Abstract:
At the time of migrating encrypted data into another storage apparatus, decrypt this data after migration is simplified, and security against tapping, falsification and the like is maintained when a calculation method of encrypted data is re-written into another calculation method, and also access performance is improved. In a storage system  100  which is provided with a storage apparatus having a volume  120  and which is accessible from a host computer, it is made possible to execute the data migration when a storage apparatus provided with a mechanism capable of decrypting the encrypted data is chosen as a migration destination of this data, and also to keep holding surely the encrypted data by updating and saving again an encryption method applied to a encryption of the encrypted data into another method by internal processing of the apparatus even when the apparatus and the encryption method become obsolete.

Description:
BACKGROUND 
   The present invention relates to a storage system in which it is possible to access a storage apparatus from a computer, and more particularly to a migration method of encrypted data and a management computer to perform management thereof. 
   First, a storage extent (volume) network which has been used from the past is explained. 
   A network which connects one or more external storage apparatuses and one or more computers is called a storage extent network (SAN) (for example, refer to Published Japanese Patent Application No. 2004-005370). This SAN has a characteristic of excellent scalability since a storage capacity and a computer can be easily added and deleted at a later date, though the SAN is often used especially when a plurality of computers share one large-scale storage apparatus. 
   Next, management of encrypted data in the storage extent network is explained. 
   There is a technology which is to prepare for tapping and falsification from the outside by encrypting data stored on a storage apparatus. There is a technology in which an encryption apparatus is installed in SAN, for example, and encryption and decryption are performed by having data once pass through this encryption apparatus at the time of input and output the data from a host computer to a storage system (refer to U.S. Patent Application Publication No. 2004/153642A1). 
   Published Japanese Patent Application No. 2001-331380 discloses a technology in which encrypted data is saved and the encrypted data is decrypted appropriately when an apparatus of a receiving side receives the encrypted data at the time of performing a data copy between storage systems using a remote copy technology. Also, an encryption processor is installed on the storage system as shown in  FIG. 5  so that the encryption and decryption of data can be performed on this apparatus. 
   In addition, Published Japanese Patent Application No. 2002-351747 discloses a method of encrypting a storage extent and saving in another storage extent in order to back up the storage extent within a disk array apparatus (equivalent to a logical storage extent of the present invention) into a tape drive. Furthermore, a method of decrypting the storage extent storing encrypted data and saving in another storage extent is also disclosed. 
   Next, management of a virtual storage extent of encrypted data is explained. 
   With respect to this virtual storage extent management technology a detailed explanation is described in Published Japanese Patent Application No. 2004-005370, and therefore only a mechanism of a system in which a virtual storage extent technology is installed is briefly described herein. 
     FIG. 2  is a diagram showing a configuration example of a virtual storage extent management system. In  FIG. 2 , a storage system  101 , a storage system  102  and a host computer  200  are connected by a network connection apparatus  400  comprising a data I/O network  401 . The network connection apparatus  400  mounts a plurality of data I/O network interfaces  440 , and respective data I/O network interfaces  440  are connected with a data I/O network interface  240  which is mounted on the host computer  200  and a data I/O network interface  140  which is mounted on the storage system  101  and the storage system  102  through a data I/O network  402 . 
   The above is a physical network configuration of the system in which the virtual storage extent technology is installed. On the other hand, it is assumed as a logical configuration of the network connection apparatus  400  that a communication path  411  is provided between the data I/O interfaces  440  which are connected with the host computer  200  and the storage system  101 , and similarly a communication path  412  is provided between the data I/O interfaces  440  which are connected with the storage system  101  and the storage system  102 . Mutual communications between the host computer  200  and the storage system  101 , and also between the storage system  101  and the storage system  102  becomes possible by the logical network configuration described hereinabove. 
   It should be noted that the storage system  101  and the storage system  102  may be connected directly by the data I/O network  402  without passing through the network connection apparatus  400 . 
   A configuration and an input/output procedure of a virtual storage extent (volume)  121  provided in this storage system  101  is described hereinafter. 
   The virtual storage extent  121  is created in the storage system  101 , and is configured such that this virtual storage extent  121  is associated with a logical storage extent  120  which is mounted on the storage system  102 . Storage extent configuration information, in which a relation of this association is written, is saved in storage extent configuration information  1107  held in the storage system  101 . Further, in this configuration, the host computer  200  transmits a data input/output command making the virtual storage extent  121  which is mounted on the storage system  101  as a target. When the storage system  101  receives this data input/output command, a virtual storage extent management program  1106  refers to the storage extent configuration information  1107  to understand that a destination of the commanded data input/output is the virtual storage extent  121 . Next, the storage system  101  transfers the data input/output command received from the host computer  200  making the logical storage extent  120 , which is associated with this virtual storage extent and is mounted on the storage system  102 , as a target. The storage system  102  executes the commanded data input/output to the logical storage extent  120  when this data input/output command is received. 
   However, there exist following problems in the prior-art technologies described hereinbefore. 
   More specifically, a first problem is that in a state where a storage system has a function to encrypt data to be stored and also stores data encrypted by this function, and at the time of migrating this encrypted data into another storage system when removing an apparatus thereof, for example, it has been necessary to choose an storage system apparatus having a function capable of decrypting and encrypting this encrypted data as a migration destination. In addition, it has been difficult to choose an appropriate apparatus as the migration destination because there has been no means for managing compatibility among a plurality of encryption methods and a mounting situation thereof. Due to this reason, there has occurred such a risk that the data can not be decrypted after transfer when an apparatus having a compatible encryption function mounted is not chosen as the migration destination. 
   Also, a second problem is that in a situation where a storage system stores encrypted data, it has been necessary in the past to have such a procedure that decrypted data is once read in a host computer and the data is written into another storage system having another encryption method after the data is encrypted again by this method in order to update an encryption method of this data into another encryption method. However, there has been a risk of tapping and falsification in this method since plaintext data once flows on a network and is processed by the host computer. 
   Moreover, it has been necessary to perform load-imposing and time-consuming processing such as migration processing on the network and computation processing by the host computer. 
   In addition, a third problem is that in a situation where encrypted data is stored on a storage system, there has been such a problem that it becomes not possible to decrypt this data when an encryption function and an apparatus necessary for decrypting this data is removed. 
   It should be noted that the invention described in Published Japanese Patent Application No. 2001-331380 is not for an object of saving encrypted data which is an object of the present invention but focuses on an object of realizing how to decrypt efficiently encrypted data to read out to a host. Explaining further details, the storage system in Published Japanese Patent Application No. 2001-331380 is not aiming at decrypting and storing the data to be saved on a disk drive like the present invention but Published Japanese Patent Application No. 2001-331380 is the one describing the opposite operation, more specifically how to decrypt at the time of saving the encrypted data (refer to Published Japanese Patent Application No. 2001-331380). 
   SUMMARY 
   Accordingly, the present invention has an object of providing with a storage system, a data migration method and a management computer which enable to realize efficient decryption and read-out to a host at the time of migrating encrypted data stored on a storage apparatus of a storage system into another storage apparatus. 
   In order to solve the first problem described hereinbefore and to achieve the object of the present invention, the present invention is provided with a management computer to manage a configuration of a storage system which has encrypted data and an encryption function. Further, at the time of migrating the encrypted data, the management computer chooses a storage system which has an encryption function compatible with a migration source as a migration destination based on the encryption method to the encrypted data. 
   In addition, the storage system of the present invention is made such that two or more encryption functions can be mounted in order to solve the second problem. Further, in case that this encryption method migrates the encrypted data within the same storage system, there is provided with a mechanism to perform update processing for changing over encryption methods by processing within an apparatus of the same storage system when data encrypted by a certain encryption method is updated into data encrypted by another encryption method. 
   Moreover, according to the present invention, in order to solve the third problem it is possible for a management computer to delete an encryption function and to remove an apparatus when an encryption method is not used and under this situation, it becomes possible to urge an interruption of the removal and to perform processing of updating into another encryption method before removal when there exists encrypted data. 
   According to the present invention, three effects described hereinafter can be obtained. 
   The first effect is that even in case of migrating data into another apparatus due to a reason that a product warranty period of an apparatus has passed and this apparatus becomes obsolete under a situation where encrypted data is stored on a storage system, it is possible to choose correctly an apparatus mounting a function capable of decrypting this data as an apparatus of a migration destination thereof. It is possible to avoid such a risk that encrypted data can not be decrypted at the migration destination since a management computer manages the compatibility of encryption method and an apparatus having a compatible function of the encryption method mounted on the apparatus of the migration source is chosen as the migration destination. 
   The second effect is that it is possible to perform update processing within the same storage system without passing through a host computer even when the encryption method becomes obsolete and it is tried to update into another encryption method under the situation where the encrypted data is stored on the storage system. In addition, although the encrypted data is once decrypted after loading into a cache memory within the storage system and is written in a storage extent after encrypting again by another encryption method during the update processing, plaintext data does not flow on a network, which is different from a method of passing through the host computer. More specifically, it is possible to eliminate a risk of tapping and falsification since the update processing is completed within the storage system. 
   Moreover, it is not necessary to keep separately cache data for decryption and cache data for encryption, which is different from the method of passing through the host computer, since decryption processing and encryption processing are performed directly to the data read in the cache memory during the update processing. As a result, it is possible to obtain such an effect that consumption of the cache memory can be restrained. 
   Furthermore, it is also possible to obtain such an effect that a processing speed improves since there is neither time consumed nor a load imposed due to data migration on the network and computation on the host computer by performing the update processing within the storage system, which is different from the method of passing through the host computer. 
   The third effect is that it is possible to avoid a problem caused by the uninstall or removal of the function and the apparatus required for decrypting the encrypted data under the situation where the encrypted data is stored. More specifically, since the management computer judges at the time of removing the function and the apparatus required for the above-described decryption so that a warning can be given and the update into another encryption method can be performed when there exists the encrypted data required at the time of decryption, it is possible to eliminate such a risk that the encrypted data can not be decrypted after removal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an outline diagram showing a configuration example of a network according to the present invention; 
       FIG. 2  is a configuration example of a virtual storage extent management system according to the present invention; 
       FIG. 3  is a configuration example of a storage system according to the present invention; 
       FIG. 4  is a configuration example of a host computer according to the present invention; 
       FIG. 5  is a configuration example of a management computer according to the present invention; 
       FIG. 6  is an implementation example of data encryption management information held in the storage system according to the present invention; 
       FIG. 7  is an implementation example of storage extent configuration information held in the storage system according to the present invention; 
       FIG. 8  is an implementation example of program management information held in the storage system according to the present invention; 
       FIG. 9  is an implementation example of asset management information held in the management computer according to the present invention; 
       FIG. 10  is an implementation example of data encryption management information held in the management computer according to the present invention; 
       FIG. 11  is an implementation example of storage extent configuration information held in the management computer according to the present invention; 
       FIG. 12  is an implementation example of encryption method compatibility information held in the management computer according to the present invention; 
       FIG. 13  is a flow chart showing processing of migrating encrypted data to another storage apparatus according to the present invention; 
       FIG. 14  is a flow chart showing processing of migrating encrypted data to another storage apparatus according to the present invention; 
       FIG. 15  is a flow chart showing processing of migrating encrypted data to another storage apparatus according to the present invention; 
       FIG. 16  is a flow chart showing processing of updating encrypted data into encrypted data encrypted by another encryption method according to the present invention; 
       FIG. 17  is a flow chart showing processing of updating encrypted data into encrypted data encrypted by another encryption method according to the present invention; 
       FIG. 18  is a flow chart showing processing of updating encrypted data into encrypted data encrypted by another encryption method according to the present invention; 
       FIG. 19  is a flow chart showing transfer processing of encrypted data using a technology of virtual storage extent management according to the present invention; 
       FIG. 20  is a flow chart showing migration processing of encrypted data using a technology of virtual storage extent management according to the present invention; 
       FIG. 21  is a flow chart showing update processing of encryption method using a technology of virtual storage extent management according to the present invention; 
       FIG. 22  is a flow chart showing update processing of encryption method using a technology of virtual storage extent management according to the present invention; 
       FIG. 23  is a flow chart showing processing of deleting an encryption program according to the present invention; 
       FIG. 24  is a flow chart showing processing of deleting an encryption program according to the present invention; 
       FIG. 25  is an outline diagram showing a configuration example of another network according to the present invention; 
       FIG. 26  is a configuration example of a magnetic tape storage apparatus according to the present invention; 
       FIG. 27  is a configuration example of an external encryption apparatus according to the present invention; and 
       FIG. 28  is an implementation example of data encryption management information held in a management computer according to the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, an embodiment of the present invention is explained in detail referring to the accompanied drawings. It should be noted that the present invention is obviously not limited to the embodiment explained hereinafter. 
   A configuration example of a network according to an embodiment of the present invention is shown in  FIG. 1 . A host computer  200  is connected to a storage system  100  through a data I/O network  401 . The storage system  100  and the data I/O network  401 , and also the host computer  200  and the data I/O network  401  are connected by a data I/O network  402 . The data I/O network  401  may be comprised of a prior-art network connection apparatus such as Fiber channel and Ethernet (registered trademark), for example. The data I/O network  402  may use an optical fiber cable or an Ethernet (registered trademark) cable, for example, depending on a type of the data I/O network  401 . The host computer  200  and the storage system  100  are in a state of being capable of performing communications mutually by the network configuration explained hereinabove. Moreover, two or more storage systems  100  are in a state of being capable of performing communications mutually through the data I/O network  401 . 
   A management computer  300  is connected to the storage system  100  through a management network  501 . In addition, the management computer  300  is connected to the host computer  200  through another management network  502 . Similarly to the data I/O network  401 , the management network  501  and the management network  502  are ones which are formed by implementing a prior-art communication technology. In another form of implementation, the management network  501  and the management network  502  may be such a form that one single network is shared instead of being the independent ones respectively. In furthermore another form of implementation, the management network  501 , the management network  502  and the data I/O network  401  may be such a form that one single network is shared instead of being the independent ones. The management computer  300  and the storage system  100 , and also the management computer  300  and the host computer  200  are connected to be in a state of being capable of performing communications mutually by the above-described configuration. 
     FIG. 3  shows a configuration example of the storage system  100 . The storage system  100  is configured to have the data I/O network interface  140  for performing data input/output which is connected with the data I/O network  401 , a management network interface  150  for input/output management information which is connected with the management network  501 , a storage controller  160  for performing control within the storage system, a program memory  110  that is a memory to store programs required for operation of the storage system  100 , the logical storage extent  120  that is a storage extent storing data to be input/output by the host computer  200  and a data I/O cache memory  130  that is a temporary memory for performing input/output of the logical storage extent  120 , which are mutually connected through the storage controller  160 . 
   The data I/O network interface  140  and the management network interface  150  may be implemented using a network I/O apparatus of prior-art communication technology such as Fiber channel and Ethernet (registered trademark). It should be noted that the number of data I/O network interfaces  140  and the number of management network interfaces  150  can be any number in the present invention. In addition, the management network interface  150  may be such a form that the data I/O network interface  140  is shared for management instead of being the independent one. 
   The logical storage extent  120  is one which re-configures a storage device such as a magnetic disk and an optical medium, a non-volatile memory or a volatile memory, into a logical unit for providing to the host computer  200 . It should be noted that the number and capacity of logical storage extents  120  can be any number and capacity in the present invention. 
   Although it is general to implement the data I/O cache memory  130  using a volatile memory, a magnetic disk may be used as a substitute. It should be noted that the capacity of the data I/O cache memory may be any capacity in the present invention. 
   The program memory  110  is a memory space implemented using a magnetic disk and a volatile semiconductor memory, and is used for a purpose of holding basic programs and information required for operation of the storage system  100 . Stored in the program memory  110  are a data encryption program  1101  for encrypting input data and decrypting output data, a data encryption management program  1102  for managing encrypted data, data encryption management information  1103 , a data encryption update program  1104  for controlling a function to update an encryption method of encrypted data into another encryption method, a data replication program  1105  for replicating data stored on a logical storage extent  120  into another logical storage extent, a virtual storage extent management program  1106  for behaving to the host computer  200  as if a logical storage extent  120  mounted on another storage system  100  were mounted within the apparatus, storage extent configuration information  1107  that is configuration information of the logical storage extent  120 , a program install management program  1108  for managing install, update and deletion of a program to this storage system  100 , program management information  1109 , and a management information I/O program  1110  for input and output management information between management computers  300 . 
   Herein, the virtual storage extent means one which corresponds to the virtual storage extent shown in  FIG. 2 . Therefore, when this virtual storage extent is used, the host computer  200  recognizes only the virtual storage extent for the storage system  100  and is to make access to the virtual storage extent. Further, the storage system  100  is to execute access to the logical storage extent associated with the virtual storage extent. Hereinafter, a virtual storage extent shown in  FIG. 7  described later is also similar. It should be noted that the virtual storage extent and the logical storage extent associated with the virtual storage extent may be provided over different storage systems  100 , or within the same storage system  100 , and furthermore over different storage apparatuses or in the same storage apparatus within the same storage system  100 . 
     FIG. 4  is a diagram showing a configuration example of the host computer  200 . The host computer  200  is configured to have a data I/O network interface  240  for performing data input/output which is connected to the data I/O network  401 , a management network interface  250  for input/output management information which is connected to the management network  502 , an input interface  270  for an operator to input information such as a keyboard and a mouse for example, an output interface  280  for output information to an operator such as a general-purpose display for example, an arithmetic processing unit  290  equivalent to CPU for performing various calculations, a hard disk  220  implemented using a magnetic disk, and a data I/O cache memory  230  implemented generally using a volatile memory, which are mutually connected by a communication bus  260 . The data I/O network interface  240  and the management network interface  250  can be implemented using a network I/O apparatus of prior-art communication technology such as Fiber channel and Ethernet (registered trademark). It should be noted that the number of data I/O network interfaces  240  and the number of management network interfaces  250  may be any number in the present invention. In addition, the management network interface  250  may be such a form that the data I/O network interface  240  is shared for management instead of being the independent one. 
   The host computer  200  is configured similarly to a prior-art general-purpose computer (PC) as described hereinbefore. In addition, the host computer  200  operates an operating system and also operates application programs such as a data base and an accounting program on the operating system similarly to the general-purpose computer. These application programs perform input/output of data to the logical storage extent  120  mounted on the storage system  100  and update data stored on the logical storage extent  120 . 
     FIG. 5  shows a configuration example of the management computer  300 . The management computer  300  is configured to have a management network interface  350  for input and output management information, an input interface  370  for an operator to input information such as a keyboard and a mouse for example, an output interface  380  for output information to an operator such as a general-purpose display for example, an arithmetic processing unit  390  which is equivalent to a CPU for performing various calculations, a hard disk  320  implemented using a magnetic disk, and a program memory  310  that is a storage extent for storing programs required for operation of the management computer  300 , which are connected mutually by a communication bus  360 , and the management computer  300  is connected to the management network  501  and the management network  502 . 
   The program memory  310  is a memory space implemented using a magnetic disk and a volatile memory, and is used for a purpose of holding basic programs and information required for operation of the management computer  300 . Stored in the program memory  310  are an asset management program  3101  for managing a program configuration of the storage system  100  connected to the system, asset management information  3102 , a data replication program  3103  for giving a command of data replication between the logical storage extent  120 , a data encryption update management program  3104  for issuing a command to update an encryption method of encrypted data to another encryption method, data encryption management information  3105  for managing encrypted data, storage extent configuration information  3107  that is configuration information of the logical storage extent  120  mounted on one or more storage systems  100 , a management information I/O program  3110  for input/output management information between the management computers  300 , and encryption method compatibility information  3111  recording compatibility between encryption programs  1101  described hereinbefore. 
     FIG. 6  is a diagram showing one example of the data encryption management information  1103  which is provided in the storage system  100 . The data encryption management information  1103  is information recording an encryption status of all encrypted logical storage extents  120  among the logical storage extents  120  mounted on the storage system  100 . 
   Logical storage extent identification information  11031  shows a value enabling to identify uniquely a logical storage extent  120 .  FIG. 6  shows an example in which the number assigned to each logical storage extent  120  is adopted as identification information and is recorded in the logical storage extent identification information  11031 . An encryption method applied to data stored in the logical storage extent  120  is recorded in encryption method identification information  11032 . In addition, a generally known encryption algorithm and a bit size of the encryption key thereof (number of bits) are recorded in the encryption method identification information  11032 . An encryption and decryption key to the data stored in the logical storage extent  120  is recorded in encryption key information  11033 . The encryption key information  11033  is a hash value to a password set beforehand for example, and is used as information for encrypting data or oppositely for decrypting data by computing the above-described hash value to original text data. Access control information  11034  is managed as a sub-table in which client information for permitting input/output to this logical storage extent  120  is written. The access control information sub-table may be expressed by a network address ( 11037 ) of the host computer  200  permitted to input/output to this logical storage extent  120  for example, or may be expressed by an ID ( 11038 ) and a password ( 11039 ) of a client user. 
     FIG. 7  shows one example of the storage extent configuration information  1107  which is provided in the storage system  100 . Configuration information including a virtual configuration in addition to a physical configuration of the logical storage extent  120  mounted on the storage system  100  is recorded in the storage extent configuration information  1107 . 
   Data I/O network interface identification information  11071  shows the data I/O network interface  140  of the storage system  100  to which the logical storage extent  120  described hereinafter is connected. This data I/O network interface identification information  11071  is expressed by the number uniquely determined within the apparatus of the data I/O network interface  140 , a World Wide Name of Fiber Channel, and an MAC address of Ethernet (registered trademark), for example. Logical storage extent identification information  11072  shows the logical storage extent  120  which is connected to the data I/O network interface  140  shown in the above-described data I/O network interface identification information  11071 . Information recorded in this logical storage extent identification information  11072  is expressed by an internal apparatus number assigned to each logical storage extent  120 . A logical storage extent capacity  11073  is one which a memory capacity of the logical storage extent  120  shown in the above-described logical storage extent identification information  11072  is written with a unit such as GB (gigabyte) and MB (megabyte), for example. 
   Virtual storage extent judgment information  11074  is a boolean parameter to specify whether the logical storage extent  120  shown in the logical storage extent identification information  11072  is the one physically mounted within the same storage system  100 , or whether the logical storage extent  120  is physically mounted on another storage system  100  and is treated as the one virtually mounted within the same storage system  100 . If this logical storage extent  120  is one which is physically stored in another storage system  100  and is associated with the virtual storage extent, “1” showing YES is recorded in the virtual storage extent judgment information  11074 . On the contrary, when the logical storage extent  120  is physically mounted within the same storage system  100  and is not the virtual storage extent, “0” showing NO is recorded in the virtual storage extent judgment information  11074 . It should be noted that a method of managing a virtual storage extent is described in detail in Published Japanese Patent Application No. 2004-005370. 
   Information to identify uniquely the storage system  100  having the above-described virtual storage extent physically mounted is recorded in virtual storage extent apparatus identification information  11075 . This virtual storage extent apparatus identification information  11075  is one which is expressed by an apparatus manufacturing number (serial number) that is a number to identify uniquely the storage system  100  and the World Wide Name of Fiber Channel. Alternatively, this information may be expressed by a Target ID of SCSI protocol. Identification information for identifying uniquely the virtual storage extent  120  of the above-described virtual storage extent within the storage system  100  which is identified by the above-described virtual storage extent apparatus identification information  11075  is recorded in virtual logical storage extent identification information  11076 . Further, the virtual logical storage extent identification information  11076  is expressed by the internal apparatus number in the storage system  100  identified by the above-described virtual storage extent apparatus identification information  11075 , for example. As an alternative, this information may be expressed by a LUN (Logical Unit Number) within the apparatus shown by the above-described Target ID. 
     FIG. 8  is one example of the program management information  1109  provided in the storage system  100 . A list of programs having been installed within the storage system  100  is recorded in this program management information  1109 . 
   Program identification information  11091  shows information which enables to identify uniquely the programs installed on the program memory  110  within the storage system  100 . For example, a name of the installed data encryption program  1101  is expressed in the program identification information  11091  by a character string containing version information like “first encryption algorithm”. Install date information  11092  shows a date when the program identified by the program identification information  11091  is installed on the storage system  100 . 
     FIG. 9  shows one example of the asset management information  3102  provided in the management computer  300 . The management computer  300  make an inquiry to the storage system  100  of a management object about the program installed into this storage system  100 . The storage system  100  which has received the inquiry from the management computer  300  sends the above-described program management information  1109  to the management computer  300 . The management computer  300  extracts a program corresponding to the above-described encryption program  1101  out of the received program management information  1109  and records in the asset management information  3102 . 
   Apparatus identification information  31021  exhibits information which enables to identify uniquely the storage system  100  mounting an encryption method described hereinafter. This apparatus identification information  31021  is one which is expressed by the apparatus manufacturing number (serial number) that is the number to identify uniquely the storage system  100  and the World Wide Name of Fiber Channel, for example. In addition, encryption method identification information  31022  exhibits the identification information of the encryption program  1101  which is mounted on the storage system  100  identified by the above-described apparatus identification information  31021 . Further, install date information  31023  is one which shows a date when the encryption program  1101  identified by the encryption method identification information  31022  described hereinbefore is installed on the storage system  100  identified by the above-described apparatus identification information  31021 . 
     FIG. 10  shows one example of the data encryption management information  3105  provided in the management computer  300 . The management computer  300  commands the storage system  100  of the management object to send the above-described data encryption management information  1103  held in the storage system  100 . The storage system  100  which has received the command from the management computer  300  sends the above-described data encryption management information  1103  to the management computer  300 . The management computer  300  writes additionally apparatus identification information  31055  into the received data encryption management information  1103 , and records in the data encryption management information  3105  shown in  FIG. 10   
   In  FIG. 10 , the apparatus identification information  31055  exhibits the storage system  100  mounting the logical storage extent  120  which is identified by logical storage extent identification information  31051  described hereinafter. Also, the logical storage extent identification information  31051  shows information for identifying uniquely the logical storage extent  120  similarly to the above-described logical storage extent identification information  11031 , and encryption method identification information  31052  shows the encryption program  1101  applied to the data which is stored in the logical storage extent  120  identified by the above-described logical storage extent identification information  31051  similarly to the encryption method identification information  11032  described hereinbefore. Similarly to the above-described encryption key information  11033 , encryption key information  31053  is key information used for encryption and decryption of the logical storage extent  120  identified by the logical storage extent identification information  31051  described hereinbefore. Similarly to the above-described access control information  11034 , access control information  31054  is information on access authority to the logical storage extent  120  identified by the above-described logical storage extent identification information  31051 , and is one which is expressed by a list of sub-table. 
     FIG. 11  shows one example of the storage extent configuration information  3107  provided in the management computer  300 . The management computer  300  commands the storage system  100  of the management object to send the above-described storage extent configuration information  1107  held in the storage system  100 . The storage system  100  receives the command and sends the above-described storage extent configuration information  1107  to the management computer  300 . The management computer  300  writes additionally apparatus identification information  31077  into the storage extent configuration information  1107  received from the storage system  100 , and records in this storage extent configuration information  3107 . 
   The storage system  100  mounting the logical storage extent  120  identified by logical storage extent identification information  31072  described later is recorded in the apparatus identification information  31077 . Similarly to the above-described data I/O network interface identification information  11071 , Data I/O network interface identification information  31071  shows information for identifying uniquely the data I/O network interface  140  to which the logical storage extent identification information  31072  described later is connected. Further, similarly to the above-described logical storage extent identification information  11072 , the logical storage extent identification information  31072  shows information for identifying uniquely the logical storage extent  120  within the storage system identified by the above-described apparatus identification information  11077 , and similarly to the above-described logical storage extent capacity  11073 , a logical storage extent capacity  31073  shows a memory capacity of the logical storage extent  120  identified by the above-described logical storage extent identification information  31072 . Similarly to the above-described virtual storage extent judgment information  11074 , virtual storage extent judgment information  31074  exhibits a truth-value for judging whether this logical storage extent  120  is a virtual storage extent, and similarly to the above-described virtual storage extent apparatus identification information  11075 , virtual storage extent apparatus identification information  31075  shows information for identifying uniquely the storage system  100  mounting physically this logical storage extent  120 . Similarly to the above-described virtual logical storage extent identification information  11076 , virtual logical storage extent identification information  31076  is information for identifying uniquely a physical logical storage extent  120  of a virtual storage extent. 
     FIG. 12  shows one example of the encryption method compatibility information  3111  provided in the management computer  300 . This encryption method compatibility information  3111  is one which expresses the compatibility between one encryption method and another encryption method by a boolean value. In  FIG. 12 , the compatibility between a data encryption program  1101  shown in the vertical axis and a data encryption method  1101  shown in the horizontal axis is written with the boolean value in a cell where both axes intersect. In the present embodiment, “1” meaning YES is recorded when the data encryption program  1101  of the horizontal axis is upwardly compatible with the data encryption program  1101  of the vertical axis, and “0” meaning NO is recorded when there exists no compatibility. For example, it is exhibited that there is the upward compatibility in “second encryption algorithm” and “third encryption algorithm” with respect to “first encryption algorithm” of  FIG. 12 , more specifically that data encrypted by “first encryption algorithm” can be decrypted by “second encryption algorithm” and “third encryption algorithm”. On the other hand, there exists no data encryption program  1101  having the upward compatibility with “second encryption algorithm”, and data encrypted by “second encryption algorithm” can not be decrypted by another data encryption program  1101 . 
     FIG. 12  is explained more specifically. For example, data encrypted by “DES” encryption method of key length of 64 bits can be decrypted by another data encryption method  1101  of “DES” encryption method which is capable of calculating by a key length of 128 bits. In further another example, data encrypted by the “DES” encryption method can be decrypted by a data encryption program  1101  of “TRIPLEDES” encryption method which repeats trebly this “DES” method. 
   One of assumed cases in the present invention is that a storage system  100  having stored encrypted data becomes obsolete after a long time has passed and the data is migrated into a storage system  100  of a new model. Under such situation, it is necessary to migrate the data in such a manner that the data encrypted by the data encryption program  1101  of the old model storage system  100  can also be decrypted by the new model storage system  100 . Then, by managing this encryption method compatibility information  3111 , the new model storage system  100  is made to be able to judge whether a data encryption program  1101  compatible with the data encryption program  1101  of the old model storage system  100  is mounted or not. 
     FIG. 13 ,  FIG. 14  and  FIG. 15  are flow charts showing a procedure of a migration method of encrypted data between apparatuses in the present embodiment. 
   First, when migrating data between storage systems  100  in  FIG. 13 , an operator of a management computer  300  specifies a logical storage extent  120  which is a migration object and inputs this logical storage extent from the input interface  370  (step s 1 ). Next, the data encryption update management program  3104  of the management computer  300  retrieves the data encryption management information  3105  and judges whether the logical storage extent  120  of the migration object inputted at step s 1  is encrypted (step s 2 ). When a result of judgment at step s 2  is YES, the data encryption update management program  3104  retrieves the encryption method compatibility information  3111  and searches for an encryption method having upward compatibility with the logical storage extent  120  of the migration object. Moreover, the asset management information  3102  is retrieved and a storage system  100  having a compatible encryption method mounted is searched. The storage system  100  mounting this compatible encryption method is chosen as a storage system  100  of a destination of data migration (step s 3 ). 
   On the other hand, when the result of judgment at step s 2  is NO, more specifically when the logical storage extent  120  of the migration object is not encrypted, a storage system  100  of a migration destination is chosen in an ordinary manner (step s 4 ). Next, the data encryption update management program  3104  chooses one which is made into a logical storage extent  120  of the destination of data migration out of logical storage extents  120  mounted on the storage system  100  of the migration destination chosen in step s 3  or in step s 4 . At this time, a logical storage extent  120  having the same or larger capacity than the logical storage extent  120  of a migration source is chosen as the logical storage extent  120  of the migration destination (step s 5 ). It should be noted that each storage apparatus may be specified at the time of choosing the logical storage extent  120  as the migration object in step s 1 . In addition, a warning may be generated if a storage apparatus satisfying with the condition can not be found at the time of choosing the storage system  100  having the compatible encryption method mounted as the storage system  100  of the destination of data migration in step s 3 . Furthermore, though only a encrypted data migration operation of the management computer  300  is shown in  FIG. 13 , the operation is not limited to this, but the storage system  100  or the host computer  200  may perform similar encrypted data migration operation to the management computer  300  by providing the storage system  100  or the host computer  200  with a configuration similar to the above-described management computer  300 . 
   After going through the processing described hereinabove, the process moves to (A) shown in a flow chart of  FIG. 14 . First, the data replication program  3103  commands the storage system  100  of the migration source to replicate the logical storage extent  120  chosen in step s 1  into the logical storage extent  120  chosen in step s 5  which is mounted on the storage system  100  of the migration destination chosen in step s 3  or step s 4  (step s 6 ). The logical storage extent  120  of the migration source, the storage system  100  of the migration destination and the logical storage extent  120  of the migration destination are written in a data replication command message transmitted at this time. Communications of all management information are performed through the management information I/O program  3110 . The management information I/O program  1110  mounted on the storage system  100  receives the data replication command message transmitted in step s 6  (step s 7 ). Next, if there is a necessity, the data replication program  1105  sets the storage systems  100  of the migration source and the migration destination to establish a relation of replication pair between the logical storage extent  120  of the migration source and the logical storage extent  120  of the migration destination (step s 8 ). Furthermore, the data replication program  1105  performs data replication from the logical storage extent  120  of the migration source to the logical storage extent  120  of the migration destination (step s 9 ). After data replication, since new encrypted data is being produced in the storage system  100  of the migration destination in case that this data is encrypted data, this is updated into the data encryption management information  1103 . After this is completed, the storage system  100  transmits a replication completion notice to the management computer  300  through the management information I/O program  1110  (step s 10 ). When the replication completion notice is transmitted in step s 10 , the management computer  300  receiving this notice receives this replication completion notice through the management information I/O program  3110  (step s 11 ), and successively the data encryption management information  3105  is updated. Next, the management computer  300  requests the host computer  200  to change a logical storage extent  120  of a connection destination to the logical storage extent  120  of the replication destination which is replicated in step s 9  (step s 12 ). 
   As a result thereof, there is no host computer  200  which makes access to the logical storage extent  120  before migration, and this logical storage extent  120  becomes unnecessary. Next, the process moves to (B) and (C) of the flow chart shown in  FIG. 15 . First, the management computer  300  commands the storage system  100  of the migration source to delete the logical storage extent  120  of the migration source (step s 13 ). Identification information on the logical storage extent as a deletion object is written in this deletion command message, and this deletion command message is sent to the storage system  100  through the management information I/O program  3110 . The storage system  100  receives the deletion command message sent through the management information I/O program  3110  (step s 14 ). Further, the storage system  100  releases and deletes the logical storage extent  120  (step s 15 ). Since the cryptic data disappears from the storage system  100  of the migration source as a result of deletion, the logical storage extent  120  is deleted from the data encryption management information  1103  and at the same time, is also deleted from the storage extent configuration information  1107 . Thereafter, the management information I/O program  1110  transmits a deletion completion notification message to the management computer  300  (step s 16 ). Subsequently, the management computer  300  receives the deletion completion notice through the management information I/O program  3110  (step s 18 ), and updates the data encryption management information  3105 . Furthermore, the storage extent configuration information  3107  is also updated. 
   The storage system  100  having the compatible data encryption program  1101  mounted has been chosen as the migration destination of the encrypted data and the processing of migrating the data to this apparatus has been achieved by the processing described hereinbefore. 
     FIG. 16 ,  FIG. 17  and  FIG. 18  are flow charts showing a procedure of processing of updating securely and at high speed the encryption method of the encrypted data stored on the storage system  100 . 
   First, in  FIG. 16 , an operator of the management computer  300  chooses a logical storage extent  120  as an object to update the encryption method into another encryption method, and inputs this logical storage extent from an input interface  170  (step s 20 ). Furthermore, the operator inputs a newly applied encryption method from the input interface  170  (step s 21 ). The data encryption update management program  3104  provided in the management computer  300  refers to the asset management information  3102 , and judges whether the encryption method inputted in step s 21  is mounted on the storage system  100  mounting the logical storage extent  120  inputted in step s 20  (step s 22 ). When a result of judgment thereof is YES, the process is continued to processing of step s 26  described later. On the contrary, when the result is NO, the data encryption update management program  3104  urges the operator to input further, and inquires whether a new updated encryption method is installed on the storage system  100  mounting the logical storage extent  120  inputted in step s 20  (step s 23 ). When a result of input by the operator is YES in judgment step s 23 , more specifically when it is judged to install the inputted encryption method, the operator installs a new data encryption program  1101  on the storage system  100  (step s 24 ). It should be noted that the program install management program  1108  provided in the storage system  100  may be used to install this data encryption program  1101 . The program install management program  1108  is a program to support the install of a new program and the deletion of an existing program. 
   On the other hand, when the result of judgment in step s 23  is NO, more specifically when it is judged not to install the updated encryption method, this processing is performed again from the beginning after the logical storage extent  120  inputted in step s 20  is once transferred to the storage system  100  mounting the encryption method inputted in step s 21  (step s 25 ) in order to continue this processing. It should be noted that the above-described method shown in  FIG. 12  only has to be applied to the processing of migrating data between apparatuses in step s 25 . Next, when the data encryption program  1101  corresponding to the updated encryption method is mounted on the storage system through processing in step s 22  or step s 24 , the data encryption update management program  3104  chooses a logical storage extent  120  having the same or larger capacity than the logical storage extent  120  chosen in step s 20 , which is made into a logical storage extent  120  for storing encrypted data after update (step s 26 ). 
   Next, the process moves to (D) in the flow chart shown in  FIG. 17 . First, the data encryption update management program  3104  provided in the management computer  300  commands the storage system  100  to update the encryption method (step s 27 ). A logical storage extent  120  to be updated, an encryption method to be updated and newly applied, and a logical storage extent  120  to store encrypted data after update are written in this update command message of encryption method. It should be noted that communications of all management information are performed through the management information I/O program  3110 . The storage system  100  receives the update command message of encryption method through the management information I/O program  1110  (step s 28 ). The data encryption update program  1104  repeats following processing from step s 29  to step s 33  to all data blocks stored on the logical storage extent  120  of the update object. 
   First, the data encryption update program  1104  reads out data from the logical storage extent  120  of the update object by a unit of data block (step s 30 ). This read-out data is stored temporarily on the data I/O cache memory  130 . Since this data is encrypted, the data encryption update program  1104  requests the data encryption program  1101  to once decrypt this data within the cache memory  130  (step s 31 ). Next, the data encryption update program  1104  requests the data encryption program  1101  corresponding to the encryption method applied after update so as to encrypt the data by this encryption method (step s 32 ). Furthermore, the data encryption update program  1104  writes the encrypted data in the logical storage extent  120  after update (step s 33 ). The update of the encryption method is completed when the processing from step  29  to step  33  is repeated to all data blocks. 
   Then, the process proceeds to the flow chart in  FIG. 18 . In  FIG. 18 , the storage system  100  transmits a completion notification message of the update of the encryption method to the management computer  300  through the management information I/O program  1110  (step s 34 ). The management information I/O program  3110  of the management computer  300  receives this completion notice (step s 35 ). The data encryption update management program  3104  provided in the management computer  300  changes the host computer  200  such that the logical storage extent  120  of a connection destination is updated from the logical storage extent  120  before update of the encryption method inputted in step s 20  into the logical storage extent  120  after update which is chosen in step s 26  (step s 35 A). 
   By the processing described hereinbefore, the logical storage extent  120  before update of the encryption method is not accessed from any of the host computers  200 , and practically becomes unnecessary. Next, the management computer  300  commands the storage system  100  to delete the logical storage extent  120  before update (step s 36 ). Then, the management information I/O program  1110  of the storage system  100  receives the deletion command message (step s 37 ). Next, the storage system  100  releases and deletes the requested logical storage extent  120  (step s 38 ). Furthermore, the storage extent configuration information  1107  and the data encryption management program  1102  are updated at this point of time. The storage system  100  transmits a completion notification message of the deletion of the logical storage extent  120  through the management information I/O program  1110  (step s 39 ). The management computer  300  receives the above-described deletion completion notification message through the management information I/O program  3110  (step s 41 ). The storage extent configuration information  3107  and the data encryption management information  3105  are updated at this point of time. 
   The logical storage extent  120  having stored the encrypted data is updated to another encryption method and is stored on another logical storage extent  120  by the above-described series of processing shown in  FIG. 16 ,  FIG. 17  and  FIG. 18 . 
     FIG. 19  and  FIG. 20  are flow charts of migration processing of encrypted data using a technology of virtual storage extent management. When the migration processing of a virtual storage extent between storage systems  100  is performed in this flow chart, the virtual storage extent management program  1106  provided in the storage system  100  makes the host computer  200  recognize only the virtual storage extent of the storage system  100 . Further, the virtual storage extent management program  1106  controls an input/output command from the host computer  200  to this virtual storage extent, and actually performs input/output to a logical storage extent associated with this virtual storage extent. A mechanism of this virtual storage extent management is used to realize the migration of encrypted data. It should be noted that this method of migrating the encrypted data can be a substitute of the method of migrating the encrypted data in  FIG. 13 . 
   First, similarly to step s 1 , an operator of the management computer  300  inputs a logical storage extent  120  of a migration object from the input interface  370  in  FIG. 19  (step s 43 ). Next, similarly to step s 3 , a storage system  100  provided with a compatible encryption method is chosen as a migration destination (step s 44 ). Successively, the data encryption update management program  3104  commands the storage system  100  chosen in step s 44  as the migration destination to create a virtual storage extent (step s 46 ). More specifically, the command requests such that the virtual storage extent is created within the storage system  100  of the migration destination and the logical storage extent  120  on the apparatus of the migration source inputted in step s 43  is associated with this created logical storage extent to make a storage extent configuration as if the logical storage extent  120  of the migration source were mounted within the storage system  100  of the migration destination. The storage system  100  of the migration destination receives the virtual storage extent creation command message through the management information I/O program  1110  (step s 47 ). The virtual storage extent management program  1106  associates the logical storage extent  120  stored on the apparatus of the migration source with the virtual storage extent within the storage system  100  in accordance with the above-described virtual storage extent creation command (step s 48 ). Further, the virtual storage extent management program  1106  reflects a result thereof to the storage extent configuration information  1107  (step s 49 ). Successively, the management information I/O program  1110  transmits a completion notification message of the creation of the virtual storage extent to the management computer  300  (step s 50 ). Then, the management information I/O program  3110  provided in the management computer  300  receives this completion notice (step s 51 ). 
   Furthermore, the management computer  300  reflects a result thereof to the storage extent configuration information  3107  in  FIG. 20  (step s 52 ). Next, the data encryption update management program  3104  chooses a logical storage extent  120 , which has the same or larger capacity than the logical storage extent  120  of the migration source inputted in step s 43  and which is stored on the storage system  100  of the migration destination, as a logical storage extent  120  to store encrypted data after update of the encryption method (step s 53 ). At this time, a destination to save the data after update can also be set to another storage system  100  by making the chosen logical storage extent  120  further into a virtual storage extent. 
   The logical storage extents  120  of the migration source and the migration destination are chosen by the processing described hereinbefore. At this time, since the logical storage extent  120  of the migration source can be treated as the virtual storage extent within the storage system  100  of the migration destination, data replication processing can be performed as processing within this storage system  100 . Since data migration processing performed thereafter is similar to the procedure shown in  FIG. 14  and  FIG. 15 , an explanation herein is omitted. 
     FIG. 21  and  FIG. 22  are flow charts of update processing of an encryption method using the technology of the virtual storage extent management. This flow chart is an example showing a case where a logical storage extent is transferred between storage systems  100  and update processing of an encryption method is performed. First, the virtual storage extent management program  1106  provided in the storage system  100  makes the host computer  200  recognize only a virtual storage extent of the storage system  100 . Then, the storage system  100  executes access to the logical storage extent associated with the virtual storage extent by making access to this recognized virtual storage extent from the host computer  200 . Thereby, the migration method of encrypted data and the update method of an encryption method are achieved. It should be noted that these methods can be a substitute of the method of updating into the encrypted data by the other encryption method of  FIG. 16 . 
   Although each processing shown in  FIG. 21  and  FIG. 22  is almost similar to each processing shown in  FIG. 19  and  FIG. 20 , there is a difference in a point where the storage system  100  after update is provided with both the encryption method before update and the encryption method after update in step s 45 B of  FIG. 21 . Furthermore, at a point of time that step s 53 B of  FIG. 22  is completed, there becomes such a state that a logical storage extent  120  before update mounted on another storage system  100  is associated as a virtual storage extent within the storage system  100  provided with the encryption methods before and after update. More specifically, there becomes such a configuration that both of the logical storage extent  120  recorded by the encryption method before update and the logical storage extent  120  to be recorded by the encryption method after update exist within a single apparatus. This configuration makes it possible to create the logical storage extent  120  having the encryption method updated by continuing thereafter processing starting from (D) of  FIG. 17 . 
     FIG. 23  and  FIG. 24  are flow charts showing a processing procedure to delete the encryption program  1101 . 
   In  FIG. 23 , an operator of the management computer  300  inputs a deletion command of the encryption program  1101  mounted on the storage system  100  from the input interface  370  (step s 54 ). At this time, the operator had better make it possible to choose the encryption method  31022  which is to be deleted by output information recorded in the asset management information  3102  from the management computer  300  through the output interface  380 . Next, the asset management program  3101  retrieves the data encryption management information  3105 , and judges whether data encrypted by the encryption method inputted in step s 54  is held within the storage system  100  identified by the apparatus identification information  31055  (step s 55 ). For example, it is assumed that a deletion command of an encryption method of a “first encryption algorithm” is inputted in step s 54  by the operator from an apparatus “50:00:01:E8:A0:C3:B0” shown in the example of  FIG. 9 . Then, the asset management program  3101  retrieves the data encryption management information  3105  shown in the example of  FIG. 10 , and judges whether a logical storage extent  120  encrypted by the “first encryption algorithm” exists within this apparatus. In this embodiment, since logical storage extents “00:01” and “00:02” encrypted by the “first encryption algorithm” exist within the apparatus “50:00:01:E8:A0:C3: B0” in case of  FIG. 10 , a result of judgment in step s 55  becomes YES. 
   When this result is YES, there occurs such a problem that the data thereof can not be decrypted if this data encryption program  1101  is deleted. Accordingly, the asset management program  3101  gives a warning on an operation screen from the output interface  380 , and urges an input whether to continue the deletion processing (step s 56 ). When the continuation of the deletion processing is requested in this input (YES in step s 57 ), the asset management program  3101  repeats the update processing of the encryption method to all logical storage extents  120  recorded by this encryption method (step s 58 ). The above-described method shown in  FIG. 16 ,  FIG. 17  and  FIG. 18  or shown in  FIG. 21  may be used as this update processing of the encryption method (step s 59 ). Since the logical storage extent  120  encrypted by the data encryption program  1101  of the deletion object inputted in step s 54  disappears as the result of those update processing, the problem does not occur even if this data encryption program  1101  is deleted. 
   Furthermore, the asset management program  3101  transmits a deletion command of the data encryption program  1101  inputted in step s 54  to the storage system  100  in  FIG. 24  (step s 60 ). The storage system  100  receives the deletion command message through the management information I/O program  1110  (step s 61 ). The program install management program  1108  provided in the storage system  100  deletes the requested data encryption program  1101  from the program memory  110  (step s 62 ). When the deletion is succeeded, the program install management program  1108  updates in such a manner that information relating to this program is deleted from the program management information  1109 . When the deletion is completed, the storage system  100  transmits a deletion completion notice of the data encryption program  1101  to the management computer  300  (step s 63 ). The management computer  300  receives this notice (step s 64 ). The management computer  300  updates in such a manner that information relating to this program is deleted from the asset management information  3102 . 
   By the above-described processing, it becomes possible to urge an interruption by giving a warning to a deletion from the management computer  300  even when the operator tries to delete the data encryption program  1101 , and to avoid such a risk that there remains data which is unable to decrypt since the encrypted data by this encryption method is updated and kept into encrypted data by another encryption method. 
   Hereinafter, a specific processing procedure in the above-described embodiment is shown when the information shown in  FIG. 6  through  FIG. 12  is used especially as an example. 
   First, a system administrator tries to migration the logical storage extent  120  identified by “00:02” (the third line of  FIG. 11 ), which is stored on the storage system  100  identified by “50:00:01:E8:A0:C3:B0”, to another storage system  100  (step s 1  in  FIG. 13 ). When the data encryption management information  3105  is referred (the third line of  FIG. 10 ) in order to judge whether this logical storage extent  120  is encrypted data, it is noticed that this is the data encrypted by the “first encryption algorithm” (step s 2  in  FIG. 13 ). Next, the management computer  300  refers to the asset management information  3102 , and it is noticed that the “first encryption algorithm” is mounted on the storage system  100  identified by “50:00:01:1E:0A:E8:02” provided with this encryption method (the third line of  FIG. 9 ). Then, this apparatus is adopted as the migration destination (step s 3  in  FIG. 13 ). The management computer  300  retrieves the storage extent configuration information  3107 , and since the capacity of the logical storage extent  120  in step s 1  is 20 GB (the third line of  FIG. 11 ), the logical storage extent  120  of the same capacity identified by “05:02” (the eighth line of  FIG. 11 ) is adopted as the migration destination (step s 5  in  FIG. 13 ). 
   Thereafter, the data is replicated from the migration source to the logical storage extent  120  of the migration destination by the above-described procedure (steps s 6  through s 11  in  FIG. 14 ), furthermore the logical storage extent  120  of the migration source is deleted, and the processing is ended (steps s 13  through s 18  in  FIG. 15 ). 
   Although the logical storage extent “00:02” mounted on “50:00:01:E8:A0:C3: B0” is migrated to “05:02” mounted on “50:00:01:1E:0A:E8:02” by the above-described processing, there occurs no problem in continuing input/output of encrypted data because the apparatus after migration is also provided with the “first encryption algorithm” similarly to the migration source. 
   Next, the system administrator tries to update the encryption method of the logical storage extent “05:02” of “50:00:01:1E:0A:E8:02” which was the migration destination in the above example (step s 20  in  FIG. 16 ). In addition, a “second encryption algorithm” is specified as an encryption method which is newly applied after update (step s 21  in  FIG. 16 ). The management computer  300  retrieves the asset management information  3102 , and confirms that the “second encryption algorithm” (the fourth line of  FIG. 9 ) is mounted on this apparatus (step s 22  in  FIG. 16 ). Furthermore, the storage extent configuration information  3107  is referred to, and since the capacity of “05:02” is 20 GB, “06:01” having larger capacity (the ninth line of  FIG. 11 ) is adopted as the update destination (step s 26  in  FIG. 16 ). 
   Thereafter, the processing of updating the encryption method from the update source to the logical storage extent  120  of the update destination is performed by the above-described procedure (from step s 27  in  FIG. 17  to step s 35  in  FIG. 18 ), furthermore the logical storage extent  120  of the update source is deleted, and the processing is ended (from step s 36  to step s 41  in  FIG. 18 ). 
   Following shows an example in which the encryption method is updated using the virtual storage extent management. 
   It is assumed that the system administrator inputs “00:01” mounted on “50:00:01:E8:A0:C3:B0” as the logical storage extent  120  to which the encryption method is updated (step s 43 B in  FIG. 21 ). Furthermore, the “second encryption algorithm” is specified as the encryption method which is newly applied after update (step s 44 B in  FIG. 21 ). When the data encryption management information  3105  is referred to, it is noticed that this logical storage extent “00:01” is encrypted by the “first encryption algorithm” (the second line of  FIG. 10 ). Then, the asset management information  3102  is referred to, and “50:00:01:1E:0A:E8:02” mounting the “first encryption algorithm” and the “second encryption algorithm” is adopted as the storage system  100  of the update destination (step s 45 B in  FIG. 21 ). The management computer  300  requests this “00:01” to be associated as the virtual storage extent on “50:00:01:1E:0A:E8:02” (step s 46 B in  FIG. 21 ). “50:00:01:1E:0A:E8:02” receives this request (step s 47 B in  FIG. 21 ), and associate this “00:01” with the virtual storage extent.  FIG. 11  shows an example in which the logical storage extent having the identification number of “05:01” (the seventh line of  FIG. 11 ) is associated within “50:00:01:1E:0A:1E:0A:E8:02” as the virtual storage extent of “00:01” provided within the above-described “50:00:01:E8:A0:C3:B0”. Thereafter, it is only necessary that “05:02” or “06:01” is adopted as the logical storage extent  120  of the update destination (step s 53 B in  FIG. 22 ) and the update processing is continued similarly to the above-described example. 
   According to the method which uses this virtual storage extent management, it is possible to obtain such an effect that the update processing of the encryption method directly aiming at the logical storage extent  120  on another storage system  100  can be performed without performing the data migration processing shown in  FIG. 13 ,  FIG. 14  and  FIG. 15 . 
   Next, a configuration diagram in another embodiment of the present invention is shown in  FIG. 25 . This configuration is an example in which an external encryption apparatus  600  and a magnetic tape storage apparatus  700  are added besides the configuration example of  FIG. 1 . This configuration makes it possible to encrypt data to be stored and to decrypt data to be read out by having input-output data once pass through the external encryption apparatus  600  when a host computer  200  reads and writes the data to the magnetic tape storage apparatus  700 . 
     FIG. 26  shows a configuration example of the magnetic tape storage apparatus  700 . The magnetic tape storage apparatus  700  is configured to have one or more magnetic tapes  720 , a magnetic tape loading function  730  to insert or extract the magnetic tape  720  into/from a tape drive, a tape drive  710  to read and write data to the loaded magnetic tape  720 , a tape inserter/ejector interface  750  which is an interface for detaching the magnetic tape  720  from a case and loading a new magnetic tape into the case, a data I/O network interface  740 , an input interface  770 , and an output interface  780 , which are connected by a tape I/O controller  760 . 
   The magnetic tape storage apparatus  700  reads out data requested by the host computer  200  from the tape drive and outputs through the data I/O network interface  740 , and stores data on the magnetic tape  720  by loading the magnetic tape  720  for input and output into the tape drive using the magnetic tape loading function  730 , for example. 
     FIG. 27  shows a configuration example of the external encryption apparatus  600 . The external encryption apparatus  600  has a configuration in which the logical storage extent  120 , the virtual storage extent management program  1106  and the like are omitted from the configuration of the storage system  100  shown in  FIG. 3 . When the host computer  200  commands the external encryption apparatus  600  to output data, the external encryption apparatus  600  reads out data from the magnetic tape storage apparatus  700 , stores the data on a cache memory  630 , decrypts this by a data encryption program  6101 , and supplies this data to the host computer  200 . Write-in from the host computer  200  is also performed similarly in such a manner that the external encryption apparatus  600  once encrypts input data and the encrypted data is written in the magnetic tape  720 . 
     FIG. 28  is one example of the data encryption management information  3105  maintained by the management computer  300  in the present embodiment. Magnetic tape identification information  31051  is written instead of the logical storage extent identification information  31051  according to the data encryption management information  3105  of the present embodiment. Identification information on the external encryption apparatus  600  is written in the apparatus identification information  31055 . By having this configuration, it becomes possible to access the magnetic tape  720  which is a management object of the external encryption apparatus  600  and the data encryption program  6101  thereof. 
   It should be noted that data encryption management information  6103  held in the external encryption apparatus  600  also similarly stores the magnetic tape identification information instead of the logical storage extent identification information. 
   The deletion procedure of the data encryption program  6101  shown in  FIG. 23  and  FIG. 24  can be also applied in the present embodiment. 
   Furthermore, in case of the present embodiment, it is also possible to use such that the system administrator inquires the management computer  300  whether it is OK to remove the external encryption apparatus  600 . For example, it is assumed that an asset administrator inquires the management computer  300  whether it is OK to remove the external encryption apparatus  600  in  FIG. 23  (step s 54 ). The asset management program  3101  judges whether there exists a magnetic tape  720  storing data encrypted by an encryption method mounted only on this external encryption apparatus  600  (step s 55 ). When a result of judgment thereof is YES, the asset management program  3101  displays a warning message and urges not to remove this external encryption apparatus  600  (step s 56 ). When there is still a request for continuing the removal (step s 57 ), the encryption method of the data recorded on the magnetic tape  720  is updated into another method (step s 58  and step s 59 ). At this time, such one that compatible data encryption program  1101  is mounted on another apparatus is adopted as the encryption method after update. In the present embodiment, the processing is ended here without performing the processing from step s 60  onward shown in  FIG. 24 . Since the magnetic tape  720  encrypted by this external encryption apparatus  600  does not remain by the processing up to this point, it is assured that a problem does not occur even if this encryption apparatus is removed. 
   More specific procedure of removal judgment processing of an encryption apparatus according to the present embodiment is explained. 
   It is assumed that the system administrator has inputted a removal of an external encryption apparatus “30:00:12:C0:0A:1C:32” (step s 54  in  FIG. 23 ). The management computer  300  refers to the data encryption management information  3105 , and it is examined that magnetic tapes “Label — 0001” and “Label — 0002” managed by this apparatus are encrypted by the “first encryption algorithm” (step s 55  in  FIG. 23 ). Then, a risk of not being able to decrypt the magnetic tape  720  stored by this encryption method is eliminated by giving a warning to urge an interruption of the removal (steps s 56  and s 57  in  FIG. 23 ), performing processing of updating “Label — 0001” and “Label — 0002” into other magnetic tapes by using the latest encryption method (step s 59 ), and so on. Since the external encryption apparatus “30:00:12:C0:0A:1C:32” is removed thereafter (step s 60  through step s 64  in  FIG. 24 ), there does not occur such a problem that encrypted data which can not be decrypted remains after removal. 
   Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments and that various changes and modifications could be effected therein by one skilled in the art without departing from the spirit or scope of the invention as defined in the appended claims.