Patent Publication Number: US-7904426-B2

Title: System and method for identifying a removable storage device

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a support system for data migration suitable for providing support for efficiently migrating data from an old storage device to a new storage device and removing the old storage device within a computer system, particularly in a large-scale computer system, to which a plurality of storage devices are connected, a data migration support program, a method for identifying such a removable storage device, and a system for migrating data with a removable storage medium. 
     In an information system that handles a large amount of data, the capacity of a storage device for data storage needs to be large. The storage device capacity can be increased either by enlarging the size of an employed storage device or by using a large number of storage devices. 
     If it is anticipated that the stored information might be lost due to prolonged use of a storage device for a period longer than the estimated lifetime or if the storage device&#39;s defect detection rate is increased, the storage device is replaced with a new one that is less likely to deteriorate or become defective. Before the existing storage device is replaced, the data stored in it is transferred to another storage device. This transfer is called “data migration.” The same is also true for optical disks and other storage media. 
     A generally employed data migration method is to back up the data on an existing storage device to a tape or other storage medium and then restore it to a new storage device. To make such a backup, it is necessary to halt a host computer&#39;s access to the existing storage device. If the existing storage device has a large capacity, the resulting access halt time for backup is long. 
     In a situation where the old existing storage device and a new migration destination storage device are connected to the host computer via a network, data migration can be achieved, for instance, by allowing individual users using the existing storage device to copy necessary data to the new storage device before the old storage device is replaced by the new storage device. For example, the storage devices disclosed by Japanese Patent Laid-open No. 2000-187608 accomplish data migration between the old and new storage devices on an individual file basis and without intervention of a host computer. U.S. Pat. Ser. No. 6,108,748 disclosed a migration destination storage device, which uses a table that indicates whether data elements are migrated. When a host computer issues a transfer request about one or more data elements, the disclosed migration destination storage device judges whether the data elements are already migrated. If the data elements are already migrated, the migration destination storage device responds to the transfer request. If, on the other hand, the data elements are not migrated, the migration destination storage device migrates the data elements, responds to the transfer request, and writes into the table to indicate that the data elements are now migrated. While there are no services or requests, the migration destination storage device migrates data elements in the background. Thus, data migration requests can be fulfilled immediately. 
     SUMMARY OF THE INVENTION 
     When replacing a large-capacity storage device or a large number of storage devices, it generally takes a long time to back up the whole data stored on an existing storage device to a tape or copy it to another storage device. 
     When the storage devices disclosed by Japanese Patent JP Laid-open No. 2000-187608 or U.S. Pat. No. Ser. 6,108,748 are used, it is possible to migrate data from an old storage device to a new storage device while accepting a processing request from a host computer and migrate data on an individual file basis. Since only desired data can be selectively migrated, the time required for data migration can be more or less reduced even when the storage devices store a large amount of data. 
     However, when a large-scale system is used so that data migration involves both a data owner and a system administrator, it is difficult to accurately determine whether data other than the selected migration data in the storage device to be removed is unnecessary. 
     Meanwhile, if the same data is duplicated in a large number of storage devices, it means that the storage devices are wasted unless such duplication aims at providing high-speed access or reliability enhancement. Even when the entire data stored on a certain storage device or storage medium is unnecessary or the same data is stored on another storage device, such storage device or storage medium may be left unremoved. However, such results are contrary to the demand for effective use of storage devices and storage media. 
     The present invention has been made to solve the above problems, and it is an object of the present invention to provide a method for providing support for data migration, identifying a removable storage device accurately and quickly, and identifying a storage medium that has completed data migration in a computer system to which a removable storage device or a storage device for storing data on a removable storage medium is connected. 
     To achieve the above object, a data migration support system according to the present invention is used, in a computer system to which a computer and a plurality of storage devices are connected or storage devices for storing data on a removable storage medium are connected, in order to register the identification information about unnecessary files, judge whether the files stored on a storage device or storage medium coincide with the registered unnecessary files, judge whether the files stored on the storage device or storage medium, if they are not unnecessary, are migrated to another storage device, and conclude, if all the files stored on the storage device or storage medium are unnecessary, that the storage device or the storage medium may be removed as migration is completed. 
     The above-mentioned unnecessary files are the files that need not be migrated. Such unnecessary files may be selectable from a list of unnecessary-file candidates that meet certain conditions. 
     If an unnecessary file is specified, its identification information is registered to generate an unnecessary-file database. When a judgment needs to be formulated, the identification information about files stored on a plurality of storage devices is acquired, and the unnecessary-file database is used to judge whether the identification information about the files matches the unnecessary-file conditions. 
     A data migration history may be referenced or a file duplicately stored on another storage device or storage medium may be checked for in order to judge whether the file is migrated to another storage device or storage medium. 
     Files stored on the storage device or storage medium identified as described above are unnecessary, that is, need not be migrated or are already migrated. Therefore, the system administrator can remove the storage device or storage medium in compliance with system instructions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates the configuration of a data migration support system according to a first embodiment of the present invention; 
         FIG. 2  is a hardware configuration diagram of a host computer for the data migration support system according to the first embodiment of the present invention; 
         FIG. 3  is a hardware configuration diagram of a storage device that is directly connected to a network for the data migration support system according to the first embodiment of the present invention; 
         FIG. 4  is a schematic diagram that illustrates the constituent elements of migration file information according to the first embodiment of the present invention; 
         FIG. 5  is a schematic diagram that shows a typical format of an unnecessary-file table; 
         FIG. 6  is a schematic diagram that shows a typical format of a storage-device-specific file table; 
         FIG. 7  is a schematic diagram that shows a typical format of an unnecessary-file candidate table; 
         FIG. 8  is a flowchart that illustrates a process for unnecessary-file database operations; 
         FIG. 9  is a flowchart that illustrates an unnecessary-file database display process; 
         FIG. 10  is a flowchart that illustrates an unnecessary-file candidate process; 
         FIG. 11  is a flowchart that illustrates a data migration completion judgment process according to the first embodiment of the present invention; 
         FIG. 12  is a flowchart that illustrates a removable storage device detection process; 
         FIG. 13  illustrates the configuration of a data migration support system according to a second embodiment of the present invention; 
         FIG. 14  is a schematic diagram that illustrates the constituent elements of migration file information according to the second embodiment of the present invention; 
         FIG. 15  is a schematic diagram that shows a typical format of a migration history table; and 
         FIG. 16  is a flowchart that illustrates a data migration completion judgment process according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described below with reference to  FIGS. 1 through 16 . 
     A first embodiment of the present invention will now be described with reference to  FIGS. 1 through 12 . 
     (I) Data Migration Support System Configuration 
     First of all, the configuration of a data migration support system according to the first embodiment will be described with reference to  FIGS. 1 through 3 . 
       FIG. 1  illustrates the configuration of the data migration support system according to the first embodiment of the present invention.  FIG. 2  is a hardware configuration diagram of a host computer  200  for the data migration support system according to the first embodiment of the present invention.  FIG. 3  is a hardware configuration diagram of a storage device  170  that is directly connected to a network for the data migration support system according to the first embodiment of the present invention. 
     The data migration support system according to the first embodiment configured so that a management computer  100 , a host computer  200 , and storage devices  170  and  180  are interconnected via a network. The host computer  200  is also connected to a storage device  190 . 
     Data migration may be performed by the storage devices  170  and  180 , which are directly connected to the network, or by the storage device  190 , which is connected to the host computer. 
     To be more precise, the storage device  170  is a disk array device or a NAS (Network Attached Storage). The storage device  190  is, for instance, an external SCSI hard disk drive. 
     The disk array device provides data migration for each disk volume to be replaced, whereas the external hard disk drive provides data migration for the entire hard disk drive. 
     The host computer  200  executes a processing program while accessing the data stored on the storage devices  170 ,  180 , and  190 . 
     The management computer  100  comprises a memory  140 , a communication device  120 , a CPU  130 , an input device  150 , and an output screen  160 . 
     A migration support program  110  is loaded into the memory  140  for execution. The migration support program  110  has a migration completion judgment program  111 , an unnecessary-file database operation program  112 , and a removable device detection program  113  as subroutines. It performs data migration in accordance with a migration file  114  in the memory  140 . The operations of these programs and the structure of the migration file  114  will be described in detail later. 
     The foregoing description assumes that the present embodiment performs data migration by running the migration support program  110  on the management computer. However, the migration support program  110  may alternatively be executed on the host computer  200 , which runs an application that handles files. Another alternative is to furnish the storage device  170  with a data migration function or provide the system with a dedicated data migration support device. 
     As shown in  FIG. 2 , the hardware configuration for the host computer  200  includes a CPU  2030 , a memory  2040 , a communication device  2020  for communicating with the network, an input device  2050 , and a display device  2060 . 
     The CPU  2030  creates a necessary file by executing, for instance, a business program. The input device  2050  is used to enter a command or data for executing the business program. The display device  2060  displays the processing results of the business program. 
     The storage device  170 , which is directly connected to the network, comprises a controller  1740 , a communication device  1710 , a cache memory  1720 , a control memory  1730 , and normally a plurality of disk drives  1741 ,  1742 ,  1743 , and so on. 
     The controller  1740  is capable of controlling the components of the storage device  170 . The cache memory  1720  caches data to permit high-speed access to the disk drives  1741 ,  1742 ,  1743 , and so on. The control memory  1730  caches control data for use in the controller. 
     Files and other data are stored on the disk drives  1741 ,  1742 ,  1743 , and so on. Removal is performed on an individual disk drive basis. 
     (II) Migration File Information 
     The structure of file migration information for the data migration support system according to the present embodiment will now be described with reference to  FIGS. 4 through 7 . 
       FIG. 4  is a schematic diagram that illustrates the constituent elements of migration file information  114  according to the first embodiment of the present invention.  FIG. 5  is a schematic diagram that shows a typical format of an unnecessary-file table  122 .  FIG. 6  is a schematic diagram that shows a typical format of a storage-device-specific file table  121 .  FIG. 7  is a schematic diagram that shows a typical format of an unnecessary-file candidate table  123 . 
     The migration file information  114  for data migration support may vary with the system specifications. The present embodiment, however, assumes that the migration file information  114  comprises three tables: an unnecessary-file table  122 , a storage-device-specific file table  121 , and an unnecessary-file candidate table  123 . The migration file information  114  can be stored on storage device  170 ,  180 , or  190 , which are targeted for data migration. 
     When the storage device  170 ,  180 , or  190  is to be removed, the user uses the unnecessary-file table  122  to register an unnecessary file, that is, the identification information about a file that need not be migrated, by executing the unnecessary-file database operation program  112 . Storing the name of a file in the unnecessary-file table  122  does not mean that the file is to be deleted. It will be simply concluded that the file need not be migrated at the time of data migration. 
     The unnecessary-file candidate table  123 , on the other hand, is an area for storing the conditions for file candidates that may be unnecessary in the future, that is, need not be migrated although it cannot be presently deemed unnecessary. 
     The storage-device-specific file table  121  is used to register the identification information about files that are stored in the storage device  170 ,  180 , or  190 , which is connected to the network. This registration is performed on an individual storage medium basis. 
     As shown in  FIG. 5 , the unnecessary-file table  122  comprises a directory field  1220 , a file name field  1221 , an extension filed  1222 , a creation date/time field  1223 , an update date/time field  1224 , a user field  1225 , and a device field  1226 . 
     The directory field  1220 , file name field  1221 , and extension field  1222  respectively store the directory name, file name, and extension of an unnecessary file. 
     The creation date/time field  1223  and update date/time field  1224  respectively store the creation date/time and update date/time of the unnecessary file. 
     The user field  1225  stores the name of a person who owns the unnecessary file. The device field  1226  stores the identifier of a storage device on which the unnecessary file is stored. 
     As shown in  FIG. 6 , the storage-device-specific file table  121  comprises a device field  1210 , a directory field  1211 , a file name field  1212 , an extension field  1213 , a creation date/time field  1214 , an update date/time field  1215 , and a user field  1216 . This table indicates that a file having attributes indicated in the directory field  1211 , file name field  1212 , extension field  1213 , creation date/time field  1214 , update date/time field  1215 , and user field  1216  are stored on a storage device corresponding to a device identifier stored in the device field  1210 . The table is used to check whether duplicate files are stored on a storage device. 
     Further, an expression and wildcard character can be specified in the fields of the unnecessary-file table  122 . In the example shown in  FIG. 5 , a negation symbol is used in the user field  1225  to specify users other than “user 2 .” An inequality sign is used in the creation date/time field  1223  and update date/time field  1224  to indicate dates/times earlier than the entered date/time. 
     An update needs to be performed each time a file stored on the storage device  170 ,  180 , or  190  is accessed. 
     When file information stored on a storage device is to be directly accessed to check for duplicate files on a storage device, the storage-device-specific file table  121  need not be furnished. 
     The unnecessary-file candidate table  123  comprises a directory candidate field  1230 , a file name candidate field  1231 , an extension candidate field  1232 , a candidate condition field  1233 , and a device candidate field  1234 . 
     The directory candidate field  1230 , file name candidate field  1231 , and extension candidate field  1232  respectively store the directory name, file name, and extension of an unnecessary-file candidate. If nothing is specified in these fields, all files are regarded as matching items. If, for instance, “file 1 ” is specified in the file name candidate field  1231  as in the first record, files that are stored on storage devices targeted for the system and named “file 1 ” will be regarded as unnecessary-file candidates without regard to the directory or extension. Further, wildcard characters such as “*” and “?” can be used. 
     The candidate condition field  1233  is used to specify the conditions for unnecessary-file candidates. For example, it is possible to specify “files created today” or files updated between certain dates. 
     (III) Data Migration Support Process 
     The process for data migration support is described below with reference to  FIGS. 8 through 12 . 
     (III-1) Unnecessary-file Database Process 
     The process for an unnecessary-file database will now be described with reference to  FIGS. 8 through 10 . 
       FIG. 8  is a flowchart that illustrates a process for unnecessary-file database operations. The unnecessary-file operations that can be performed by the user are registering an unnecessary file, displaying databased information, and displaying/registering unnecessary-file candidates. 
     The unnecessary-file database operation program  112  is used to perform unnecessary-file database operations. 
     To operate the unnecessary-file database, the user uses the input device  150  to issue instructions for starting an unnecessary-file database operation and enter the type of operation (step  510 ). 
     If the type of operation is a request for registered data display (step  520 ), the system proceeds to perform an unnecessary-file database display process (step  700 ). The unnecessary-file database display process will be described in detail later. 
     If the type of operation is a request for unnecessary-file candidate operation (step  530 ), the system proceeds to perform an unnecessary-file candidate process (step  1110 ). The unnecessary-file candidate process will also be described in detail later. 
     If the type of operation is neither of the above two, the user selects either unnecessary-file registration or unnecessary-file deregistration as the type of operation and specifies the target unnecessary file (step  535 ). 
     The unnecessary file can be designated by uniquely specifying its directory name, file name, and extension. An alternative is to specify the unnecessary-file conditions, for instance, by designating all files having a certain extension or all files in subdirectories under a certain directory. It is also possible to specify the unnecessary-file conditions, for instance, by designating all files that were created during a certain period of time and left unaccessed during a certain period of time. 
     If an operating instruction entered in step  535  is for registration (step  540 ), the system acquires an unoccupied entry area within the unnecessary-file table  122  (step  550 ) and writes unnecessary-file identification information in that area (step  560 ). 
     Since two or more sets of conditions may be combined for specifying unnecessary files as described above, the system checks for some other specified conditions (step  570 ). If it is found in step  570  that some other conditions are specified, the system returns to step  560 . If it is found in step  570  that no other conditions are specified, the system checks whether the registration of any other file is specified (step  580 ). If it is found in step  580  that another unnecessary file needs to be registered, the system returns to step  550 . 
     On the other hand, if it is found in step  540  that the deregistration of an unnecessary file is specified, the system searches the unnecessary-file information registered in the unnecessary-file table  122  for the unnecessary-file information entry to be deleted (step  555 ). When such an entry is detected in step  555 , the system deletes the file identification information about the detected entry (step  565 ), and then checks whether any other file identification information needs to be deleted in compliance with instructions (step  575 ). If it is found in step  575  that some other file identification information needs to be deleted, the system returns to step  565 . On the other hand, if it is found in step  575  that no other file identification information needs to be deleted, the system terminates the process. 
     Next, the unnecessary-file database display process, which is performed in step  700 , will be described in detail with reference to  FIG. 9 . 
       FIG. 9  is a flowchart that illustrates the unnecessary-file database display process. 
     First of all, the input device  150  is used to make an entry to specify the unnecessary-file display method (step  710 ). For unnecessary-file display purposes, it is possible, for instance, to specify all unnecessary files, specify unnecessary files contained in a certain directory, or specify unnecessary files having a certain extension. 
     The system checks whether the entry made in step  710  specifies the output of the entire information (step  720 ). If the entry specifies the output of the entire information, the output screen  160  displays all the unnecessary-file entries registered in the unnecessary-file table  122  (step  760 ). 
     If it is found in step  720  that the entry stipulates specific display conditions, the system searches the entries registered in the unnecessary-file table  122  for entries conforming to the entered conditions (step  730 ) and displays them on the output screen  160  (step  740 ). 
     The system then checks whether any other display instructions are entered (step  750 ). If it is found that some other display instructions are entered, the system returns to step  730 . If there are no more display instructions, the system terminates the process. 
     The unnecessary-file candidate process, which is performed in step  1100 , will now be described with reference to  FIG. 10 . 
       FIG. 10  is a flowchart that illustrates the unnecessary-file candidate process. 
     If any files conform to the unnecessary-file candidate conditions (step  1010 ), the system displays them in a candidate list (step  1020 ). 
     The user can view the candidate list and specify unnecessary-file entries, for instance, by putting a check mark on them (step  1030 ). 
     When the unnecessary files are specified, the system acquires an unoccupied area as needed from the unnecessary-file table  122  (step  1040 ) and registers file identification information (step  1050 ). 
     If it is found that unnecessary-file candidate conditions are entered (step  1060 ), the system registers the entered unnecessary-file candidate conditions in the unnecessary-file candidate table  123  (step  1070 ). 
     The unnecessary-file candidate conditions may be defined by specifying the directory name, file name, and extension or by specifying all the files having a certain extension as the candidates. As described above, the user is prompted to roughly specify the unnecessary-file candidates and then select actual unnecessary files. 
     The system repeats the above sequence until all the conditions are completely entered (step  1080 ). 
     (III-2) Data Migration Completion Judgment Process 
     A data migration completion judgment process according to the first embodiment will now be described with reference to  FIG. 11 . 
       FIG. 11  is a flowchart that illustrates the data migration completion judgment process according to the first embodiment. 
     It is assumed that the storage device  170  serves as a migration source storage device, and that the storage device  180  serves as a migration destination storage device. First of all, the system uses the device identifier of the storage device  170  as a key to search the device field  1210  of the storage-device-specific file table  121  for the information about files stored on the storage device  170  (step  410 ). The system then checks whether the storage-device-specific file table  121  contains an entry having the device identifier of the storage device  170  (step  420 ). If it is judged that such an entry is contained, the system checks the unnecessary-file table  122  to determine whether the entry&#39;s file information in fields  1210  through  1215  is registered (step  430 ). 
     If it is found in step  430  that the file information is not registered in the unnecessary-file table  122 , the system searches the storage-device-specific file table  121  for the file information stored on the storage device  180 , which is used as the migration destination storage device (step  440 ). Since the migration destination storage device is the storage device  180 , step  440  is performed to search the device field  1210  and file name field  1212  of the storage-device-specific file table  121  while using the identifier of the storage device  180  and a file name as keys. 
     To investigate the files at the migration destination file, the present embodiment checks the contents of the storage-device-specific file table  121 . Alternatively, however, the system may directly send an inquiry as needed to the file system for the migration destination storage device without furnishing such a storage-device-specific file table. 
     If it is not confirmed in step  440  that a file has been migrated to the storage device  180 , which is the migration destination storage device, the file is not an unnecessary file and does not exist on the migration destination storage device. It is therefore concluded that the file is not migrated. The system then saves the file identifier of the file into a memory  110  (step  450 ) and returns to step  420 . 
     When all the files are judged and the system concludes that there is no unjudged file on the migration source storage device (step  420 ), the system judges whether unmigrated file identifiers are saved in the memory  110  (step  460 ). When it is judged that the unmigrated files are saved, the system displays the unmigrated file identifiers on the output screen  160  (step  470 ). If, on the other hand, it is judged in step  460  that the unmigrated files are not saved, the system causes the output screen  160  to indicate that the files stored on the migration source storage are completely migrated (step  480 ). 
     In step  470  and step  480 , the system may notify the file migration judgment result to the host computer  200 . If the host computer  200  receives this notification from the management computer  100 , the host computer  200  can synchronize the operation of the application with the completion of the file migration. Moreover, the file migration judgment result can be shared between computers. 
     (III-3) Removable Storage Device Detection Process 
     A removable storage device detection process will now be described with reference to  FIG. 12 . 
       FIG. 12  is a flowchart that illustrates the removable storage device detection process. 
     When all the files stored on a storage device existing in the system are migrated to another storage device or unnecessary, the former storage device can be removed. In the removable storage device detection process, the identification information about the target storage device to be checked for removability is first entered (step  610 ). 
     Next, the storage-device-specific file table  121  is used to search the files stored on the target storage device (step  630 ) to check whether any file information indicate that migration verification is not finished (step  650 ). When it is concluded in the data migration completion judgment process (III-2) that data migration is completed, it means that migration verification is finished. 
     If any unverified file is found in step  650 , the system checks whether the file is unnecessary. This check is performed by judging whether it conforms to the entry conditions in the unnecessary-file table  122  (step  660 ). If it is found in step  660  that the file is unnecessary, the system returns to step  630 . If, on the other hand, it is found in step  660  that the file is not unnecessary, the system checks whether the file is already migrated to another storage device (step  670 ). When a file having the same contents as the checked file is found on another storage device in step  670 , the system returns to step  630 . If it is found in step  670  that the file is not migrated, the system concludes that the currently investigated target storage device is not removable, and then proceeds to investigate another storage device. 
     In step  680 , the system checks whether all the devices specified in step  610  have been investigated. If it is found in step  680  that a certain device is still not investigated, the system returns to step  630 . If, on the other hand, it is found in step  680  that no more devices are to be investigated, the system terminates the process. 
     If it is found in step  650  that there are no more unverified files, the system concludes that the currently investigated target storage device is removable, displays the identification information about the removable storage device on the output screen  160  (step  640 ), and proceeds to step  680 . 
     A second embodiment will now be described with reference to  FIGS. 13 through 16 . 
     (I) Data Migration Support System Configuration 
     First of all, the configuration of a data migration support system according to a second embodiment will be described with reference to  FIG. 13 . 
       FIG. 13  illustrates the configuration of the data migration support system according to the second embodiment of the present invention. 
     In the first embodiment, the storage device  170 , which is typically a network-connected disk array device, or the storage device  190 , which is typically an external hard disk drive connected to a host computer, is targeted for data migration. In the second embodiment, however, a storage device storing data on a storage medium can also be targeted for data migration. 
     As is the case with the data migration support system according to the first embodiment of the present invention, the data migration support system according to the second embodiment is also connected to a data migration support system management computer  100  and a host computer  200 . 
     The second embodiment differs from the first embodiment in connected storage devices. More specifically, storage devices  175  and  180  are connected to a network, and storage devices  190  and  195  are connected to the host computer  200 . 
     The storage devices  175  and  195  store data on a removable storage medium  177  or  197 . Available removable storage media include optical disks such as an MO (Magneto-Optical) disk, CD (Compact Disk), and DVD (Digital Versatile Disk), magnetic disks such as an MT (Magnetic Tape) and floppy (registered trademark) disk, and semiconductor memories such as a flash memory card. 
     As the storage device  175 , which is connected to the network, an optical disk library device or MT library device may be typically used. As the storage device connected to the host computer  200 , a SCSI MO disk drive or PC card device may be typically used. 
     The second embodiment is similar to the first embodiment in that the data migration support program runs on the management computer  100 . However, the second embodiment differs from the first embodiment in that a migration monitoring program  115  is added to the data migration support program used in the first embodiment. 
     The first embodiment verifies the completion of data migration by checking whether a duplicate file exists on the migration destination storage device. The second embodiment, however, causes the migration monitoring program  115  to store a migration history in the area for file migration information  114   a  at the time of data migration, and references such a migration history to judge whether data migration is completed. 
     Further, the migration support program  110   a  may be executed by the host computer  200 , or storage device  175 ,  180 ,  190 , or  195  as is the case with the first embodiment. 
     (II) Migration File Information 
     The structure of file migration information for the data migration support system according to the present embodiment will now be described with reference to  FIGS. 14 and 15 . 
       FIG. 14  is a schematic diagram that illustrates the constituent elements of migration file information  114   a  according to the second embodiment.  FIG. 15  is a schematic diagram that shows a typical format of a migration history table  125 . 
     The migration file information  114   a  according to the present embodiment comprises an unnecessary-file table  122 , an unnecessary-file candidate table  123 , and a migration history table  125 . Unlike the first embodiment, the migration file information according to the present embodiment does not have the storage-device-specific file table  121  but newly incorporates the migration history table  125 . The migration file information  114   a  can be stored on storage medium  177  or  197 , which is targeted for data migration. 
     The structures of the unnecessary-file table  122  and unnecessary-file candidate table  123  and the processes performed on these tables are the same as those of the first embodiment. However, the storage device field can additionally store a volume identifier to permit the use of a storage medium. 
     The migration history table  125  comprises a directory field  1250 , a file name field  1251 , an extension field  1252 , a creation date/time field  1253 , an update date/time field  1254 , a user field  1255 , a device/volume field  1256 , a migration date/time field  1257 , and a migration destination device/migration destination volume field  1258 . 
     The directory field  1250 , file name field  1251 , extension field  1252 , creation date/time field  1253 , update date/time field  1254 , and user field  1255  are the same as those stated in the previous description of the file information. 
     The device/volume field  1256  stores the identifier of a device or the volume identifier of a storage medium in order to indicate the storage location that is used before migration. 
     The migration date/time field  1257  stores the date/time of migration. The migration destination device/migration destination volume field  1258  stores the identifier of a migration destination storage device when the migration destination is a storage device or the volume identifier of a migration destination storage medium when the migration destination is a storage medium. 
     For data migration according to the present embodiment, the storage-device-specific file table  121  need not be used if the migration source directly accesses the file information and the migration destination stores a migration history in the migration history table  125  and references it. 
     (III) Data Migration Support Process 
     The process for data migration support is the same as described in conjunction with the first embodiment except that a storage medium can be used at the migration source and migration destination and that the migration history table  125  is used for migration judgment. 
     When data migration is performed, it is necessary to store in the migration history table  125  the information about a migrated file, the date/time of migration, and the volume information about a storage device or storage medium used for migration. 
     The data migration completion judgment process according to the second embodiment will now be described with reference to  FIG. 16 . 
       FIG. 16  is a flowchart that illustrates the data migration completion judgment process according to the second embodiment, which is basically the same as the counterpart of the first embodiment. However, the data migration completion judgment process according to the second embodiment references the migration history table for migration destination judgment purposes and determines whether migration is terminated (step  440   a ). 
     The present invention provides a method for providing support for data migration, identifying a removable storage device accurately and quickly, and identifying a storage medium that has completed data migration in a computer system to which a removable storage device or a storage device for storing data on a removable storage medium is connected.