Abstract:
This invention provides a user or an operator with a management apparatus or method for displaying logical connection information between an interface connected to a computer and a switch and a storage system or a logical unit in the storage system in a virtual storage system, wherein the switch receives a first access request from said computer, converts said first access request to a second access request to one of said plural storage systems, and sends said second access request to one of said plural storage systems or one logical unit.

Description:
This is a divisional application of U.S. Ser. No. 10/769,922, filed Feb. 3, 2004, now U.S. Pat. No. 6,910,102; which is a continuation application of U.S. Ser. No. 10/405,645, filed on Apr. 3, 2003, now U.S. Pat. No. 6,851,029; which is a continuation application of U.S. Ser. No. 10/095,581, filed Mar. 13, 2002, now U.S. Pat. No. 6,701,411; which is a continuation application of U.S. Ser. No. 09/468,327, filed on Dec. 21, 1999, now U.S. Pat. No. 6,542,961. This application is related to U.S. Ser. No. 10/095,578, filed Mar. 13, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a disk control system for controlling a plurality of disk devices and relates in particular to a method for improving the high speed operation of the disk control system, achieving a lower cost and improving the cost performance. 
     A diskarray system for controlling a plurality of disk devices is utilized as a storage system in computers. A diskarray system is for instance disclosed in “A Case for Redundant Arrays of Inexpensive Disks (RAID)”; In Proc. ACM SIGMOD, June 1988 (Issued by Cal. State Univ. Berkeley). This diskarray operates a plurality of disk systems in parallel and is a technique that achieves high speed operation compared to storage systems utilizing disks as single devices. 
     A method using the fabric of a fiber channel is a technique for mutually connecting a plurality of hosts with a plurality of diskarray systems. A computer system using this technique is disclosed for instance in “Serial SCSI Finally Arrives on the Market” of Nikkei Electronics, P. 79, Jul. 3, 1995 (No. 639) as shown in  FIG. 3 . In the computer system disclosed here, a plurality of host computers (hereafter simply called hosts) and a plurality of diskarray systems are respectively connected to a fabric device by way of fiber channels. The fabric device is a switch for the fiber channels and performs transfer path connections between the desired devices. The fabric device is transparent to (or passes) “frame” transfers which age packets on the fiber channel. The host and diskarray system communicate between two points without recognizing the fabric device. 
     SUMMARY OF THE INVENTION 
     In diskarray systems of the conventional art, when the number of disk devices were increased in order to increase the storage capacity and achieving a controller having high performance matching the number of disk units was attempted, the internal controller buses were found to have only limited performance and likewise, the processor performing transfer control was also found to have only limited performance. In order to deal with these problems, the internal buses were expanded and the number of processors was increased. However, attempting to solve the problem in this manner made the controller structure more complex due to the control required for a greater number of buses and caused increased overhead and complicated software control due to non-exclusive control of data shared between processors, etc. The rise in cost consequently became extremely high and performance reached its limits so that cost performance was unsatisfactory. Though the cost for this kind could be justified in terms of performance in a large scale system, in systems not on such a large scale the cost did not match performance, expandability was limited and the development period and development costs increased. 
     The overall system storage capacity and performance can be increased by connecting a plurality of diskarray systems in parallel with a fabric device. However, in this method, there is absolutely no connection between the diskarray systems, and access concentrated on a particular diskarray system cannot be distributed among the other devices so that high performance cannot be achieved to actual operation. Also, the capacity of a logical disk device (hereafter logic unit) as seen from the host is limited to the capacity of one diskarray system so that a high capacity logic unit cannot be achieved. 
     In an attempt to improve diskarray system reliability, a diskarray system can be comprised of a mirror structure where, in two diskarray systems, the host unit has a mirroring function. However, this method requires overhead due to control required of the mirroring by the host and also has the problem that performance is limited. This method also increases the load that the system administrator must supervise since many diskarray systems are present inside the system. The maintenance costs thus increase since a large number of maintenance personnel must be hired and maintenance fees must be paid for each unit. The plurality of diskarray systems and fabric devices are further all autonomous devices so that the settings must be made by different methods according to the respective device, creating the problem that operating costs increase along with a large increase in operating time and system administrator training time, etc. 
     In order to resolve these problems with the related art, this invention has the object of providing a disk storage system capable of being structured according to the scale and requirements of the computer system, and a disk storage system that responds easily to needs for high reliability and future expansion. 
     The disk storage system of this invention contains a storage device having a record medium for holding the data, a plurality of storage sub-systems having a controller for controlling the storage device, a first interface node coupled to a computer using the data stored in the plurality of storage sub-systems, a plurality of second interface nodes connected to any or one of the storage sub-systems, a switch connecting between a first interface node and a plurality of second interface nodes to perform frame transfer between a first interface node and a plurality of second interface nodes based on node address information added to the frame. 
     The first interface node preferably has a configuration table to store structural information for the memory storage system and a processing unit to analyze the applicable frame in response to the frame sent from the computer, converts information relating to the transfer destination of that frame based on structural information held in the configuration table, and transfers that frame to the switch. Further, when transmitting a frame, the first interface node adds the node address information about the node that must receive the frame, to that frame. A second interface node then removes the node address information from the frame that was received, recreates the frame and transfers that frame to the desired storage sub-system. 
     In the embodiment of this invention, the disk storage system has a managing processor connecting to the switch. The managing processor sets the structural information in the configuration table of each node according to the operator&#39;s instructions. Information for limiting access from the computer is contained in this structural information. 
     In another embodiment of this invention, the first interface node replies to the command frame sent from the computer instructing the writing of data, makes copies of that command frame and the following data frames, adds different nodes address information to each frame so the received frame and the copied command frames will be sent to the different respective nodes and sends these frames to the switch. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing the structure of the computer system of the first embodiment of this invention. 
         FIG. 2  is block diagram of the diskarray subset of the first embodiment. 
         FIG. 3  is block diagram of diskarray switch of the first embodiment. 
         FIG. 4  is a block diagram of the crossbar switch of the diskarray switch of the first embodiment. 
         FIG. 5  is block diagram of the host I/F node for the diskarray switch of the first embodiment. 
         FIG. 6A  is sample diskarray system configuration table. 
         FIG. 6B  is sample diskarray system configuration table. 
         FIG. 7  is a block diagram of the frame of the fiber channel. 
         FIG. 8  is a block diagram of the frame header of the fiber channel. 
         FIG. 9  is a block diagram of the frame payload of the fiber channel. 
         FIG. 10  is a model view showing the sequence of frames sent by way of the fiber channel during read operation from the host. 
         FIG. 11  is a model view showing the interactive relationship of the host-LU, the LU for each diskarray subset, as well as each diskarray unit. 
         FIG. 12  is a block diagram of the S packet. 
         FIG. 13A through 13C  are flowcharts of the processing in the host I/F node during write processing. 
         FIG. 14  is a block diagram showing a plurality of diskarray switches in a cluster-connected diskarray system. 
         FIG. 15  is a block diagram of the computer system of the second embodiment of this invention. 
         FIG. 16  is a block diagram of the diskarray switch IC of the fourth embodiment of this invention. 
         FIG. 17  is a block diagram of the computer system of the fifth embodiment of this invention. 
         FIG. 18  is a screen configuration view showing a typical display of the logic connection structure. 
         FIG. 19  is a model diagram showing the frame sequence in the sixth embodiment of this invention. 
         FIGS. 20A through 20D  are flowcharts showing the processing on the host I/F node during the mirroring write processing in the sixth embodiment of this invention. 
         FIG. 21  is an address spatial diagram of the diskarray system for the seventh embodiment of this invention. 
         FIG. 22  is a flowchart showing the processing in the host I/F node of the seventh embodiment of this invention. 
         FIG. 23  is a block diagram of the disaster recovery system of the eight embodiment of this invention. 
         FIG. 24  is a descriptive view of the alternative path setup. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       FIG. 1  is a block diagram showing the structure of the computer system of the first embodiment of this invention. In the figure, reference numeral  1  denotes a diskarray system, and  30  is the (host) computer connected to the diskarray system. The diskarray system  1  contains a diskarray subset  10 , a diskarray switch  20  and a diskarray system configuration manager  70  for handling the configuration of the overall disarray system. The diskarray system  1  further has a communication interface (communication I/F)  80  between the diskarray switch  20  and the diskarray system configuration manager  70 , and also between the diskarray subset  10  and the diskarray system configuration manager  70 . A host  30  and the diskarray system  1  are connected by a host interface (host I/F))  31 . The host I/F  31  is connected to the diskarray switches  20  of the diskarray system  1 . The diskarray switch  20  and the diskarray subset  10  inside the diskarray system  1  are connected by the diskarray interface (diskarray I/F  21 ). 
     The hosts  30  and the diskarray subsets  10  are shown as four units each however this number is optional and is not limited. The hosts  30  and the diskarray subsets  10  may also be provided in different numbers of units. The diskarray switches  20  in this embodiment are duplexed as shown in the drawing. Each host  30  and each diskarray subset  10  are connected to both of the duplexed diskarray switches  20  by the respective host I/F 31  and a diskarray I/F 21 . Thus even if one of the diskarray switches  20 , the host I/F  31  or the diskarray I/F 21  is broken, the other diskarray switches  20 , the host I/F  31  or the diskarray I/F 21  can be utilized to allow access from the host  30  to the diskarray system  1 , and a high amount of usage can be achieved. However, this kind or duplication or duplexing is not always necessary and is selectable according to the level of reliability required by the system. 
       FIG. 2  is block diagram of a diskarray subset  10  of the first embodiment. The reference numeral  101  denotes the host adapter for interpreting the commands from the host system (host  10 ), executing the cache hit-miss decision and controlling the data transfer between the host system and the cache. The reference numeral  102  denotes the cache memory/shared memory that comprises the cache memory for performing high speed disk data access and a shared memory for storing data shared by the host adapters  101  and the lower adapters  103 . The reference numeral  104  denotes a plurality of disk units stored inside the diskarray subset  10 . Reference numeral  103  is the lower adapter for controlling a disk unit  104  and controlling the transfer of data between the disk unit  104  and the caches. Reference numeral  106  is the diskarray subset configuration manner to perform communications between the diskarray system configuration manager  70  and the overall diskarray system  1 , and also manage the structural parameter settings and reporting of trouble information, etc. The host adapter  101 , the cache memory/shared memory  102 , and the lower adapter  103  are respectively duplexed here. The reason for duplexing is to attain a high degree of utilization, just the same as with the diskarray switch  20  and is not always required. Each disk unit  104  is also controllable from any of the duplexed lower adapters  103 . In this embodiment, the cache and shared memories jointly utilize the same memory means in view of the need of low costs however the caches and shared memories can of course be isolated from each other. 
     The host adapter  101  comprises an host MPU 1010  to execute control of the adapter  101 , an host system or in other words a diskarray I/F controller  1011  to control the diskarray switches  20  and the connecting I/F which is the diskarray I/F 21 , and an host bus  1012  to perform communications and data transfer between the cache memory/shared memory  102  and host MPU 1010  and the diskarray I/F controller  1011 . The figure shows one diskarray I/F controller  1011  for each host adapter  101  however a plurality of diskarray I/F controllers  1011  can also be provided for each one host adapter. 
     The lower adapter  103  contains a lower MPU 103  to execute control of the lower adapter  103 , a desk I/F controller  1031  to control the disk  104  and interface which is the disk I/F, and a lower bus  1032  to perform communications and data transfer between the cache memory/shared memory  102  and host MPU 1030  and the diskarray I/P controller  1031 . The figure shows four diskarray I/F controllers  1031  for each lower adapter  103  however the number of diskarray I/F controllers is optional and can be changed according to the diskarray configuration and the number of disks that are connected. 
       FIG. 3  is block diagram of the diskarray switch  20  of the first embodiment. The diskarray switch  20  contains a Managing Processor (MP) which is a processor for performing management and control of the entire diskarray swatch, a crossbar switch  201  for comprising n×n mutual switch paths, a diskarray I/F node  202  formed for each diskarray I/F 21 , a host I/F node  203  formed for each host I/F  31 , and a communication controller  204  for performing communications with the diskarray system configuration manager  70 . The reference numeral  2020  denotes a path for connecting the diskarray IF node  202  with the crossbar switch  201 , a path  2030  connects the host I/F node  203  and the crossbar switch  201 , a path  2040  connects with the other diskarray switch  20  and other IF for forming clusters, a path  2050  connects the MP 200  with a crossbar switch  201 . 
       FIG. 4  is a block diagram showing the structure of the crossbar switch  201 . A port  2010  is a switching part (SWP) for connecting the paths  2020 ,  2030 ,  2050  and cluster I/F  2040  to the crossbar switch  201 . The switching ports  2010  all have the same structure and perform switching control of the transfer paths to other SWP from a particular SWP. The figure shows on SWP however identical transfer paths exist between all the SWP. 
       FIG. 5  is a block diagram showing the structure of the host I/F node  203 . In this embodiment, use of a fiber channel is assumed for both the diskarray I/F 21  and the host I/F 31  in order to provide a specific description. The host I/F 31  and the diskarray I/F 21  can of course be implemented with interfaces other than fiber channels. By utilizing an identical interface, the host I/F node  203  and the diskarray I/F node  202  can both have the same structure. In this embodiment, the diskarray I/F node  202  has the same structure as the host I/F node  203  as shown in the figure. Hereafter, the host I/F node  203  will be described by using an example. A Searching Processor (SP) searches for what frame to connect the fiber channel frame (hereafter simply called frame) to, an Interface Controller (IC)  2023  transmits and receives the frames with the host  30  (the diskarray subset  10  when using the diskarray I/F node  202 ), a Switching Controller (SC)  2022  performs conversion based on results found by the SP 2021  for frames received by the IC 2023 , a Switching Packet Generator (SPG)  2024  packetizes the frame converted by the SC 2021  into a configuration that can pass the crossbar switch  201  to transfer to other nodes, a Frame Buffer (FB)  2025  temporarily stores the received frame, an Exchange Table (ET)  2026  supervises use of exchange numbers for identifying a plurality of frame strings corresponding to a disk access request command (hereafter simply called command) from one host, and a Diskarray Configuration Table (DCT)  2027  stores structural information for a plurality of diskarray subsets  10 . 
     Each structural section of the diskarray switch  20  are preferably all comprised of hardware logic from the viewpoint of performance. However, program control utilizing general purpose processors is allowable for the SP 2021  and the SC 2022  functions if the specified performance can be achieved. 
     Each diskarray subset  10  has disk units  104  as one or a plurality of logical disk units. These logical disk units are referred to as Logical Units (LU). The LU need not correspond in a ratio of one to one, to the logical disk units  104  and one disk unit  104  can be comprised of a plurality of LU or one LU can comprise a plurality of disk units  104 . One LU is recognized as one disk device as seen externally of the diskarray unit  10 . In this embodiment, a logical LU is comprised further by a diskarray switch  20  and the host  30  functions to access this LU. In these specifications, when one LU is recognized as one LU by the host  30 , then the LU is called independent LU (ILU) and when a plurality of LUs are recognized as one LU by the host  30 , then the one LU recognized by the host  30  is called combined LU (CLU). 
       FIG. 11  shows the address spatial relation for each level when one combined LU (CLU) is comprised of four LUs ox four diskarray subsets. In the figure, the numeral  1000  indicates an LU address space for one combined LU (CLU) of the diskarray system  1  as seen from the host “#2”, the numeral  1100  is an LU address space for the diskarray subset  10 , the numeral  1200  indicates an address space for the disk unit  104  (Here, shown only for the diskarray subset #0.) The LU for each diskarray subset  10  is comprised as a RAID 5 (Redundant Arrays of Inexpensive Disks Level 5) type diskarray, by four disk units  104 . Each diskarray subset  10  has an LU with respective capacities of n0, n1, n2, n3. Each diskarray switch  20  combines the address spaces held by these four LU to obtain a combined capacity (n0+n1+n2+n3) and achieve a combined LU (or CLU) recognized from the host  30 . 
     In this embodiment, when for instance the host #2 is accessing the region A 1001 , an access request is made specifying the region A 1001 , and this access request is converted by the diskarray switch  20  into a request for accessing the region A′  1101  of the LU of the diskarray subset #0 and this request then sent to the diskarray subset #0. This diskarray subset #0 then performs access and mapping of the region A′  1101  onto of the region A″  1202  on the disk unit  104 . The mapping between the address space  1000  and the address space  1100  is based on structural information held in the DCT 207  in the diskarray switch  20 . The details of this processing are related later on. The mapping performed in the diskarray subset is a technical method already well known in the prior art so a detailed explanation is omitted here. 
     In this embodiment, the DCT 207  contains a Diskarray System Configuration Table and Diskarray Subset Configuration Tables. The structure of the Diskarray System Configuration Table is shown in  FIG. 6A  and the structure of the Diskarray Subset Configuration Tables are shown in  FIG. 6B . 
     As shown in  FIG. 6A , the Diskarray System Configuration Table  20270  has a Host-LU Configuration Table  20271  holding information showing the structure of the host-LU, and a Diskarray I/F Node Configuration Table  2072  showing the related connections of the diskarray subset  10  and the diskarray I/F node  202  of the diskarray switch  20 . 
     The Host-LU Configuration Table  20271  has LU information (LU Info.) relating to the condition and Host LU of the diskarray subset  10  LU, which is information showing the LU type, CLU class, CLU stripe size and Host-LU indicating the affiliation of the LU and the Host-LU No. which is a number for identifying that LU. The LU Type in the table is information on the LU type showing that the Host-LU is a CLU or one LU. The CLU class is information showing the class is any one of “Joined”, “Mirrored” or “Striped” when the LU type of this Host-LU is shown to be a CLU. Here, “Joined” indicates as shown in  FIG. 11  the CLU is one large memory space consisting of a group of LU connected together. As related later in the sixth embodiment, “Mirrored” indicated two LU achieved by a duplexed LU. As related later on in the seventh embodiment, “Striped” indicates an LU stored with data distributed into a plurality of these LU. When the CLU Stripe Size is shown by ‘Striped’ for the CLU class, then the striping size (A block size showing the units the data is distributed in.) is indicated. The status shown in the Condition box is one of four types consisting of “Normal”, “Warning”, “Fault” and “Not Defined”. Of these types, “Normal” indicates the Host-LU status is correct. “Warning” indicates contraction is being performed for reasons such as problems occurring in a disk unit corresponding to an LU comprising this Host-LU. “Fault” indicates that this Host-LU cannot be operated due to a problem in the diskarray subset  10 . The “Not Defined” type indicates the Host-LU is not defined for the corresponding Host-LU No. The LU Info contains information specifying the diskarray subset  10  affiliated with that LU, the LUN inside the diskarray subset, as well as information showing the size for LU that comprise this Host-LU. When the Host-LU is an ILU, then information for the sole LU is registered. When the Host-LU is a CLU, then information relating to all the respective LU comprising that CLU are registered. In the Figure for instance, a Host-LU with a Host-LU No. of “0” is a CLU comprised from four LU that are LUN “0” of the diskarray subset “#0”, LUN “0” of the diskarray subset “#1”, LUN “0” of the diskarray subset “#2”, and LUN “0” of the diskarray subset “#3”. As can be seen in the table, this CLU is in the “Joined” CLU class. 
     The diskarray I/F node configuration table  20272  contains information on what diskarray I/F node  202  of diskarray switch  20  is connected to each port of the diskarray subset  10  connected to the diskarray I/F  21 . More specifically, this table holds the Subset NO. specifying the diskarray subset  10 , the Subset Port No. specifying the port, the Switch No. specifying the diskarray switch  40  connected to that port, and an I/F Node No., specifying the diskarray I/F node  202  of the diskarray switch  20 . When the diskarray subset  10  has a plurality of ports, information is set for each of those ports. 
     As shown in  FIG. 6B  the diskarray subset configuration table has a plurality of tables  202720  through  202723  corresponding to each of the diskarray subsets  10 . These tables include the RAID Group Configuration Table  202730  holding information showing the structure of the RAID Group inside the diskarray subset  10 , and the LU Configuration Table  202740  holding information showing the structure of the LU inside the diskarray subset  10 . 
     The RAID Group Configuration Table  202730  has a Group No. showing the number added to the RAID Group, a level showing the RAID Level of that RAID Group, and Disks with information showing the number of disk comprising that RAID Group. When that RAID Group is comprised of striping such as for RAID Level 0, 5, then information showing that Stripe Size is included. As shown for instance, in the figure in the table, a RAID Group “0” is a RAID Group comprised of four disk units. The RAID Level is 5 and the Stripe Size is 0. 
     The LU Configuration Table  202740  has an LU No. showing the number (LUN) added to the LU, a RAID Group showing now that LU is configured in the RAID Group, a Condition showing the status of the LU, a Size showing the size (Capacity) of that LU, a Port showing what ports of the diskarray subset  10  are capable of providing access, and also an Alt. Port showing port that can be used as alternates for that Port No. The status showing the condition are of four types just as with the Host-LU and comprise “Normal”, “Warning” “Fault” and “Not Defined”. The port specified by information set in the Alt. Port is utilized when a problem occurs in the port specified with information set in the Port (item) however can also be used just for accessing the same LU from a plurality of ports. 
       FIG. 7  is a diagram of the frame for the fiber channel. A frame  40  of the fiber channel has an SOF (Start Of Frame) showing the beginning portion of the frame, a frame header  401 , a frame payload  402  which is a segment storing data for transfer, a CRC (Cyclic Redundancy Check)  403  which is a bit error detection code, and a EOF (End Of Frame) showing the end of the frame. The frame header  401  has the structure shown in  FIG. 8 . The ID of the frame transfer originator (S_ID), the ID for the frame transfer destination (D_ID), Exchange IDs respectively specified by the Exchange Originator and the Exchange Responder (OX_ID, RX_ID), and the Sequence ID for specifying the frame group within the exchange (SEQ_ID) are all stored in the frame header  401 . In this embodiment, the ID assigned as S_ID to the host  30  in the frame issued from the host  30  are also used as the ID assigned to the port of the diskarray switch  20  as the D_ID. One pair of Exchange ID (OX_ID, RX_ID) are assigned for one host command. When a plurality of data frames must be issued for the same Exchange, then an identical SEQ_ID is assigned to all of these data frames, and each one is identified as Sequence Count (SEQ_CNT). The Frame Payload  402  has a maximum length of 2112 byte and the contents stored in each type frame are different. In the case for instance of FCP_CMD frame related later on, the Logical Unit Number (LUN) of the SCSI and the Command Description Block (CDB) are stored as shown in  FIG. 9 . The CDB contains the command bytes required to access the disk (diskarray), the transfer start logic address (LBA) and the transfer length (LEN). 
     The operation of the disk address system of this embodiment is described next. 
     In order to use the diskarray system, the setting of structural information of the diskarray subset  10  must be made for the diskarray switch  20 . The system administrator can acquired structural setup information for the diskarray switch  20  and the diskarray subset  10  from a management console  5  by way of the diskarray configuration manager  70 . The administrator can make different kinds of required entries of setup information such as logic unit structural setup for the desired system structure, RAID level settings, alternative path settings for use when trouble occurs. The diskarray configuration manager (means)  70  can receive that setting information, and transfer that setting information to the each diskarray subset  10  and diskarray switch  20 . The entry of setup information on the management console  5  is described separately in the fifth embodiment. 
     In the diskarray switch  20 , the communications controller  204  acquires the setup information and sets the structural information such as the address space information or each of the diskarray subsets  10  by means of the MP 200 . The MP 200  distributes the structural information of the diskarray subset  10  to the each of the host I/F nodes  203  and the diskarray I/F nodes  202  by way of the crossbar switch  201 . When the nodes  202  and  203  receive this information, the SP 2021  stored this structural information in the DCT 2027 . In the diskarray subset  10 , the diskarray subset configuration manager (means)  106  acquires the setup information and stores it in the shared memory  102 . The host MPU 1010  and the lower MPU  1030  refer to this setup information in the shared memory  102  and perform configuration management. 
     The operation when the read command is issued in described next for the diskarray system  1  with a host “#2”.  FIG. 10  is a model view showing the sequence of frames sent by way of the fiber channel during read operation from the host  FIG. 13A through 13C  are flowcharts of the processing in the host I/F node  203  during write processing In the following description, it is assumed the host “#2” is accessing the storage area A 1001  in  FIG. 11 . The actual storage area A″ corresponding to the storage area A 1101  is present in the address space of the disk unit #2 comprising the LU for LUN=0 of the diskarray subset “0”. In the definition of the LU comprising the address space  1000 , in the Configuration Table  20271 , the LU Type is defined as “CLU” and the CLU Class is defined as “Joined”. 
     During reading of data, the host  30  issues a command frame “FCP_CMD” stored with the read command, to the diskarray switch  20  (arrow (a) in  FIG. 10 ). The host I/F node “#2” of the diskarray switch  20  receives the command frame “FCP_CMD” (step  20001 ) by way of the host I/F  31  from the IC 2023 . The IC 2023  transfers the command frame to the SC 2022 . The SC 2022  temporarily stores the received command frame in the Frame Buffer (FB)  2025 . At that time, the SC 2022  calculates the CRC of the command frame and inspect the received information to determine if it is correct. If an error is found in the CRC inspection, the SC 2022  reports the error to the IC 2023 . When the IC 2023  the error report from the SC 2022 , a report of the CRC error is made to the host  30  by way of the host I/F 31  (step  20002 ). 
     When the CRC inspection shows that the information is correct, the SC 2022  reads the frame held in the FB 2021 , recognizes this frame as the command frame, and analyzes the Frame Header  401  (step  20003 ). The SC 2022  then instructs the SP 2021  and registers the Exchange information such as S_ID, D_ID, OX_ID in the ET 2026  (step  20004 ). Next, the SC 2022  analyzes the frame payload  402  and acquires the LUN and CDB specified by the host  30  (step  20005 ). The SC 2021  searches the DCT 2020  at the instruction of the SC 2022  and acquires the structural information of the diskarray subset  10 . More specifically, the SC 2021  searches the host-LU configuration table  20271  and finds information having a host-LU no. matching the LUN stored in the frame payload  402  that was received. The SC 2021  recognizes the structure of the Host-LU from the information set in the LU Type, and CLU class, and based on the information held in the LU Info., identifies the disk subset  10  that must be accessed and its LUN in the LU as well as the LBA in the LU. Next, the SC 2021  refers to the LU configuration table  202740  of the Diskarray Subset Configuration Table  202720  and confirms the connection port for the destination diskarray subset  10 , and acquires from the Diskarray I/F Node Configuration Table  20272 , the node No. of the diskarray I/F node  202  connected to that port. The SC 2021  in this way acquires the convention information such as the No. LUN, LBA for recognizing the diskarray subset  10  and reports this information to the SC 2022  (step  20006 ). Next, using the acquired conversion information, the SC 2022  converts the LBA from the LUN and CDB of the frame payload  402 . Also, the D_ID of the frame header  401  is converted to the D_ID of the host I/F controller  1011  of the diskarray subset  10 . The S_ID is not rewritten at this point (step  20007 ). The SC 2022  transfers the converted command frame and the diskarray I/F node  40 , connected to the corresponding diskarray subset  10 , to the SPG 2024 . The SPG 2024  generates a packet added with a simple expansion header  601  such as shown in  FIG. 12  for the converted command that was received. This packet is called the Switching Packet (S Packet)  60 . The expansion header  601  of this S Packet  60  contains an added transfer originator (white node) No., a transfer responder node No. and a transfer length. The SPG 2024  send the generated S Packet  60  to the crossbar switch  201  (step  20008 ). 
     The crossbar switch  201  receives the S Packet  60  from the SWP 2010  connected to the host I/F node “#2”. The SWP 2010  refers to the expansion header  601  of the S Packet  60 , establishes a path for carrying out switch control for the SWP connecting with the transfer responder node, and transfers the S Packet  60  to the transfer responder of the diskarray I/F node  202  (Here, the diskarray I/F node “#0”). The SWP 2010  establishes a path whenever the S Packet  60  is received and releases that path when transfer of the S Packet  60  is finished. In the diskarray I/F node “#0”, the SPG 2024  receives the S Packet  60 , removes the expansion header  601  and delivers the command frame portion to the SC 2022 . The SC 2022  writes its own ID in the S_ID of the frame header of the command frame that was accepted. Next, the SC 2022  instructs the SP 2021  to register the Exchange information such as the S_ID, D_ID, OX_ID, of the command frame as well as the frame transfer originator host I/F node No. into the ET 2026 , and transfers this command frame to the IC 2023 . The IC 2023  complies with instructions of the frame header  401  and transfers the command frame (arrow (b) of  FIG. 10 ) to the connected diskarray subset  10  (Here, the diskarray subset “#0”.). 
     The diskarray subset “#0” receives the command frame “FCP_CMD” after conversion, in the diskarray I/F controller  1011 . The host MPU 1010  acquires the LUN and CDB stored in the frame payload  402  of the command frame and recognizes that the LEN length data from the LBA of the specified logical unit is the read command. The host MPU 1010  refers to the cache management information stored in the cache/shared memory  102  and performs cache miss-hit/ht identification. If a hit then the data is transferred from the cache  102 . If a miss then reading of data from the disk unit is necessary so that address conversion is implemented based on the structure of RAID 5 and a cache space is secured. Processing information required for read processing from the disk unit  2  is generated, and processing information for continued processing in the lower MPU  1030  is stored in the cache/shared memory  102 . The lower MPU  1030  starts processing when the processing information is stored in the cache/shared memory  102 . The lower MPU  1030  specifies an appropriate disk I/F controller  1031  and generates a read command to the disk unit  2 , and issued a command to the disk I/F controller  1031 . The disk I/F controller  1031  stored the data read from the desk unit  2  in the address specified by the cache/shared memory  102  and issues a completion report to the lower MPU  1030 . The lower MPU  1030  stores the processing completion report in the cache/shared memory  102  for reporting to the host MPU 1010  that processing was completed correctly. The host MPU 1010  restarts the processing when the processing completion report is stored in the cache/shared memory  102  and reports that read data setup is complete to the diskarray I/F controller  1011 . The diskarray I/F controller  1011  issues a “FCP_XFER_RDY” which is a data transfer setup completion frame on the fibber channel for the applicable diskarray I/F node “#0” of the diskarray switch  20  (arrow (c) of  FIG. 10 ). In the disk ray I/F node “#0”, when the data transfer setup completion fame “FCP_XFER_RDY” is received, the SC 2022  acquires the reply responder Exchange ID (RX_ID) received from the diskarray subset  10 , specifies the S_ID, D_ID, OX_ID, instructs the SP 2021  and registers the RX_ID in the applicable Exchange of the ET 2026 . The SC 2022  acquires the host I/F node No. of the transfer responder (transfer originator of the command frame) for the data transfer completion frame. The SC 2022  renders the S_ID of this frame invalid and transfers it to the SPG 2024 . The SPG 2024  generates the S Packet as described previously and transfers the S Packet to the corresponding host I/F node “#2” by way of the crossbar switch  201 . 
     When the SPG 2024  in the host I/F node “#2” receives the S Packet of the data transfer completion frame, the expansion header or the S Packet is removed, and the “FCP_XFER_RDY” reproduced and delivered to the SC 2022  (step  20011 ). The SC 2022  instructs the SC 2021 , searches the ET 2026  and specifies the applicable Exchange (step  20012 ). Next, the SC 2022  investigates whether the frame is “FCP_XFER_RDY” (step  20013 ) and if “FCP_XFER_RDY”, instructs the SP 2021  to rewrite the originator Exchange ID (RX_ID) of ET 2026 . The value added to this frame is used as the originator Exchange ID (step  20014 ). The SC 2022  then converts the S_ID, D_ID of the frame header  401  to an appropriate value used by the ID of the host  30  and the ID of the host I/F node  203  (step  20015 ) The frame header  401  is thus converted to a frame corresponding to the host “#2” by means of this processing. The IC 2023  issues a “FCP_XFER_RDY” data transfer completion frame for this host “#2” (arrow (d) of  FIG. 10 ) (step  20016 ). 
     The diskarray I/F controller  1011  for the diskarray subset “#0” On generates a data frame “FCP_DATA” for performing data transfer, and transfers it to the diskarray switch  20  (arrow (e) of  FIG. 10 ). A limit of a maximum data length of 2 kilobytes for one frame is set to limit the data transfer length of the frame payload. When this data length is exceeded, data frames just equal to the required number are generated and issued. An identical SEQ_ID is assigned to all the data frames. Except for the case where a plurality of frames are generated for the same SEQ_ID (in other words SEQ_CNT changes), data frame issue is the same as for the data transfer setup completion frame. The diskarray switch  20  implements conversion of the frame header  401  for the data frame “FCP_DATA” just the same as for the data transfer setup completion frame. However, an RX_ID has previously been established when transferring the data frame so that the processing of step  20014  for the data transfer setup completion frame is skipped. After conversion of the frame header  401 , the diskarray switch  20  transfer the data fame to the host “#2” (arrow (f) of  FIG. 10 ). 
     Next, the diskarray subset “#0” of the diskarray I/F controller  1011  generates a status frame “FCP_RSP” to perform the end status transfer and issued this frame to the diskarray switch  20  (arrow (g) of  FIG. 10 ). In the diskarray switch  20 , the expansion header is removed from the S Packet by the SPG 2024 . Just the same as the processing for the data transfer setup completion frame, the “FCP_RSP” frame is recreated (step  20021 ) and the ET 2026  is searched by the SP 2021  and the Exchange information acquired (step  20022 ). The SC 2022  converts the frame based on this information (step  20023 ). The converted frame is transferred to the port “#2” by the IC 2023  (arrow (h) of  FIG. 10 ) (step  20024 ). Finally, the SP 2021  deletes the exchange information from the ET 2026  (step  20025 ). 
     The read processing is thus performed from the diskarray. In the write processing for the diskarray system  1 , only the transfer direction of the data frame is reverse and the processing is otherwise the same as the read processing. 
     The diskarray switch  20  as shown in  FIG. 3  is provided with an intercluster I/F  2040  in the crossbar switch  201 . In the system structure shown in  FIG. 1 , an intercluster I/F  2040  is not used. In the diskarray switch of this embodiment, other diskarray switches can be mutually connected as shown in  FIG. 14 , utilizing the intercluster I/F  2040 . In this embodiment, only a total of eight diskarray subsets  10  and host  30  can be connected in a single diskarray switch  20  however a plurality of diskarray switches  20  can be mutually connected by utilizing the intercluster I/F  2040  and an increased number of diskarrays and hosts  10  can be connected. In the system shown in  FIG. 14  for example, four diskarray switches  20  are used to connect up to a total of 32 units of the diskarray subset  10  and the hosts  30 , and data can be mutually transferred between these subsets and hosts. In this way, the number of diskarray subsets and the number of hosts that can be connected are increased according to the need for performance and disk capacity in this embodiment. Also, the capacity, performance and expandability of connection units can be drastically improved since connections can be made between the host—diskarray system by utilizing the necessary amount of host I/F transfer bandwidth. 
     In the embodiment as described above, even if the performance of one diskarray subset unit is limited by the internal bus and the internal MPU, mutual connections can be made between the host and the diskarray subset by utilizing a plurality of the diskarray subsets, by means of the diskarray switch. In this way, high performance can be achieved as a total diskarray system. Even if the performance of a diskarray subset is relatively low, high performance can be attained by utilizing a plurality of diskarray subsets. Accordingly, low cost diskarray subsets can be connected in just the required number to match the scale of the computer system, and a diskarray system can be constructed at a cost appropriate to the desired scale. Further, when improvement in performance of increasing the disk capacity is required, then the diskarray subsets can be added in just the required amount. Still further, since a plurality of diskarray switches can be utilized to connect an optional number of hosts and diskarray subsets, a drastic improvement can be made in the capacity, the performance or the number of units for connection, and a system with high expandability obtained. Even still further, reduced elements of a diskarray system itself of the conventional art can be utilized in this embodiment so that large scale software that was previously developed can be utilized without changes, thus reducing development costs and achieving a short development period. 
     Second Embodiment 
       FIG. 15  is a block diagram of the computer system of the second embodiment of this invention. In this embodiment, the structure differs from the first embodiment in that, in the host I/F node of the diskarray switch, only the frame header  401  is converted, the frame payload  402  is not operated and also in that the diskarray switch, the host I/F and the diskarray I/F are not duplexed (duplicated). The elements of the structure are therefore not greatly different from the first embodiment and a detailed description of those similar sections is omitted. 
     In  FIG. 15 , the diskarray subsets  10  are comprised of a plurality of logical units (LU)  110 . Each LU 110  is configured as an independent LU. The serial numbers assigned to the LUN in the LU 110  inside the diskarray subsets  10  generally start from 0 (zero). Therefore, when showing to a host  30 , consecutive LUN for all LU 110  in the diskarray system  1 , then converting the LUN field for the frame payload  402  is necessary, the same as in the first embodiment. In this embodiment, the LUN of the diskarray subsets  10  are shown unchanged to the host  30 , so conversion of the frame payload  402  is not necessary and the control of the diskarray switches is extremely simple. 
     In the diskarray switches of this embodiment, it is assumed that a specified diskarray subset  10  can be accessed for each host I/F node  203 . When one host I/F  31  is used in this case, only the LU 110  in one diskarray subset  10  can be accessed. When accessing LU 110  in a plurality of diskarray subsets  10  from one host unit is needed, then that host is connected to a plurality of host I/F nodes  203 . Further, when setting access of LU 110  of one diskarray subset  10  from a plurality of host  30 , then loop topology or fabric topology can be utilized in the same host I/F node  203  to connect to the plurality of hosts  30 . When configured in this way, during access of one LU 110  from one host  10 , a diskarray subset  10  can be set for each D_ID of the host I/F node  203  so that the LUN of each LU can be shown as is, to the host  30 . 
     Since in this embodiment, the LU of each LU 110  inside the diskarray subsets  10  can be shown unchanged to the host  30  for the above related reasons, then conversion of the LUN is no longer required in the diskarray switch  20 . Accordingly, when the diskarray switch  20  receives a frame from the host  30 , only the frame header  30  is converted the sa me as in the first embodiment, and the frame payload  402  is transferred without conversion to the diskarray subset  10 . In the operation of each section of this embodiment, excluding the fact that the conversion of the frame payload  402  is not performed, the embodiment is the same as the first embodiment so that a detailed explanation of the identical sections is omitted. The diskarray switch  2  can be easily developed in this embodiment. 
     Third Embodiment 
     In the second embodiment, in the host I/F node of the diskarray switch, only the frame header  401  is converted, however in the third embodiment described hereafter, frame conversion, including the frame header is not performed. The computer system of this embodiment is configured the same as the computer system in the first embodiment as shown in  FIG. 1 . 
     In the first and second embodiments, the internal structure of the diskarray system  1  such as the number of diskarray subsets  10  and the configuration of the LU 110  are concealed from the host  30 . The host  30  therefore sees the entire diskarray system  1  as one storage device. In contrast, in this embodiment, the diskarray subset  10  is revealed to the host  30 , and the host  30  directly uses the D_ID of the Frame header as the port ID for the diskarray subset. By this arrangement the diskarray switch can control frame transfer just by complying with the frame header information, and the fabric of the fiber channel in the conventional art can be used instead of the diskarray switch  20  to achieve an equivalent switch device. 
     The diskarray system configuration manager (means)  70  communicates with the communication controller  106  of the diskarray subset  10  as well as the communication means  204  of the diskarray switch  20  and acquires or sets structural information of the diskarray subsets  10  and the diskarray switches  20 . 
     The diskarray switches  20  have a structure basically the same as the diskarray switches of the first embodiment as shown in  FIG. 3 . However, in this embodiment, the frame header information for frames issued from the host  30  is used unchanged to control frame transfer so that the conversion function of the first and second embodiments, in which a frame header is achieved by a DCT 2027 , SC 2022 , SPG 2024  of the diskarray I/F node  202  and host Z/F node  203  of the diskarray switch, is not necessary. The crossbar switch  201  in the diskarray switch  20 , performs transfer of fiber channel frames between the host I/F node  203 , and the diskarray I/F node  202 , according to the frame header information. 
     In this embodiment, to achieve total management of the diskarray system structure with the diskarray system configuration manager  70 , a diskarray management table (hereafter this table is called DCT, is provided in the diskarray system configuration manager  70 . The DCT comprising the diskarray system configuration manager  70  consists of a group of two tables; a Diskarray System Configuration Table  20270  and a Diskarray Subset Configuration Table  202720 - 202723 . The host-LU in this embodiment are all comprise as one LU so that the “LU Type” in the Host-LU-Configuration table  20271  are all “ILU”, and the “CLU Class” and CLU Stripe Size” are not significant. 
     The administrator operates the management console  5 , communicates with the diskarray system configuration manager  70  and acquires information such as the number of disk units, and disk capacity of the diskarray subset  10 , and performs setting of the LU 110  of the diskarray subset  10  and setting of the RAID level. Next, the administrator communicates with the diskarray system configuration manager  70  from the management console  5 , controls the diskarray switch  20  and sets related information among the host  30  and the diskarray subsets  10 . This operation establishes the structure of the diskarray system  1  and allows LU 1  to be seen as the administrator wishes, from the host  30 . The diskarray system configuration manager  70  saves the above setting information, verifies the configuration according operation by the administrator and performs changes in the structure (configuration). 
     In this embodiment, once the diskarray system  1  is configured, a plurality of diskarray systems  1  can be handled the same as one diskarray system and without making the administrator aware of the presence of the diskarray switch  20 . Further in this embodiment, the diskarray subsets  10  and the diskarray switches  20  can be operated together by means of the same operating environment and confirming their configuration (or structure) and making changes in the configuration is also simple. Still further in this embodiment, when substituting the diskarray system of this embodiment with a diskarray system used in the conventional art, no changes are made in the host  30  settings, and the structure of the diskarray system  1  wean work with the diskarray system structure used up until then, and interchangeability can be maintained. 
     Fourth Embodiment 
     A fiber channel was used in the host I/F in the first through third embodiments described above. In the embodiment hereafter described, an interface other than the fiber channel might also be used. 
       FIG. 16  is a block diagram of the IC (Interface Controller)  2023  inside the host I/F node  203 , when the host I/F is parallel SCSI. An SCSI protocol controller (SPC)  20230  performs the protocol control of the parallel SCSI. A fiber channel protocol controller (FPC)  20233  performs control of the fiber channel. A protocol exchanging processor (PEP)  20231  converts the protocol of the serial SCSI of the fiber channel and the parallel SCSI. A buffer (BUF)  20232  temporarily stores the data of the protocol being converted. 
     The host  30  in this embodiment, issues a SCSI command to the diskarray I/F node  203 . In the case of a read command, the SPC 20230  stores this in the BUF  20232  and reports reception of the command by breaking into the PEP  20231 . The PEP  20231  uses the command stored in the BUF 20232 , and converts the command to FPC 20233  and sends it to the FPC 20233 . When the FPC 20233  receives this command, in convert the command into a frame configuration and delivers it to the SC 2022 . At this time, the Exchange ID, Sequence ID, Source ID and Destination ID are added to PEP  20231  capable of the following processing. The remaining command processing is performed the same as in the first embodiment When the setup of data is complete, the data array subset  10  issues a data transfer setup completion frame, and after the data transfer ends correctly, implements issue of a status frame. In the period from the diskarray subset  10  to the IC 2023 , while the frame header  401  and the frame payload  402  are being converted as required, the transfer of each frame is performed. The FPC 20233  of the IC 2023  receives the data transfer setup completion frame, then receives the data and stores it in the BUF  20232  and if the transfer has ended correctly, receives the status report, and breaks into the PTP 20231  to report that transfer of data is complete. When the PTP 20231  receives the break-in (interruption), the SPC 20230  starts up and instructs the start of data transfer to the host  30 . The SPC 20230  transmits the data to the host  30 , and after confirming normal completion, interrupts the PTP 20231  to report the data transfer ended correctly. 
     A parallel SCSI was used as an example here of a host I/F other than a fiber channel however other interfaces wan be implemented such as for ESCON in the same manner as a host I/F to the main frame. Host I/F nodes corresponding for instance, to the fiber channel, parallel SCSI and ESCON can be provided as the host I/F node  203  of the diskarray switch  20  so that all kinds of so-called open systems such a personal computers and work stations can be connected with the main frame to one diskarray system  1 . In this embodiment, a fiber channel was utilized as the diskarray I/F in the first through the third embodiments however the desired optional I/F can also be used as the diskarray I/F. 
     Fifth Embodiment 
     A method for configuration management of the diskarray system  1  is described using the fifth embodiment.  FIG. 17  is a system diagram of this embodiment. A total of four host  30  units are provided in this embodiment. The I/F  30  connecting between the host “#0”, “#1” and the diskarray system  1  is a fiber channel, the host “#2” and the diskarray system  1  are connected by a parallel SCSI (Ultra SCSI). The host “#3” and the diskarray system  1  are connected by a parallel SCSI (Ultra2SCSI). The connection to the diskarray switch  20  of the parallel SCSI is performed in the same way as the fourth embodiment. The diskarray system  1  has four diskarray subsets  30 . The diskarray subset “#0” has four independent LU. The diskarray subset “#1” has two independent LU. The diskarray subset “#2” and the diskarray subset “#3” are comprised of one combined LU (CLU). In this embodiment, just the same as the first embodiment, the diskarray subset  10  is concealed from the host  30 , and the frame of the fiber channel is converted. The LUN assigned to each LU, in order from the diskarray subset “#0” are seven, LUN=0, 1, 2, . . . to 6. 
       FIG. 18  is a screen view showing on the management console screen  5 . This figure shows the logical connection structure corresponding to the logical units (LU) and the host I/F  31 . The logical connection configuration screen  50  shows the information  3100  relating to each host I/F  31 , the information  11000  relating to each LU 110 , and the relation of the diskarray subset  10  and the Lu 110 . Information relating to the host I/F  31  includes the I/F type, the I/F speed and status, etc. Information relating to the Lu 110  such as the storage subset No, LUN, capacity, RAID level, status, and information are displayed. The administrator refers to this information and can easily manage the configuration of the diskarray system  1 . The lines drawn between the host I/F and the LU on the logical connection configuration screen  50  shows the LU 110  accessible by way of each of the host I/F  31 . Those LU 110  to which a line is not drawn from the host I/F cannot be accessed from the host  30  connected to that host I/F. The data configuration that is handled differs according to the host  30 , and also differs according to the user so that appropriate restrictions on access must be provided in order to maintain security. The administrators setting the system thereupon utilize this screen, to implement restrictions on access by granting or denying access between the host I/F and each LU 110 . In the figure, the LU “#0” can be accessed from the host I/F “#0” and “#1” however, the LU “#0” cannot be accessed from the host I/F “#2” and “#3”. The LU “#4” can only be accessed from the host I/F “#2”. In order to implement these kind of access restrictions, the access restriction information is sent from the diskarray system configuration manager  70  to the diskarray switch  20 . The access restriction information sent to the diskarray switch  20  is distributed to each host I/F node  203  and registered in the DCT 2027  of each host I/F node  203 . When an LU search check command has been issued for an LU with access restrictions, the host I/F node  203  performs a search of the DCT 2027  and if a response is not obtained to the search command or if an error is returned, than that LU is no longer recognized (authorized) from the host. The Test Unit Ready command of the Inquiry command are not typically used when in the case of SCSI protocol as search command for the presence of an LU. Since read/write cannot be implemented without this search command, restrictions on access are easy to apply. In this embodiment, access restrictions are applied to each host I/F  31  however by extending this the implementing of access restrictions on each host  30  is easily accomplished. Further, the host I/F  31 , host  30 , or an address space can be specified, and access restrictions can be applied according to the type of command so that read only, write only, read and write permit, and read/write prohibit are enforced. In this case, the host I/F No, the host ID, the address space or the restriction command are specified as the access restriction information and the restriction set in the disk access switch  20 . 
     Next, the addition of another diskarray subset  10  is described. When adding a new diskarray subset  10 , the administrator connects the diskarray subset  10  to be added, to an empty I/F node  202  of the diskarray switch  20 . The administrator next operates the management console  5  and presses the “Show Latest Status” button  5001  displayed on the logical connection configuration screen  50 . A picture showing the diskarray subsets not yet set appears on the screen (not shown in drawing) in response to pressing the button  5001 . When the picture for this diskarray subset is selected, the setup screen for the diskarray subsets then appears. The on this setup screen, the administrator executes the various settings for the newly added diskarray subset items set on this screen include the RAID level and the LU configuration. Next, on switching to the logical connection configuration screen of  FIG. 19 , the new diskarray subset and the LU appear. From here on, the settings for restricting access for the host I/F 31  are made, and the “Setup Execution” button  5002  is pressed, access restriction information, as well as diskarray subsets, and LU information for the diskarray switch  20  are transferred and the settings enabled. The procedure when adding a LU 110  to the diskarray subset  10  is performed the same as in the above related procedure. The deletion of the diskarray subset, and the LU are also performed with approximately the same procedure. One point of difference is that the administrator selects the sections for deletion on the screen and presses the “Delete” button, and the deletion is implemented after making an appropriate check. Thus by utilizing the management console  5 , the administrator can collectively manage the entire diskarray system. 
     Sixth Embodiment 
     Next the mirroring process by means of the diskarray switch  20  is described utilizing the sixth embodiment. The mirroring described here, is a method to support duplexed (duplicated) writing by means of two independent LU of two diskarray subsets, and duplicating including up to the controller of the diskarray subset. The reliability therefore is different from the method duplexing only the disks. 
     The system configuration (structure) of this embodiment is the same as shown in  FIG. 1 . In the configuration of  FIG. 1 , the diskarray subsets “#0” and “#1” are provided with completely the same LU configuration. These two diskarray subsets are seen from the host  30  as one diskarray. For reasons of convenience, the pair No. of the diskarray subset that was mirrored is called “#01”. Also, a mirroring pair is formed by the LU “#1” and the LU “#0” of the diskarray subset, and this LU pair is conveniently named, LU “#01”. Information for managing the LU#01 is set as “Mirrored” in the CLU class on the Host-LU Configuration Table  20271  of the DCT 2027 , and information relating to LU#0 and LU#1 is set as the LU Info. The configuration of the other sections is the same as in the first embodiment. 
     The operation of each section of this embodiment is largely the same as the first embodiment. Hereafter, the points differing from the first embodiment are explained mainly with the operation of the host I/F node of the diskarray switch  20 .  FIG. 19  is a model diagram showing the sequence of frames being transferred in the write operation of this embodiment.  FIGS. 20A through 20D  are flowcharts showing the processing in the host I/F node  203  during the write operation. 
     In the write operation, the write command frame (FCP_CMD) issued by the host  30  is received by the IC 2023  (arrow (a) of  FIG. 19 ) (step  21001 ). The write command frame received by the IC 2023  is processed the same as in steps  20002 - 20005  in the write operation described for the first embodiment (step  21002 - 21005 ). The SC 2022  searches the DCT 2027  using the SP 2021  and verifies that there is a write access request to the LU “#01” of the mirrored diskarray subset “#01” (step  21006 ). The SC 2022  makes duplicates of the command frame that was received in FB 2025  (step  2107 ). The SC 2022  converts the command frame based on the structural information set in the DCT 2027 , and makes separate command frames for both the LU “#1” and the LU “#0” (step  21008 ) The LU “#0” is here called the master LU, and the LU “#1” the slave LU. The command frames are also called respectively the master command frame and the stave command frame. Both of these separate frames are stored in the exchange information in ET 2026 , and a command frame issued for the diskarray subset “#0” and the diskarray subset “#1” (arrows (b 0 )(b 1 ) of  FIG. 19 ) (step  21009 ). 
     The diskarray subsets “#0” and “#1” receive the command frames and the respective, independent, data transfer setup completion frames “FCP_XFER_RDY” are distributed to the diskarray switch  20 ″ (arrows (c 0 ) (c 1 ) of  FIG. 19 ). In the diskarray switch  20 , the data transfer setup completion frames transferred by the same processing as in steps  20011 - 20013  of the read operation in the first embodiment, are processed in the host I/F node  203  (step  21011 - 21013 ). At the stage that the data transfer setup completion frames from each diskarray subsets are arranged (step  21014 ), the SC 2022  converts the master data transfer setup completion frames (step  21015 ), and after frame conversion by the IC 2023  sends the frame to the host  30  (arrow (d) of  FIG. 19 ) (step  21015 ). 
     After receiving the data transfer setup completion frame, the host  30  sends the data frame (FCP_DATA) to the diskarray switch  20  (arrow (e) of  FIG. 19 ). When the data frame from the host  30  is received by the IC 2023  (step  21031 ), the read command frame and the write command frame are both stored in the FB 2025 , and a CRC check and frame header analysis are performed (steps  21032 ,  21033 ). The ET 2026  is searched by the SP 2021  based on the frame header analysis results, and the Exchange information is acquired (step  21034 ). The SP 2022  makes duplicates the same as during the write command frame (step  21035 ). One copy is sent to the LU “#0” of the diskarray subset “#0” and the other is sent to the LU “#1” of the diskarray subset “#1” (arrow (f 0 )(f 1 ) of  FIG. 19 ) (step  21037 ). 
     The diskarray subsets “#0” and “#1” receive each of the data frames, respectively write these frames in the disk unit  104 , and set the status frame (FCP_RSP) to the diskarray switch  20 . When the SP 2022  receives the status frames from the respective diskarray subsets “#0” and “#1”, their respective expansion headers are removed from their status frames, the frame header restored and the exchange information acquired from the ET 2026  (step  21041 ,  21042 ). When the status frames from both the diskarray subsets “#0” and “#1” are arranged (step  21043 ), conversion of the master status frame from the LU “#0” is performed (step  21044 ) after checking that the status has completed correctly, and the slave status frame is deleted (step  21045 ). Then, the IC 2023  sends a command frame to the host to report correct completion (arrow (h) of  FIG. 19 ) (step  21046 ). Finally, the SP 2021  deletes the exchange information of ET 2026  (step  21047 ). 
     The write processing in the mirrored structure is thus completed. The read processing for the mirrored LU “#01” differs only in the direction of data transfer, and is performed largely the same as the above described write processing except that the issue of a read command to two diskarray subsets is not necessary, and a command frame can be issued just to either diskarray subset. A command frame for instance can be issued mainly to the master LU however for high speed operation, methods such as alternate issue of command frames for both the master/slave LU will prove effective in distributing the load. 
     In the above related processing, in steps  21014  and step  21043 , a reply from the two diskarray subsets LU “#0” and “#1” is awaited, both synchronized with and the process then proceeds. With this kind of control, handling of errors is simple since the process proceeds after verifying the success of the processing for both of the diskarray subsets. On the other hand this kind of control has the drawback performance declines since the overall processing speed depends on which of the replies is slower. To resolve this problem, in the diskarray switch, control such as by proceeding to the next process without waiting for a reply from the diskarray subset or a “Asynchronous type” control that proceeds to the next process at the print where a reply from either one of the diskarray subsets is received are possible. The frame sequence when this asynchronous type control is used is shown by the dashed arrow lines in  FIG. 19 . In the frame sequence shown by the dashed arrow lines, the sending of the data transfer setup complete frame to the host performed in step  21016 , is implemented after the processing in step  21009 , without waiting for the data transfer setup complete frame from the diskarray subset  10 . In this case, the data transfer setup complete frame sent to the host, is generated by the SC 2022  of the diskarray switch  20  (dashed arrow line (d′)). The data frame from the host  30  is transferred to the diskarray switch  20  at the timing shown by the dashed arrow line (e′). In the diskarray switch  20 , this data frame is temporarily stored in the FB 2025 . The SC 2022  makes a reply after receiving the data transfer setup complete frame from the diskarray subset  10 , and transfers the data frame held in the FB 2025  (dashed arrow lines (f 0 ′), (f 1 ′)) per the data transfer setup complete frame sent from the diskarray subset  10 . The completion report to the host  30  from the diskarray switch  20  is performed (dashed arrow line (h′)) when there is a report (dashed arrow lines (g 0 ′), (g 1 ′)) from both of the diskarray subsets  10 . This kind of processing can shorten the processing time by an amount equal to the time Ta shown in  FIG. 19 . 
     The following processing is implemented when an error occurs during frame transfer between the diskarray subset  10  and the diskarray switch  20 . When the process being implemented is write processing, then a retry process is performed on the LU in which the error occurred. If the retry process is a success, then the process continues unchanged. However, when the retry process fails after a preset number of retries, then the diskarray switch  20  prohibits access to this diskarray set  10  (or LU) and information showing this prohibition is registered in the DCT 2027 . The diskarray switch  20  also reports this information to the diskarray system configuration manager  70  by way of the communication controller  204  and the MP 200 . The diskarray system configuration manager  70  then issues an alarm to the management console  5  in response to this report. The administrator can thus recognize that trouble has occurred. Afterwards, the diskarray switch  20  continues the operation by utilizing a normal diskarray subset. The host  30  also continues processing without recognizing that an error has occurred. 
     This embodiment utilizes a mirror configuration in a two unit diskarray subsystem to that the disk is made more resistant to problems that occur. The resistance of the diskarray controller, diskarray I/F, and the diskarray I/F node can also be improved, and the reliability of the overall diskarray system can be improved without taking measures such as duplexing (duplicating) the internal buses. 
     Seventh Embodiment 
     In the seventh embodiment, a method is described for combining three or more diskarray subsets  10  and configuring them into one logical diskarray subset group. In this embodiment, data is distributed and stored into a plurality of diskarray subsets  10 . Distributing and storing the data in this way allows distributing the access to the diskarray subsets, to prevent the access being concentrated in a particular diskarray subset so that the throughput of the total group is improved. A diskarray switch is used in this embodiment to implement this kind of striping. 
     An address map of the disk address system  1  of this embodiment is shown in  FIG. 21 . The address space for the diskarray subsets  10  is striped at a stripe size S. The address spaces of the disk address system  1  as seen from the host are distributed into the diskarray subsets “#0”, “#1”, “#2” and “#3”. The size of the stripe size S is optional however should not be reduced very much. If the stripe size S is too small, the possibility of the occurrence of the stripe crossover, which is a phenomenon that the target data attaches to a plurality of stripes across diskarray subsets, will be risen and overhead may occur in the process. When the stripe size S is set large, then the probability that stripe crossover will occurs diminishes, so a large stripe size S is preferable in terms of improved performance. The number of LU that can be set is optional. 
     Hereafter, the operation of the host I/F node  203  in this embodiment is described while referring to the operation flowchart shown in  FIG. 22  and points differing from the first embodiment are described. In this embodiment, as information relating to the striped Host-LU, “Striped” is set in the CLU Class and “S” is set in the CLU Stripe Size, in the Host-LU Configuration Table  20271  of the DCT 2027 . 
     When a command frame is issued from the host  30 , the diskarray switch  20  receives this command frame with the IC 2023  of the host I/F node  203  (step  22001 ). The SC 2022  accepts this command frame from the IC 2023 , searches the DCT 2027  using the SP 2021  and verifies that striping is necessary (step  22005 ). Next, SC 2022  searches the DCT 2027  using the SP 2021 , finds from the structural information containing the stripe size S, the stripe No. for the stripe belonging to the data being accessed, and designates what diskarray subset  10  this stripe is stored in (step  22006 ). Stripe crossover may possible occur at this time however this processing in such a case is related later. When no stripe crossover occurs, the SC 2022  implements conversion of the command frame (step  22007 ) based on SP 2020  calculation results, and stores the exchange information in the ET 2026  (step  22008 ). The subsequent processing is the same as for the first embodiment. 
     When stripe crossover has occurred, the SP 2021  generates two command frames. These frames are generated for instance, by duplicating the command frame issued from the host  30 . New settings are made such as for the frame header and frame payload of the generated command frame. After duplicating the command frame in SC 2022 , conversion can also be implemented the same as in the sixth embodiment however in this embodiment is newly made by SP 2022 . Wlen the two command frames are made, the SC 2022  sends there frames to the respective diskarray subsets  10 . Data transfer is then performed the same as in the first embodiment. The point in this embodiment differing from the first embodiment is that the data itself must be transferred between one host  30  and two diskarray subsets  10 . In the read process for instance, the data frame transferred from the two diskarray subsets  10 , must be transferred to all the hosts  30 . The SC 2022  at this time, complies with the information registered in the ET 2026 , and adds the appropriate exchange information, in the appropriate order to the data frame transferred from the diskarray subset  10  and sends this to the host  30 . In the write process, two data frames are made, the same as for the command frame, and transferred to the applicable diskarray subset  10 . The sequential control of the data frames at the host or the diskarray subset is called the “Out of Order” function. This “Out of Order” function is not required if the configuration is compatible with nonsequential processing. Finally, when all data transfer is complete, and the diskarray switch  20  has received the status frames respectively from the two diskarray subsets  10 , the SP 2021  (or the SC 2022 ) makes a status frame for the host  30 , and the IC 2023  sends this status frame to the host  30 . 
     This embodiment as described above, is capable of distributing the access (load) into a plurality of diskarray subsets, so that along with improving the total throughput, the access latency can be reduced. 
     Eighth Embodiment 
     Next, the duplicating operation between the two diskarray systems (or the diskarray subsets) is described using the eighth embodiment. In the system described here, one of two diskarray systems is installed at a remote location to provide recovery assistance in case of damage to the other diskarray system due to a natural or man-made calamity, etc. This kind of countermeasure for dealing with damage from disasters is referred to as disaster recovery and the making of copies performed with the diskarray system at the remote location is referred to as remote copy. 
     In the mirroring as described in the sixth embodiment, the mirror function is achieved with the diskarray subsets  10  installed at largely the same location geographically so that diskarray I/F 21  can use a fiber channel. However when diskarrays (diskarray subsets) are performing remote copy at remote locations in excess of 10 kilometers, then a fiber channel cannot be used to transfer a frame unless relay equipment is added. A mutual distance of some several hundred kilometers is used during disaster recovery so that use of fiber channels for connecting between diskarrays is impractical. Therefore methods such as satellite communications or high speed public telephone lines with ATM (Asynchronous Transfer Mode) are utilized. 
       FIG. 23  is a block diagram of the disaster recovery system of the embodiment. In the figure, the reference numeral  81  denotes site A,  82  denotes site B. Both sites are installed at geographically remote locations. Reference numeral  9  denotes a public telephone line, through which the ATM packet passes. The site A 81  and the site B 82  each have a diskarray system  1 . In this case, the site A 81  is the normally used site, while site B 82  is used as the remote disaster recovery site when site A 81  is down due to a disaster. The contents of the diskarray subset “#0” and “#1” of the diskarray system  10  of the site A 81  are copied to the remote copy diskarray subset “#0” and “#1” of the diskarray system  10  of site B 82 . The node for connection to the remote site from among the I/F nodes of the diskarray switch  20  is connected to the public telephone line  9  by utilizing ATM. This node is called the ATM node  205 . The ATM node  205  is configured the same as the host I/F node shown in  FIG. 5 , and the IC 2023  performs ATM—fiber channel conversion. This conversion is achieved by same method as the SCSI—fiber channel conversion in the fourth embodiment. 
     The remote copy process in this embodiment is similar to the mirroring process in the sixth embodiment. The points differing from the mirroring process of the sixth embodiment are explained next. When the host  30  issues a write command frame, the diskarray system  10  of site A 81  performs frame duplicating the same as in the sixth embodiment, and transfers one of the copied (duplexed) frames to its own diskarray subset  10 . The other frame is converted from a fiber channel frame to an ATM packet by the ATM node  205  and sent to the site B 82  by way of the public telephone line  9 . At the site B 82 , the ATM node  205  of the diskarray switch  20  receives this packet. The IC 2023  of the ATM node  205 , restores the fiber channel frame from the ATM packet, and transfers the fiber channel frame to the SC 2022 . The SC 2022  implements frame conversion the same as when the write command was received from the host  30  and transfers the frame to the remote copy diskarray subset. From hereon, fiber channel—ATM conversion is performed for all the data transfer setup completion frames, data frames and status frame, and by implementing the same frame transfer process, remote copy can be achieved. When the read command frame was issued from the host  30 , the diskarray switch  20  transfers the command frame only to the diskarray subset  10  only for its own site and reads this data only from the diskarray subset  10  of its own site. The operation at this time is the same as in the first embodiment. 
     This embodiment is capable of making backups of user data in real-time and providing recovery assistance when damage has occurred to a diskarray system site due to a disaster, etc. 
     Ninth Embodiment 
     The combining of a plurality of LU in one diskarray subset  10  is described next. The disk storage device for a main frame for instance, has a logical volume size set to a maximum value of 2 GB in order to maintain interchangeability with the previous system. When using this kind of diskarray system as an open system, the LU receive the same restrictions on the logical volume size, so that the hosts see this configuration as a large number of small size LU. This kind of method has the problem that operating the system is difficult when the system has developed to a high capacity level. To deal with this problem, a method was contrived for combining these logical volume (in other words LU) units into one large combine LU (CLU) structure by means of the diskarray switch  20 . The forming of a combined LU (CLU) is achieved in this embodiment by the diskarray switch  20 . The combining of LU in this embodiment is the same as the forming of combined LU by means of a plurality of diskarray subsets  10  in the first embodiment. The differing point is only that in this embodiment, a plurality of LU are combined within the same diskarray subset  10 . The operation as a diskarray system is completely the same as in the first embodiment. 
     By combining a plurality of LU in the same diskarray subset  10  in this way, to form one large LU, a diskarray system is achieved having excellent operability, reduced management cost and in which there is no need for the host to manage a large number of LU. 
     Tenth Embodiment 
     Next, a method for setting alternative paths by means of the diskarray switch  10  is explained while referring to FIG  24 . The structure of each section in the computer system shown in  FIG. 24  is the same as in the first embodiment. Here, it is assumed that the two hosts  30  are accessing the diskarray subset  10  by utilizing the different diskarray I/F 21 . The diskarray subsets, the host I/F nodes  203  of the diskarray switch  20  and the diskarray I/F nodes  202  in the figure are shown only in the numbers required for this explanation. The diskarray subset  10  has the same structure as shown in  FIG. 2 , with two diskarray I/F controllers each connected to one diskarray switch  20 . An alternative path for the diskarray I/F 21  is set in the DCT 227  of each node of the diskarray switch  20 . The alternative path is a substitute path to provide access in the event trouble occurs on a particular path. 
     Here, the alternative path for the diskarray I/F “#0”, is set as the diskarray I/F “#1”, while the alternative path for the diskarray I/F “#1” is set as the diskarray I/F “#0”1. Alternative paths are set in the same way respectively for the host adapter in the diskarray subset  10 , the cache memory/shared memory, and the lower adapter. 
     Next, the setting of the alternative path is described, assuming that a problem has occurred and the path connecting the diskarray I/F 21  to the host adapter “#1” of the diskarray subset  1  is broken or unusable as shown in  FIG. 24 . At this time, the host “#1” utilizing the diskarray I/F  21  where the problem occurred, is unable to access the diskarray subset  10 . The diskarray switch  20  detects an abnormality in the frame transfer with the diskarray subset  10  and when the path cannot be restored after retry processing is implemented, verifies a problem to have occurred on this path. When a problem occurs on the path, the SP 2021  registers the information that a problem has occurred in the diskarray I/F “#1” in the DCT 2027 . Hereafter, the SC 2022  of the host I/F node  203  functions to transfer frames from the host “#1” to the diskarray I/F node  202  connected to the diskarray I/F node “#0”. The host adapter  101  of the diskarray subset  10  continues the processing of the command from the host “#1”. The diskarray switch  20  reports the occurrence of a problem to the diskarray system configuration manager  70 , and the occurrence of a problem is then reported to the administrator by means of the diskarray system configuration manager  70 . 
     The embodiment described above, can therefore switch to an alternative path when a problem occurs on a path, without this switch being recognized by the host and render the setting of substitutes on the host side unnecessary. Thus the utilization of the system can be improved. 
     In this invention as described above, a storage system can be achieved that easily improves the storage device expandability, and reliability according to various requirements and the scale of the computer system. The above explanations of the each of the embodiments all utilized a diskarray system having a disk device. However, this, invention is not limited to use of a disk device as a storage media and is also applicable to optical disk devices, tape devices, DVD devices and semiconductor storage devices, etc.