Abstract:
A connection monitoring device includes: first and second connection systems in which monitored devices are connected in cascade in forward and backward directions, respectively; a storage unit to store configuration information on connection configuration of the monitored devices and connection permitting information including information on a path permitted between the connection monitoring device and the monitored devices within paths undefined in the configuration information; and a control unit to change from a first monitoring state in which the connection configuration of the monitored devices is monitored in accordance with the configuration information to a second monitoring state in which the connection configuration of the monitored devices is monitored in accordance with the configuration information and the connection permitting information in a case where a configuration modification, accompanied with cutting of any one of connections of the first and second connection systems, of the monitored devices is performed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2014-160251 filed on Aug. 6, 2014, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are related to a connection monitoring device, and a connection monitoring method. 
       BACKGROUND 
       [0003]    As an amount of data accompanied by an information processing is increased in recent years, the size of a storage device where the data are written is being increased as well. Further, the storage device includes two or more redundant connection routes in preparation for an occurrence of a fault and switches the connection route when the fault is detected. For example, the storage device is equipped with a redundancy for the fault occurrence by being provided with a forward connection route in which equipment are connected in cascade in a forward direction and a backward connection route in which equipment are connected in cascade in a backward direction which is opposite to the forward direction. 
         [0004]    As described above, in a storage device, the number of constitutional equipment such as a controller module or a disk enclosure is increasing and a connection route which connects the constitutional equipment is becoming complicated. In the storage device, a controller module is utilized as, for example, a connection monitoring device which monitors a connection of a monitored device such as, for example, a disk enclosure and detects an erroneous connection of the monitored device in coping with the increase in the number of constitutional equipment or complication of the connection route. 
         [0005]    Related technologies are disclosed in, for example, Japanese Laid-Open Patent Publication No. 2006-146489, Japanese Laid-Open Patent Publication No. 2005-222379, and Japanese Laid-Open Patent Publication No. 2007-272702. 
       SUMMARY 
       [0006]    According to an aspect of the invention, a connection monitoring device includes: a first connection system in which a plurality of monitored devices are connected in cascade in a forward direction on which data is transmitted from the connection monitoring device to a first monitored device of the monitored devices; a second connection system in which the monitored devices are connected in cascade in a backward direction on which data is transmitted from the connection monitoring device to a last monitored device of the monitored devices; a storage unit configured to store configuration information on connection configuration of the monitored devices and connection permitting information including information on a path permitted between the connection monitoring device and the monitored devices within paths undefined in the configuration information; and a control unit configured to change a monitoring state from a first monitoring state in which the connection configuration of the monitored devices is monitored in accordance with the configuration information to a second monitoring state in which the connection configuration of the monitored devices is monitored in accordance with the configuration information and the connection permitting information in a case where a configuration modification, accompanied with cutting of any one of connections of the first connection system and the second connection system, of the monitored devices is performed. 
         [0007]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0008]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is a diagram illustrating an exemplary configuration of a connection monitoring device according to a first embodiment; 
           [0010]      FIG. 2  is a diagram illustrating an exemplary storage system according to a second embodiment; 
           [0011]      FIG. 3  is a diagram illustrating an exemplary RAID device according to the second embodiment; 
           [0012]      FIG. 4  is a diagram illustrating an example of a connection configuration between a controller module and a DE according to the second embodiment; 
           [0013]      FIG. 5  is a diagram illustrating an example of an operation state transition diagram according to the second embodiment; 
           [0014]      FIG. 6  is a diagram illustrating an example of IOM configuration information according to the second embodiment; 
           [0015]      FIG. 7  is a diagram illustrating an example of DE configuration information according to the second embodiment; 
           [0016]      FIG. 8  is a diagram illustrating an example of a connection configuration of the RAID device which is in a normal state according to the second embodiment; 
           [0017]      FIG. 9  is a diagram illustrating another example of the connection configuration of the RAID device which is in a normal state according to the second embodiment; 
           [0018]      FIG. 10  is a diagram illustrating an example of the connection configuration of the RAID device according to the second embodiment; 
           [0019]      FIG. 11  is a diagram illustrating an example of the connection configuration of the RAID device which is in an addition state according to the second embodiment; 
           [0020]      FIG. 12  is a diagram illustrating an example of IOM list information according to the second embodiment; 
           [0021]      FIG. 13  is a diagram illustrating an example of DE list information according to the second embodiment; 
           [0022]      FIG. 14  is a diagram illustrating another example of the connection configuration of the RAID device according to the second embodiment; 
           [0023]      FIG. 15  is a diagram illustrating another example of the IOM list information according to the second embodiment; 
           [0024]      FIG. 16  is a diagram illustrating another example of the DE list information according to the second embodiment; 
           [0025]      FIG. 17  is a diagram illustrating still another example of the connection configuration of the RAID device according to the second embodiment; 
           [0026]      FIG. 18  is a diagram illustrating still another example of the IOM list information according to the second embodiment; 
           [0027]      FIG. 19  is a diagram illustrating still another example of the DE list information according to the second embodiment; 
           [0028]      FIG. 20  is a diagram illustrating still yet another example of the connection configuration of the RAID device according to the second embodiment; 
           [0029]      FIG. 21  is a diagram illustrating still yet another example of the IOM list information according to the second embodiment; 
           [0030]      FIG. 22  is a diagram illustrating still yet another example of the DE list information according to the second embodiment; 
           [0031]      FIG. 23  is a diagram illustrating still yet another example of the connection configuration of the RAID device according to the second embodiment; 
           [0032]      FIG. 24  is a diagram illustrating still yet another example of the IOM list information according to the second embodiment; 
           [0033]      FIG. 25  is a diagram illustrating still yet another example of the DE list information according to the second embodiment; 
           [0034]      FIG. 26  is a flowchart illustrating an addition process connection monitoring processing according to the second embodiment; 
           [0035]      FIG. 27  is a flowchart illustrating a 0-system addition processing according to the second embodiment; 
           [0036]      FIG. 28  is a flowchart illustrating a 1-system saving processing; 
           [0037]      FIG. 29  is a flowchart illustrating a 1-system addition processing; 
           [0038]      FIG. 30  is a flowchart illustrating a 1-system recovery processing; 
           [0039]      FIG. 31  is a diagram illustrating an example of a connection configuration of a RAID device according to a third embodiment; 
           [0040]      FIG. 32  is a diagram illustrating another example of the connection configuration of the RAID device according to the third embodiment; 
           [0041]      FIG. 33  is a diagram illustrating still another example of the connection configuration of the RAID device according to the third embodiment; 
           [0042]      FIG. 34  is a diagram illustrating an example of a connection configuration of a RAID device according to a fourth embodiment; and 
           [0043]      FIG. 35  is a diagram illustrating another example of the connection configuration of the RAID device according to the fourth embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0044]    In a storage device where the number of constitutional equipment such as a controller module or a disk enclosure is increasing, a connection route connecting the constitutional equipment is becoming complicated. The controller module is utilized as, for example, a connection monitoring device which monitors the connection of a monitored device such as, for example, the disk enclosure and detects an erroneous connection of the monitored device. As a result, a time required for a configuration modification work such as an addition of a constitutional equipment tends to increase. 
         [0045]    For example, when an addition of an equipment which constitutes a storage device is performed, the storage device may lose some of its redundancies due to the recombination in the connection of the equipment. The loss of redundancy may be limited to a short time period, but the increase of the time period required for configuration modification work makes it difficult to limit the loss of redundancy to the short time period. 
         [0046]    Hereinafter, descriptions will be made on an embodiment of a technology of securing a working hour by limiting the time period during which the redundancy is lost when the configuration of the monitored device is modified, with reference to accompanying drawings. 
       First Embodiment 
       [0047]    Descriptions will be made on a connection monitoring device of a first embodiment with reference to  FIG. 1 .  FIG. 1  is a diagram illustrating an exemplary configuration of a connection monitoring device according to a first embodiment. The connection monitoring device  1  monitors a connection state of a plurality of monitored devices  6  ( 6   a , . . . ,  6   n ). The plurality of monitored device  6   s  ( 6   a , . . . ,  6   n ) are connected by a redundancy relation in a first connection system and a second connection system. The connection monitoring device  1  is one of an information processing device and includes, for example, a controller module of a RAID (Redundant Arrays of Independent Disks) device. 
         [0048]    The monitored device  6  is connected with the connection monitoring device  1  and is a target to be detected by the connection monitoring device  1 . The monitored device  6  is, for example, a disk enclosure constituting the RAID device. In the first connection system, a plurality of monitored devices  6  is connected in cascade in a forward direction. In the second connection system, a plurality of monitored devices  6  is connected in cascade in a backward direction. For example, in the first connection system, the plurality of monitored devices  6  are connected in cascade in a predetermined sequence (a sequence in a sequential flow starting from the monitored device  6   a  to the monitored device  6   n  which serves as a terminating device) which starts from the connection monitoring device  1  as a starting point. For example, in the second connection system, the plurality of monitored devices  6  are connected in cascade in a predetermined sequence (a sequence in a sequential flow starting from the monitored device  6   n  to the monitored device  6   a  which serves as a terminating device) which starts from the connection monitoring device  1  as a starting point. 
         [0049]    The connection monitoring device  1  includes a storage unit  2  and a control unit  4 . The storage unit  2  stores configuration information  3   a  and connection permitting information  3   b . The storage unit  2  is a device capable of storing information and includes, for example, a HDD (Hard Disk Drive) or various memories. The configuration information  3   a  is information about a connection configuration of the monitored device  6 . The configuration information  3   a  is, for example, information about an access path between the connection monitoring device  1  and the plurality of monitored device  6  ( 6   a , . . . ,  6   n ). 
         [0050]    The connection permitting information  3   b  is information which permits a connection which is not defined in the configuration information  3   a . The connection permitting information  3   b  includes information about the access path permitted between the connection monitoring device  1  and the plurality of monitored devices  6  ( 6   a , . . . ,  6   n ) among the access paths that are not defined in, for example, the configuration information  3   a . The access path defined in the connection permitting information  3   b  maintains multiple access paths (redundancy) during a work for an addition. 
         [0051]    A control unit  4  disconnects any one of connections made in the first connection system and the second connection system. When the configuration modification for the monitored device  6  is performed, the control unit  4  switches from a first monitoring state  5   a  to a second monitoring state  5   b . The configuration modification for the monitored device  6  includes an addition, a replacement, and a separation of the monitored device  6 . The first monitoring state  5   a  is a state where the control unit  4  monitors a connection configuration of the monitored device  6  according to the configuration information  3   a . In the second monitoring state  5   b , the control unit  4  monitors the connection configuration of the monitored device  6  according to the configuration information  3   a  and the connection permitting information  3   b.    
         [0052]    Accordingly, the connection monitoring device  1  may permit the connection which is not defined in the configuration information  3   a  in a state where any one of connections made in the first connection system and the second connection system is disconnected when the configuration modification of the monitored device  6  is being performed. Therefore, the connection monitoring device  1  may secure a working hour by limiting a lost time period of redundancy during the configuration modification of the monitored device  6 . 
         [0053]    Here, descriptions will be made on an a case where the monitored device  6   n  is added to the plurality of monitored devices  6  ( 6   a , . . . ,  6   m ). First, the connection monitoring device  1  monitors the monitored device  6  in the first monitoring state  5   a . The connection monitoring device  1  permits a link “A” by which the monitored device  6   n  intended to add is connected to the monitored device  6   m  based on the configuration information  3   a . Accordingly, the monitored device  6   n  is connected with the connection monitoring device  1  by the link “A” and the first connection system, and connected with the terminating device in cascade in the forward direction. Further, the link may be a connection route through a physical wiring such as a cable and otherwise, a connection route through a wireless communication. 
         [0054]    In the backward cascade connection, the monitored device  6   a  serves as a terminating device, and the monitored device  6   n  tries to be connected between the monitored device  6   m  and the connection monitoring device  1 . Therefore, the monitored device  6   m  is disconnected from a link “B” connecting the monitored device  6   m  and the connection monitoring device  1 . In this connection state, the connection monitoring device  1  loses the redundancy in a connection with the monitored device  6 . 
         [0055]    The connection monitoring device  1  switches its connection from the first monitoring state  5   a  to the second monitoring state  5   b  such that a link “C” which is not permitted by the configuration information  3   a  is permitted by the connection permitting information  3   b . Accordingly, the connection monitoring device  1  may recover the redundancy to secure the working hours. Further, the link “B” and link “C” may be distinguished from each other by a port of a connection destination. 
         [0056]    Thereafter, the monitored device  6   m  and the monitored device  6   n  are connected by a link “D” and the monitored device  6   n  and the connection monitoring device  1  are connected by a link “E” such that the monitored device  6  is connected in cascade in a backward direction. The connection work is complex and requires time, but the redundancy in the connection during the work is maintained by the link “C”. The monitored device  6  may be disconnected from the link “C” accompanied by being connected with the links “D” and “E” so as to complete the addition work in a connection state permitted by the configuration information  3   a.    
       Second Embodiment 
       [0057]    Next, a storage system of the second embodiment will be described with reference to  FIG. 2 .  FIG. 2  is a diagram illustrating an exemplary configuration of a storage system of a second embodiment. 
         [0058]    A storage system  10  includes a host  11  and an RAID device  13  connected to the host  1  through a network  12 . The storage system  10  writes data into the RAID device  13  or reads data from the RAID device  13  according to an I/O request (input/output request) by the host  11 . Further, the storage system  10  may include a plurality of hosts  11  and a plurality of RAID devices  13 . 
         [0059]    Next, the hardware configuration of the RAID device  13  of the second embodiment will be described with reference to  FIG. 3 .  FIG. 3  is a diagram illustrating an example of a hardware configuration of an RAID device of the second embodiment. The RAID device  13  includes a controller module  21  ( 21   a  and  21   b ) and a disk enclosure (DE)  20  ( 20   a ,  20   b ,  20   c , and  20   d ). The DE  20  is connected in one system where the DE  20  is connected with the controller module  21   a  in cascade in a forward direction and other one system where the DE  20  is connected with the controller module  21   b  in cascade in a backward direction. Further, when a single controller module  21  exists, the DE  20  may be connected with the single controller module  21   b  in two systems. Details of the connection configuration between the controller module  21  and the DE  20  will be described later with reference to  FIG. 4 . 
         [0060]    The controller module  21  includes a host interface  14 , a processor  15 , an RAM (Random Access Memory)  16 , a HDD  17 , an equipment connection interface  18 , and a disk interface  19 . 
         [0061]    The controller module  21  is controlled by the processor  15  in its entirety. The RAM  16  and a plurality of peripheral equipment are connected to the processor  15  through a bus. The processor  15  may be a multi-core processor composed of two or more processors. Further, a master/slave relationship is established between the controller modules  21   a  and  21   b , and the processor  15  of the controller module  21  which serves as a master may control the controller module  21  and the entirety of the RAID device  13 . 
         [0062]    The processor  15  is, for example, a CPU, an MPU (Micro Process Unit), a DSP (Digital Signal Processor), an ASIC (Application Specific Integrated Circuit), or a PLD (Programmable Logic Device). 
         [0063]    The RAM  16  is used as a primary storage device of the controller module  21 . In the RAM  16 , at least a portion of an OS (Operating System) program or an application program executed by the processor  15  is temporarily stored. Further, various data needed for a process to be executed by the processor  15  are stored in the RAM  16 . Further, the RAM  16  functions as a cache memory of the processor  15 . 
         [0064]    The peripheral equipment connected to the bus may include the host interface  14 , the HDD  17 , the equipment connection interface  18 , and the disk interface  19 . The host interface  14  transmits and receives data to and from the host  11  through the network  12 . 
         [0065]    The HDD  17  performs writing and reading data into and from a built-in disk magnetically. The HDD  17  is used as an auxiliary storage device of the RAID device  13 . The OS program, the application program, and various data are stored in the HDD  17 . In the meantime, a semiconductor storage device such as a flash memory may be used as the auxiliary storage device. 
         [0066]    The equipment connection interface  18  is a communication interface for connecting the peripheral equipment to the controller module  21 . For example, a memory device or a memory reader/writer which is not illustrated may be connected to the equipment connection interface  18 . The memory device is a recording medium equipped with a function for communicating with the equipment connection interface  18 . The memory reader/writer is a device which performs writing data into the memory card or reading data from the memory card. The memory card is, for example, a card type recording medium. 
         [0067]    Further, the equipment connection interface  18  may be connected with a monitor not illustrated. In this case, the equipment connection interface  18  has a function that displays information on a display unit according to an instruction from the processor  15 . 
         [0068]    Further, the equipment connection interface  18  may be connected with a keyboard or a mouse which is not illustrated. In this case, the equipment connection interface  18  transmits signal sent from the keyboard or the mouse to the processor  15 . Further, the mouse is an example of a pointing device, and other pointing device may be used. The other pointing device may include, for example, a touch panel, a tablet, a touch pad, and a track ball. 
         [0069]    Further, the equipment connection interface  18  may be connected with an optical drive device which is not illustrated. The optical drive device reads data written into an optical disk by using, for example, laser light. The optical disk is a portable recording medium in which data is written to be capable of being read by reflection of light. The optical disk may include, for example, a DVD (Digital Versatile Disc), a DVD-RAM, a CD-ROM (Compact Disc Read Only Memory), or a CD-R (Recordable)/RW (ReWritable). 
         [0070]    The disk interface  19  transmits and receives data to and from a single DE or two or more DEs  20 . The DE  20  is connected with the controller module  21  through the disk interface  19 . The DE  20  includes one or more disks  30  and stores data based on the instruction from the controller module  21 . The disk is a storage device and includes, for example, a HDD or SSD (Solid State Drive). 
         [0071]    With the hardware configuration described above, the processing function of the RAID device  13  may be implemented. The RAID device  13  executes a program recorded in, for example, the computer-readable recording medium to implement the processing function of the RAID device  13 . The program in which process contents to be executed by the RAID device  13  are described may be recorded into various recording media. For example, the program to be executed by the RAID device  13  may be stored in the HDD  17 . The processor  15  loads at least a portion of the program stored in the HDD  17  onto the RAM  16  and executes the program. Further, the program to be executed by the RAID device  13  may be recorded in the portable recording medium such as the optical disk, the memory device, or the memory card. The program stored in the portable recording medium becomes executable after being installed on the HDD  17  by the control from the processor  15 . Further, the processor  15  may directly read a program from the portable recording medium to execute the program. 
         [0072]    Next, descriptions will be made on a connection configuration between the controller module  21  and the DE with reference to  FIG. 4 .  FIG. 4  is a diagram illustrating an example of a connection configuration between a controller module and a DE according to the second embodiment. 
         [0073]    The controller module  21  ( 21   a  and  21   b ) is connected with the DE  20  ( 20   a ,  20   b ,  20   c , and  20   d ) in two systems. In two systems for connection, one system (0-system) connects the controller module  21   a  with the DE  20 , and other one system (1-system) connects the controller module  21   b  and the DE  20 . 
         [0074]    The controller module  21  includes an I/O controller  22  and an expander  23  in the disk interface  19 . The I/O controller  22  controls an I/O between the controller module  21  and the DE  20 . The expander  23  includes a plurality of In ports  24  and a plurality of Out ports  25  and extends connectivity between the I/O controller  22  and the DE  20 . The In port  24  is a port to be connected with the I/O controller  22  and the Out port  25   24  is a port to be connected with the DE  20 . 
         [0075]    For example, the controller module  21   a  and the controller module  21   b  include the I/O controller  22   a  and I/O controller  22   b , respectively, and include the expander  23   a  and expander  23   b , respectively. The expander  23   a  includes In ports  24   a   1  and  24   a   2  and Out ports  25   a   1  and  25   a   2 , and the expander  23   b  includes In ports  24   b   1  and  24   b   2  and Out ports  25   b   1  and  25   b   2 . 
         [0076]    For example, the controller module  21   a  is connected with the I/O controller  22   a  at the In port  24   a   1 , and the controller module  21   b  is connected with the I/O controller  22   b  at the In port  24   b   2 . 
         [0077]    Further, the controller module  21   a  and the controller module  21   b  are connected with each other through the expander  23 . For example, the controller module  21   a  is connected with the I/O controller  22   b  at the In port  24   a   2 , and the controller module  21   b  is connected with the I/O controller  22   a  at the In port  24   b   1 . 
         [0078]    The DE  20  includes an IOM (I/O Module)  26 . For example, the DE  20   a  includes IOMs  26   a   1  and  26   b   1 . Similarly, the DE  20   b  includes IOMs  26   a   2  and  26   b   2 , the DE  20   c  includes IOMs  26   a   3  and  26   b   3 , and the DE  20   d  includes IOMs  26   a   4  and  26   b   4 . 
         [0079]    The IOM  26  performs a data input/output for the DE  20 . The IOM  26  includes an In port  27  and an Out port  28  that perform the data input/output. The In port  27  is a port to be connected in a direction toward the controller module  21  from the DE  20 , and the Out port  28  is a port to be connected in a connection terminating direction toward from the DE  20 . 
         [0080]    For example, the IOM  26   a   1  and the IOM  26   b   1  include an In port  27   a   1  and an In port  27   b   1 , respectively, and include an Out port  28   a   1  and an Out port  28   b   1 , respectively. Similarly, the IOM  26   a   2  and the IOM  26   b   2  include an In port  27   a   2  and an In port  27   b   2 , respectively, and include an Out port  28   a   2  and an Out port  28   b   2 , respectively. Similarly, the IOM  26   a   3  and the IOM  26   b   3  include an In port  27   a   3  and an In port  27   b   3 , respectively, and include an Out port  28   a   3  and an Out port  28   b   3 , respectively. Similarly, the IOM  26   a   4  and the IOM  26   b   4  include an In port  27   a   4  and an In port  27   b   4 , respectively, and include an Out port  28   a   4  and an Out port  28   b   4 , respectively. 
         [0081]    In the connection configuration of the 0-system, the DE  20   b , the DE  20   c , and the DE  20   d  are connected in cascade from the DE  20   a  in a sequence which starts from the controller module  21   a  as a starting point. For example, the Out port  25   a   1  of the controller module  21   a  is connected with the In port  27   a   1  of the DE  20   a . The Out port  28   a   1  of the DE  20   a  is connected with the In port  27   a   2  of the DE  20   b . The Out port  28   a   2  of the DE  20   b  is connected with the In port  27   a   3  of the DE  20   c . The Out port  28   a   3  of the DE  20   c  is connected with the In port  27   a   4  of the DE  20   d , and the DE  20   d  terminates the connection of the 0-system. 
         [0082]    In the connection configuration of the 1-system, the DE  20   c , the DE  20   b , and the DE  20   a  are connected in cascade from the DE  20   d  in a sequence which starts from the controller module  21   b  as a starting point. For example, the Out port  25   b   1  of the controller module  21   b  is connected with the In port  27   b   4  of the DE  20   d . The Out port  28   b   4  of the DE  20   d  is connected with the In port  27   a   3  of the DE  20   c . The Out port  28   b   3  of the DE  20   c  is connected with the In port  27   b   2  of the DE  20   b . The Out port  28   b   2  of the DE  20   d  is connected with the In port  27   b   1  of the DE  20   a  and the DE  20   a  terminates the connection of the 1-system. 
         [0083]    Further, when it is assumed that the connection sequence in the 0-system is a normal sequence, the DE  20  to be connected to the controller module  21  is connected in a connection sequence, which is opposite to the connection sequence in the 0-system, in the 1-system. Further, when a single controller module  21  exists, the single controller module  21  is connected with the DE  20  in two systems. Two ports (In port  27  and Out ports  25  and  28 ) are connected with each other through a link and connecting the two ports needs a connection work by a worker. Further, the link may be a connection route through a physical wiring such as a cable and otherwise, a connection route through a wireless communication. 
         [0084]    The RAID device  13  may be connected to the DE  20  by the controller module  21  ( 21   a  and  21   b ) in two systems such that multiple accessing (redundancy) to DE  20  may be achieved. Accordingly, when any one of two controller modules  21   a  and  21   b  is in failure, other one of two controller modules  21   a  and  21   b  may continue accessing to the DE  20  in the RAID device  13 . 
         [0085]    In the RAID device  13 , the controller module  21  and the DE  20  are accommodated in a predetermined case and disposed in a rack in a predetermined sequence (e.g., an order according to identification information). In general, in the 0-system, the DE  20  is connected in a disposition sequence from the controller module  21  and in the 1-system, the DE  20  is connected in a sequence, which is opposite to the sequence in the 0-system, from the controller module  21 . Therefore, in the connection in the 1-system, a distance from the controller module  21  to the DE  20  of the terminating device is longer, a wiring is more complicate, and a load applied on the connection work is larger than those of the 0-system. 
         [0086]    Next, descriptions will be made on an operation state of the RAID device  13  with reference to  FIG. 5 .  FIG. 5  is a diagram illustrating an example of an operation state transition diagram according to the second embodiment. An operation state transition diagram  600  illustrates an operation state and a state transition condition of the RAID device  13 . The operation state of the RAID device  13  includes a normal operation mode  601 , a maintenance mode  602 , and a redundant configuration mode  603 . 
         [0087]    The normal operation mode  601  is an operation state which becomes a normal state and in which, for example, the controller module  21  is connected with the DE  20  in two systems composed of the 0-system and the 1-system. The maintenance mode  602  is an operation state which becomes a maintenance state and in which, for example, the controller module  21  is monitoring an addition work. The redundant configuration mode  603  is an operation state in which a connection configuration not permitted in the maintenance state is permitted and for example, a redundant configuration not provided in the normal state is provided. 
         [0088]    The normal operation mode  601  transits to the maintenance mode  602  when a maintenance mode flag becomes ON. Further, the maintenance mode  602  transits to the normal operation mode  601  when the maintenance mode flag becomes OFF. The maintenance mode  602  transits to the redundant configuration mode  603  when a redundant configuration mode flag becomes ON. Further, the redundant configuration mode  603  transits to the maintenance mode  602  when the redundant configuration mode flag becomes OFF. 
         [0089]    Descriptions will be made on the connection configuration of the RAID device  13  which is in the normal state with reference to  FIG. 6  to  FIG. 8 . First, descriptions will be made on IOM configuration information  211  with reference to  FIG. 6 .  FIG. 6  is a diagram illustrating an example of IOM configuration information according to the second embodiment. 
         [0090]    The IOM configuration information  211  is information capable of specifying an equipment configuration for each connection system. The IOM configuration information  211  is previously stored in the RAID device in the normal operation mode  601  and is used for confirming the equipment configuration for each connection system. The IOM configuration information  211  is information previously set by, for example, a maintenance worker and is stored in, for example, the HDD  17 . The IOM configuration information  211  includes identification information of an equipment to be detected for each connection system and information capable of specifying a detection sequence. The identification information of the equipment to be detected for each connection system is, for example, a 0-system port E 00  identification information or 1-system port E 10  identification information. Further, the information capable of specifying the detection sequence is, for example, a detection sequence (1, 2, . . . ). The identification information of the equipment is information capable of uniquely specifying an equipment or a port of equipment, and may include, for example, WWPN (World Wide Port Name). 
         [0091]    In a field for the 0-system port E 00  identification information, the identification information of respective equipment is arranged in an order of equipment capable of being detected from the port E 00  of the expander  23  of the 0-system. Further, in a field for the 1-system port E 10  identification information, the identification information of respective equipment are arranged in an order of equipment capable of being detected from the port E 10  of the expander  23  in the 1-system. Further, each of the ports E 00  and E 10  of the expander  23  indicated in the IOM configuration information  211  is the Out port  25  used in the normal operation mode  601  by the RAID device  13 . 
         [0092]    Next, descriptions will be made on DE configuration information  221  with reference to  FIG. 7 .  FIG. 7  is a diagram illustrating an example of DE configuration information according to the second embodiment. The DE configuration information  221  is information capable of specifying the IOM  26  of each DE  20  for each connection system. The DE configuration information  221  is information capable of being configured from the IOM configuration information  211  and is generated by, for example, the RAID device  13  after the IOM configuration information  211  is set. The DE configuration information  221  includes identification information of the DE  20 , identification information of the IOM  26  of the 0-system, and identification information of the IOM  26  of the 1-system. The DE configuration information  221  is used in determination of whether the IOM  26  of the 0-system is normally connected with the IOM  26  of the 1-system for the DE  20  in the normal operation mode  601 . 
         [0093]    Next, descriptions will be made on the connection configuration of the RAID device  13  which is in the normal state.  FIG. 8  is a diagram illustrating an example of a connection configuration of the RAID device which is in a normal state according to the second embodiment. The connection configuration  501  is a connection configuration of the RAID device  13  which is in the normal state and is configured based on the IOM configuration information  211 . The connection configuration  501  is the same connection configuration as that of  FIG. 4 , but the expander  23 , the DE  20 , the IOM  26 , the Out port  25 , the In port  27 , and the Out port  28  are denoted using identification information instead of reference symbols in order to simplify the description. 
         [0094]    One of two expanders  23  is denoted by the identification information EXP 0  and other one is denoted by the identification information EXP 1 . Four DEs  20  are denoted by identification information DE 00 , identification information DE 01 , identification information DE 02 , and identification information DE 03 , respectively. One of two IOMs  26  of the DE 00  is denoted by identification information IOM 00  and other one is denoted by identification information IOM 01 . Other IOMs  26  provided in other DE  20  is similarly denoted by identification information. Among ports provided in an IOM 00 , the In port is denoted by the identification information IP 00  and the Out port is denoted by the identification information OP 00 . Other ports provided in other IOM  26  are denoted by identification information similarly to two ports provided in the IOM 00 , and denoting by identification information as described above is similarly applied to  FIG. 9  to  FIG. 11 ,  FIG. 14 ,  FIG. 17 ,  FIG. 20 , and  FIG. 23 . 
         [0095]    In the connection configuration  501 , the connection between the expanders (EXP 0  and EXP 1 ) and the DE (DE 00 , DE 01 , DE 02 , DE 03 ) is indicated using links K 01 , K 02 , K 03 , K 04 , K 11 , K 12 , K 13 , and K 14 . The links K 01 , K 02 , K 03 , and K 04  belong to the 0-system. The links that belong to the 0-system connect the DE (DE 00 , DE 01 , DE 02 , and DE 03 ) in cascade manner from the port E 00  of the expander EXP 0  in a predetermined sequence. For example, the predetermined sequence is a sequence in which the identification information DE 00 , DE 01 , DE 02 , and DE 03  of the DE  20  are listed in an ascending order. The links K 11 , K 12 , K 13 , and K 14  belong to the 1-system. The links that belong to the 1-system connect the DE (DE 00 , DE 01 , DE 02 , and DE 03 ) in cascade manner from the port E 10  of the expander EXP 10  in a sequence, which is opposite to that in the 0-system. For example, the predetermined sequence is a sequence in which the identification information DE 03 , DE 02 , DE 01 , and DE 00  of the DE  20  are listed in a descending order. 
         [0096]    Next, descriptions will be made on a connection configuration in which equipment are erroneously connected in the RAID device  13  which is in the normal state with reference to  FIG. 9 .  FIG. 9  is a diagram illustrating another example of the connection configuration of the RAID device which is in a normal state according to the second embodiment. A connection configuration  502  indicates a connection configuration in which equipment are erroneously connected in the normal operation mode  601 . The connection configuration  502  is the connection configuration deviated from the IOM configuration information  211  or the connection configuration  501 , and is a state of becoming an erroneous connection. 
         [0097]    For example, in the connection configuration  502 , a link KG 1  which is not present in the IOM configuration information  211  exists, and links K 11  and K 12  that are present in the IOM configuration information  211  do not exist. The inconsistency between the connection configuration  502  and the IOM configuration information  211 , that is, the connection configuration in which equipment are erroneously connected may be detected by, for example, the execution of a discovery command by the RAID device  13 . 
         [0098]    Descriptions will be made on a process of adding the DE 04  to the RAID device  13  with reference to  FIG. 10  to  FIG. 25 . First, descriptions will be made on a preparation step for adding the DE 04  to the RAID device  13  with reference to  FIG. 10 . Then, descriptions will be made on a 0-system addition process with reference to  FIG. 11  to  FIG. 13 , a 1-system saving process with reference to  FIG. 14  to  FIG. 19 , a 1-system addition process with reference to  FIG. 20  to  FIG. 22 , and a 1-system recovery process with reference to  FIG. 23  to  FIG. 25 . 
         [0099]      FIG. 10  is a diagram illustrating an example of the connection configuration of the RAID device according to the second embodiment. A connection configuration  503  is a connection configuration formed in the preparation step for adding the DE 04  to the RAID device  13  and one of connection configurations that may exist in the maintenance mode  602 . The DE 04  is provided in the vicinity of the DE 03  to be connected to the terminating device of the 0-system. 
         [0100]    Further, in the maintenance mode  602 , the RAID device  13  receives the identification information of the DE 04  to be added in advance and permits an inconsistency regarding the DE 0  even when the inconsistency between the IOM configuration information  211  and the DE configuration information  221  exists in the connection configuration. 
         [0101]    Descriptions will be made on the 0-system addition process with reference to  FIG. 11  to  FIG. 13 . First, descriptions will be made on a connection configuration which is in an addition state.  FIG. 11  is a diagram illustrating an example of the connection configuration in an addition state according to the second embodiment. 
         [0102]    A connection configuration  504  is a connection configuration formed by adding the DE 04  to the connection configuration  503  through a link K 05  in the 0-system and is one of the connection configurations that may exist in the maintenance mode  602 . Further, the RAID device  13  is being operated in the maintenance mode  602 . 
         [0103]    The port E 10  of the expander EXP 1  is connected to the In port IP 31  of the DE 03  through the link K 11 . As the work to be performed after the connection, in the RAID device  13 , a connection needs to be changed from the In port IP 31  to the In port IP 41  as a connection destination of the 1-system at the port E 10 . Therefore, the release of the link K 11  is needed in the next working in the RAID device  13 . 
         [0104]    Next, descriptions will be made on IOM list information which corresponds to the connection configuration  504  with reference to  FIG. 12 .  FIG. 12  is a diagram illustrating an example of IOM list information according to the second embodiment. The IOM list information  212  is information capable of specifying the equipment to be connected to the expander  23  for each port. The IOM list information  212  is information generated by detecting the equipment connected to the expander  23  for each port in the connection configuration  504 . The IOM list information  212  is used for confirming the connection configuration by being compared with the IOM configuration information  211 . 
         [0105]    The IOM configuration information  212  includes identification information of the equipment detected for each port of the expander  23  and information capable of specifying the detection sequence. In the field for the 0-system port E 00  identification information, the identification information of respective equipment are arranged in an order of equipment detected from the port E 00  of the expander  23  in the 0-system. Further, in the field for the 1-system port E 10  identification information, the identification information of respective equipment are arranged in an order of equipment detected from the port E 10  of the expander  23  in the 1-system. Further, in the field for the 1-system port E 11  identification information, the identification information of respective equipment are arranged in an order of equipment detected from the port E 11  of the expander  23  in the 1-system. However, since the equipment is not detected from the port E 11  of the expander  23  of the 1-system in the 1-system port E 11  identification information, the 1-system port E 11  identification information does not include any identification information. Further, descriptions on the port E 01  of the expander  23  of the 0-system will be omitted. 
         [0106]    Further, since the DE 04  is connected through the link K 05 , the 0-system port E 00  identification information includes the identification information of the DE 04  as a fifth item in the detection sequence. In the meantime, since a link is not yet established for the DE 04 , the 1-system port E 10  identification information does not include the identification information of the DE 04 . 
         [0107]    Further, even though the IOM list information  212  has a portion which is not consistent with the IOM configuration information  211 , the IOM list information  212  permits identification information of the added DE 04  as long as the inconsistent portion corresponds to inconsistency on the DE 04  to be added. 
         [0108]    Next, descriptions will be made on DE list information which corresponds to the connection configuration  504  with reference to  FIG. 13 .  FIG. 13  is a diagram illustrating an example of the DE list information according to the second embodiment. A DE list information  222  is information capable of specifying the IOM  26  of each DE  20  for each connection system. The DE list information  222  is information capable of being configured from the IOM list information  212  and is generated by, for example, the RAID device  13  after the IOM list information  212  is generated. The DE list information  222  includes the DE identification information, the 0-system IOM identification information, and the 1-system IOM identification information. 
         [0109]    Further, since the DE 04  is connected by the link K 05 , the 0-system IOM identification information includes identification information IOM 40  of the IOM  26  of the DE 04 . In the meantime, since a link is not yet established for the DE 04  in the 1-system, the 1-system IOM identification information does not include the identification information of the IOM  26  of the DE 04 . 
         [0110]    Further, even though the IOM list information  212  has a portion which is not consistent with the IOM configuration information  221 , the IOM list information  212  permits identification information of the added DE 04  as long as the inconsistent portion corresponds to inconsistency on the DE 04  to be added. Descriptions will be made on the release of link of the 1-system in the 1-system saving process with reference to  FIG. 14  to  FIG. 16 . First, descriptions will be made on the connection configuration of the RAID device  13  with reference to  FIG. 14 .  FIG. 14  is a diagram illustrating another example of the connection configuration of the RAID device according to the second embodiment. 
         [0111]    The connection configuration  505  is the connection configuration of the RAID device  13  in which the link K 11  of the 1-system is released from the connection configuration  504 , and is one of connection configurations that may exist in the redundant configuration mode  603 . Further, the connection configuration  505  is the connection configuration after the operation state has transited from the maintenance mode  602  to the redundant configuration mode  603 . 
         [0112]    Since the link K 11  of the 1-system is released, the connection configuration  505  is the connection configuration which is not permitted in the maintenance mode  602 . Since the connection configuration  505  is the connection configuration that may exist in the redundant configuration mode  603 , the DE list information when the redundant configuration mode flag becomes ON is used as a criterion for determining whether the connection configuration  505  is the connection configuration to be permitted. Therefore, it is determined that the connection configuration  505  is the connection configuration permitted by the DE list information  222 . 
         [0113]    Accordingly, an access redundancy may be secured in the redundant configuration mode  603  in the RAID device  13 . Next, descriptions will be made on the IOM list information which corresponds to the connection configuration  505  with reference to  FIG. 15 .  FIG. 15  is a diagram illustrating another example of the IOM list information according to the second embodiment. 
         [0114]    The IOM list information  213  is information generated by detecting the connected equipment for each port of the expander  23  in the connection configuration  505 . The IOM list information  213  is used for confirming the connection configuration by comparing with the IOM configuration information  211 . Further, in the IOM list information  213 , since the link K 11  is released even though the IOM list information  213  has the same configuration as that of the IOM list information  212 , the 1-system port E 10  identification information and the 1-system port E 11  identification information do not include any identification information. The IOM list information  213  indicates that even though the IOM list information  213  has a portion which is not consistent with the IOM configuration information  211 , the connection configuration  505  is permitted as long as the inconsistent portion corresponds to the inconsistency on the DE 04  to be added or the inconsistency on securing of the redundant configuration. 
         [0115]    Next, descriptions will be made on the DE list information which corresponds to the connection configuration  505  with reference to  FIG. 16 .  FIG. 16  is a diagram illustrating another example of DE list information according to the second embodiment. The DE list information  223  is a copy of the DE list information  222  being maintained in the redundant configuration mode  603 . Since it is determined whether the connection configuration  505  is the connection configuration to be permitted by the DE list information  223  which is a copy of the DE list information  222 , the connection configuration  505  is permitted in the redundant configuration mode  603 . 
         [0116]    Descriptions will be made on the connection in the redundant configuration of the 1-system saving process with reference to  FIG. 17  to  FIG. 19 . First, descriptions will be made on the connection configuration of the RAID device  13  with reference to  FIG. 17 .  FIG. 17  is a diagram illustrating still another example of the connection configuration of the RAID device according to the second embodiment. 
         [0117]    The connection configuration  506  is the connection configuration of the RAID device  13  in which a redundant link KJ 1  is connected and is one of connection configurations that may exist in the redundant configuration mode  603 . The redundant link KJ 1  is a link which secures the access redundancy for the existing DE (DE 00 , DE 01 , DE 02 , and DE 03 ). The RAID device  13  may access the DE 00 , DE 01 , DE 02 , and DE 03  in two systems configured by the 0-system and the 1-system by the connection of the redundant link KJ 1 . The redundant link KJ 1  connects the Out port E 11  of the expander EXP 1  with the In port IP 31  of the DE 03  in the 1-system. The redundant link KJ 1  is a link for the connection configuration which is different from the access path between the DE  20  and the controller module  21  in the normal operation mode  601 . The redundant link KJ 1  is a link which accesses the expander  23  without using the Out port  25  used in the normal operation mode  601 . 
         [0118]    Further, the RAID device  13  alleviates the chances of determining that the connection configuration is abnormal to permit the connection of the redundant link in the redundant configuration mode  603 . Accordingly, the RAID device  13  may limit a lost time of the redundancy during the work process. 
         [0119]    Next, descriptions will be made on the IOM list information which corresponds to the connection configuration  506  with reference to  FIG. 18 .  FIG. 18  is a diagram illustrating still another example of the IOM list information according to the second embodiment. The IOM list information  214  is information generated by detecting the connected equipment for each port of the expander  23  in the connection configuration  506 . The IOM list information  214  is used for confirming the connection configuration by being compared with the IOM configuration information  211 . Further, in the IOM list information  214 , since the link is released even though the IOM list information  214  has the same configuration as that of the IOM list information  212 , the 1-system port E 10  identification information does not include any identification information. Further, since the redundant link KJ 1  is connected, identification information of respective equipment is arranged in an order of equipment detected from the port E 11  in the 1-system port E 11  identification information. The IOM list information  214  indicates that even though the IOM list information  214  has a portion which is not consistent with the IOM configuration information  211 , the connection configuration  506  is permitted as long as the inconsistent portion corresponds to the inconsistency on the DE 04  to be added or the inconsistency on securing of the redundant configuration. 
         [0120]    Next, descriptions will be made on the DE list information which corresponds to the connection configuration  506  with reference to  FIG. 19 .  FIG. 19  is a diagram illustrating still another example of DE list information according to the second embodiment. The DE list information  224  is a copy of the DE list information  222  being maintained in the redundant configuration mode  603 . The DE list information  224  indicates that since it is determined whether the connection configuration  505  is the connection configuration to be permitted by the DE list information  224  which is a copy of the DE list information  222 , the connection configuration  506  is permitted in the redundant configuration mode  603 . 
         [0121]    Descriptions will be made on the 1-system addition process with reference to  FIG. 20  to  FIG. 22 . First, descriptions will be made on the connection configuration of the RAID device  13  with reference to  FIG. 20 .  FIG. 20  is a diagram illustrating still yet another example of the connection configuration of the RAID device according to the second embodiment. 
         [0122]    The connection configuration  507  is the connection configuration after the operation mode has transited from the redundant configuration mode  603  to the maintenance mode  602  by confirming the connection of the redundant link KJ 1 . The connection configuration  507  is the connection configuration in which the added DE 04  and the expander EXP 1  are connected with the link K 15 , and is one of connection configurations that may exist in the maintenance mode  602 . The link K 15  connects the Out port E 10  of the expander EXP 1  and the In port IP 41  of the DE 04  in the 1-system. 
         [0123]    Next, descriptions will be made on the IOM list information which corresponds to the connection configuration  507  with reference to  FIG. 21 .  FIG. 21  is a diagram illustrating still yet another example of the IOM list information according to the second embodiment. The IOM list information  215  is information generated by detecting the connected equipment for each port of the expander  23  in the connection configuration  507 . The IOM list information  215  is used for confirming the connection configuration by being compared with the IOM configuration information  211 . Further, in the IOM list information  215 , since the link K 15  is connected even though the IOM list information  215  has the same configuration as that of the IOM list information  212 , identification information of respective equipment are arranged in an order of the equipment detected from the port E 10  in the 1-system port E 10  identification information. Further, since the redundant link KJ 1  is connected, identification information of respective equipment is arranged in an order of the equipment detected from the port E 11  in the 1-system port E 11  identification information. 
         [0124]    Further, the IOM list information  215  indicates that even though the IOM list information  214  has a portion which is not consistent with the IOM configuration information  211 , the connection configuration  507  is permitted as long as the inconsistent portion corresponds to the inconsistency on the DE 04  to be added. Further, the IOM list information  215  indicates that since the identification information of the DE  20  are matched with each other in the 0-system and the 1-system among the 0-system port E 00  identification information, the 1-system port E 10  identification information, and the 1-system port E 11  identification information, the connection configuration  507  is permitted. 
         [0125]    Next, descriptions will be made on the DE list information which corresponds to the connection configuration  507  with reference to  FIG. 22 .  FIG. 22  is a diagram illustrating still yet another example of DE list information according to the second embodiment. The DE list information  225  is information capable of being configured from the IOM list information  215  in the maintenance mode  602 . The DE list information  225  includes the identification information of the DE  20 , the identification information of the IOM  26  of the 0-system, and the identification information of the IOM  26  of the 1-system. Further, the DE list information  225  indicates that even though the IOM list information  214  has a portion which is not consistent with the DE list information  221 , the connection configuration  507  is permitted as long as the inconsistent portion corresponds to the inconsistency on the DE 04  to be added. 
         [0126]    Descriptions will be made on the 1-system recovery process with reference to  FIG. 23  to  FIG. 25 . First, descriptions will be made on the connection configuration of the RAID device  13  with reference to  FIG. 23 .  FIG. 23  is a diagram illustrating still yet another example of the connection configuration of the RAID device according to the second embodiment. 
         [0127]    The connection configuration  508  is the connection configuration in which the redundant link KJ 1  is released, and the added DE 04  and the existing DE 03  are connected with the link K 16 . The connection configuration  508  is one of the connection configurations that may reside in the maintenance mode  602 . The link K 16  connects the Out port OP 41  of the DE 04  with the In port IP 31  of the DE 03  in the 1-system. Further, the connection configuration  508  is the connection configuration in which the operation state has transited from the maintenance mode  602  to the normal operation mode  601 , and the addition of the DE 04  is completed by confirming the connection of the link K 16 . 
         [0128]    Next, descriptions will be made on the IOM list information which corresponds to the connection configuration  508  with reference to  FIG. 24 .  FIG. 24  is a diagram illustrating still yet another example of the IOM list information according to the second embodiment. The IOM list information  216  is information generated by detecting the connected equipment for each port of the expander  23  in the connection configuration  508 . The IOM list information  216  is used for confirming the connection configuration by being compared with the IOM configuration information  211 . Further, in the IOM list information  216 , since the link K 16  is connected even though the IOM list information  216  has the same configuration as that of the IOM list information  212 , identification information of respective equipment are arranged in an order of the equipment detected from the port E 10  in the 1-system port E 10  identification information. Further, since the link is released, the 1-system port E 11  identification information does not include any identification information. The IOM list information  216  indicates that even though the IOM list information  216  has a portion which is not consistent with the IOM configuration information  211 , the connection configuration  508  is permitted as long as the inconsistent portion corresponds to the inconsistency on the DE 04  to be added and securing the redundant configuration. 
         [0129]    Next, descriptions will be made on the DE list information which corresponds to the connection configuration  508  with reference to  FIG. 25 .  FIG. 25  is a diagram illustrating still yet another example of DE list information according to the second embodiment. The DE list information  226  is information capable of being configured from the IOM list information  216  in the maintenance mode  602 . The DE list information  226  includes the identification information of the DE  20 , the identification information of the IOM  26  of the 0-system, and the identification information of the IOM  26  of the 1-system. Further, the DE list information  226  indicates that even though the DE list information  226  has a portion which is not consistent with the DE list information  221 , the connection configuration  507  is permitted as long as the inconsistent portion corresponds to the inconsistency on the DE 04  to be added. 
         [0130]    Descriptions will be made on a monitoring processing of the connection of the DE  20  during an addition process in the RAID device  13  with reference to  FIG. 26  to  FIG. 30 . First, descriptions will be made on an addition process connection monitoring processing of the second embodiment with reference to  FIG. 26 .  FIG. 26  is a flowchart illustrating an addition process connection monitoring processing according to the second embodiment. 
         [0131]    The addition process connection monitoring processing is a processing in which the RAID device  13  monitors the connection established during the process of adding an equipment. The control unit (processor  15 ) of the RAID device  13  receives an instruction to monitor the connection to execute the addition process connection monitoring processing. 
         [0132]    The control unit executes the 0-system addition processing (Operation S 11 ). The 0-system addition processing is a processing in which the RAID device  13  confirms the connection of the DE  20  intended to add to the 0-system. The 0-system addition processing will be described later with reference to  FIG. 27 . 
         [0133]    The control unit executes the 1-system saving processing (Operation S 12 ). The 1-system saving processing is a processing in which the RAID device  13  suppresses the I/O of the 1-system, release the link of the 1-system, and confirms the connection of the redundant configuration. The 1-system saving processing will be described later with reference to  FIG. 28 . 
         [0134]    The control unit executes the 1-system addition processing (Operation S 13 ). The 1-system addition processing is a processing in which the RAID device  13  confirms the connection of the DE  20  added by a link belonged to the 1-system. The 1-system addition processing will be described later with reference to  FIG. 29 . 
         [0135]    The control unit executes the 1-system recovery processing (Operation S 14 ). The 1-system recovery processing is a processing in which the RAID device  13  confirms the connection of link of the 1-system and the release of the redundant configuration, recovers the I/O of the 1-system, and ends the maintenance mode. The 1-system recovery processing will be described later with reference to  FIG. 30 . 
         [0136]    Next, descriptions will be made on a flowchart of the 0-system addition processing according to the second embodiment with reference to  FIG. 27 .  FIG. 27  is a flowchart illustrating a 0-system addition processing according to the second embodiment. 
         [0137]    The 0-system addition processing is a processing of confirming the connection of an addition equipment (an equipment intended to be added) to the 0-system. The 0-system addition processing is a processing executed by the control unit (processor  15 ) of the RAID device  13  at Operation S 11  of the connection monitor processing. 
         [0138]    The control unit turns a maintenance mode flag ON (Operation S 21 ). Accordingly, the RAID device  13  transits from the normal operation mode  601  to the maintenance mode  602 . The control unit receives the identification information of addition equipment and the addition process link information (information of link in the addition process) (Operation S 22 ). The addition process link information is the identification information about the connection sites or the release sites (Out port  25 , In port  27 , and Output port  28 ) of the link in the process of addition. The links in the process of addition includes the link which connects the addition equipment, the link which connects or releases an existing equipment (equipment having been existed), and the redundant link. 
         [0139]    Further, the addition process link information may include information indicating which link is to be connected or released at which timing or information about a work procedure in the addition process such as information indicating which link is to be connected or released in what sequence. 
         [0140]    The control unit generates IOM configuration information which complies with the addition (Operation S 23 ). For example, the control unit may generate the IOM configuration information which complies with the addition based on the received identification information of the addition equipment and the IOM configuration information  211 . The control unit adds the identification information of the addition equipment in the field of the 0-system port E 00  identification information as the fifth (last) item in the detection sequence. The control unit adds the identification information of the addition equipment in the field of the 1-system port E 10  identification information as the first item in the detection sequence and shifts the original identification information. 
         [0141]    The control unit notifies a connection link (Operation S 24 ). The notification of the connection link is to notify a connection site of the addition equipment in the 0-system. The connection site of the 0-system is identification information of an Out port of a terminating equipment of the 0-system and identification information of an In port of the DE  20  intended to be added. Further, the control unit may notify the connection site by displaying information on a display unit or turning ON a lighting device such as an LED (Light Emitting Diode) provided to be corresponded to the Out ports  25  and  28  or the In port  27  of the RAID device  13 . Further, the control unit may notify the connection site by transmitting information through a network. 
         [0142]    Further, the control unit may notify information about the work procedure along with notifying the connection site of the link which belongs to the 0-system. Further, the information about the work procedure may include identification information of the equipment, information of instruction to connect or release the link, information of connection or release timing of the link, or precaution at a configuration modification work. Further, the control unit may notify a notification unit (e.g., display unit, LED, terminal) of the work procedure. 
         [0143]    The control unit generates IOM list information (Operation S 25 ). For example, the control unit may detect, by the discovery command, that the DE 04  intended to be added to the 0-system is connected to the connection configuration  503  through the link K 05  and generate the IOM list information  212  in the connection configuration  504 . 
         [0144]    Further, the control unit detects the connection or the release of the link and issues the discovery command. The control unit determines whether the connection of the existing equipment belonged to the 0-system is normal or not (Operation S 26 ). The control unit compares the IOM configuration information with the IOM list to determine whether the connection of the existing equipment in the 0-system is normal. For example, the control unit may compare the IOM configuration information  211  with the IOM list information  212  for the identification information of the existing equipment to determine whether the connection of the existing equipment is normal. Further, the control unit may compare the DE configuration information  221  with the DE list information  222  for the identification information of the existing equipment to determine whether the connections of the 0-system and the 1-system for each of the existing DE  20  are normal or not. 
         [0145]    The 0-system addition processing performed by the control unit proceeds to Operation S 27  when the existing equipment of the 0-system is normal, and the 0-system addition processing proceeds to an abnormal end of the 0-system addition processing when the connection of the 0-system is not normal. When the 0-system addition processing is abnormally ended, the control unit performs a processing for a case of an occurrence of abnormality such as notifying an abnormality occurrence or outputting an error log, and ends the connection monitoring process. 
         [0146]    The control unit determines whether the connection of the addition equipment belonged to the 0-system is normal or not (Operation S 27 ). For example, the control unit may determine that the connection is normally established for the identification information of the 0-system when the IOM configuration information which complies with the addition is identical with the IOM list information. Further, since the RAID device  13  is in the maintenance mode  602 , the RAID device  13  compares the IOM configuration information  211  with the IOM list information  212 , permits inconsistency in the identification information of the added DE  20  even when the inconsistency exists, and determines that the connection of the added DE  20  is normal. 
         [0147]    The 0-system addition processing performed by the control unit proceeds to Operation S 28  when the connection in the 0-system is normally established and proceeds to Operation S 24  when the connection in the 0-system is not normally established. The control unit determines whether an unconnected addition equipment is present (Operation S 28 ). For example, the control unit compares the IOM configuration information which complies with the addition with the IOM list information to determine whether an unconnected DE  20  is present or not. The 0-system addition processing performed by the control unit proceeds to Operation S 24  when the unconnected addition equipment is present, and ends the 0-system addition processing when the unconnected addition equipment is not present. 
         [0148]    As described above, the RAID device  13  may monitor the connection configuration using, for example, the IOM configuration information, the IOM list information, the DE configuration information, the DE list information, or the addition process link information. Next, descriptions will be made on a flowchart of the 1-system saving processing according to the second embodiment with reference to  FIG. 28 .  FIG. 28  is diagram illustrating a flowchart of a 1-system saving processing. 
         [0149]    The 1-system saving processing is a processing in which the I/O of the 1-system is suppressed, the link of the 1-system is released, and connection of the redundant configuration is confirmed. The 1-system saving processing is a processing executed by the control unit (processor  15 ) of the RAID device  13  at Operation S 12  of the connection monitoring process. 
         [0150]    The control unit suppresses the I/O of the 1-system (Operation S 31 ). Accordingly, the control unit switches the I/O being processed at two systems composed of the 0-system and the 1-system to the I/O to be processed only in one system of the 0-system. Therefore, the RAID device  13  may limit the influence on the I/O process caused by the release of the link of the 1-system. 
         [0151]    The control unit acquires link information (Operation S 32 ). The link information includes the link information of a release link and the link information of a connection link. The link information of the release link is the identification information of the release sites (Out port  25 , In port  27 , and Out port  28 ) of the link received at Operation S 22 . The link information of the redundant link is the identification information of the connection sites (Out port  25 , In port  27 , and Out port  28 ) of the redundant link received at Operation S 22 . For example, the control unit acquires the identification information of a port belonged to a path which makes an access to the existing DE  20  redundant as the information of the connection sites for the connection by the redundant link. 
         [0152]    The control unit turns ON the redundant configuration mode flag (Operation S 33 ). The control unit transits from the maintenance mode  602  to the redundant configuration mode  603 . The control unit maintains the DE list information when the redundant configuration mode flag is turned ON. 
         [0153]    The control unit may determine the connection configuration by referencing the DE list information maintained at the time when the redundant configuration mode flag is turned ON even when the IOM list information is changed according to the connection modification in the redundant configuration mode  603 . Accordingly, the control unit permits the connection of the redundant link in the redundant configuration mode  603 . 
         [0154]    The control unit performs a notification of the release link (Operation S 34 ). For example, the control unit notifies the identification information of the Out port  25  of the expander  23  connected with the DE  20  and the identification information of the In port  27  of the DE  20  connected with the expander  23  in the 1-system. 
         [0155]    Further, the connection configuration  505  is a connection configuration in which the release link is released from the connection configuration  504 . Further, the link K 11  is a release link. Further, the control unit may notify information about the work procedure along with notifying the release site of the link which belongs to the 1-system. For example, the control unit notifies a message such as “A link is excluded from a port of the expander of the 1-system.” as the information about the work procedure. The control unit may maintain the information about the work procedure in a memory or acquire the information through a network. 
         [0156]    The RAID device  13  may reduce an occurrence of erroneous connection by notifying the release site of the link or the information about the work procedure. The control unit notifies the redundant link (Operation S 35 ). For example, in the 1-system, the control unit notifies the identification information of the In port of the existing DE  20  connected with the expander  23  and the identification information of the Out port  25  (Out port  25  being emptied in the normal operation mode  601 ) of the expander  23 , for which the identification information of equipment is not yet acquired in the IOM configuration information. 
         [0157]    Further, the connection configuration  506  is a connection configuration in which the redundant link is connected. Further, the link KJ 1  is a redundant link. Further, the control unit may notify the information about the work procedure. For example, the RAID device  13  may notify a message such as “A redundant link is connected based on connection site information” as the information about the work procedure. 
         [0158]    The RAID device  13  may reduce an occurrence of erroneous connection by notifying the release site of the link or the information about the work procedure. The control unit generates the IOM list information (Operation S 36 ). For example, the control unit may detect, by the discovery command, that the redundant link KJ 1  is connected and generate the IOM list information  214  in the connection configuration  506 . 
         [0159]    The control unit determines whether the connection other than the redundant link is normal or not (Operation S 37 ). The control unit may compare the IOM configuration information and the IOM list information to determine whether the connection other than the connection site of the redundant link is normal or not. When it is determined that the connection is normal, the 1-system saving processing performed by the control unit proceeds to Operation S 38  and otherwise, when the connection is not normal, the control unit ends the 1-system saving processing. 
         [0160]    When the 1-system saving processing is abnormally ended, the control unit performs a processing for an occurrence of abnormality such as notifying an abnormality occurrence or outputting an error log, and ends the connection monitoring process. The control unit determines whether the connection of the redundant link is normal or not (Operation S 38 ). For example, the control unit may compare the identification information of the connection site of the redundant link received at Operation S 22  with the identification information of the IOM list information to determine whether the connection of the redundant link is normal or not. When it is determined that the connection of the redundant link is normal, the 1-system saving processing performed by the control unit proceeds to Operation S 39  and otherwise, when the connection is not normal, the 1-system saving processing proceeds to Operation S 34 . 
         [0161]    The control unit recovers the I/O of the 1-system (Operation S 39 ). Even though the I/O was being processed only in one system of the 0-system, the control unit recovers the I/O of the 1-system in accordance with an establishment of the connection of the redundant link and processes the I/O in two systems composed of the 0-system and the 1-system. 
         [0162]    The control unit turns OFF the redundant configuration mode flag (Operation S 40 ). The control unit transits from the redundant configuration mode  603  to the maintenance mode  602 . The control unit ends the 1-system saving processing. 
         [0163]    As described above, the RAID device  13  may connect the redundant link to reduce the time required for accessing the existing DE  20  only by the link of the 0-system (only one system) and achieve redundancy in accessing to the existing DE  20  (accessing in two systems). 
         [0164]    As described above, the RAID device  13  transits from the maintenance mode  602  to the redundant configuration mode  603  such that the connection of the redundant link is permitted and the redundancy in I/O accessing to an equipment that has an impaired redundancy in I/O access is secured. 
         [0165]    As described above, the RAID device  13  may secure an access to the equipment by the redundant link during an addition work to secure a time required for the addition work of the equipment. Next, descriptions will be made on a flowchart of the 1-system addition processing according to the second embodiment with reference to  FIG. 29 .  FIG. 29  is a flowchart illustrating a 1-system addition processing. 
         [0166]    The 1-system addition processing is a processing of confirming the connection of the DE  20  added by the link which belongs to the 1-system. The 1-system addition processing is a processing executed by the control unit (processor  15 ) of the RAID device  13  at Operation S 12  of the connection monitoring process. 
         [0167]    The control unit notifies the connection link (Operation S 51 ). For example, the control unit notifies the identification information of the In port of the added DE  20  and the identification information of the Out port  25  of the expander  23  in the 1-system. Further, the control unit may notify the identification information of the site to be connected by the link based on the link information received at Operation S 22 . Further, the control unit may notify the information about the work procedure along with notifying the site to be connected by the link. 
         [0168]    The control unit generates the IOM list information (Operation S 52 ). For example, the control unit may detect, by the discovery command, that the DE 04  is connected to the 1-system through the link K 15  and generate the IOM list information  215  in the connection configuration  507 . 
         [0169]    The control unit determines whether the connection of the existing equipment belonged to the 1-system is normal or not (Operation S 53 ). For example, regarding the 1-system, the control unit may compare the identification information of the IOM configuration information  211  with the identification information of the IOM list information  215  to determine whether the connection of the existing equipment is normal or not. 
         [0170]    When it is determined that the connection of the existing equipment belonged to the 1-system is normal, the 1-system addition processing performed by the control unit proceeds to Operation S 54  and otherwise, when the connection of the existing equipment belonged to the 1-system is not normal, the 1-system addition processing proceeds to an abnormal end of the 1-system addition processing. When the 1-system addition processing is abnormally ended, the control unit performs a processing for an occurrence of abnormality such as notifying an abnormality occurrence or outputting an error log, and ends the connection monitoring process. 
         [0171]    The control unit determines whether the connection of addition equipment of the 1-system is normal or not (Operation S 54 ). For example, regarding the identification information of the 1-system, the control unit may compare the IOM configuration information, which complies with the addition, with the IOM list information  215  to determine whether the connection of the addition equipment is normal or not. 
         [0172]    When it is determined that the addition equipment is normally connected, the 1-system addition processing performed by the control unit proceeds to Operation S 55  and otherwise, when the addition equipment is not normally connected, the 1-system addition processing proceeds to Operation S 51 . The control unit determines whether an unconnected addition equipment is present (Operation S 55 ). For example, the control unit compares the IOM configuration information which complies with the addition with the IOM list information to determine whether an unconnected DE  20  is present or not. 
         [0173]    The 1-system addition processing performed by the control unit proceeds to Operation S 51  when it is determined that the unconnected addition equipment is present, and ends the 1-system addition processing when the unconnected addition equipment is not present. Next, descriptions will be made on a flowchart of the 1-system recovery processing according to the second embodiment with reference to  FIG. 30 .  FIG. 30  is a flowchart illustrating the 1-system recovery processing according to the second embodiment. 
         [0174]    The 1-system recovery processing is a processing in which the connection of the link of the 1-system and the release of the redundant configuration are confirmed, the I/O of the 1-system is recovered, and the maintenance mode is ended. The 1-system recovery processing is a processing executed by the control unit (processor  15 ) of the RAID device  13  at Operation S 14  of the connection monitoring process. 
         [0175]    The control unit suppresses the I/O of the 1-system (Operation S 61 ). Accordingly, the control unit switches the I/O being processed at two systems composed of the 0-system and the 1-system to the I/O to be processed only in one system of the 0-system. Therefore, the RAID device  13  may limit the influence on the I/O process caused by the release of the link of the 1-system. 
         [0176]    The control unit notifies the release of the redundant link (Operation S 62 ). For example, the control unit notifies the identification information of the port connected by the redundant link KJ 1 . Further, the control unit may notify the information about the work procedure at the time when notifying the site for which the redundant link is to be released. For example, the control unit may notify a message such as “A redundant link is released.” as the information about the work procedure. 
         [0177]    The control unit notifies the connection link (Operation S 63 ). For example, the control unit notifies, in the 1-system, the identification information of the Out port of the DE  20  to be added and the identification information of the In port  25  of the existing DE  20  connected to the DE  20  to be added. Further, the control unit may notify the identification information of the site for which the link is connected based on the link information received at Operation S 22 . 
         [0178]    Further, the control unit may notify the identification information about the work procedure at the time when notifying the site for which the link is connected. For example, the control unit may notify a message such as “A connecting addition equipment is connected with the existing equipment of the 1-system after confirming the release of the redundant link.” as the information about the work procedure. 
         [0179]    The control unit generates the IOM list information (Operation S 64 ). For example, the control unit may detect, by the discovery command, that the DE 04  is connected to the 1-system through a link K 16  and generate the IOM list information  216  in the connection configuration  508 . 
         [0180]    The control unit determines whether the connection of the existing equipment of the 1-system is normal or not (Operation S 65 ). For example, the control unit may compare the IOM configuration information and the IOM list information to determine whether the connection of the existing equipment is normal or not. When it is determined that the addition equipment of the 1-system is normally connected, the 1-system recovery processing performed by the control unit proceeds to Operation S 66  and otherwise, when the addition equipment of the 1-system is not normally connected, the 1-system recovery processing proceeds to an abnormal end of the 1-system recovery processing. 
         [0181]    When the 1-system recovery processing is abnormally ended, the control unit performs a processing for an occurrence of abnormality such as notifying an abnormality occurrence or outputting an error log, and ends the connection monitoring process. The control unit determines whether the connection of all equipment is normal or not (Operation S 66 ). For example, the control unit may compare the IOM configuration information, which complies with the addition, with the IOM list information to determine whether the connection of all equipment is normal or not. When it is determined that the connection of all equipment is normal, the 1-system recovery processing performed by the control unit proceeds to Operation S 67  and otherwise, when the connection of all equipment is not normal, the 1-system recovery processing proceeds to Operation S 62 . 
         [0182]    Further, when it is determined that the connection is not normal, the control unit may perform a processing such as notifying the occurrence of error. The control unit recovers the I/O of the 1-system (Operation S 67 ). Even though the I/O was being processed only in one system of the 0-system, the control unit recovers the I/O of the 1-system in accordance with the connection of all equipment normally established and processes the I/O in two systems composed of the 0-system and the 1-system. 
         [0183]    The control unit turns OFF the maintenance mode flag (Operation S 68 ). The RAID device  13  transits from the maintenance mode  602  to the normal operation mode  601 . The control unit ends the 1-system recovery processing. 
         [0184]    With this configuration, the RAID device  13  switches the operation state to allow the connection of the redundant link in the process of adding the equipment. Accordingly, the RAID device  13  may reduce an operation time during which the access redundancy is impaired for the existing equipment in the addition process. Accordingly, the RAID device  13  may secure a work time while maintaining the redundancy in accessing to the existing equipment. 
         [0185]    Further, the processing described in the second embodiment may be applied to an information processing device in which two or more connection routes are established. 
       Third Embodiment 
       [0186]    Descriptions will be made on the connection of the redundant link in the connection configuration of a RAID device in which the DE  20  is arranged in two column with reference to  FIG. 31  to  FIG. 33 . First, descriptions will be made on the connection configuration of the normal operation mode  601  in the RAID device  13  in which the DE  20  is arranged in two columns with reference to  FIG. 31 . The expander  23 , DE  20 , Out port  25 , In port  27 , and Out port  28  are denoted using identification information instead of reference symbols in order to simplify the description. Further, the denoting by identification information as described above is similarly applied to  FIG. 32  and  FIG. 33 . 
         [0187]    A connection configuration  531  is a connection configuration in which the expanders EXP 0  and EXP 1  and the DE (DE 00 , DE 01 , DE 02 , DE 03 , DE 10 , DE 11 , DE 12 , and DE 13 ) are connected with each other. Further, descriptions of the IOM  26  included in the DE  20  will be omitted. 
         [0188]    The port E 00  of the expander EXP 0  connects the DE 00 , DE 01 , DE 02 , and DE 03  in a cascade configuration in a forward direction. The port E 01  of the expander EXP 0  connects the DE 10 , DE 11 , DE 12 , and DE 13  in a cascade configuration in a forward direction. The port E 10  of the expander EXP 0  connects the DE 00 , DE 01 , DE 02 , and DE 03  in a cascade configuration in a backward direction. The port E 11  of the expander EXP 0  connects the DE 10 , DE 11 , DE 12 , and DE 13  in a cascade configuration in a backward direction. 
         [0189]    A link K 30  is a link to be released at the time when the DE  20  intended to be added is connected to the DE 03 . A link K 31  is a link to be released at the time when the DE  20  intended to be added is connected to the DE 13 . 
         [0190]    Further, the DE  20  which corresponds to the terminating device in the cascade connection configuration has a port which is not connected (empty port). For example, the DE 03  which corresponds to the terminating device of the 0-system has an empty port OP 030 . Further, the DE 13  which corresponds to the terminating device of the 0-system has an empty port OP 130 . Further, the DE 00  which corresponds to the terminating device of the 1-system has an empty port OP 001 . Further, the DE 10  which corresponds to the terminating device of the 1-system has an empty port OP 101 . 
         [0191]    Next, descriptions will be made on the connection configuration of the RAID device according to the third embodiment with reference to  FIG. 32 .  FIG. 32  is a diagram illustrating an example of the connection configuration of the RAID device according to the third embodiment. The connection configuration  532  illustrated in the diagram indicates a connection configuration of the redundant link KJ 31  when the DE 04  is added. 
         [0192]    The DE 04  intended to be added needs to be connected with the expander EXP 1  in the normal operation mode  601 . Therefore, the link K 30  in the connection configuration  531  is released in the connection configuration  532 . Even though the redundancy in accessing to the DE (DE 00 , DE 01 , DE 02 , and DE 03 ) is impaired due to the release of the link K 30  in the RAID device  13 , the connection may be established by the redundant link KJ 31  such that the access redundancy may be secured in the RAID device  13 . The redundant link KJ 31  is a link which connects the In port IP 031  of the DE 03  and the Out port OP 101  of the DE 10  which is an empty port of the 1-system capable of being accessed with the expander EXP 1 . 
         [0193]    With this configuration, the RAID device  13  connects the redundant link using an empty port capable of being accessed with the controller module  21  such that it becomes possible to secure the access redundancy for the existing DE  20  for which the access redundancy is impaired during the addition work. 
         [0194]    Further, the RAID device  13  may perform a process of adding the DE  20  by applying the method described in the second embodiment. Next, descriptions will be made on a connection configuration according to the third embodiment with reference to  FIG. 33 .  FIG. 33  is a diagram illustrating still another example of the connection configuration of the RAID device according to the third embodiment. 
         [0195]    The connection configuration  533  illustrated in the diagram indicates a connection configuration of the redundant link KJ 33  when the DE 04  is added to the RAID device  13 . The DE 04  intended to be added needs to be connected with the expander EXP 1  in the normal operation mode  601 . Therefore, the link K 31  in the connection configuration  531  is released in the connection configuration  532 . Even though the redundancy in accessing to the DE (DE 00 , DE 01 , DE 02 , and DE 03 ) is impaired due to the release of the link K 31  in the RAID device  13 , the connection may be established by the redundant link KJ 32  such that the access redundancy may be secured in the RAID device  13 . The redundant link KJ 32  is a link which connects the In port IP 131  of the DE 13  and the Out port OP 001  of the DE 00  which is an empty port of the 1-system capable of being accessed with the expander EXP 1 . 
         [0196]    With this configuration, the RAID device  13  connects the redundant link using an empty port capable of being accessed with the controller module  21  such that it becomes possible to secure the access redundancy for the existing DE  20  for which the access redundancy is impaired during the addition work. 
         [0197]    Further, the RAID device  13  may perform a process of adding the DE  20  by applying the method described in the second embodiment. Further, the RAID device  13  may set the identification information of a port which becomes a connection destination of the redundant link in advance. Further, the RAID device  13  may determine a connection destination of the redundant link using other method. 
         [0198]    As described above, even in a state where an empty port of the expander  23  does not exist, the RAID device  13  may establish the connection by the redundant link using an empty port of the DE  20  and secure an access path to the DE  20  for which the redundancy is impaired during the addition. 
         [0199]    Further, the RAID device  13  may perform a process of adding the DE  20  by applying the method described in the second embodiment. With this configuration, the RAID device  13  switches the operation state to allow the connection of the redundant link in the process of adding the equipment. Accordingly, the RAID device  13  may reduce an operation time during which the access redundancy is impaired for the existing equipment in the addition process. Accordingly, the RAID device  13  may secure a work time while maintaining the redundancy in accessing to the existing equipment. 
       Fourth Embodiment 
       [0200]    Descriptions will be made on a connection of the redundant link in a case where the DE 02  is in failure with reference to  FIG. 34  and  FIG. 35 . First, descriptions will be made on the connection configuration in a case where the DE 02  is in failure with reference to  FIG. 34 .  FIG. 34  is a diagram illustrating an example of a connection configuration of a RAID device according to a fourth embodiment. The expander  23 , the DE  20 , the IOM  26 , the Out port  25 , the In port  27 , and the Out port  28  are denoted using identification information instead of reference symbols in order to simplify the description. Further, the denoting by identification information as described above is similarly applied to  FIG. 35 . 
         [0201]    The connection configuration  541  is the connection configuration in which accessing to the DE  20  by the link (KF 1 , KF 2 , KF 3 , and KF 4 ) becomes disabled for a case where the DE 02  is in failure. In the RAID device  13 , when the DE 02  is in failure, the DE 00  and DE 01  may be accessed only in the 0-system and thus the access redundancy is impaired. Further, in the RAID device  13 , when the DE 02  is in failure, the DE 03  and DE 04  may be accessed only in the 1-system and thus the access redundancy is impaired. 
         [0202]    Next, descriptions will be made on a connection configuration according to the fourth embodiment with reference to  FIG. 35 .  FIG. 35  is a diagram illustrating another example of the connection configuration of the RAID device according to the fourth embodiment. The connection configuration  542  illustrated in the diagram indicates a connection configuration in which the redundant links (KJ 41  and KJ 42 ) are connected when a work of replacing the DE 02  which is in failure with a new DE  20  is performed. 
         [0203]    The redundant link KJ 41  connects one end thereof to the E 01  which has been the empty port of the expander EXP 0  of the 0-system and connects the other end thereof to the In port IP 30  of the DE 03 . The RAID device  13  becomes able to access the DE 03  and DE 04  by the connection of the redundant link KJ 41  in two systems composed of the 0-system and the 1-system such that the multiple accessing (redundancy) may be achieved. 
         [0204]    The redundant link KJ 42  connects one end thereof to the E 11  which has been the empty port of the expander EXP 1  of the 1-system and connects the other end thereof to the In port IP 11  of the DE 01 . The RAID device  13  becomes able to access the DE 00  and DE 01  by the connection of the redundant link KJ 42  in two systems composed of the 0-system and the 1-system such that the multiple accessing (redundancy) may be achieved. 
         [0205]    In the present embodiment, in the RAID device  13 , the redundant link is connected in the 0-system and the 1-system using the empty port of the expander  23 . Accordingly, even when the DE  20  is in failure, the RAID device  13  may secure the redundancy in accessing to the DE  20 . Further, in the RAID device  13 , the information of the connection site of the redundant link may be set in advance, the connection site of the redundant link may be detected and determined by the discovery command, and the connection site of the redundant link may be set by other method. 
         [0206]    Further, the RAID device  13  may perform a process of replacing the DE  02  by applying the method described in the second embodiment. With this configuration, the RAID device  13  switches the operation state to allow the connection of the redundant link in the process of adding the equipment. Accordingly, the RAID device  13  may reduce an operation time during which the access redundancy is impaired for the existing equipment in the addition process. Accordingly, the RAID device  13  may secure a work time while maintaining the redundancy in accessing to the existing equipment. 
         [0207]    Further, the processing functions described above may be implemented by a computer. In this case, a program is provided in which the process contents of the functions to be equipped in the connection monitoring device  1  and the RAID device  13  are described. The program is executed by the computer such that the processing functions are implemented in the computer. The program having described therein the processing functions may be recorded in a computer-readable recording medium. The computer-readable recording medium may include, for example, a magnetic storage device, an optical disk, an opto-magnetic recording medium, and a semiconductor memory. The magnetic storage device may include, for example, a hard disk drive (HDD), a flexible disk (FD), and a magnetic tape. The optical disk may include, for example, a DVD, a DVD-RAM, and a CD-ROM/RW. The opto-magnetic recording medium may include, for example, an MO (Magneto-Optical disk). 
         [0208]    A program may be distributed in a portable recording medium such as, for example, a DVD or a CD-ROM in which the program is recorded. Further, a program may be stored in a storage device of a server computer and transferred from the server computer to other computer via a network. 
         [0209]    A computer which executes a program stores, for example, a program recorded in the portable recording medium or a program transferred from the server computer, in the storage device of its own. Also, the computer reads the program from the storage device of its own and executes a process according to the program. In the meantime, the computer may read the program directly from the portable recording medium and execute the process according to the program. Further, the computer may execute the process according to the program received sequentially each time when the program is transferred from the server computer connected via a network. 
         [0210]    Further, at least some of processing functions described above may be implemented by an electronic circuit such as a DSP, an ASIC or a PLD. 
         [0211]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to an illustrating of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.