Patent Publication Number: US-7908459-B2

Title: Security for logical unit in storage subsystem

Description:
The present application is a continuation of application Ser. No. 11/407,978, filed Apr. 21, 2006, now U.S. Pat. No. 7,657,727, which is a Continuation-in-part of application Ser. No. 10/902,795, filed Aug. 2, 2004, now U.S. Pat. No. 7,082,503; which is a continuation of application Ser. No. 10/076,553, filed Feb. 19, 2002, now U.S. Pat. No. 6,779,083 and claims priority from Japanese Patent Application No. 2001-213642, filed Jul. 13, 2001; and is a Continuation-in-part of application Ser. No. 11/330,261, filed Jan. 12, 2006 now U.S. Pat. No. 7,606,806; which is a continuation of application Ser. No. 10/737,477, filed Dec. 15, 2003, now U.S. Pat. No. 7,024,410; which is a continuation of application Ser. No. 09/561,404, filed Apr. 27, 2000, now U.S. Pat. No. 6,684,209 and claims priority from Japanese Patent Application Reference No. 2000-010115, filed Jan. 14, 2000 the entire disclosures of each of the above are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a storage subsystem to be accessed from a computer. More particularly, this invention relates to an access to a logical unit inside a storage subsystem. 
     2. Description of the Related Art 
     Fiber Channel protocol has been standardized in recent years and SAN (Storage Area Network) environment using this protocol as the infrastructure has become complicated and diversified. As a result, the number of computers connected to the storage subsystem and their kinds, or a kind of OS (Operation System), and the number of logical units required for the storage subsystem have drastically increased. Further, an environment in which various protocols other than the Fiber Channel such as SCCI, ESCON, TCP/IP, iSCSI, etc, can be simultaneously used has been set up. Here, the term “computer” represents those electronic appliances having electronic circuits that can be connected to a network. 
     Such an environment means that various kinds of computers gain access to one storage subsystem. The term “computer” includes so-called large-scale host computers and compact personal computers. When these various computers gain access to the storage subsystem, the expression such as “host gains access” and “host gains access” is used herein appropriately. 
     Under such circumstances, the security function to the storage subsystem resources that relies on OS, middleware and application software on the host side according to the prior art technology is not sufficient in some cases, and the necessity for a higher LUN security function for preventing an illegal access to logical units (hereinafter abbreviated as “LU” from time to time) has increased rapidly. Incidentally, the term “LUN” represents the logical unit number inside the storage subsystem. 
     JP2000276406 is one of the references that describe means for accomplishing the security function to the storage subsystem resources (logical units). The method of this reference accomplishes the security function as to access approval/rejection to LUN inside the storage subsystem but cannot cope with diversified computers that gain access to a single port. In the practical operation, therefore, the method limits the kind of host computers that can be managed under the single port to only one kind. This limitation in the practical operation cannot follow drastic expansion of the SAN environment described above. 
     To provide the logical units inside the storage subsystem to computers with the LUN security function, it is necessary to define a greater number of logical units than before under the single port of the storage subsystem and to give the logical units to host computers having a plurality of OS, a plurality of computers having mutually different kinds of OS, and other computers. 
     Nonetheless, the LUN security function in the existing storage subsystems is not free from the limitation that the kind of OS must be the same even when a large number of computers that can be managed under the single port exist. Furthermore, such a function generally has another limitation that setting of connection interface for the host computers that can be set to the single port must be one. A method for solving these problems would be the one that simply defines a large number of logical units under the single port of the storage subsystem, and divides and gives the logical units as such to a plurality of kinds of OS that gain access to this port. 
     However, various OS of existing computers have a specification such that when access cannot be made to a logical unit zero (LU 0 ) of a storage subsystem, inquiry is not at all made thereafter for subsequent LU of the same system after LU 1  next to LU 0 . Incidentally, according to the SCSI-2 standard, one system includes 8 LU, and LU 0  to LU 7  belong to the same system. 
     Therefore, when the logical unit number (LUN) inside the storage subsystem is as such given to the host computer, the computer cannot correctly recognize the logical unit as expected on the setting side of the logical units. 
     Various OS of existing computers mostly set the upper limit of logical unit numbers recognizable under the single port to 256. In other words, even when 257 or more of logical unit number are disposed, the computers cannot recognize the logical units, and this also renders the problem when the logical units inside the storage subsystem are given to the computer under the single port. 
     On the other hand, when a strong LUN security function is provided in storage subsystems, the most reliable method would be the one that serially checks access approval/rejection of the object LU whenever computers transmit commands. However, this creates the problem of performance because the processing time in the storage subsystem (overhead for security check) becomes greater. 
     It is therefore a first object of the invention to provide a storage subsystem that groups computers in accordance with OS or into an arbitrary kind without changing existing processing, limitation and other functions of the computers, limits logical units to which the computers so grouped can gain access, and makes it possible to set them on interface in the group unit and to provide a LUN security function under a single port of the storage subsystem. 
     It is a second object of the invention to provide the security function described above with high-speed access judgment logic of the storage subsystem. 
     SUMMARY OF THE INVENTION 
     A storage subsystem according to the invention includes a management table describing correspondence of information (WWN: WorldWide Name) for primarily identifying each computer (inclusive of host computers), information (GID: Group ID) for identifying a group to which the computer belongs and a logical unit number (LUN) inside the storage subsystem for which access from the computer is permitted; a nonvolatile memory for storing the management table; a management table describing correspondence of a management number (S-ID) dynamically allocated when the computer executes login to the storage subsystem and remaining effective until logout, information (WWN) for primarily identifying the computer and information (GID) for identifying the group to which this host computer belongs; a nonvolatile memory for storing the management table; at least one input terminal for setting these management table; at least one storage device; a storage control unit for controlling write/read of data to and from the storage device; and logical units (LUN) corresponding to storage areas of the storage device. 
     In this storage subsystem, a user can make setting of accessible LUN and setting on a connection interface in an arbitrary group unit of computers under a single port without changing existing processing, limitation and other functions of the computers. Therefore, this storage subsystem can accomplish an access control function, that is, a LUN security function, for computer groups having a plurality of kinds of OS under a single port. 
     Since this storage subsystem uses GID as identification information on the basis of S-ID allocated at the time of login in place of host identification information WWN, the time required for judging accessible LUN is shorter than when WWN is used, and a high-speed judgment can be made. 
     Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a structural view of hardware in an embodiment of the present invention; 
         FIG. 2  shows in detail a frame format and its frame header in the embodiment of the invention; 
         FIG. 3  shows a login process in the embodiment of the invention; 
         FIG. 4  shows in detail a frame format when an Inquiry command is transmitted in the invention; 
         FIG. 5  shows an access inquiry sequence to a logical unit by the Inquiry command in the embodiment of the invention; 
         FIG. 6  is a flowchart showing an outline of a process sequence of LUN security in the embodiment of the invention; 
         FIG. 7  shows a format of an incomplete “LUN access management table” and its first example when the invention is not utilized; 
         FIG. 8  visually shows the state of  FIG. 7 ; 
         FIG. 9  shows a format of an incomplete “LUN access management table” and its second example when the invention is not utilized; 
         FIG. 10  visually shows the state of  FIG. 9 ; 
         FIG. 11  shows a format of a “LUN access management table” and its first utilization example according to the embodiment of the invention; 
         FIG. 12  shows a format of a “LUN access management table” and its second utilization example according to the embodiment of the invention; 
         FIG. 13  visually shows the effect of LUN security in the embodiment of the invention; 
         FIG. 14  is a flowchart showing a generation sequence of the “LUN access management table” according to the embodiment of the invention; 
         FIG. 15  is a flowchart showing a generation sequence of a “WWN-S-ID-GID conversion table” according to the embodiment of the invention; 
         FIG. 16  shows a first utilization example of the “WWN-S-ID-GID conversion table” format according to the embodiment of the invention; 
         FIG. 17  is a flowchart showing a LUN access approval/rejection judgment sequence for an Inquiry command of host computer transmission of LUN security according to the embodiment of the invention; 
         FIG. 18  is a flowchart showing continuation of the flowchart shown in  FIG. 17 ; and 
         FIG. 19  shows a reference relation among tables of LUN security according to the embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENT 
     The present invention utilizes by way of example a Fiber Channel as an example of an interface protocol used between a storage subsystem and a computer and an SCSI command as an example of a command set operating on the interface protocol. Incidentally, the invention is not limited to the combination of the Fiber Channel and the SCSI command but can be applied to any combination of protocols and interfaces so long as they can provide the functions/mechanisms of login, inquiry, logout, and so forth. 
     A first embodiment of the invention will be given. Initially, the features associated with the invention on the protocol of the Fiber Channel will be explained. 
     A device having an interface of the Fiber Channel is referred to as a “node”, and a physical terminal corresponding to a practical interface is referred to as a “port”. The node can have one or more ports. The number of ports that can simultaneously participate in the overall system of the Fiber Channel is the address number of maximum 24 bits, that is, 224 (16,777,216). Hardware that mediates these connections is referred to a “fabric”. In practice, transmitting ports and destination ports need only operate by taking information related with the mutual ports into account but without the necessity for taking the fabric into account. 
     Each of the nodes and ports stores identification data that is unique worldwide and is allocated by a standardization organization (IEEE) in accordance with a predetermined rule. They correspond to MAC addresses familiar in the past such as TCP/IP, and are hardware-wise fixed addresses. The addresses include two kinds, i.e. N-Port-Name and Node-Name, each having an eight-byte size. N-Port-Name is a value (hardware address) unique to each port and Node-Name is a value (hardware address) unique to each node. Since these values are unique worldwide, they are called “WWN (World Wide Name)” as the addresses capable of primarily identifying the ports. In Examples of the invention, the term “WWN” represents N-Port-Name. 
     In the Fiber Channel, communication is executed by information of a signal level referred to as “Ordered Set” and logical information having a fixed format referred to as a “frame”.  FIG. 2  shows a structure of the frame. The frame  201  has 4-byte identification data representing the start of the frame and called “SOF” (Start Of Frame)  202 , a 24-byte frame header  203  characterizing control of a link operation and the frame, a data field  204  as a data part as the object to be practically transferred, a 4-byte cyclic redundancy code (CRC)  205  and a 4-byte identification data called “EOF” (End of Frame)  206  and representing the end of the frame. The data field  204  is variable within 0 to 2,112 bytes. 
     Next, the content of the frame header will be explained. Reference numeral  207  represents a structure of the frame header. Here, the explanation will be given on only S-ID  208  corresponding to 0 to 23 bit areas of the first word in the detailed structure  207  of the frame header  203 . S-ID (Source ID)  208  is 3-byte address identification data for identifying the port transmitting the frame, and has a value effective for all the frames to be transmitted and received. FC-PH as one of the standard sets of the Fiber Channel stipulates that the fabric allocates S-ID during the initialization procedure. The allocated value depends on N-Port-Name or Node-Name of each port. 
     Next, the login procedure of equipment of the transmitting party and the destination party for mutually exchanging information on the basis of the Fiber Channel protocol will be described.  FIG. 3  shows the exchange of information between the transmitting party (login requesting party)  301  and the destination party (login receiving party)  302 . 
     The explanation will be given on login of Class 3 though several kinds of login procedures of the Fiber Channel are available. The login requesting party transmits a PLOGI frame  303  to the login receiving party. This frame contains N-Port-Name, Node-Name, S-ID and other information of the login requesting party. 
     Equipment at the destination takes out the information contained in this frame. When approving the login, this equipment transmits a frame called “ACC304” to the login requesting party. To reject login, on the other hand, it transmits a frame called “LS-RJT305” to the login requesting party. 
     When detecting the response of the ACC frame to the PLOGI frame transmitted by the login requesting party, the login requesting party knows that login proves successful, and can now start an I/O process such as data transfer. When receiving LS-RJT, on the other hand, the login requesting party knows that login is not established, and the I/O process to the corresponding login receiving party cannot be executed. 
     Though the explanation is given on the login operation of Class 3, the information in other login processes that can be transmitted from the login requesting party to the login receiving party similarly contains N-Port-Name, Node-Name and S-ID. 
     Next, Inquiry command that is a standard command and is always supported in the SCSI command set will be explained. 
     The Inquiry command is the one that inquires a logical unit as the object of the I/O process its package state and its preparation condition.  FIG. 4  shows a detailed structure of the data field when the frame of the Fiber Channel standard transmits the Inquiry command defined by the SCSI standard. The basic structure of the frame  401  and the frame header  402  is analogous to the one shown in  FIG. 2 . Therefore, the structure  404  of the frame header  401  contains S-ID  405 . 
     The data field  403  includes areas called FCP-LUN  407 , FCP-CNTL  408 , FCP-CDB  409  and FCP-DL  410  as represented by an FCP-CMND format  406 . 
     FCP-LUN  407  stores identification data of a logical volume associated with the port of the frame transmission destination that the frame transmitting party is to inquire. Incidentally, the term “logical volume” represents a storage area virtually divided and numbered for convenience sake for a storage device (physical volume) as a visible entity. This identification data is called “LUN” (Logical Unit Number). 
     FCP-CDB  409  stores command information called “command description block” (CDB) of SCSI when the SCSI command set is used. This FCP-CDB  409  stores the Inquiry command information of SCSI, and the information is transferred with FCP-LUN  407  to the frame receiving party. 
     In other commands supported by the SCSI command set such as Write command and Read command, too, the frame has the structures of  401  and  406  in the same way as the Inquiry command. Therefore, these commands also contain S-ID and CP-LUN that are essential for executing the present invention. 
       FIG. 5  shows the inquiry sequence of the logical unit by using the Inquiry command. 
     A host computer  501  that is to gain access to the logical unit transmits the frame  503  storing the Inquiry command to a storage subsystem  502  having the logical unit to be accessed. This frame contains S-ID of the host computer and LUN as the identification data of the logical unit to be inquired. Here, LUN can be set into the format of the Inquiry command information inside FCP-CDB besides the FCP-LUN area. The effect obtained is the same when which of these values is used. This embodiment uses the value stored in FCP-LUN  407  as the LUN value. 
     Receiving the frame containing the Inquiry command, the storage subsystem  502  prepares Inquiry data necessary for the inquiry and transmits a frame  504  containing the Inquiry data so generated to the host computer. In this instance, the frame storing the Inquiry data is called “FCP-DATA”. When the storage subsystem sets ( 504 ) either a qualifier 000 (binary digit) or device type 00 to 09 (hexadecimal digit) for the logical unit inquired, the host computer that receives this Inquiry data can subsequently generate I/O for this logical unit. 
     As represented by  505 , on the other hand, when the storage subsystem sets a qualifier 001 (binary digit) or 011 (binary digit) or device type 1F (hexadecimal digit), the host computer that receives this Inquiry data  505  recognizes that subsequent generation of I/O is not possible. Therefore, it can be understood that when the storage subsystem controls the qualifier and the device type code stored in the Inquiry data, approval/rejection of the access from the host computer to the logical unit of the storage subsystem can be controlled. 
     As described above, the method of generating the frame is basically the same in the Write command and the Read command besides the Inquiry command. Therefore, when the storage subsystem on the side of the transmission destination detects S-ID and LUN designated by the transmitting host computer as illegal, access rejection can be made. 
     Subsequently, the flow of the processing in the invention will be described in detail. 
       FIG. 1  shows an apparatus construction of an embodiment of the invention. A storage subsystem  101  includes ports  102  to  104  for Fiber Channel interface, and is physically connected to host computers  105  to  107  through the Fiber Channel interface. The host computers  102  to  104 , too, have ports  108  to  112  for the Fiber Channel interface. The host computers  105  to  107  can communicate with the storage subsystem  101  by using the Fiber Channel protocol. Some host computers have a plurality of Fiber Channel ports such as  105  and  106  while the other has only a single Fiber Channel port as  107 . Several kinds of connection forms (topology) exist as the connection form between the storage subsystem  101  and the host computers  105  to  107  such as Point-to-Point, arbitration loop connection, fabric connection, and so forth. Since the present invention does not depend on the connection form, however, the channel form is described merely as the Fiber Channel  113 . 
     First, the storage subsystem  101  includes a microprocessor  114  for executing various arithmetic operations and processing, and includes also a plurality of storage unit groups  115 , a storage control device  116  for controlling data write/read to and from these storage unit groups, and a bus  117  for connecting the storage unit groups  115  to the storage control device  116 . 
     Further, the storage subsystem  101  includes a memory  118  used as a work area of various arithmetic operations and processing and a non-volatile memory  119  for preserving various management information and management tables. The storage subsystem  101  further includes a cache  120  as means for improving the response to the host computer. 
     The storage subsystem  101  includes a communication control unit  121  and is connected to maintenance terminal equipment  123  through a communication line  122 . 
     The maintenance terminal equipment  123  includes therein a microprocessor  124 , an input unit  125  as an interface with users and a display unit  126  for outputting a processing result. The user can set several tables defined in this embodiment through the input unit  125 . 
     A microprocessor  114 , a memory  118 , a nonvolatile memory  119  and a communication control unit  121  may have a discrete construction as shown in  FIG. 1  or may be disposed inside the storage control device  116 . When they cannot be arranged inside the storage control device  116  due to the physical shape (size) of the cache  120 , they are disposed outside and are connected to the outside through predetermined paths (lines). In this case, the storage control device  116  is disposed immediately below the ports  102  to  104  and is connected to each port through a predetermined path. The storage control device  116  can substitute the functions exhibited by the microprocessor  114 . 
     The maintenance terminal equipment  123  connected to the communication control unit  121  may be arranged (always connected) inside the storage subsystem  101  or may be connected (maintenance connection) through the communication line  122  only when necessary. 
       FIG. 6  shows the outline of the flow of the processing of this embodiment. 
     In Step  601 , a user generates a “LUN access management table”, that associates mutually LUN (Logic Unit Number) stipulating the logical units (LU) existing inside the storage subsystem, WWN (N-Port-Name) of the host computers that may gain access to this LUN and GID (Group ID) allocated to the host computers when they are grouped into arbitrary groups, through the input unit  125  of the maintenance terminal equipment  123 . This table is held by the nonvolatile memory  119  inside the storage subsystem. LUN of this table is seen in each host computer. WWN of each host computer is known already. 
     In Step  602 , when each host computer executes login to the storage subsystem on the basis of the Fiber Channel protocol, the storage subsystem segments WWN of this host computer and S-ID from a PLOGI frame, retrieves simultaneously GID, to which this WWN belongs, from the LUN management access table generated by the user, generates a “WWN-S-ID-GID conversion table” and holds the table on the nonvolatile memory  119 . 
     When GID, to which WWN belongs, cannot be retrieved from the LUN access management table, it means that the user does not define the host computer group to which this WWN belongs. In this case, therefore, a non-defined ID is registered to GID of the WWN-S-ID-GID conversion table corresponding to this WWN. The storage subsystem executes this operation for all the PLOGI frames. 
     In Step  603 , the storage subsystem receives the frame inclusive of the Inquiry command that each host computer transmits in order to know the condition of the logical units inside the storage subsystem. Receiving this frame, the storage subsystem segments S-ID from the header of the frame and LUN as the object of the Inquiry command from the data field. Subsequently, the storage subsystem retrieves the WWN-S-ID-GID conversion table by using S-ID as the key and acquires GID corresponding to this S-ID. 
     In Step  604 , the storage subsystem retrieves LUN as the object of the Inquiry command from the LUN access management table by using the resulting GID as the key. In Step  605 , whether or not LUN corresponding to GID is acquired as a result of Step  604  is judged. When it is acquired, that is, when LUN corresponding to GID exists on the LUN access management table, the access to LUN by the host computer group to which the present host computer belongs is permitted. When LUN does not exist on the table, on the other hand, the access to LUN by the host computer group to which the present host computer belongs is rejected. 
     When the access to LUN by the host computer is permitted as a result of Step  605 , the storage subsystem executes in Step  606  setting of LUN package (setting that access is possible) to the Inquiry command generated by the host computer, and then transmits the Inquiry data. When the access to this LU is rejected, on the other hand, the storage subsystem executes in Step  607  setting of LUN non-package, that represents that setting is not permitted, to the Inquiry command generated by the host computer, and transmits the Inquiry data. 
     Receiving the Inquiry data, the host computer analyzes the frame. When it recognizes as a result of analysis that the access to virtual LUN of the storage subsystem is permitted, the host computer can subsequently continue to generate the command (I/O) request) to this LUN. In this case, the storage subsystem can continuously receive the command to LU while login from the host computer remains effective as expressed by Step  608 . 
     On the other hand, recognizing that the access to LUN is rejected, the host computer does not again access to LU so long as login to the storage subsystem remains effective. Hereinafter, a method for controlling access approval/rejection from the host computer to specific LUN inside the storage subsystem will be called “LUN security in the invention”. 
     Next, the technical problems will be explained in further detail with reference to  FIGS. 7 to 10 , and the invention will be explained with reference to  FIG. 11  and so forth. 
     First, generation of “LUN access management table” in Step  601  will be explained. It will be assumed that LUN security in the invention is managed for each port of the storage subsystem and that the host computer gains access to LU inside the storage subsystem through this port of the storage subsystem. The most simplified method disposes a table  701  shown in  FIG. 7 , that defines correspondence between WWN as the information for primarily identifying the host computer and LUN permitting the access of the host computer, inside the storage subsystem. This can be done without any problem when the host computer and the storage subsystem are connected through a dedicated line, and the function can be accomplished. 
     In Table  701 , the storage areas inside the storage subsystem are arbitrarily numbered under a single port and the logical unit number (LUN) are as such allocated to WWN of the host computers. In  FIG. 7 , the host computer WWN  702  is permitted to gain access to only LU  0  to LU  2 . The host computer WWN  703  is permitted to gain access to only LU  3  and LU  4  and the host computer WWN  704 , to only LU  5  and LU  6 . 
     Therefore, the host computers other than WWN  702  cannot gain access to LU  0  to LU  2  and LUN security of the invention can be accomplished. 
     However, under the latest complicated environment of use where devices such as hubs corresponding to the fiber channel and switches are interposed between the host computers and the storage subsystem, the table of  701  alone is not sufficient. For, when the host computers in most of the existing host computers fail to gain access to LU 0  of the storage subsystem connected to the host computers, the host computers do not at all make any inquiry for LU of the same system after LU 0  (since one system comprises 8 LU according to the SCSI-2 standard, LU 0  to LU 7  form the same system). 
     When the access is made from the host computers, the stipulation method of the table  701  does not permit the host computers  703  and  704  to gain access to LU  0  though LU N that permits the access is stipulated. In consequence, these host computers cannot refer to LUN that are stipulated by the table  701 . Such a phenomenon remarkably lowers utilization efficiency of an apparatus capable of providing abundant storage resources such as a disk array apparatus, and waste of the storage resources develops. 
     If the host computers  703  and  704  are permitted to gain access to LU  0  to prevent such a phenomenon, exclusion of LU  0  disappears and security is not insured. Provided that the access to LU  0  is permitted, too, it is difficult for the host computers  703  and  704  to share LU  0  due to the difference of formats of OS if they have different OS. 
     It will be assumed in  FIG. 7 , on the other hand, that a group of host computers having WWN  705  to  707  and capable of inquiring the existence to all LUN exist even when the definition of LU  0  does not exist under the port of the storage subsystem. Here, the host computer of WWN  705  is permitted to gain access to only LU  0 ,  1  and  7 , the host computer of WWN  706 , to only LU  3 ,  5  and  6 , and the host computer of WWN  707 , to only LU  2  and  4 . 
       FIG. 8  visually shows this condition. Host computers  802  to  804  correspond to the host computers having WWN  705  to  707  shown in  FIG. 7 . The host computers  802  to  804  are connected to the same port  806  of the storage subsystem through a hub, switch or router  805  corresponding to the Fiber Channel. When access object LUN is defined without a plan for each host computer  802  to  804  or LUN different from LUN previously allocated is allocated as the access object under such a use environment, the representation method of LUN loses flexibility in the storage subsystem such as  801  that represents LUN arbitrarily numbered under the same port inside the storage subsystem as such to the host computers, and LUN of the subordinates to this port appear as being dispersed as in the LU group  807  and become difficult to manage for use. 
     On the other hand, some of the latest host computers recognize nine or more LU under the subordinates to one port of the storage subsystem. When LUN security is executed between such host computers and the host computers that support only eight LUN such as LU  0  to  7  under one port of the storage subsystem as in the prior art, the following problems arise. 
     Referring to  FIG. 9 , the explanation will be given on the case where the host computers having WWN  902  and  904  have a mechanism for inquiring the existence to each LU though LU  0  does not exist under the port of the connected storage subsystem  1001 , and recognize up to 16 LU under the port of the connected storage subsystem  1001 . 
     It will be assumed that the host computer having WWN  903  can inquire the existence to each LU though LU  0  does not exist under the port of the connected storage subsystem  1001  but the range of LU that can be supported is 8, that is, LU  0  to  7 . As can be seen from the table  901 , the host computer having WWN  902  is permitted to gain access within the range of LU  0  to  5 , the host computer having WWN  903 , within the range of LU  6  to  10  and the host computer having WWN  904 , within the range of LU  11  to  15 .  FIG. 10  visually shows this condition. 
     Host computers  1002  to  1004  correspond to the host computers having WWN  902  to  904  in  FIG. 9 . The host computers  1002  to  1004  are connected to the same port  1006  of the storage subsystem  1001  through a hub, switch or router  1005  corresponding to the Fiber Channel. When LU inside the storage subsystem are allocated such as the LU group  1008  to the host computers  1002  to  1004 , only the range of LU  0  to  5  in the LU group  1008  appears as the access permitted object to the host computer A 1002 , and only the range of LU  11  to  15  in the LU group  1008  appears as the access permitted object to the host computer C  1004 . In either case, the object of LUN security can be achieved. However, because the host computer B  1003  can originally recognize up to 8 LU within the range of LU  0  to  7  under one port, it can make inquiry only within the range of the LU group  1007 . Therefore, even when the access to LU  6  to  10  is permitted in the table  901 , the host computer B  1003  can practically gain access to only LU  6  and  7 . This is the problem that occurs because LU arbitrarily numbered under the same port inside the storage subsystem is as such given. 
     In view of the problems described above, the present invention defines the “LUN access management table”  1101  shown in  FIG. 11 . The table  1101  is different from the table  701  shown in  FIG. 7  and the table  901  shown in  FIG. 9  that merely and directly allocate LUN arbitrarily numbered under the same port inside the storage subsystem to WWN. 
     The table  1101  associates WWN  1103  of the host computers having the possibility of access with GID (Group ID)  1102  allocated to these host computer groups when the user arbitrarily groups them, and imparts the logical unit number (LUN)  1104  that the user can set arbitrarily to these host computer groups in the storage areas capable of permitting the access inside the storage subsystem. 
     This table is generated in the port unit of the storage subsystem. In the storage subsystem defining this “LUN access management table”  1101 , LUN can be flexibly numbered in accordance with the desire of use by the user for the host computer groups the user has arbitrarily grouped, and can be given. 
     When OS is different, the logical format for LU is generally different, too. Therefore, LU cannot be shared among different OS. For this reason, in the “LUN access management table”  1101 , the groups the user registers are generally the host computer groups having the same OS mounted thereto. 
     When the desired use condition by the user (such as exchange bus construction, cluster construction among host computers, etc) are incorporated in further detail in this host computer group registration, so-called “user friendliness” can be further improved and at the same time, the storage area inside the storage subsystem can be utilized more efficiently. A detailed set example of the “LUN access management table”  1101  will be explained with reference to  FIG. 11 . 
     In the table  1101 , the host computer group having WWN  1112  to WWN  1114  has the same OS kind  1  mounted thereto and is categorized as Group A  1105 . The access to LU  0  to  3  inside the storage subsystem is permitted to this host computer group. Storage area numbers  0  to  3  (hereinafter called “# 0  to  3 ”) are allocated to these LU  0  to  3  inside the storage subsystem. 
     A host computer group having WWN  1115  to WWN  1117  has the same OS kind  2  and is categorized as Group B  1106 . Though it seems that the access to LU  0  to  3  is also permitted to the host computer group, the storage areas # 60  to  63  are allocated to these LU  0  to  3  inside the storage subsystem and exclusion is attained from the use storage areas of Group A  1105  described above. In this way, LUN security in the invention is achieved. 
     On the other hand, a host computer group having WWN  1118  to WWN  1121  is categorized as Group C  1107  but is a mixture of a host computer group having an OS kind  3  mounted thereto and a host computer group having an OS kind  4  mounted thereto. Generally, LU cannot be shared among computer groups because the logical formats are different if their OS kinds are different. When different OS kinds that can be shared exist, however, such grouping is possible. It seems that access to LU  0  to  5  is continuously permitted in Group C  107 . In practice, discrete storage areas # 7 ,  11 ,  70 ,  79 ,  87  and  119  are allocated. 
     A host computer group having WWN  1122  and  1123  is categorized as Group D  1108 , but the host computer group has different OS kinds mounted thereto, that is, an OS kind  5  and an OS kind  6 . The host computer group D  1108  has an advanced architecture capable of discretely recognizing other LU even when LU 0  dos not exist under the port to be accessed. Therefore, accessible LU is defined by a complicated representation method of LU  50 , LU  51  and LU  62 . Storage areas # 40 ,  99  and  100  are allocated to these accessible LU. 
     Group registration to the “LUN access management table”  1101  need not necessarily have a plurality of host computers. When it is desired to stipulate LU the access to which is singly permitted for the host computer WWN  1124 , for example, Group E  1109  including one host computer needs be registered. Resolution of the host computer for which access is permitted can be improved. The access to LU  0  to  1  is permitted to Group E  1109 , and the storage areas #  4  and  5  are allocated. 
     A solution of the problem of limitation that has become a problem in the recent SAN environment will be shown. The host computer of WWN  1125  and the host computer  1126  are categorized as Group F  1110  having an OS kind  7  that can recognize only 256 LU under the single port. It will be assumed that a user&#39;s request for recognizing 512 LU under the single port exists in practice. In this case, the host computer of WWN  1125  and the host computer  1126  are again registered as a separate Group G  1111 . Since both host computers can recognize maximum 256 LU, LU 0  to  255  for Group F  1110  and LU 0  to  255  for Group G  1111  are defined as access permitted LU. The storage areas # 0  to  255  are allocated to LU 0  to  255  of Group F  1110  and the storage areas # 256  to  512  are allocated to LU 0  to  255  of Group G  1111 . In this way, 512 LU are given without changing the existing processing, limitation and other functions of the host computers, and the LUN security function of the invention is accomplished. 
     Finally, a set pattern different from those described above will be explained. The host computers of WWN  1129  and WWN  1130  and the host computers of WWN  1131  and WWN  1132  are those host computers that have the same OS kind  8  but exist on different floors. It will be assumed that a manager handling these host computers desires to give files and applications by different access LUN to these four host computers but the entity given has the same content in the same storage area. In such a case, setting of Group H  1127  and Group I  1128  of the table  1101  may be employed. In this case, LU  0  and  1  is given to Group H  1127  and LU  4  and  5 , to Group I  1128 , but the practical reference destination storage area # is the same 10 and 11. The access from other host computers is rejected. In this way, the LUN security function according to the invention can be provided to satisfy the object of the manager. 
     Grouping of the host computers by using the “LUN access management table” of the invention and association of LUN have thus been given concretely. This can be visually shown in  FIG. 13 . The corresponding “LUN access management table”  1201  is shown in  FIG. 12 . 
     Referring to the table  1201  having GID  1202  and WWN  1203 , the LU group  1204  permitting the access to each host computer group  1205  to  1207  have practically an entirely random arrangement as represented by the storage area group  1303  shown in  FIG. 13 . However, when the LU group  1204  is mapped to the LU group  1204  of the table  1201 , it takes the condition of the LU group  1302  shown in  FIG. 13 , and LU can be given without causing the host computer groups  1307  to  1309  to be aware of the practical arrangement condition  1303  of the storage area groups inside the storage subsystem. Incidentally, the host computer groups  1307  to  1309  in  FIG. 13  correspond to the host computer groups  1205  to  1207  in  FIG. 12  and are connected by a fiber channel fabric  1306 , hub switch  1304  and port  1304  to storage subsystem  1301 . 
     In this way, LUN security in the invention can be accomplished without changing the existing processing, limitation and other functions of the host computers, and flexible and efficient utilization of the storage subsystem resources becomes possible. 
     Because grouping of the host computers is accomplished as described above, connection interface information  1310  to  1312  ( FIG. 13 ) can be set for each host computer group under the single port inside the storage subsystem  1301 . 
     Connection interface information represents, for example, reception I/O of the storage subsystem, the depth of a reception queue and the response content of Inquiry. In the storage subsystems according to the prior art, interface information under the single port is generally single. 
     As represented by Steps  1401  to  1403 , the “LUN access management table”  1101  or  1201  according to the invention is defined for all the ports of the storage subsystem and is then stored in the nonvolatile memory inside the storage subsystem. Since the table is thus stored in the nonvolatile memory, it does not extinguish even when the power source of the storage subsystem is cut off. The table may also be stored in a predetermined storage device  115  (storage device  101  in  FIG. 1 ). 
     Next, the login processing from the host computer to the storage subsystem will be explained. In this embodiment, GID (Group ID) is acquired from WWN primarily identifying the host computer through a series of login processing and is allowed to correspond to S-ID that primarily identifies the host computers that are used after this login. 
     When the host computer is activated, the storage subsystem receives the PLOGI frame in Step  1501  in  FIG. 15 . Receiving the PLOGI frame, the storage subsystem acquires S-ID of the host computer from the frame header in Step  1502  and WWN (N-Port-Name) of the host computer from the data field in Step  1503 . Subsequently, the storage subsystem generates and records this WWN, S-ID and GID (Group ID) to “WWN-S-ID-GID conversion table”  1601  shown in  FIG. 16  in Step  1504 , and holds them in the nonvolatile memory inside the storage subsystem in Step  1505 . Here, GID is acquired when the “LUN access management table” generated by the user is retrieved by using WWN as the key as described above. The “WWN-S-ID-GID conversion table”  1601  is generated for each of the storage subsystems. 
     When the host computer having WWN registered to this table subsequently transmits the command, the storage subsystem acquires S-ID from its frame header, and can know GID corresponding to S-ID by using the “WWN-S-ID-GID conversion table”  1601 . Storing this “WWN-S-ID-GID conversion table”  1601  in the nonvolatile memory, the storage subsystem transmits an ACC frame representing that login of the host computer is approved, in Step  1506 . Receiving the ACC frame from the storage subsystem, the host computer can thereafter generate the Inquiry command to the storage subsystem. 
     Next, Inquiry command reception from the host computer and the security response of the storage subsystem to the former will be explained.  FIGS. 17 and 18  show the flow of a series of processing, and  FIG. 19  shows the reference relation of each table and parameters used in the flow of processing. 
     In Step  1701  in  FIG. 17 , the storage subsystem receives an FCP-CMND frame stipulated to the Fiber Channel from the host computer. Then, the storage subsystem analyzes the content of the data frame of this FCP-CMND in Step  1702 . 
     Subsequently, the storage subsystem checks whether or not the content of this FCP-CMND is the Inquiry command in Step  1703 . When it is not the Inquiry command, the storage subsystem executes a processing corresponding to the command in Step  1704 . When it is the Inquiry command, on the other hand, the storage subsystem acquires S-ID of the host computer from the header of this FCP-CMND frame in Step  1705  and then acquires object LUN from FCP-LUN of the data field of this FCP-CMND in Step  1706 . 
     In subsequent Step  1707 , the storage subsystem retrieves the “WWN-S-ID-GID conversion table”  1601  shown in  FIG. 16  by using resulting S-ID as the key and acquires GID corresponding to this S-ID. The flow up to this step represents the reference operation of Steps  1901 ,  1902  and  1903  in  FIG. 19 . 
     When GID for this S-ID is not retrieved from the table  1601  in Step  1903 , the user does not register LUN, the access of which is permitted to the host computer, and the access to LUN requested from the host computer is rejected. 
     In subsequent Step  1708  ( FIG. 17 ), the information of the access-permitted LUN is acquired for this GID. In Step  1801  ( FIG. 18 ), whether or not LUN acquired from the Inquiry command of the host computer having this GID is registered as the access-permitted LUN on the “LUN access management table” is judged. The flow up to this step represents the reference operation of Steps  1904  and  1906  in  FIG. 19 . 
     The reference operation in Steps  1904  to  1906  retrieves LUN the access to which is permitted from S-ID, by using GID as the key. Since this GID is the attribute of the group of individual WWN, the ratio of GID to access-permitted LUN generally equals to the ratio of multiple to 1. In comparison with the relation in the prior art, that is, the ratio of WWN of LUN security using WWN as key to access-permitted LUN equals to unity, the resolution capacity on the side of the host computer drops but the retrieval operation becomes easier and has generally a higher speed. 
     When LUN acquired in Step  1706  is registered to the entry of the “LUN access management table” ( FIGS. 11 and 12 ), the access from the host computer to this LUN is permitted. Therefore, in Step  1802  ( FIG. 8 ), the storage subsystem sets “000” of the binary digit to the qualifier of the Inquiry data for the response to the host computer and the device type code of the storage subsystem to the device type. 
     On the other hand, when LUN acquired in Step  1706  is not registered as virtual LUN to the corresponding entry of the “LUN access management table”, the access from the host computer to this virtual LUN is rejected. Therefore, in Step  1803 , the storage subsystem sets “001” or “011” of the binary digit to the qualifier of the Inquiry data for the response to the host computer and “1F” of the hexadecimal digit to the device type. 
     Next, in Step  1804 , the storage subsystem sets the Inquiry data for response to the FCP-DATA frame and transmits it to the host computer. In subsequent Step  1805 , the storage subsystem transmits an FCP-RSP frame representing the finish of the response of the Inquiry command of the host computer. 
     In succession to Steps  1802  and  1804  in  FIG. 18 , the host computer that receives FCP-DATA inclusive of the Inquiry data from the storage subsystem judges that the access to the corresponding LUN is possible, and can continue the access without inquiring again thereafter access approval/rejection of this LUN. Here, LUN to which the host computer gains access is practically the storage area # inside the storage subsystem that is primarily associated with LUN. 
     On the other hand, the host computer that receives FCP-DATA inclusive of the Inquiry data from the storage subsystem in succession to Steps  1803  to  1804  judges that the access to this LUN is not possible, and does not inquire again access approval/rejection to this LUN and does not try to gain access, either. 
     In this embodiment, it is only at the time of generation of the Inquiry command that the host computer inquires access approval/rejection to LUN. In other words, while login remains effective, this inquiry need not be repeated. In consequence, strong LUN security can be accomplished without lowering data transfer efficiency between the host computer and the storage subsystem. 
     Incidentally, when a function f having a correlation “storage area #=f(GID, LUN)” is set in mapping from LUN to the storage area # inside the storage subsystem, an effective storage area # is outputted for effective GID and LUN values but is not outputted for other values. 
     Here, f(n, m) is a function for effecting mapping conversion of LUN given to the host computer to the storage area # inside the storage subsystem by using GID and LUN as the parameters. Consequently, in the Write command and the Read command subsequent to the Inquiry command, the check of access approval/rejection can be executed with minimum overhead during the conversion operation from designated LUN to the storage area # without calling for the retrieval operation of Steps  1901  to  1906 . 
     As described above, when the method is employed that handles a plurality of host computer groups under the same port, and allows the user to arbitrarily select and set the allocation of LU in the group unit, LUN security can be accomplished with high-speed judgment logic and with high utilization efficiency of the memory area inside the storage subsystem without changing the existing processing, limitation and other functions on the side of the host computer. 
     This embodiment has been described about the Fiber Channel by way of example. To practice the invention, however, the invention is not particularly limited to the Fiber Channel, and the kind of the protocol environment is not restrictive so long as it can provide equivalent functions. As to the storage subsystem, too, this embodiment has been described mainly on the assumption of the disk array apparatus, but the apparatus can be ordinary magnetic disk apparatuses, and optical disk library and tape library capable of interfacing the storage system can replace this disk array apparatus. 
     The invention can be executed among a plurality of storage subsystems in consideration of recent virtualization of the SAN environment. In this case, the invention has the construction in which definition and set items of each of the tables described above are executed on one storage subsystem, communication paths are disposed so that the definition/setting can be transmitted to the logical units inside other storage subsystems, and one storage subsystem executes centralized control. 
     Such centralized control and definition of necessary tables need not always be executed on a specific storage subsystem but may be provided to program processing on the host computer or to internal processing on a switching hub or a router so long as the storage subsystems are connected by a common interface such as the Fiber Channel and the logical units inside a plurality of storage subsystems can be recognized. 
     When LUN security according to the invention is accomplished among a plurality of storage subsystems connected by the network such as the Fiber Channel, the storage subsystems having the ports for connecting the storage subsystems including the access-permitted logical units and the host computer groups, the switch or the router need not be built in the same casing. 
     The invention uses the management table inside the storage subsystem and gives the logical unit inside the storage subsystem to the host computer groups that are arbitrarily grouped by the user in accordance with the desired form of operation of the user, limits access approval/rejection to LU inside the storage subsystem in the group unit and at the same time, can provide the security function capable of setting the interface of connection in the group unit under the single port of the storage subsystem without changing the existing processing, limitation and other functions of the computer. 
     Furthermore, since the access approval/rejection judgment to LU inside the storage subsystem can be known at the point of time of generation of the inquiry command such as the Inquiry command and this judgment need not be thereafter repeated. Therefore, the strong security function to LU can be secured while the storage subsystem is kept operated with high performance. 
     It should be further understood by those skilled in the art that the foregoing description has been made on embodiments of the invention and that various changes and modifications may be made in the invention without departing from the spirit of the invention and the scope of the appended claims.