk storage device  11  replicates the predetermined volume.  
         [0098]     At step  122 , the management program B 9  creates the access destination management table  18 .  
         [0099]     At step  123 , the management program B 9  switches the volume to be accessed from the original volume to the replicated volume.  
         [0100]     At step  124 , the management program B 9  determines whether or not the access distribution processing is valid.  
         [0101]     Next, detailed description will be made below on the steps in  FIG. 9  when the user controls accesses to the logical volume P 13 .  
         [0102]     At step  117 , the user sets an upper limit value of 1000 [times/min] for the number of times of accesses to the logical volume P 13  per unit time for the management program B 9 .  
         [0103]     At step  118 , the management program B 9  creates the upper limit value management table  15  comprised of the volume name  16  and upper limit value  17 , as shown in  FIG. 4 , sets an upper limit value of 1000 [times/min] for the logical volume P 13 , and enters the logical volume P 13  and the set upper limit value into the upper limit value management table  15 .  
         [0104]     At step  119 , the management program B 9  receives data on the number of times of accesses to the logical volume P 13  per unit time from an access monitoring unit  3  of the management program B 9 . Upon receipt of the data, the management program B 9  references the upper limit value management table  15  to retrieve the upper limit value X for the logical volume P 13 .  
         [0105]     At step  120 , the management program B 9  determines whether or not the data acquired from the access monitoring unit  3  of the management program A 2  at step  111  exceeds the upper limit value of 1000 [times/min] retrieved from the upper limit value management table  15  at step  111 . When the upper limit value X is not exceeded, the processing flow proceeds to step  124 . Conversely, when the upper limit value of 1000 [times/min] is exceeded, the processing flow proceeds to step  121 .  
         [0106]     At step  121 , the management program B 9  requests the controller  12  of the disk storage device  11  to replicate the logical volume P 13 . Upon receipt of the replication request, the controller  12  of the disk storage device  11  creates a logical volume R 14  which is a mirror volume of the replication requested volume P 13 .  
         [0107]     At step  122 , after the mirror volume has been completely created at step  121 , the controller  12  of the disk storage device  11  notifies the management program B 9  running on the management computer B 8  of the completion of replication. Upon receipt of the notification of the completed replication, an access controller  10  of the management program B 9  creates the access destination management table  18  comprised of the program name  19 , access requested volume name  20 , and accessed volume name  21 , as shown in  FIG. 5 . The access requested volume name  20  indicates the name of a volume which is requested for an access by each service program that requests an access to the logical volume P 13 , while the accessed volume name  21  indicates the name of a volume which is actually accessed by the service program. When the service programs A 5  and B 6  are to access the logical volume P 13  at the time of step  122 , the management program B 9  enters the names of the access requesting programs, i.e., the service programs A 5 , B 6  into the access destination management table  18 .  
         [0108]     At step  123 , when the service program C 7  additionally requests an access to the logical volume P 13  after step  122 , the management program B 9  enters data into the access destination management table  18  such that the service program C 7  is forced to access the logical volume R 14 . In other words, the volume accessed by the service program C 7  is changed from the logical volume P 13  to the logical volume R 14 . When an access is requested to the logical volume P 13  from a service program which has been previously registered in the access destination management table  18 , the management program B 9  references the access destination management table  18  to retrieve the accessed volume name  21 . The management program B 9  notifies the controller  12  of the disk storage device  11  of the accessed volume from the accessed volume name  21 . Upon receipt of the notification, the controller  12  of the disk storage device  11  performs an input/output operation to the volume notified from the management program B 9 .  
         [0109]     At step  124 , the management program B 9  determines the validity of the access control processing for distributing the accesses to the logical volume P 13 . When determined as valid, the processing flow jumps back to step  119 . When not determined as valid, the processing flow is terminated.  
         [0110]     By executing steps  117  to  124  described above, the system internally carries out the replication of the logical volume P 13  and the switching of the accessed volume from the logical volume P 13  to the replicated volume R 14 , which are involved in the distribution of disk accesses to the logical volume P 13  specified by the user, thereby advantageously limiting the number of times of disk accesses to the logical volume P 13  to a certain value or less.  
       Fourth Embodiment  
       [0111]      FIG. 2  is a block diagram illustrating the configuration of a system according to a fourth embodiment. The illustrated system according to the fourth embodiment comprises a disk storage device  11  having a volume replication function; a computer A 1  which executes a processing program  4  for accessing the disk storage device  11 ; and a management computer B 8  which executes a management program B 9  for managing the disk storage device  11 . A service program A 5  running on the processing program  4  generates an input/output request to a certain volume in the disk storage device  11 . In response to the request, a controller  12  of the disk storage device  11  performs an input/output operation for the volume associated with the request. The disk storage device  11  is systematically managed by the management program B 9  which runs on the management computer B 8 . Such configured systems are, as shown below, capable of dynamically distributing accesses concentrated on a predetermined volume from a plurality of service programs, such as when the service program A 5 , a service program B 6 , and a service program C 7  access to a logical volume P 13 . The fourth embodiment differs from the first embodiment in that the number of times of accesses is compared with an upper limit value at a specified time predicted from the number of times of accesses, which have been made until the current time, based on previously set items.  FIG. 10  is a flow chart generally illustrating a sequence of processing steps in the first embodiment. The processing flow is outlined below.  
         [0112]     At step  125 , the processing program  4  receives an upper limit value for the number of times of accesses to a predetermined volume per unit time, a time at which data is predicted, and the number of data used for the prediction, all of which are set by the user.  
         [0113]     At step  126 , the processing program  4  creates the upper limit value management table  15 .  
         [0114]     At step  127 , the processing program  4  acquires data on the number of times of accesses per unit time at the current time from the management program A 2 .  
         [0115]     At step  128 , the processing program  4  calculates a predicted number of times of accesses per unit time at the specified time from the acquired data.  
         [0116]     At step  129 , the processing program  4  determines whether or not the acquired data exceeds the upper limit value.  
         [0117]     At step  130 , the controller  12  of the disk storage device  11  replicates the predetermined volume.  
         [0118]     At step  131 , the management program B 9  creates the access destination management table  18 .  
         [0119]     At step  132 , the management program B 9  switches the volume to be accessed from the original. volume to the replicated volume.  
         [0120]     At step  133 , the processing program  4  determines whether or not the access distribution processing is valid.  
         [0121]     Next, detailed description will be made below on the steps in  FIG. 10  when the user controls accesses to the logical volume P 13 .  
         [0122]     At step  125 , the user sets for the processing program  4  an upper limit value X for the number of times of accesses to the logical volume P 13  per unit time that is a condition for replicating the logical volume P 13 . Since the aforementioned upper limit value of 1000 [times/min] has been set for a predicted number of times of accesses per unit time in ten minutes from the current time, the user sets the current time, a time period of 10 [min] to the time at which the processing program  4  predicts the number of times of accesses per unit time, and the number of data equal to 8 [units] used for predicting the number of times of accesses per unit time.  
         [0123]     At step  126 , the processing program  4  creates an upper limit value management table  15  comprised of a volume name  16 , a time period  22 , the number of data  23 , and an upper limit value  17 , as shown in  FIG. 11 , and enters the set values into the upper limit value management table  15 .  
         [0124]     At step  127 , the processing program  4  receives data on the number of times of accesses to the logical volume P 13  per unit time from an access monitoring unit  3  of the management program A 2 .  
         [0125]     At step  128 , the processing program references the upper limit value management table  15  to retrieve the upper limit value of 1000 [times/min] for the logical volume P 13 ; the time period of 10 [min] to the time at which the processing program  4  predicts the number of times of accesses per unit time, and the number of data equal to 8 [units] used for predicting the number of times of accesses per unit time. The processing program  4  acquires eight data from a log of the number of times of accesses per unit time, which are relied on by the processing processor  4  to calculate a predicted number of times of accesses per unit time in ten minutes from the current time.  
         [0126]     At step  129 , the processing program  4  determines whether or not the predicted number of times of accesses per unit time calculated at step  128  exceeds the upper limit value of 1000 [times/min] retrieved from the upper limit value management table  15  at step  127 . When the upper limit value of 1000 [times/min] is not exceeded, as is the case shown in  FIG. 19B  where the logical volume P 13  need not be replicated, the processing flow proceeds to step  133 . Conversely, when the upper limit value of 1000 [times/min] is exceeded, as is the case shown in  FIG. 19A  where the logical volume P 13  should be replicated, the processing flow proceeds to step  130 .  
         [0127]     At step  130 , the processing program  4  requests the controller  12  of the disk storage device  11  to replicate the logical volume P 13 . Upon receipt of the replication request, the controller  12  of the disk storage device  11  creates a logical volume R 14  which is a mirror volume of the logical volume P 13 .  
         [0128]     At step  131 , after the mirror volume has been completely created at step  130 , the controller  12  of the disk storage device  11  notifies the management program B 9  running on the management computer B 8  of the completion of replication. Upon receipt of the notification of the completed replication, an access controller  10  of the management program B 9  creates the access destination management table  18  comprised of the program name  19 , access requested volume name  20 , and accessed volume name  21 , as shown in  FIG. 5 . The access requested volume name  20  indicates the name of a volume which is requested for an access by each service program that requests an access to the logical volume P 13 , while the accessed volume name  21  indicates the name of a volume which is actually accessed by the service program. When the service programs A 5  and B 6  are to access the logical volume P 13  at the time of step  131 , the management program B 9  enters the names of the access requesting volumes, i.e., the service programs A 5 , B 6  into the access destination management table  18 .  
         [0129]     At step  132 , when the service program C 7  additionally requests an access to the logical volume P 13  after step  131 , the management program B 9  enters data into the access destination management table  18  such that the service program C 7  is forced to access the logical volume R 14 . In other words, the volume accessed by the service program C 7  is changed from the logical volume P 13  to the logical volume R 14 . When an access is requested to the logical volume P 13  from a service program which has been previously registered in the access destination management table  18 , the management program B 9  references the access destination management table  18  to retrieve the accessed volume name  21 . The management program B 9  notifies the controller  12  of the disk storage device  11  of the accessed volume from the accessed volume name  21  retrieved from the access destination management table  18 . Upon receipt of the notification, the controller  12  of the disk storage device  11  performs an input/output operation to the volume notified from the management program B 9 .  
         [0130]     At step  133 , the processing program  4  determines the validity of the access control processing for distributing the accesses to the logical volume P 13 . When determined as valid, the processing flow jumps back to step  127 . When not determined as valid, the processing flow is terminated.  
         [0131]     By executing steps  125  to  133  described above, the system internally carries out the replication of the logical volume P 13  and the switching of the accessed volume from the logical volume P 13  to the replicated volume R 14 , which are involved in the distribution of disk accesses to the logical volume P 13  specified by the user, thereby advantageously limiting the number of times of disk accesses to the logical volume P 13  to a certain value or less.  
       Fifth Embodiment  
       [0132]      FIG. 6  is a block diagram illustrating the configuration of a system according to a fifth embodiment. The illustrated system according to the fifth embodiment comprises a disk storage device  11  having a volume replication function; a computer A 1  which executes a processing program  4  for accessing the disk storage device  11 ; and a management computer B 8  which executes a management program B 9  for managing the disk storage device  11 . A service program A 5  running on the processing program  4  generates an input/output request to a certain volume in the disk storage device  11 . In response to the request, a controller  12  of the disk storage device  11  performs an input/output operation for the volume associated with the request. The disk storage device  11  is systematically managed by the management program B 9  which runs on the management computer B 8 . Such configured systems are, as shown below, capable of dynamically distributing accesses concentrated on a predetermined volume from a plurality of service programs, such as when the service program A 5 , a service program B 6 , and a service program C 7  access to a logical volume P 13 . The fifth embodiment differs from the fourth embodiment in that the controller  12  of the disk storage device  11  is responsible for the creation of the upper limit value management table  15 , monitoring of the number of times of accesses, and the comparison of the monitored number of times with the upper limit value.  FIG. 12  is a flow chart generally illustrating a sequence of processing steps in the first embodiment. The processing flow is outlined below.  
         [0133]     At step  134 , the controller  12  of the disk storage device  11  receives an upper limit value for the number of times of accesses to a predetermined volume per unit time, a time at which data is predicted, and the number of data used for the prediction, all of which are set by the user.  
         [0134]     At step  135 , the controller  12  of the disk storage device  11  creates the upper limit value management table  15 .  
         [0135]     At step  136 , the controller  12  of the disk storage device  11  acquires data on the number of times of accesses per unit time at the current time from the management program A 2 .  
         [0136]     At step  137 , the controller  12  of the disk storage device  11  calculates a predicted number of times of accesses per unit time at the specified time from the acquired data.  
         [0137]     At step  138 , the controller  12  of the disk storage device  11  determines whether or not the acquired data exceeds the upper limit value.  
         [0138]     At step  139 , the controller  12  of the disk storage device  11  replicates the predetermined volume.  
         [0139]     At step  140 , the management program B 9  creates the access destination management table  18 .  
         [0140]     At step  141 , the management program B 9  switches the volume to be accessed from the original volume to the replicated volume.  
         [0141]     At step  142 , the controller  12  of the disk storage device  11  determines whether or not the access distribution processing is valid.  
         [0142]     Next, detailed description will be made below on the steps in  FIG. 12  when the user controls accesses to the logical volume P 13 .  
         [0143]     At step  134 , the user sets for the controller  12  of the disk storage device  11  an upper limit value of 1000 [times/min] for the number of times of accesses to the logical volume P 13  per unit time that is a condition for replicating the logical volume P 13 . Since the aforementioned upper limit value of 1000 [times/min] has been set for a predicted number of times of accesses per unit time in ten minutes from the current time, the user sets the current time, a time period of 10 [min] to the time at which the processing program  4  predicts the number of times of accesses per unit time, and the number of data equal to 8 [units] used for predicting the number of times of accesses per unit time.  
         [0144]     At step  135 , the controller  12  of the disk storage device  11  creates the upper limit value management table  15  comprised of the volume name  16 , time period  22 , number of data  23 , and upper limit value  17 , as shown in  FIG. 11 , and enters the set values into the upper limit value management table  15 .  
         [0145]     At step  136 , the controller  12  of the disk storage device  11  receives data on the number of times of accesses to the logical volume P 13  per unit time from an access monitoring unit  3  in the controller of the disk storage device  11 .  
         [0146]     At step  137 , the controller  12  of the disk storage device  11  references the upper limit value management table  15  to retrieve the upper limit value of 1000 [times/min] for the logical volume P 13 ; the time period of 10 [min] to the time at which the processing program  4  predicts the number of times of accesses per unit time, and the number of data equal to 8 [units] used for predicting the number of times of accesses per unit time. The processing program  4  acquires eight data from a log of the number of times of accesses per unit time, which are relied on by the processing processor  4  to calculate a predicted number of times of accesses per unit time in ten minutes from the current time.  
         [0147]     At step  138 , the controller  12  of the disk storage device  11  determines whether or not the predicted number of times of accesses per unit time calculated at step  137  exceeds the upper limit value of 1000 [times/min] retrieved from the upper limit value management table  15  at step  136 . When the upper limit value of 1000 [times/min] is not exceeded, as is the case shown in  FIG. 19B  where the logical volume P 13  need not be replicated, the processing flow proceeds to step  142 . Conversely, when the upper limit value of 1000 [times/min] is exceeded, as is the case shown in  FIG. 19A  where the logical volume P 13  should be replicated, the processing flow proceeds to step  139 .  
         [0148]     At step  139 , the controller  12  of the disk storage device  11  creates a logical volume R which is a mirror volume of the logical volume P 13 .  
         [0149]     At step  140 , after the mirror volume has been completely created at step  139 , the controller  12  of the disk storage device  11  notifies the management program B 9  running on the management computer B 8  of the completion of replication. Upon receipt of the notification of the completed replication, an access controller  10  of the management program B 9  creates the access destination management table  18  comprised of the program name  19 , access requested volume name  20 , and accessed volume name  21 , as shown in  FIG. 5 . The access requested volume name  20  indicates the name of a volume which is requested for an access by each service program that requests an access to the logical volume P 13 , while the accessed volume name  21  indicates the name of a volume which is actually accessed by the service program. When the service programs A 5  and B 6  are to access the logical volume P 13  at the time of step  140 , the management program B 9  enters the names of the access requesting programs, i.e., the service programs A 5 , B 6  into the access destination management table  18 .  
         [0150]     At step  141 , when the service program C 7  additionally requests an access to the logical volume P 13  after step  140 , the management program B 9  enters data into the access destination management table  18  such that the service program C 7  is forced to access the logical volume R 14 . In other words, the volume accessed by the service program C 7  is changed from the logical volume P 13  to the logical volume R 14 . When an access is requested to the logical volume P 13  from a service program which has been previously registered in the access destination management table  18 , the management program B 9  references the access destination management table  18  to retrieve the accessed volume name  21 . The management program B 9  notifies the controller  12  of the disk storage device  11  of the accessed volume from the accessed volume name  21  retrieved from the access destination management table  18 . Upon receipt of the notification, the controller  12  of the disk storage device  11  performs an input/output operation to the volume notified from the management program B 9 .  
         [0151]     At step  142 , the controller  12  of the disk storage device  11  determines the validity of the access control processing for distributing the accesses to the logical volume P 13 . When determined as valid, the processing flow jumps back to step  136 . When not determined as valid, the processing flow is terminated.  
         [0152]     By executing steps  134  to  142  described above, the system internally carries out the replication of the logical volume P 13  and the switching of the accessed volume from the logical volume P 13  to the replicated volume R 14 , which are involved in the distribution of disk accesses to the logical volume P 13  specified by the user, thereby advantageously limiting the number of times of disk accesses to the logical volume P 13  to a certain value or less.  
       Sixth Embodiment  
       [0153]      FIG. 8  is a block diagram illustrating the configuration of a system according to a sixth embodiment. The illustrated system according to the sixth embodiment comprises a disk storage device  11  having a volume replication function; a computer A 1  which executes a processing program  4  for accessing the disk storage device  11 ; and a management computer B 8  which executes a management program B 9  for managing the disk storage device  11 . A service program A 5  running on the processing program  4  generates an input/output request to a certain volume in the disk storage device  11 . In response to the request, a controller  12  of the disk storage device  11  performs an input/output operation for the volume associated with the request. The disk storage device  11  is systematically managed by the management program B 9  which runs on the management computer B 8 . Such configured systems are, as shown below, capable of dynamically distributing accesses concentrated on a predetermined volume from a plurality of service programs, such as when the service program A 5 , a service program B 6 , and a service program C 7  access to a logical volume P 13 . The sixth embodiment differs from the fifth embodiment in that the management program B 9  associated with the disk storage device  11  is responsible for the creation of the upper limit value management table  15 , monitoring of the number of times of accesses, and the comparison of the monitored number of times with the upper limit value.  FIG. 13  is a flow chart generally illustrating a sequence of processing steps in the first embodiment. The processing flow is outlined below.  
         [0154]     At step  143 , the management program B 9  receives an upper limit value for the number of times of accesses to a predetermined volume per unit time, a time at which data is predicted, and the number of data used for the prediction, all of which are set by the user.  
         [0155]     At step  144 , the management program B 9  creates the upper limit value management table  15 .  
         [0156]     At step  145 , the management program B 9  acquires data on the number of times of accesses per unit time at the current time from the management program A 2 .  
         [0157]     At step  146 , the management program B 9  calculates a predicted number of times of accesses per unit time at the specified time from the acquired data.  
         [0158]     At step  147 , the management program B 9  determines whether or not the acquired data exceeds the upper limit value.  
         [0159]     At step  148 , the controller  12  of the disk storage device  11  replicates the predetermined volume.  
         [0160]     At step  149 , the management program B 9  creates the access destination management table  18 .  
         [0161]     At step  150 , the management program B 9  switches the volume to be accessed from the original volume to the replicated volume.  
         [0162]     At step  151 , the management program B 9  determines whether or not the access distribution processing is valid.  
         [0163]     Next, detailed description will be made below on the steps in  FIG. 13  when the user controls accesses to the logical volume P 13 .  
         [0164]     At step  143 , the user sets for the management program B 9  an upper limit value of 1000 [times/min] for the number of times of accesses to the logical volume P 13  per unit time that is a condition for replicating the logical volume P 13 . Since the aforementioned upper limit value of 1000 [times/min] has been set for a predicted number of times of accesses per unit time in ten minutes from the current time, the user sets the current time, a time period of 10 [min] to the time at which the management program B 9  predicts the number of times of accesses per unit time, and the number of data equal to 8 [units] used for predicting the number of times of accesses per unit time.  
         [0165]     At step  144 , the management program B 9  creates the upper limit value management table  15  comprised of the volume name  16 , time period  22 , number of data  23 , and upper limit value  17 , as shown in  FIG. 11 , and enters the set values into the upper limit value management table  15 .  
         [0166]     At step  145 , the management program B 9  receives data on the number of times of accesses to the logical volume P 13  per unit time from an access monitoring unit  3  of the management program B 9 .  
         [0167]     At step  146 , the management program B 9  references the upper limit value management table  15  to retrieve the upper limit value of 1000 [times/min] for the logical volume P 13 ; the time period of 10 [min] to the time at which the management program B 9  predicts the number of times of accesses per unit time, and the number of data equal to 8 [units] used for predicting the number of times of accesses per unit time. The management program B 9  acquires eight data from a log of the number of times of accesses per unit time, which are relied on by the management program B 9  to calculate a predicted number of times of accesses per unit time in ten minutes from the current time.  
         [0168]     At step  147 , the management program B 9  determines whether or not the predicted number of times of accesses per unit time calculated at step  146  exceeds the upper limit value of 1000 [times/min] retrieved from the upper limit value management table  15  at step  145 . When the upper limit value of 1000 [times/min] is exceeded, as is the case shown in  FIG. 19B  where the logical volume P 13  need not be replicated, the processing flow proceeds to step  151 . Conversely, when the upper limit value of 1000 [times/min] is not exceeded, as is the case shown in  FIG. 19A  where the logical volume P 13  should be replicated, the processing flow proceeds to step  148 .  
         [0169]     At step  148 , the management program B 9  requests the controller  12  of the disk storage device  11  to replicate the logical volume P 13 . Upon receipt of the replication request, the controller  12  of the disk storage device  11  creates a logical volume R 14  which is a mirror volume of the logical volume P 13 .  
         [0170]     At step  149 , after the mirror volume has been completely created at step  148 , the controller  12  of the disk storage device  12  notifies the management program B 9  running on the management computer B 8  of the completion of replication. Upon receipt of the notification of the completed replication, an access controller  10  of the management program B 9  creates the access destination management table  18  comprised of the program name  19 , access requested volume name  20 , and accessed volume name  21 , as shown in  FIG. 5 . The access requested volume name  20  indicates the name of a volume which is requested for an access by each service program that requests an access to the logical volume P 13 , while the accessed volume name  21  indicates the name of a volume which is actually accessed by the service program. When the service programs A 5  and B 6  are to access the logical volume P 13  at the time of step  149 , the management program B 9  enters the names of the access requesting programs, i.e., the service programs A 5 , B 6  into the access destination management table  18 .  
         [0171]     At step  150 , when the service program C 7  additionally requests an access to the logical volume P 13  after step  149 , the management program B 9  enters data into the access destination management table  18  such that the service program C 7  is forced to access the logical volume R 14 . In other words, the volume accessed by the service program C 7  is changed from the logical volume P 13  to the logical volume R 14 . When an access is requested to the logical volume P 13  from a service program which has been previously registered in the access destination management table  18 , the management program B 9  references the access destination management table  18  to retrieve the accessed volume name  21 . The management program B 9  notifies the controller  12  of the disk storage device  11  of the accessed volume from the accessed volume name  21  retrieved from the access destination management table  18 . Upon receipt of the notification, the controller  12  of the disk storage device  11  performs an input/output operation to the volume notified from the management program B 9 .  
         [0172]     At step  151 , the management program B 9  determines the validity of the access control processing for distributing the accesses to the logical volume P 13 . When determined as valid, the processing flow jumps back to step  145 . When not determined as valid, the processing flow is terminated.  
         [0173]     By executing steps  143  to  151  described above, the system internally carries out the replication of the logical volume P 13  and the switching of the accessed volume from the logical volume P 13  to the replicated volume R 14 , which are involved in the distribution of disk accesses to the logical volume P 13  specified by the user, thereby advantageously limiting the number of times of disk accesses to the logical volume P 13  to a certain value or less.  
       Seventh Embodiment  
       [0174]      FIG. 2  is a block diagram illustrating the configuration of a system according to a seventh embodiment. The illustrated system according to the seventh embodiment comprises a disk storage device  11  having a volume replication function; a computer A 1  which executes a processing program  4  for accessing the disk storage device  11 ; and a management computer B 8  which executes a management program B 9  for managing the disk storage device  11 . A service program A 5  running on the processing program  4  generates an input/output request to a certain volume in the disk storage device  11 . In response to the request, a controller  12  of the disk storage device  11  performs an input/output operation for the volume associated with the request. The disk storage device  11  is systematically managed by the management program B 9  which runs on the management computer B 8 . Such configured systems are, as shown below, capable of dynamically distributing accesses concentrated on a predetermined volume from a plurality of service programs, such as when the service program A 5 , a service program B 6 , and a service program C 7  access to a logical volume P 13 . The seventh embodiment differs from the first embodiment in that the user does not set an upper limit value but sets a replication management schedule  24  for creating a replica at a specified time, such that a volume is replicated based on the replication management schedule  24 .  FIG. 14  is a flow chart generally illustrating a sequence of processing steps in the seventh embodiment. The processing flow is outlined below.  
         [0175]     At step  152 , the processing program  4  receives the replication management schedule  24  set by the user for a predetermined volume.  
         [0176]     At step  153 , the processing program  4  creates a replication management table  25 .  
         [0177]     At step  154 , the processing program  4  determines whether or not the current time is specified as a replication time.  
         [0178]     At step  155 , the controller  12  of the disk storage device  11  replicates the predetermined volume.  
         [0179]     At step  156 , the management program B 9  creates the access destination management table  18 .  
         [0180]     At step  157 , the management program B 9  switches the volume to be accessed from the original volume to the replicated volume.  
         [0181]     At step  158 , the processing program  4  determines whether or not the access distribution processing is valid.  
         [0182]     Next, detailed description will be made below on the steps in  FIG. 14  when the user controls accesses to the logical volume P 13 .  
         [0183]     At step  152 , the user creates for the processing program  4  the replication management schedule  24  which indicates a change in the number of replicas of the logical volume P 13  over time.  FIG. 15  shows the replication management schedule  24 . The replication management schedule  24  indicates the number of replicas at each time, and  FIG. 15  represents a schedule for creating one replica at specified time 10:00, and creating another replica at specified time 11:00.  
         [0184]     At step  153 , the processing program  4  creates the replication management table  25  which indicates replication times based on the replication management schedule  24  created at step  152  and is comprised of a volume name  16 , the total number of volumes to be replicated  26 , and a replication end time  27 , as shown in  FIG. 16 , and enters set values into the replication management table  25 .  
         [0185]     At step  154 , the processing program  4  acquires the current time from the operating system, and references the replication management table  25  to determine whether or not any replication end time is equal to the sum of the current time and the time required to replicate a volume. If no such replication end time is found in the replication management table  25 , the processing flow proceeds to step  158 . Conversely, if such a replication end time is found, the processing flow proceeds to step  155 .  
         [0186]     At step  155 , the processing program  4  requests the controller  12  of the disk storage device  11  to replicate the logical volume P 13 . Upon receipt of the replication request, the controller  12  of the disk storage device  11  creates a logical volume R 14  which is a mirror volume of the replication requested volume P 13 .  
         [0187]     At step  156 , after the mirror volume has been completely created at step  155 , the controller  12  of the disk storage device  11  notifies the management program B 9  running on the management computer B 8  of the completion of replication. Upon receipt of the notification of the completed replication, an access controller  10  of the management program B 9  creates the access destination management table  18  comprised of the program name  19 , access requested volume name  20 , and accessed volume name  21 , as shown in  FIG. 5 . The access requested volume name  20  indicates the name of a volume which is requested for an access by each service program that requests an access to the logical volume P 13 , while the accessed volume name  21  indicates the name of a volume which is actually accessed by the service program. When the service programs A 5  and B 6  are to access the logical volume P 13  at the time of step  156 , the control program B 9  enters the names of the access requesting programs, i.e., service programs A 5 , B 6  into the access destination management table  18 .  
         [0188]     At step  157 , when the service program C 7  additionally requests an access to the logical volume P 13  after step  156 , the management program B 9  enters data into the access destination management table  18  such that the service program C 7  is forced to access the logical volume R 14 . In other words, the volume accessed by the service program C 7  is changed from the logical volume P 13  to the logical volume R 14 . When an access is requested to the logical volume P 13  from a service program which has been previously registered in the access destination management table  18 , the management program B 9  references the access destination management table  18  to retrieve the accessed volume name  21 . The management program B 9  notifies the controller  12  of the disk storage device  11  of the accessed volume from the accessed volume name  21  retrieved from the access destination management table  18 . Upon receipt of the notification, the controller  12  of the disk storage device  11  performs an input/output operation to the volume notified from the management program B 9 .  
         [0189]     At step  158 , the processing program  4  determines the validity of the access control processing for distributing the accesses to the logical volume P 13 . When determined as valid, the processing flow jumps back to step  154 . When not determined as valid, the processing flow is terminated.  
         [0190]     By executing steps  152  to  158  described above, the system internally carries out the replication of the logical volume P 13  and the switching of the accessed volume from the logical volume P 13  to the replicated volume R 14 , which are involved in the distribution of disk accesses to the logical volume P 13  specified by the user, thereby advantageously limiting the number of times of disk accesses to the logical volume P 13  to a certain value or less.  
       Eighth Embodiment  
       [0191]      FIG. 6  is a block diagram illustrating the configuration of a system according to an eighth embodiment. The illustrated system according to the eighth embodiment comprises a disk storage device  11  having a volume replication function; a computer A 1  which executes a processing program  4  for accessing the disk storage device  11 ; and a management computer B 8  which executes a management program B 9  for managing the disk storage device  11 . A service program A 5  running on the processing program  4  generates an input/output request to a certain volume in the disk storage device  11 . In response to the request, a controller  12  of the disk storage device  11  performs an input/output operation for the volume associated with the request. The disk storage device  11  is systematically managed by the management program B 9  which runs on the management computer B 8 . Such configured systems are, as shown below, capable of dynamically distributing accesses concentrated on a predetermined volume from a plurality of service programs, such as when the service program A 5 , a service program B 6 , and a service program C 7  access to a logical volume P 13 . The eighth embodiment differs from the seventh embodiment in that the controller  12  of the disk storage device  11  is responsible for the creation of the replication management schedule  24  and replication management table  25 , and the determination as to whether or not a replication time is reached.  FIG. 17  is a flow chart generally illustrating a sequence of processing steps in the eighth embodiment. The processing flow is outlined below.  
         [0192]     At step  159 , the controller  12  of the disk storage device  11  receives the replication management schedule  24  set by the user for a predetermined volume.  
         [0193]     At step  160 , the controller  12  of the disk storage device  11  creates the replication management table  25 .  
         [0194]     At step  161 , the controller  12  of the disk storage device  11  determines whether or not the current time is specified as a replica creation time.  
         [0195]     At step  162 , the controller  12  of the disk storage device  11  replicates the predetermined volume.  
         [0196]     At step  163 , the management program B 9  creates the access destination management table  18 .  
         [0197]     At step  164 , the management program B 9  switches the volume to be accessed from the original volume to the replicated volume.  
         [0198]     At step  165 , the controller  12  of the disk storage device  11  determines whether or not the access distribution processing is valid.  
         [0199]     Next, detailed description will be made below on the steps in  FIG. 17  when the user controls accesses to the logical volume P 13 .  
         [0200]     At step  159 , the user creates for the controller  12  of the disk storage device  11  the replication management schedule  24  which indicates a change in the number of replicas of the logical volume P 13  over time.  FIG. 15  shows the replication management schedule  24 . The replication management schedule  24  indicates the number of replicas at each time, and  FIG. 15  represents a schedule for creating one replica at specified time 10:00, and creating another replica at specified time 11:00.  
         [0201]     At step  160 , the controller  12  of the disk storage device  11  creates the replication management table  25  shown which indicates replication times based on the replication management schedule  24  created at step  152  and is comprised of the volume name  16 , total number of volumes to be replicated  26 , and replication end time  27 , as shown in  FIG. 16 , and enters set values into the replication management table  25 .  
         [0202]     At step  161 , the controller  12  of the disk storage device  11  acquires the current time from the operating system, and references the replication management table  25  to determine whether or not any replication end time is equal to the sum of the current time and the time required to replicate a volume. If no such replication end time equal to the sum is found in the replication management table  25 , the processing flow proceeds to step  165 . Conversely, if such a replication end time equal to the sum is found, the processing flow proceeds to step  162 .  
         [0203]     At step  162 , the controller  12  of the disk storage device  11  creates a logical volume R 14  which is a mirror volume of the replication requested volume P 13 .  
         [0204]     At step  163 , after the mirror volume has been completely created at step  162 , the controller  12  of the disk storage device  11  notifies the management program B 9  running on the management computer B 8  of the completion of replication. Upon receipt of the notification of the completed replication, an access controller  10  of the management program B 9  creates the access destination management table  18  comprised of the program name  19 , access requested volume name  20 , and accessed volume name  21 , as shown in  FIG. 5 . The access requested volume name  20  indicates the name of a volume which is requested for an access by each service program that requests an access to the logical volume P 13 , while the accessed volume name  21  indicates the name of a volume which is actually accessed by the service program. When the service programs A 5  and B 6  are to access the logical volume P 13  at the time of step  163 , the control program B 9  enters the names of the access requesting programs, i.e., the service programs A 5 , B 6  into the access destination management table  18 .  
         [0205]     At step  164 , when the service program C 7  additionally requests an access to the logical volume P 13  after step  163 , the management program B 9  enters data into the access destination management table  18  such that the service program C 7  is forced to access the logical volume R 14 . In other words, the volume accessed by the service program C 7  is changed from the logical volume P 13  to the logical volume R 14 . When an access is requested to the logical volume P 13  from a service program which has been previously registered in the access destination management table  18 , the management program B 9  references the access destination management table  18  to retrieve the accessed volume name  21 . The management program B 9  notifies the controller  12  of the disk storage device  11  of the accessed volume from the accessed volume name  21  retrieved from the access destination management table  18 . Upon receipt of the notification, the controller  12  of the disk storage device  11  performs an input/output operation to the volume notified from the management program B 9 .  
         [0206]     At step  165 , the controller  12  of the disk storage device  11  determines the validity of the access control processing for distributing the accesses to the logical volume P 13 . When determined as valid, the processing flow jumps back to step  161 . When not determined as valid, the processing flow is terminated.  
         [0207]     By executing steps  159  to  165  described above, the system internally carries out the replication of the logical volume P 13  and the switching of the accessed volume from the logical volume P 13  to the replicated volume R 14 , which are involved in the distribution of disk accesses to the logical volume P 13  specified by the user, thereby advantageously limiting the number of times of disk accesses to the logical volume P 13  to a certain value or less.  
       Ninth Embodiment  
       [0208]      FIG. 8  is a block diagram illustrating the configuration of a system according to a ninth embodiment. The illustrated system according to the ninth embodiment comprises a disk storage device  11  having a volume replication function; a computer A 1  which executes a processing program  4  for accessing the disk storage device  11 ; and a management computer B 8  which executes a management program B 9  for managing the disk storage device  11 . A service program A 5  running on the processing program  4  generates an input/output request to a certain volume in the disk storage device  11 . In response to the request, a controller  12  of the disk storage device  11  performs an input/output operation for the volume associated with the request. The disk storage device  11  is systematically managed by the management program B 9  which runs on the management computer B 8 . Such configured systems are, as shown below, capable of dynamically distributing accesses concentrated on a predetermined volume from a plurality of service programs, such as when the service program A 5 , a service program B 6 , and a service program C 7  access to a logical volume P 13 . The ninth embodiment differs from the eighth embodiment in that the management program B 9  associated with the disk storage device  11  is responsible for the creation of the replication management schedule  24  and replication management table  25 , and the determination as to whether or not a replication time is reached.  FIG. 18  is a flow chart generally illustrating a sequence of processing steps in the ninth embodiment. The processing flow is outlined below.  
         [0209]     At step  166 , the management program B 9  receives the replication management schedule  24  set by the user for a predetermined volume.  
         [0210]     At step  167 , the management program B 9  creates the replication management table  25 .  
         [0211]     At step  168 , the management program B 9  determines whether or not the current time is specified as a replica creation time.  
         [0212]     At step  169 , the controller  12  of the disk storage device  11  replicates the predetermined volume.  
         [0213]     At step  170 , the management program B 9  creates the access destination management table  18 .  
         [0214]     At step  171 , the management program B 9  switches the volume to be accessed from the original volume to the replicated volume.  
         [0215]     At step  172 , the management program B 9  determines whether or not the access distribution processing is valid.  
         [0216]     Next, detailed description will be made below on the steps in  FIG. 18  when the user controls accesses to the logical volume P 13 .  
         [0217]     At step  166 , the user creates for the management program B 9  the replication management schedule  24  which indicates a change in the number of replicas of the logical volume P 13  over time.  FIG. 15  shows the replication management schedule  24 . The replication management schedule  24  indicates the number of replicas at each time, and  FIG. 15  represents a schedule for creating one replica at specified time 10:00, and creating another replica at specified time 11:00.  
         [0218]     At step  167 , the management program B 9  creates the replication management table  25  which indicates replication times based on the replication management schedule  24  created at step  166  and is comprised of the volume name  16 , total number of volumes to be replicated  26 , and replication end time  27 , as shown in  FIG. 16 , and enters set values into the replication management table  25 .  
         [0219]     At step  168 , the management program B 9  acquires the current time, and references the replication management table  25  to determine whether or not any replication end time is equal to the sum of the current time and the time required to replicate a volume. If no such replication end time equal to the sum is found in the replication management table  25 , the processing flow proceeds to step  172 . Conversely, if such a replication end time equal to the sum is found, the processing flow proceeds to step  169 .  
         [0220]     At step  169 , the management program B 9  requests the controller  12  of the disk storage device  11  to replicate the logical volume P 13 . Upon receipt of the replication request, the controller  12  of the disk storage device  11  creates a logical volume R 14  which is a mirror volume of the replication requested volume P 13 .  
         [0221]     At step  170 , after the mirror volume has been completely created at step  169 , the controller  12  of the disk storage device  11  notifies the management program B 9  running on the management computer B 8  of the completion of replication. Upon receipt of the notification of the completed replication, an access controller  10  of the management program B 9  creates the access destination management table  18  comprised of the program name  19 , access requested volume name  20 , and accessed volume name  21 , as shown in  FIG. 5 . The access requested volume name  20  indicates the name of a volume which is requested for an access by each service program that requests an access to the logical volume P 13 , while the accessed volume name  21  indicates the name of a volume which is actually accessed by the service program. When the service programs A 5  and B 6  are to access the logical volume P 13  at the time of step  170 , the control program B 9  enters the names of the access requesting programs, i.e., the service programs A 5 , B 6  into the access destination management table  18 .  
         [0222]     At step  171 , when the service program C 7  additionally requests an access to the logical volume P 13  after step  170 , the management program B 9  enters data into the access destination management table  18  such that the service program C 7  is forced to access the logical volume R 14 . In other words, the volume accessed by the service program C 7  is changed from the logical volume P 13  to the logical volume R 14 . When an access is requested to the logical volume P 13  from a service program which has been previously registered in the access destination management table  18 , the management program B 9  references the access destination management table  18  to retrieve the accessed volume name  21 . The management program B 9  notifies the controller  12  of the disk storage device  11  of the accessed volume from the accessed volume name  21  retrieved from the access destination management table  18 . Upon receipt of the notification, the controller  12  of the disk storage device  11  performs an input/output operation to the volume notified from the management program B 9 .  
         [0223]     At step  172 , the management program B 9  determines the validity of the access control processing for distributing the accesses to the logical volume P 13 . When determined as valid, the processing flow jumps back to step  168 . When not determined as valid, the processing flow is terminated.  
         [0224]     By executing steps  166  to  172  described above, the system internally carries out the replication of the logical volume P 13  and the switching of the accessed volume from the logical volume P 13  to the replicated volume R 14 , which are involved in the distribution of disk accesses to the logical volume P 13  specified by the user, thereby advantageously limiting the number of times of disk accesses to the logical volume P 13  to a certain value or less.  
         [0225]      FIG. 20  shows a still further another embodiment according to the present invention. In this embodiment, upon a detection of the access number larger than the upper limit value having been set in advance, a plurality of disk volumes are created for reducing loads for each of volumes. That is, in the embodiment shown in  FIG. 1 , mirror volumes  14  are prepared in response to the detection of the access number for a pair of volumes P including data A, B, C and D. In the embodiment shown in  FIG. 20 , data A, B, C and D are recorded into each of disk volumes. In such configured arrangement, it becomes possible to reduce loads of each of disk volumes.  
         [0226]     It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.