Abstract:
A data backup device according to the present invention comprises a first table, a second table, an update management part configured to perform recording in the second table an identifier of updated portion of a first memory, a table rewriting part configured to perform rewriting the first table such that the first table identifies the portion of the first memory identified by the second table, and a data copy control part configured to perform output of first data from the portion of the first memory identified by the first table.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a data backup device, a data backup method, and a recording medium storing data backup program. In particular, the present invention relates to backing up data between plural data centers in a disaster recovery system. 
         [0003]    2. Description of the Related Art 
         [0004]    A disaster recovery system with a primary data center and backup center (secondary data center) is known. The secondary data center backs up the primary data center in case of a disaster such as earthquake or flood. 
         [0005]    In many disaster recovery systems having the secondary data center, the primary data center and the secondary data center are geographically separate from each other. And replicated data of a memory unit in a storage device of the primary data center is stored in the memory unit in the storage device of the secondary data center. 
         [0006]    The following two types of methods are used for copying data from the memory unit in the primary data center (primary memory unit) to the memory unit in the secondary data center (secondary. memory unit). 
         [0007]    1. A method in which the contents of the primary memory unit are copied to a removable storage medium such as a magnetic tape, and mailed to the secondary data center, and the contents of the storage medium are stored to the secondary memory unit. 
         [0008]    2. A method in which data is copied from primary memory unit to secondary memory unit using a data copying function of the storage device via a communication line that connects the primary data center and the secondary data center. 
         [0009]    In the first backup method which uses a removable storage medium, 1) the data of the primary memory unit are saved in the recording medium, 2) the storage medium is mailed to the secondary data center from the primary data center, and 3) the data in the recording medium are written to the secondary memory unit. The above troublesome work is required every time data is backed up from the primary data center to the secondary data center. The disadvantage becomes more conspicuous when a frequent back ups are required. The frequency of data back ups may be decreased to reduce the work. But there arises such a disadvantage that the data between the primary and secondary data centers often does not coincide with each other because periods during which the data of the secondary data center are old becomes long. 
         [0010]    On the other hand, a problem of a second method using the communication line resides in how data to be communicated is appropriately selected. 
         [0011]    Japanese Unexamined Patent Publication No. JP 2004-303122A has reported a method using a communication line. In this method, the storage device has a differential map, which is used to manage a difference of data stored in a primary memory unit and a secondary memory unit. In this method, the storage area in each of the primary and secondary memory units are divided into blocks of a certain length, and a bit is allocated to each pair of corresponding blocks in the primary memory unit and the secondary memory unit to produce a bit map. Each bit is controlled so as to indicate whether data in respective blocks of a pair to which the bit is allocated coincides with each other. When the data in respective blocks of a pair does not coincide with each other, the data copying function of the storage devices transfer data from a primary memory unit to a secondary memory unit. Thus, updated data in a primary memory unit is copied to a secondary memory unit. 
         [0012]    A disadvantage of this method is that when the data copying function of the storage device begins to work, such as when a disaster recovery system starts its back up service, the function copies the entire data stored in the primary memory unit to the secondary memory unit through a communication line that connects the primary and the secondary data centers, requiring much time and costs for data communication. It is because when the function begins to work, the differential map indicates that the data of the entire blocks in the primary memory unit and the secondary memory unit does not coincide with each other. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention has been made to improve the above conventional arts. For example, the present invention makes it easy to use a copying method using a removable storage medium, such as tapes, CDs and memory sticks, together with a copying method using a communication line to complement each other. An object of the present invention is to provide a data backup device, a data backup method, and a recording medium storing data backup program capable of keeping the latest data in a secondary data center without frequently sending and receiving removable media and transferring much data via a communication line. 
         [0014]    The present invention may be appropriately applied to the disaster recovery system with a primary data enter and a secondary data center. Such a disaster recovery system is widely employed in central or local administrative bodies, banks, finance companies, banking facilities including credit card companies, communication companies, broadcast companies, internet providers, or transport facilities including railroads, plains, or ships to prepare for disaster or unexpected situations. 
         [0015]    The first data backup device according to the present invention comprises a first table, a second table, an update management part configured to perform recording in the second table an identifier of updated portion of a first memory, a table rewriting part configured to perform rewriting the first table such that the first table identifies the portion of the first memory identified by the second table, and a data copy control part configured to perform output of first data from the portion of the first memory identified by the first table. 
         [0016]    The second data backup device according to the present invention further comprise a backup part configured to perform copying second data of the first memory to a removable recording medium to be stored to a second memory, wherein the data copy control part is configured to perform the output of the first data via a communication line to a secondary device to be copied to the second memory. 
         [0017]    The third data backup device according to the present invention has the configuration of the second backup device, wherein the update management part is configured to start the recording after the backup part performs the copying, the table rewriting part is configured to perform the rewriting after the storing of the second data to the second memory, and the data copy control part is configured to start the output after the table rewriting part performs the rewriting. 
         [0018]    The fourth data backup device according to the present invention has the configuration of the third data backup device, wherein the backup part is configured to perform the copying in two stage, first stage being copying the second data from the first memory to a third memory and second stage being copying the second data from the third memory to the removable recording medium, and the update management part is configured to start the recording before the back up part performs the second stage. 
         [0019]    The first data backup system according to the present invention comprises the second data back up device, the first memory unit, the secondary device, and the second memory. 
         [0020]    The second data backup system according to the present invention comprises the third data backup device, the first memory unit, the secondary device, and the second memory. 
         [0021]    The third data backup system according to the present invention comprises the fourth data backup device, the first memory unit, the secondary device, the second memory, and the third memory. 
         [0022]    The first data backup method according to the present invention comprises recording an identifier of updated portion of a first memory in a second table, rewriting the first table such that the first table identifies the portion identified by the second table, and outputting first data from the portion of the first memory identified by the first table. 
         [0023]    The second data backup method according to the present invention further comprises copying second data of the first memory to a removable recording medium to be stored to a second memory, wherein the outputting the first data is performed via a communication line to a secondary device to be copied to the second memory. 
         [0024]    The third data backup method according to the present invention has the configuration of the second data backup method, wherein the recording starts after the copying, the rewriting is performed after the storing of the second data to the second memory, and the outputting starts after the rewriting. 
         [0025]    The fourth data backup method according to the present invention has the configuration of the third data backup method, wherein the copying performed in two stages, first stage being copying the second data from the first memory to a third memory and second stage being copying the second data from the third memory to the removable recording medium, and the recording starts before the second stage. 
         [0026]    The first computer readable medium according to the present invention stores thereon a control program enabling a computer to execute the first data backup method. 
         [0027]    The second computer readable medium according to the present invention stores thereon a control program enabling a computer to execute the second data backup method. 
         [0028]    The third computer readable medium according to the present invention stores thereon a control program enabling a computer to execute the third data backup method. 
         [0029]    The fourth computer readable medium according to the present invention stores thereon a control program enabling a computer to execute the fourth data backup method. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  is a schematic structural diagram showing an embodiment of the present invention; 
           [0031]      FIG. 2  is a flowchart showing the operation of initial data identical type copying means in the embodiment shown in  FIG. 1 ; 
           [0032]      FIG. 3  is a flowchart showing the operation of initial data quasi-identical type copying means in the embodiment shown in  FIG. 1 ; 
           [0033]      FIG. 4  is a flowchart showing the operation of initial data quasi-identical type and non-stop copying means in the embodiment shown in  FIG. 1 ; 
           [0034]      FIG. 5  is a flowchart showing the operation of update-management-map control means in the embodiment shown in  FIG. 1 ; and 
           [0035]      FIG. 6  is a flowchart showing the operation of a difference map rewriting means in the embodiment shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    A detailed description of an embodiment of the present invention will now be given. 
         [0037]    In  FIG. 1 , reference numeral  100  denotes a primary data center, and reference numeral  200  denotes a secondary data center. The secondary data center  200  is a backup center. In other words, the secondary data center  200  is so disposed as to take over and execute the business when the primary data center cannot function exemplary due to a disaster. The secondary data center  200  copies the data stored in a memory unit  117  of the primary data center  100  to a memory unit  217 , and holds the stored data in the memory unit  217 . 
         [0038]    The primary data center  100  and the secondary data center  200  often have similar configuration and similar function, respectively; because the primary data center  100  and the secondary data center  200  exchange their roles with each other according to the circumstance. However, a description will be given in the case where, data stored in the primary data center  100  is copied to the secondary data center  200 . 
         [0039]    The respective data centers  100  and  200  include host computers  101 ,  201 , and storage devices  109 ,  209 . The storage devices  109  and  209  have memory units  117  and  217  that store data which is referred to and updated by the host computers  101  and  201 . 
         [0040]    The storage devices  109  and  209  of the respective data centers  100  and  200  are connected to each other via a communication line  300 . Therefore, the contents of the memory unit  117  of the storage device  109  in the primary data center  100  can be copied to the memory unit  217  of the storage device  209  in the secondary data center  200  through the communication line  300 . 
         [0041]    Further, the respective primary and secondary data centers  100  and  200  include tape-like storage medium  108  and  208  as storage medium that inputs and outputs data required by the above-mentioned host computers  101  and  201 , and tape devices  107  and  207  as storage medium control means that reads and writes the tape-like storage medium  108  and  208 , respectively. Any removable recording medium and its drive device can be used in place of tape and tape device. Such media include CDs, memory cards and memory sticks. 
         [0042]    As shown in  FIG. 1 , the host computer  101  includes a business application  102 , backup software  103 , and copying means  104 ,  105 , and  106  each of them specifying the copying procedure which will be described later. In this example, in the host computer  101 , the business application  102  is executed, and refers to and updates the data with respect to the memory unit  117  in the storage device  109 . And in the host computer  201 , the business application  202  is in a standby status while the business application  102  functions, and takes over the business in the case where the business application  102  stops. To take over the business, the host computer  201  uses data of the memory unit  217  which has been copied from the memory unit  117 . Each of the host computers may have other applications than applications  102  and  202 . 
         [0043]    A data copy control section  112  of the storage device  109  copies the data from the memory unit  117  in the storage device  109  to the memory unit  118  in the same storage device. In addition, the data copy control section  112  copies the data from the memory unit  117  in the storage device  109  to the memory unit  217  in the storage device  209  by communicating with the storage device  209  through the communication line  300 . 
         [0044]    The storage device  109  has a difference map  119  that identifies the memory portions containing different data between the primary memory unit  117  and the secondary memory unit  217  to manage that differences, and the data copy control section  112  transfers the data identified by the difference map from the primary memory unit  117  to the secondary memory unit  217  to update the data in the secondary memory unit  217 . 
         [0045]    The storage device  109  also includes a memory unit access control section  110 , a difference map rewriting means  111  and a update-management-map control-means  113 . 
         [0046]    The memory unit access control section  110  controls the access restriction of the memory unit  117 . The difference map rewriting means  111  rewrites the difference map  119  according to a request from the host computer  101 . The update-management-map control means  113  creates an update-management-map  114  for identifying the updated portion added to the memory unit  117  after a certain time, and manages the update information. In order to identify and manage the updated portion that is added to the memory unit after a certain time, the update-management-map control means  113  divides an area of the memory unit  117  by a block unit of a certain unit length, allocates bits to each block unit in order to indicate whether data in the corresponding block has been updated, or not, and creates the update-management-map in the memory in the storage device  109 . 
         [0047]    In this example, the update-management-map  114  is made up of 1) a memory unit identification section  115  that stores information to uniquely specify the memory unit to be managed (for example, the memory unit  117 ), and 2) an update management section  116  that identifies the updated portion of the memory unit to be managed. The update-management-map  114  is easily implemented as a bit map as shown in the explanation below. But it can be any type of set of information that contains information mentioned above. 
         [0048]    The backup software  103  and  203  are respectively executed by the host computers  101  and  201 , and write data to and read data from the tapes  108  and  208  mounted in the tape devices (recording medium control means)  107  and  207 . 
         [0049]    In this exemplary embodiment, the host computer  101  includes three types of copying means. They are an initial data identical type copying means  104 , an initial data quasi-identical type copying means  105 , and an initial data quasi-identical type and non-stop copying means  106 . In copying the data, any one of the combination of those means is employed. 
         [0050]    (Initial Data Identical Type Copying Means  104 ) 
         [0051]    The initial data identical type copying means  104  stops the operation of the business application  102  that updates the primary memory unit  117 , provides the read-only access restriction of the primary memory unit  117 , and thereafter copies data from the primary memory unit  117  to the removable memory medium  108  in the primary data center  100 . The removable recording medium  108  is transported to the secondary data center  200  by a user, and the recorded contents are copied to the primary memory unit  217 . After the completion of copying, the initial data identical type copying means  104  sets all bits of the difference map  119  so as to indicate “no difference” using the difference map rewriting means  111 . The initial data identical type copying means  104  starts the data copy control section  112 , starts copying referring to the difference map  119 , returns the access restriction of the primary memory unit  117  in a read and write enable state, and restarts the operation of the business application  102 . In this example, the difference map  119  indicates that there is “no difference” between the primary memory unit  117  and the secondary memory unit  217  when the data copy control section  112  is started. So the data copying function of the storage device  109  does not transfer the data to the secondary memory unit  217  from the primary memory unit  117  when the function begins to work. 
         [0052]    (Initial Data Quasi-Identical Type Copying Means  105 ) 
         [0053]    The initial data quasi-identical type copying means  105  stops the operation of the business application  102  that updates the primary memory unit  117 , provides the read-only access restriction of the primary memory unit  117 , and copies the data from the primary memory unit  117  to the memory medium  108  in the primary data center  100 . The initial data quasi-identical type copying means  105  creates the update-management-map  114  that manages the update information regarding the primary memory unit  117  by the update-management-map control means  113 , returns the access restriction of the primary memory unit  117  in a read and write enable state, and restarts the operation of the business application  102 . 
         [0054]    The removable recording medium  108  is transported to the secondary data center  200  by a user, and the recorded contents are copied to the secondary memory unit  217 . After the completion of copying, the initial data quasi-identical type copying means  105  using the difference map rewriting means  111  sets the difference map  119  according to the contents of the update-management-map  114  of the primary memory unit  117 . That is when a bit in the update-management-map  114  indicates the update of a block in the primary memory unit  117 , corresponding bit in the difference map  119  is set so as to indicate there is the difference due to the update. After this rewriting, the difference map  119  identifies all the updated portions recoded or identified in the update-management-map  114 . Thereafter the initial data quasi-identical type copying means  105  starts the data copy control section  112  and the data copying function of the storage device  109 . 
         [0055]    The data copying function of the storage device  109  rapidly copies the contents of the primary memory unit  117  updated after the removable storage medium  108  is written to the secondary memory unit  217  through the communication line  300 . 
         [0056]    (Initial Data Quasi-Identical Type and Non-Stop Copying Means  106 ) 
         [0057]    The initial data quasi-identical type and non-stop copying means  106  stops the operation of the business application  102  that updates the primary memory unit  117 , provides the read-only access restriction of the primary memory unit  117 , and copies the data from the primary memory unit  117  to the memory unit  118  in the same storage device  109  by the data copying function of the subject storage device  109 . The initial data quasi-identical type and non-stop copying means  106  produces the update-management-map  114  that manages the update information regarding the primary memory unit  117  by the update-management-map control means  113 , returns the access restriction of the primary memory unit  117  in a read and write enable state, and restarts the operation of the business application  102 . The initial data quasi-identical type and non-stop copying means  106  copies the data from the memory unit  118  to the storage medium  108 . 
         [0058]    The recording medium  108  is transported to the secondary data center by a user, and the recorded contents are written to the secondary memory unit  217 . The initial data quasi-identical type and non-stop copying means  106  sets the update-management-map  114  of the primary memory unit  117  according to the difference map  119  by the difference map rewriting means  111 . That is when a bit in the update-management-map  114  indicates the update of a block in the primary memory unit  117 , corresponding bit in the difference map  119  is set so as to indicate the difference due to the update. Thereafter the initial data quasi-identical type and non-stop copying means  106  starts the data copy control section  112  and the data copying function of the storage device  109 . 
         [0059]    When this means is employed, the un-operative period of the business application  112  is limited to the short periods necessary for ensuring the consistency of data in the above data copying process from the primary memory unit  117  to the memory unit  118 . And the data copying function of the storage device  109  rapidly copies the contents of the primary memory unit  117  updated after the removable storage medium  108  is written to the secondary memory unit  217  through the communication line  300 . 
         [0060]    A description will now be given in more detail of the operation of the respective copying means  104 ,  105  and  106  and their advantages in this embodiment. 
         [0061]    (A) Initial Data Identical Type Copying Means ( 104 ) 
         [0062]    As shown in  FIG. 2 , a system manager of the primary data center  100  requests the execution of a first phase of copying from the memory unit  117  in the storage device  109  to the memory unit  217  in the storage device  209 . 
         [0063]    The initial data identical type copying means  104  receives the request, issues a stop request to the business application  102  that conducts update, and waits for the stoppage of the business application  102  (S 11 : business application stop process). The initial data identical type copying means  104  gives an instruction to the memory unit access control unit  110  of the storage device  109  to change the access restriction of the memory unit  117  to read only (S 12 : a copying read only process). 
         [0064]    In this example, the access restriction instruction function program is executed in the host computer  101  and the access control function program is executed in the storage device  109 . 
         [0065]    The initial data identical type copying means  104  gives a request to the backup software  103  to copy the contents of the memory unit  117  to the tape  108 , and waits for the completion of writing (S 13 ). The first phase is completed with the above process. 
         [0066]    A system manager sends the tape  108  to the secondary data center  200 . A system manager of the secondary data center  200  sets the tape  108  in the tape device  207 , and copies the contents of the tape  108  to the memory unit (secondary memory unit)  217  in the storage device  209  (S 14 : a copying process at the secondary data center). If online copying operation from the memory unit (primary memory unit)  117  at the storage device  109  to the secondary memory unit  217  is in progress by the data copy control section  112 , this operation stops at this time (online copy stop process). 
         [0067]    When the writing to the memory unit  217  completes, the system manager at the secondary data center  200  reports the completion to the primary data center  100  (S 15 : copy completion confirmation process). 
         [0068]    Upon receiving the report, the system manager at the primary data center  100  issues to the initial data identical type copying means  104  a request for executing the second phase of copying from the memory unit  117  in the storage device  109  to the memory unit  217  in the storage device  209 . 
         [0069]    The initial data identical type copying means  104  receives the request and gives an instruction to the difference map writing means  111  in the storage device  109  to set the difference map  119  for the memory unit  117  in the storage device  109  and the memory unit  217  in the storage device  209  into a “no difference” state (S 21 : difference map initialization process) In the “no difference” state, no bits in the difference map  119  indicate the existence of difference between data stored in the primary memory unit  117  and secondary memory unit  217 . 
         [0070]    The initial data identical type copying means  104  issues to the data copy control section  112  of the storage device  109  an instruction to start the data copying function for the memory unit  117  in the storage device  109  and the memory unit  217  in the storage device  209  (S 22 : data copy restart process). The initial data identical type copying means  104  gives the memory unit access control section  110  of the storage device  109  an instruction to change the access restriction of the memory unit  117  to the read and write enable state (S 23 : copying write restart process). The initial data identical type copying means  104  issues a restart request to the business application  102  (S 24 : business application restart process). The second phase is completed then. 
         [0071]    As described above, the use of the initial data identical type copying means  104  enables the initial data of the primary memory unit  117  to be copied to the secondary memory unit  217  located at a remote place using the storage medium  108  such as a tape medium. Accordingly, it is unnecessary to transfer bulky initial data through the communication line  300  and the communication costs and time can be reduced. Also, the updated data of the primary memory unit  117  after the first data copying means  104  is employed can be copied to the secondary memory unit  217  by the data copying function of the storage device  109 , thereby making it possible to keep the latest data in the secondary memory unit  217 . 
         [0072]    (B) Initial Data Quasi-Identical Type Copying Means  105   
         [0073]    As shown in  FIG. 3 , the system manager of the primary data center  100  requests the initial data quasi-identical type copying means  105  to execute the first phase of copying from the memory unit  117  in the storage device  109  to the memory unit  217  in the storage device  209 . 
         [0074]    The initial data quasi-identical type copying means  105  receives the request, issues a stop request to the business application  102  that updates the memory unit  117 , and waits for the stoppage of the business application  102  (S 31 : business application stop process). 
         [0075]    The initial data quasi-identical type copying means  105  instructs the memory unit access control section  110  of the storage device  109  to change the access restriction of the memory unit  117  to read only (S 32 : read only process at the primary data center) The initial data quasi-identical type copying means  105  instructs the backup software  103  to copy the contents of the memory unit  117  to the tape (storage medium)  108 , and waits for the completion of copying (S 33 : storage medium copying process). 
         [0076]    If online copying operation from the memory unit (primary memory unit)  117  at the storage device  109  to the secondary memory unit  217  is in progress by the data copy control section  112 , this operation stops at this time (online copy stop process). 
         [0077]    The initial data quasi-identical type copying means  105  instructs the update-management-map control means  113  of the storage device  109  to record in the update-management-map  114  the information identifying the portion updated in the memory unit  117  thereafter (S 34 : update management start process). 
         [0078]    The initial data quasi-identical type copying means  105  instructs the memory unit access control section  110  of the storage device  109  to change the access restriction of the memory unit  117  to a read and write enable state (S 35 : write restart process at the primary data center) and issues the restart request to the business application  102  (S 36 : business application restart process). The first phase is completed with the above operation. 
         [0079]    The system manager of the primary data center  100  sends the tape  108  to the secondary data center  200 . At the secondary data center  200 , the system manager thereof sets the tape  108  in the tape device  207 , and stores the contents of the tape  108  in the memory unit  217  of the storage device  209  (S 37 : copying process at the secondary data center). When the storing is completed, the system manager of the secondary data center  200  reports the completion to the primary data center  100  (S 38 : copy completion confirming process). 
         [0080]    Upon receiving the report, the system manager of the primary data center  100  issues the request for the second phase of the copying to the initial data quasi-identical type copying means  105 . 
         [0081]    The initial data quasi-identical type copying means  105  receives the request and inquires of the update-management-map control means  113  in the storage device  109  whether the update-management-map  114  of the memory unit  117  exists or not (S 41 ) When the update-management-map  114  of the memory unit  117  does not exist, the update-management-map control means  113  issues an error notification (S 44 ). 
         [0082]    When the update-management-map  114  of the memory unit  117  exists, the initial data quasi-identical type copying means  105  instructs the update-management-map control means  113  in the storage device  109  to rewrite the difference map  119  which manages the memory unit  117  and the memory unit  217  based on the contents of the update-management-map  114  (S 42 : difference map rewrite process). After this rewriting, the difference map  119  identifies the the updated portions recoded or identified in the update-management-map  114 . The update management by the update-management-map control means  113  ends its operation at the same time (update management completion process). 
         [0083]    The initial data quasi-identical type copying means  105  instructs the data copy control section  112  of the storage device  109  to start the online data copying from the memory unit  117  to the memory unit  217  (S 43 : online copy restart process). 
         [0084]    The second phase is completed with the above operation. And the setup of the online data copying function by the data copy control section  112  of the storage device  109  is completed. In this embodiment, when the online data copying starts, a difference between memory unit  117  and memory unit  217 , which has been managed by the update-management-map  114 , exists. 
         [0085]    As described above, the use of the second data copying means  105  enables the initial data in the primary memory unit  117  to be copied to the secondary memory unit  217  not through the communication line  300  but via the storage medium. Accordingly, the costs and time for communication can be remarkably reduced. 
         [0086]    In addition, since the operation of the business application  102  can start after data of the primary memory unit  117  has been written into the memory medium  108 , the period during which operation of the business application  102  stops is shorter than when the data copy by the initial data identical type copying means  104  is used. Also, since the update of the initial data of the primary memory unit  117  is copied online to the secondary memory unit  217  by the data copying function by the data copy control section of the storage device  109 , the data of the secondary memory unit  217  can be kept to the latest data. Therefore, delay in copying the updated date is avoided. Such a delay occurs when only the storage medium  108  is used for the data coping. 
         [0087]    (C) Initial Data Quasi-Identical Type and Non-Stop Copying Means 
         [0088]    A description will now be given of copying by the initial data quasi-identical type and non-stop copying means  106  in the host computer  101  with reference to  FIG. 4 . 
         [0089]    The storage device  109  is set in advance so that the data copying function thereof can copy the data of the memory unit  117  to the memory unit  118 . 
         [0090]    The system manager of the primary data center  100  requests the initial data quasi-identical type and non-stop copying means  106  to execute the first phase of copying from the memory unit  117  to the memory unit  217 . 
         [0091]    Receiving the request, the initial data quasi-identical type and non-stop copying means  106  requests the business application  102  to stop its operation, and waits for its stoppage (S 51 : business application stop process). The initial data quasi-identical type and non-stop copying means  106  requests the memory unit access control section  110  of the storage device  109  to change the access restriction of the memory unit  117  to read only (S 52 : read only process at the primary data center). 
         [0092]    The initial data quasi-identical type and non-stop copying means  106  instructs the data copy control section  112  of the storage device  109  to copy the data in the memory unit  117  to the memory unit  118  within the same storage device  109  (S 53 : temporary copy storing process). A process of online copying from the primary memory unit  117  to the secondary memory unit  217  is temporarily stopped before execution of the temporary copy storing process (S 53 ) (online copy stop process). 
         [0093]    The initial data quasi-identical type and non-stop copying means  106 , 1) requests the update-management-map control means  113  of the storage device  109  to record the portion that is updated in the memory unit  117  thereafter (S 54 : update management start process), 2) requests the memory unit access control section  110  of the storage device  100  to change the access restriction of the primary memory unit  117  to the read and write enable state (S 55 : write restart process at the primary data center), 3) requests the business application  102  to restart (S 56 : business application restart process) and 4) requests the backup software  103  to write the contents of the memory unit  118 , which is a copy of the memory unit  117 , to the tape  108 , and waits for the completion (S 57 : storage medium copying process) The first phase is completed with the above operation. 
         [0094]    The system manager of the primary data center  100  sends the tape  108  to the secondary data center  200 . The system manager of the secondary data center  200  loads the tape  108  into the tape device  207 , and writes the contents of the tape  108  to the memory unit  217  in the storage device  209  (S 58 : copying process at the secondary data center). When the writing to the memory unit  217  completes, the system manager of the secondary data center  200  reports the completion to the system manager of the primary data center  100  (S 59 : copy completion confirming process). 
         [0095]    Upon receiving the report, the system manager at the primary data center  100  requests the initial data quasi-identical type and non-stop copying means  106  to begin the second phase of the copying. 
         [0096]    The initial data quasi-identical type and non-stop copying means  106  receives the request and inquires of the update-management-map control means  113  in the storage device  109  whether the update-management-map of the memory unit  117  exists or not (S 61 ). When the update-management-map of the memory unit  117  does not exist, the update-management-map control means  113  issues an error notification (S 64 ). 
         [0097]    When the update-management-map of the memory unit  117  exists, the initial data quasi-identical type and non-stop copying means  106  instructs the update-management-map control means  113  in the storage device  109  to rewrite the contents of the difference map  119  which manages the memory unit  117  and the memory unit  217  based on the contents of the update-management-map  114  (S 62 : difference map rewrite process). After this rewriting, the difference map  119  identifies the updated portions recoded or identified in the update-management-map  114 . The update management by the update-management-map control means  113  ends its operation at the same time (update management completion process). 
         [0098]    The initial data quasi-identical type and non-stop copying means  106  instructs the data copy control section  112  to start the data online copying from the memory unit  117  to the memory unit  217  (S 63 : online copy restart process). 
         [0099]    The second phase is completed with the above operation. And the setup of the data copying function by the data copy control section  112  of the storage device  109  is completed. In this embodiment, when the online data copying starts, a difference between memory unit  117  and the memory unit  217 , which has been managed by the update-management-map  114 , exists. 
         [0100]    Additional to the merits of the second copying means  105  described above, the periods for which the business application  102  stops its operation can be reduced further since the data which the third data copying means  106  writes to the storage medium  108  are not the contents of the primary memory unit  117  but are their copy produced in the memory unit  118 . 
         [0101]    (Operation of Update Management Control Means  113 ) 
         [0102]    A description will now be given of the update-management-map control means  113  that is used in order to record and manage the updated portion of the primary memory unit  117 . 
         [0103]    As shown in  FIG. 5 , upon receiving the request to manage the memory unit  117  from the host computer  101 , the update-management-map control means  113  creates the update-management-map  114  in the memory area in the storage device  109  (S 71 ). 
         [0104]    The update-management-map  114  is made up of 1) the memory unit identification section  115  to indicate the memory unit which the map manages, and 2) the update management section  116  where the information for identifying the updated portion of the memory unit  117  is recorded. For this purpose, the storage area of the memory unit  117  is divided into a block of a certain unit length and bits are allocated to the update management section  116  such that each bit represents a block and indicates whether the data in the block is updated or not. 
         [0105]    The update management section  116  has the same format as that of the difference map  119  which is used by the online data copying function of the data copy control section  112  in the storage device  109  with respect to the memory unit  117  and the memory unit  217 . 
         [0106]    The respective bits of the update management section  116  can have two values that express “updated” or “not updated”. For example, a value indicative of “undated” is identical with a value indicative of a difference in the difference map of the online data copying function, and a value indicative of “not undated” is identical with a value indicative of no difference in the difference map. The update-management-map control means  113  writes an identifier for the memory unit  117  in the memory unit identification section  115  (S 72 ). 
         [0107]    The update-management-map control means  113  sets initial value “not updated” to all of the bits in the update management section  116  (S 73 ). Thereafter, when the data of the memory unit  117  is updated, the update-management-map control means  113  sets the value indicative of “updated” in the bits in the update management section  116  corresponding to the updated block (S 74 ). Thus the update management section  116  records the identifying information of the updated block of the memory unit  117 . 
         [0108]    When the update-management-map control means  113  receives the reference request of the update-management-map of the memory unit  107  from the host computer  101 , the update-management-map control means  113  refers to the identifier of the memory unit identification section  115  of all the update-management-maps  114 , thereby retrieving the update-management-map  114  of the subject memory unit (S 81 ) When no update-management-map  114  of the memory unit exists, the update-management-map control means  113  issues an error notification and completes the operation (S 83 ). When the update-management-map  114  of the memory unit exists, the update-management-map control means  113  returns the retrieved information of the update-management-map  114 (S 82 ). 
         [0109]    (Difference Map Writing Means  111 ) 
         [0110]    A description will now be given of the difference map rewriting means  111  for rewriting the difference map  119  with respect to the primary memory unit  117  and the secondary memory unit  217 . 
         [0111]    As shown in  FIG. 6 , the difference map writing means  111  responds to the difference map write request from the host computer  101 . When requested to set to “no difference”, the difference map writing means  111  sets all the bits of the difference map  119  to a value that expresses no difference (S 91 ). When requested to reflect an update-management-map  114  to the difference map  119 , the difference map writing means  111  refers to the update-management-map  114  of the subject memory unit (S 101 ) and copies the contents of the update management section  116  of the update-management-map  114  to the difference map  119 (S 102 ) if the update-management-map  116  exists. The difference map writing means  111  issues an error notification and completes the operation (S 103 ) when the update-management-map  114  dose not exist. Thus, the difference map  119  identifies the memory portion identified by the update-management-map  116 . 
         [0112]    Any of the initial data identical type copying means  104 , the initial data quasi-identical type copying means  105 , and the initial data quasi-identical type and non-stop copying means  106 , the memory unit access control section  110 , the difference map rewriting means  111 , the data copying control section  112 , and the update-management-map control means  113  can be embodied as a program executable by a computer. 
         [0113]    The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.