Patent Publication Number: US-8543762-B2

Title: Computer system for controlling allocation of physical links and method thereof

Description:
CROSS-REFERENCE TO PRIOR APPLICATION 
     This is a Continuation of application Ser. No. 13/029,011 filed Feb. 16, 2011, which is a Continuation of application Ser. No. 11/414,675 filed Apr. 27, 2006. The entire disclosure of the prior application, application Ser. Nos. 13/029,011 and 11/414,675 are considered part of the disclosure of the accompanying Continuation application and are hereby incorporated by reference. 
     This application relates to and claims priority from Japanese Patent Application No. 2006-76505, filed on Mar. 20, 2006 the entire disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a computer system comprising physical links, and more specifically, to a computer system in which physical links for SAS (Serial Attached SCSI)-compliant communications are provided in the backend, for example. 
     2. Description of the Related Art 
     A storage system that comprises a plurality of storage devices (disk drives such as hard disk drives and DVD (Digital Versatile Disk, for example) is known as one type of computer system. A storage system is capable of receiving an I/O command (an I/O command constituting a write command or read command) from an access source device (a host computer or other storage system, for example) and of transmitting data corresponding with the received I/O command to the access source device by writing the data to a storage device or reading the data from a storage device. 
     The disk device disclosed in the Japanese Patent Application Laid Open No. 2005-149173, for example, is known as a storage system of this kind. In this disk drive, a plurality of disk drives are connected to a Fiber Channel-Arbitrated Loop (FC-AL). 
     Further, SAS (Serial Attached SCSI) is known as a communication I/F. SAS is an I/F technology that allows disk drives of different protocol types (SCSI and ATA, for example) to be connected by the same physical wiring. As a computer system that performs SAS-compliant communications to be performed by the backend, a storage system that comprises a plurality of disk drives and a controller that controls access to each disk drive may be considered. In this case, providing the storage system with an SAS expander comprising a plurality of physical communication ports (‘physical phys’ hereinbelow) that is a switch for connecting disk drives for expansion may be considered. A plurality of SAS expanders can be provided and, when a controller is provided at the highest point upstream, a plurality of SAS expanders can be cascade-connected working downstream from the highest point upstream (connected in series or as a tree structure, for example). However, the controller need not be at the highest point upstream and an SAS initiator can be connected to any point of the SAS expander. A controller, an upstream SAS expander, downstream SAS expander, or disk drive can be connected to an optional physical phy of each SAS expander. 
     In this storage system, physical wiring (‘physical link’ hereinbelow) is run between the controller and an SAS expander, between SAS expanders, and between an SAS expander and disk drive in the backend. When a disk drive (SAS target) is accessed, the controller (SAS initiator) is able to access a disk drive via each physical link from the controller to the disk drive. More specifically, for example, when the disk drive connected to the first SAS expander directly below the controller is accessed, the controller is able to access the disk drive via a first physical link that links the controller and the first SAS expander and a secondary physical link that links the first SAS expander and the first SAS expander and the disk drive. 
     SAS includes a technology known as ‘wide link’ that makes it possible to collect a plurality of parallel physical links between single devices as one logical link. That is, a wide link can be formed by a plurality of parallel physical links that connect one device with another device such as between an SAS expander and another SAS expander and between an SAS initiator and an SAS expander. Further, a wide link can also be formed automatically between an SAS expander and another SAS expander or between an SAS initiator and an SAS expander without an SAS-initiator instruction. 
     Further, SAS includes a technology that makes it possible to form a plurality of virtual physical links (‘logical links’ hereinbelow) through time division of a single physical link. Therefore, a plurality of logical links can be constituted in individual physical links forming a wide link. For example, in a case where two physical links with a transfer speed of 6 Gbps are formed by a single wide link, because a 1.5 Gbps logical link with ¼ the transfer speed can be formed by means of a single physical link, a total of eight logical links can be formed in the wide link. In this case, the SAS initiator device is capable of sending and receiving frames simultaneously by establishing a connection with eight SAS target devices at the same time. 
     The controller is able to establish a connection at the same time with a plurality of devices via a plurality of physical links constituting the wide link. When the controller and SAS expander are connected by a wide link and a plurality of disk drives are connected to the SAS expander, the controller is able to simultaneously establish connections with a plurality of disk drives in a quantity equal to the number of physical links constituting the wide link. One controller is able to execute a frame transfer to a plurality of disk drives at the same time by means of a wide link. 
     A characteristic problem can arise with this storage system in each of the first and second cases below, for example. 
     The first case is a case where disk drives with different communication I/Fs are connected to the SAS expander. For example, this case is a case where a disk drive with an SAS I/F (‘SAS drive’ hereinbelow) and a disk drive with a SATA (Serial ATA) I/F (‘SATA drive’ hereinbelow) are connected to one or a plurality of SAS expanders, for example. This case can be implemented by using the same physical link to transfer an SSP (Serial SCSI Protocol) frame for accessing an SAS drive or SAS device and an STP (Serial ATA Tunneled Protocol) frame that tunnels the SATA protocol for accessing the SATA drive. Here, SATA and SAS have different transfer efficiencies (specifically, the transfer efficiency of SATA is inferior to the transfer efficiency of SAS and the time occupied by the physical link is longer). As a result, when there are a large number of SATA-frame I/O transfer requests, there is the possibility of an adverse effect on the throughput with respect to the SAS drive. A problem of this kind is not limited to these two types of I/F and can also exist between I/Fs of other types. 
     The second case is a case where two or more disk drives are one group (‘RAID group’ hereinbelow) that follows the rules of RAID (Redundant Array of Independent (or Inexpensive) Disks) and the RAID groups are connected to an SAS expander. Because a plurality of SAS expanders are cascade-connected, a wide link of a path from the controller to a certain RAID group and a wide link of a path from the controller to another RAID group are common on the upstream side within the backend. As a result, when access to a specified RAID group increases, there is the possibility of an adverse effect on the throughput of the other RAID groups. 
     The above problems are not limited to storage systems and can also exist in other types of computer system. For example, in a case where a plurality of SAS target devices exist in a computer system, when a specified SAS target device is accessed, the possibility of the throughput of the computer system dropping may be considered. 
     Furthermore, the procedure for selecting a physical link for executing a frame transfer from a plurality of physical links that constitute a wide link based on the restrictions of protocols such as SAS cannot be controlled by an SAS initiator device. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to prevent a drop in the throughput of the computer system as much as possible even when there is a concentration of access to a specified SAS target device (e.g. SAS drive, SATA drive, and so on) among a plurality of SAS target devices. This object is preferably implemented without violating the restrictions of the communication protocol of the backend. 
     Further objects of the present invention will become evident from the following description. 
     The computer system according to the present invention comprises a plurality of SAS target devices constituting targets that follow the SAS protocol; an SAS initiator device constituting an initiator that follows the SAS protocol; and a switch section that is connected to each SAS target device by means of a physical link which is physical wiring and that is connected to the SAS initiator device by means of a wide link constituted by a plurality physical links. The service delivery subsystem is one or a plurality of switch devices (e.g. SAS Expander devices) and, when the service delivery subsystem is a plurality of switch devices, the switch devices are cascade-connected with one switch device connected to the SAS initiator device in the leading position and the switch devices are connected to one another by means of a wide link. The computer system further comprises a physical-link allocation control section. The physical-link allocation control section controls how many physical links of at least one wide link among the wide link in the service delivery subsystem and the wide link between the service delivery subsystem and the SAS initiator device are allocated to a particular SAS target device. An I/O from the SAS initiator device to the SAS target device is made via a physical link allocated to the SAS target device and cannot pass a physical link that is not allocated to the SAS target device. 
     In a first embodiment, the computer system may further comprise a monitoring section that monitors, with respect to each SAS target device, the I/O request performance which is the I/O performance requested for the SAS target device. The physical link allocation control section is able to control the number of physical links allocated to each SAS target device on the basis of the I/O request performance for each SAS target device. 
     In second embodiment, the physical link allocation control section according to the first embodiment is capable of allocating a larger number of physical links to an SAS target device with a high I/O request performance than to an SAS target device with a lower I/O request performance. 
     In a third embodiment, SAS target devices of different communication protocols are mixed in the plurality of SAS target devices. The physical link allocation control section is able to control the number of physical links allocated to each SAS target device on the basis of the type of communication protocol of the SAS target device. 
     In a fourth embodiment, the physical link allocation control section according to the third embodiment is capable of allocating a larger number of physical links to an SAS target device that communicates by means of a communication protocol of a poor transfer efficiency than to an SAS target device that communicates by means of a communication protocol of a good transfer efficiency. Conversely, the physical link allocation control section is also able to allocate a larger number of physical links to an SAS target device that communicates by means of a communication protocol of good transfer efficiency than to an SAS target device that communicates by means of a communication protocol of poor transfer efficiency. 
     In a fifth embodiment, each SAS target device is a storage device. Two or more storage devices may constitute a RAID group as a result of grouping in accordance with RAID rules. The physical link allocation control section is able to control the number of allocated physical links in RAID group units. 
     In a sixth embodiment the computer system may further comprise a zone setting section that performs zone setting in which an access path from the SAS initiator device to the plurality of SAS target devices is divided into a plurality of logical zones. The physical link allocation control section is able to control the number of physical links allocated to each SAS target device on the basis of the set plurality of zones. 
     In the seventh embodiment, when a plurality of SAS target devices belong to one zone, the physical link allocation control section according to the sixth embodiment is able to control the number of physical links allocated to each of the plurality of SAS target devices within the range of this one zone. 
     In an eighth embodiment, the computer system may further comprise a resource monitoring section that issues at fixed intervals a resource monitoring command for monitoring the resource (SAS target device, for example) of an enclosure connecting the plurality of SAS target devices at fixed intervals. In this case, the zone setting section is able to set an I/O dedicated zone that is used for I/Os with respect to the SAS target devices and that is not used to issue the resource monitoring command and a resource monitoring dedicated zone that is used to issue the resource monitoring command and that is not used for I/Os. 
     In the ninth embodiment, the SAS initiator device according to the first embodiment is able to receive an I/O request from an access source that exists outside the computer system, perform a first I/O with respect to a first SAS target device corresponding with the I/O request, and perform a second I/O with respect to a second SAS target device by means of a backend irrespective of the I/O request from the access source. The physical link allocation control section is able to control the number of physical links allocated to the first SAS target device and the number of physical links allocated to the second SAS target device on the basis of the I/O request performance of the first I/O and the I/O request performance of the second I/O respectively. 
     In the tenth embodiment, the physical link allocation control section according to the ninth embodiment is able to allocate a larger number of physical links to the first SAS target device than to the second SAS target device when the I/O request performance of the first I/O is higher than the I/O request performance of the second I/O. 
     In the eleventh embodiment, the SAS initiator device is able to receive an I/O request from a plurality of access sources that exist outside the computer system and performs an I/O with respect to the SAS target device corresponding with the I/O request. The physical link allocation control section is able to allocate, based on the respective priority levels of the plurality of access sources, a larger number of physical links to an SAS target device corresponding with an I/O request from an access source of higher priority than to an SAS target device corresponding with an I/O request from an access source of a lower priority. 
     In the twelfth embodiment, the physical link allocation control section is able to prevent an I/O with respect to a certain SAS target device by making the number of physical links allocated to the certain SAS target device zero or releasing the allocation of physical links connecting the certain SAS target device and the service delivery subsystem, in at least one wide link among the wide link between the service delivery subsystem and the SAS initiator device and the wide link in the service delivery subsystem. 
     In the thirteenth embodiment, each of the one or plurality of switch devices can comprise a plurality of communication ports respectively connected to a plurality of physical links and a storage area that stores switch control information. The switch control information records, for each of the plurality of communication ports, direct device data representing devices that are directly attached without the interposition of another communication port and indirect device data representing SAS target devices that are connected indirectly via another communication port. When the direct device data for the communication ports are data representing SAS target devices, the SAS target device can be an SAS target device to which physical links connected to the communication ports are allocated. The indirect device data for the communication ports can be data representing SAS target devices to which physical links connected to the communication ports are allocated. The physical link allocation control section controls the physical links allocated to the SAS target devices by updating the switch control information for at least one switch device of the one or plurality of switch devices. 
     In the fourteenth embodiment, if each of the one or plurality of switches according to the thirteenth embodiment receives a connection request for establishing a connection with a certain SAS target device via a physical link that is not allocated to the certain SAS target device, an error can be sent back to the source that issued the connection request via the physical link so that a connection is not established via the physical link. 
     In the fifteenth embodiment, a management terminal for managing the computer system may be communicably connected to the computer system. The physical link allocation control section is able to control how many physical links are allocated to a particular SAS target device in accordance with an instruction from the management terminal. 
     In the sixteenth embodiment, the computer system may be a storage system comprising a plurality of storage devices. The plurality of SAS target devices may be the plurality of storage devices. The SAS initiator device may be a controller for controlling I/Os with respect to the respective storage devices. The service delivery subsystem may be a plurality of switch devices. Each of the plurality of switch devices can comprise a plurality of communication ports respectively connected to a plurality of physical links and a storage area for storing switch control information. The switch control information may record, for each of the plurality of communication ports, direct device data representing devices that are directly attached without the interposition of another communication port and indirect device data representing storage devices that are connected indirectly via another communication port. When the direct device data for the communication ports are data representing storage devices, the storage devices can be storage devices to which physical links connected to the communication ports are allocated. The indirect device data for the communication ports can be data representing storage devices to which physical links connected to the communication ports are allocated. The storage system may further comprise a monitoring section for monitoring, for each of the storage devices, the I/O request performance which is the I/O performance requested for the storage device. The physical link allocation control section can control the number of physical links allocated to each of the storage devices by updating the switch control information for at least one of the plurality of switch devices on the basis of the I/O request performance with respect to each storage device. 
     In the seventeenth embodiment, two or more storage devices according to the sixteenth embodiment can form a RAID group as a result of grouping in accordance with RAID rules and the physical link allocation control section can control the number of allocated physical links in RAID group units. 
     In the eighteenth embodiment, the computer system may be a storage system comprising a plurality of storage devices. The plurality of SAS target devices may be the plurality of storage devices. The plurality of storage devices may be a mix of a SCSI storage device, which is a storage device that performs communications that follow the SCSI protocol, and an ATA storage device, which is a storage device that performs communications that follow the ATA protocol. The SAS initiator device may be a controller that controls I/Os with respect to the respective storage devices. The service delivery subsystem may be a plurality of switch devices. Each of the plurality of switch devices can comprise a plurality of communication ports connected to a plurality of physical links and a storage area that stores switch control information. The switch control information may record, for each of the plurality of communication ports, direct device data representing devices that are directly attached without the interposition of another communication port and indirect device data representing storage devices that are connected indirectly via another communication port. When the direct device data for the communication ports are data representing storage devices, the storage devices may be storage devices to which physical links connected to the communication ports are allocated. The indirect device data for the communication ports may be data representing storage devices to which physical links connected to the communication ports are allocated. The physical link allocation control section can control the number of physical links allocated to each of the storage devices by updating the switch control information for at least one of the plurality of switch devices on the basis of whether the communication protocol of each storage device is SCSI or ATA. 
     In the nineteenth embodiment, the physical links whose allocation is controlled may be virtual physical links. The virtual physical links are logical links formed by time-dividing one physical link. The I/O from the SAS initiator device to the SAS target device is made via a logical link that is allocated to the SAS target device and cannot pass a logical link that is not allocated to the SAS target device. The SAS initiator device is capable of establishing a connection at the same time as a plurality of the SAS targets by means of a logical link of one physical link. 
     The respective parts above may be called the respective means. The respective parts can also be implemented by hardware (circuits, for example) and computer programs or a combination thereof (for example, one or a plurality of CPUs that read and execute computer programs). Each computer program can be read from a storage resource (memory, for example) contained in a computer machine. Each computer program can be installed on the storage resource via a recording medium such as a CD-ROM or DVD (Digital Versatile Disk) or can be downloaded via a communication network such as the Internet or a LAN. 
     Further, at least one of the control units or monitoring sections to which the above physical link is allocated may be installed in an SAS initiator device. 
     Further, for example, said ‘service delivery subsystem’ is the part of a SCSI I/O system that transmits information between a SCSI initiator port and a SCSI target port. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a constitutional example of the storage system of a first embodiment of the present invention; 
         FIG. 2  is a block diagram showing a constitutional example of a storage controller  200 ; 
         FIG. 3  is a constitutional example of a control program  300 ; 
         FIG. 4  shows a constitutional example of a direct device table  195   a  in an SAS expander  130   a  and information that is registered in the table  195   a;    
         FIG. 5  shows a constitutional example of a direct device table  195   b  in an SAS expander  130   b  and information that is registered in the table  195   b;    
         FIG. 6  shows a constitutional example of an expander route table  196   a  in an SAS expander  130   a  and information that is registered in the table  196   a;    
         FIG. 7  shows a constitutional example of an expander route table  196   b  in an SAS expander  130   b  and information that is registered in the table  196   b;    
         FIG. 8  shows an example of the flow of processing that is performed when the storage system is booted; 
         FIG. 9  shows an example of the flow of processing for changing the number of physical links  108  allocated to a zone  150 ; 
         FIG. 10  shows an example of the flow of processing that is performed in step  600  of  FIG. 9 ; 
         FIG. 11  shows a constitutional example of a zone state management table  700 ; 
         FIG. 12A  shows the allocation of physical links prior to changing the allocation in a first case where the allocation of the physical links is changed; 
         FIG. 12B  shows the allocation of physical links after changing the allocation; 
         FIG. 13  shows the allocation of physical links prior to changing the allocation in a second case where the allocation of the physical links is changed; 
         FIG. 14  shows the allocation of physical links after changing the allocation; 
         FIG. 15A  shows the allocation of physical links prior to changing the allocation in a third case where the allocation of the physical links is changed; 
         FIG. 15B  shows the allocation of physical links after changing the allocation; 
         FIG. 16  is an explanatory diagram of a first modified example of the first embodiment of the present invention; 
         FIG. 17  is an explanatory diagram of a second modified example of the first embodiment of the present invention; 
         FIG. 18  is an explanatory diagram of a third modified example of the first embodiment of the present invention; 
         FIG. 19  is an explanatory diagram of a fourth modified example of the first embodiment of the present invention; 
         FIG. 20  is an explanatory diagram of a fifth modified example of the first embodiment of the present invention; 
         FIG. 21  shows an example of the flow of processing to establish a connection between an SAS target device and an SAS initiator device; and 
         FIG. 22  shows an example in which a physical link and a logical link are mixed in one wide link. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A storage system in which a computer system according to a first embodiment of the present invention will be described hereinbelow by way of example with reference to the drawings. 
       FIG. 1  is a block diagram showing a constitutional example of the storage system of a first embodiment of the present invention. The description is provided hereinbelow by adding the same parent numbers to elements of the same type and adding child numbers to the parent numbers when elements of the same type are described individually. 
     A storage system  100  can be connected by an interface  103  such as an FC (Fiber Channel), a SCSI (Small Computer System Interface), SAS (Serial Attached SCSI), or IP (Internet Protocol) to a SAN (storage area network)  102  to which one or a plurality (two, for example) of host computers  101   a  and  101   b  are connected. Further, the storage system  100  can also be connected to a management network  106  to which a management terminal  104  is connected, for example. Various networks (such as a LAN (Local Area Network), for example) can be adopted as the management network  106 . Another type of network may be adopted in place of the SAN  102 . Further, the management network  106  and SAN  102  may be one communication network. 
     Each of the host computers  101   a  and  101   b  is a computer comprising hardware resources such as a CPU, a memory, and an I/O port to be used for communicating with the storage system  100 , for example. Each of the host computers  101   a  and  101   b  is able to access data in the storage system  100  via the SAN  102 . 
     The management terminal  104  is a computer comprising hardware resources such as a CPU, an I/O device, a memory, and an interface. The CPU of the management terminal  104  is able to control the storage system  100  by executing a storage system management program  105  (operating instruction for configuration information acquisition, for example). 
     The storage system  100  comprises a plurality of disk drives  114  that are capable of storing data, one or a plurality of SAS expanders  130  which are switches for connecting the disk drives  114  for expansion, and one or a plurality of storage controllers  200  that control the storage system  100 . The disk drives  114  are hard disk drives but disk drives of other types such as DVD (Digital Versatile Disk) drives and CD (Compact Disk) drives may also be adopted. Where the physical links  108  that are connected to the SAS expander  130  are concerned, disk drives  114  that use different protocols can be connected to the same physical link  108 . The physical link  108  can transfer frames of protocols supported by the drives  114 . The SAS expander  130  can be constituted by a hardware circuit base. 
       FIG. 1  shows three disk drives  114   a ,  114   b , and  114   c , two SAS expanders  130   a  and  130   b , and one storage controller  200  by way of example. The following description is provided by suitably using this example. Further, in the following description, the storage controller  200  is at the highest point upstream. 
     Two SAS expanders  130   a  and  130   b  are cascade-connected from an upstream position to a downstream position. In this example, because there are two SAS expanders, there is a serial connection. However, when there are three or more SAS expanders, a tree structure may be used with the SAS expander  130   a  in the leading position. 
     The storage controller  200  and the SAS expander  130   a  directly below same are connected by a plurality of physical links  108   a ,  108   b , and  108   c , and one wide link  120   a  is formed by the plurality of physical links  108   a ,  108   b , and  108   c . Likewise, the SAS expander  130   a  and SAS expander  130   b  are also connected by a plurality of physical links  108   d ,  108   e , and  108   f  and a wide link  120   b  is formed by the plurality of physical links  108   d ,  108   e , and  108   f . An ID is allocated to each of the SAS expanders  130   a  and  130   b  in order to identify the ports to which the physical links are connected (the each port could be called ‘physical phy’ hereinbelow). ‘Physical phy’ is a phy that contains a transceiver and electrically interfaces to a physical link to communicate with another physical phy. ‘phy’ is an object in a device that is used to interface to other devices (e.g. an expander phy or a SAS phy). In this embodiment, phy identifier  0  of the SAS expander  130   a  corresponds with physical link  108   a , phy identifier  1  of the SAS expander  130   a  corresponds with physical link  108   b , phy identifier  2  of the SAS expander  130   a  corresponds with physical link  108   c , phy identifier  3  of the SAS expander  130   a  corresponds with physical link  108   g , phy identifier  4  of the SAS expander  130   a  corresponds with physical link  108   d , phy identifier  5  of the SAS expander  130   a  corresponds with physical link  108   e , and phy identifier  6  of the SAS expander  130   a  corresponds with physical link  108   f . Likewise, phy identifier  1  of the SAS expander  130   b  corresponds with physical link  108   d , phy identifier  2  of the SAS expander  130   b  corresponds with physical link  108   e , phy identifier  3  of the SAS expander  130   b  corresponds with physical link  108   f , phy identifier  4  of the SAS expander  130   b  corresponds with physical link  108   h , and phy identifier  5  of the SAS expander  130   b  corresponds with physical link  108   i . ‘phy identifier’ is an identifier for a phy that is unique within the device containing it. 
     The phy identifiers  4  to  6  of the SAS expander  130   a  are established as downstream physical phys. The phy identifiers  1  to  3  of the SAS expander  130   b  are established as upstream physical phys. From the perspective of the SAS expander  130   b , the SAS expander  130   a  is an upstream device. 
     A plurality of disk drives  114  may be constituted only by disk drives that perform communications by means of the same type of protocol (in other words, comprising the same type of I/F) or disk drives of different protocols may be mixed. As an example of the latter, a disk drive with a SCSI I/F (‘SCSI drive’ hereinbelow) and a disk drive with an ATA I/F (‘ATA drive’ hereinbelow), for example, may be mixed. A disk drive with an SAS I/F can be adopted as the SCSI drive. A disk drive with a SATA I/F (or PATA (Parallel ATA) I/F) can be adopted as the ATA drive. Further, when a PATA I/F drive is adopted, processing (PATA and SATA physical layer conversion) to convert serial transmission to parallel transmission is performed by means of communication between this drive and the SAS expander  130 . 
     The disk drive  114  sometimes also has a plurality of physical phys with the object of redundancy within the storage system  100 . For example, when the disk drive  114  is a SATA drive, a SATA port selector is sometimes interposed between the SAS expander  130  and the SATA drive (a SATA port selector is not shown in  FIG. 1 ) in order to increase the number of ports with the object of redundancy. 
     The disk drive  114   a  is connected to phy identifier  3  of the SAS expander  130   a  via the physical link  108   g . Disk drive  114   b  is connected to phy identifier  4  of the SAS expander  130   b  via the physical link  108   h . Disk drive  114   c  is connected to phy identifier  5  of the SAS expander  130   b  via the physical link  108   i.    
     The disk drives  114   b  and  114   c  constitute a group according to RAID rules (‘RAID group’ hereinbelow)  140 . One RAID group  140  can be constituted by a plurality of disk drives  114  but each of the plurality of disk drives  114  may be connected to one SAS expander  130  or may be connected to different SAS expanders  130 , under the governance of one storage controller  200 . Alternatively, the plurality of disk drives  114  may be governed by different storage controllers  200 . That is, the RAID group  140  can be constituted to extend across a plurality of SAS expanders  130  and can be constituted to extend across a plurality of storage controllers  200 . 
     The SAS expander  130  comprises a storage area (memory, for example). The storage area stores a zone setting program  190 , a direct device table  195 , and an expander route table  196 . Information on devices that are directly attached to the SAS expander  130  comprising this table  195  is stored in the direct device table  195 . On the other hand, information on devices that are indirectly attached to the SAS expander  130  comprising the table  196  is recorded in the expander route table  196 . Tables  195  and  196  may be integrated. 
     The zone setting program  190  changes the content of the direct device table  195  and/or expander route table  196  by means of an instruction from an SAS expander control program  320  ( FIG. 3 ) in the storage controller  200  and, as a result, the setting of zone  150  can be changed. Details of the direct device table  195 , expander route table  196 , and zone  150  will be provided subsequently. 
     One or a plurality of zones  150  can be established virtually in the storage system  100 . The storage system  100  is capable of controlling the allocation of physical links on the basis of the setting of the zone  150 . Zone  150  can be set on the basis of various conditions. More specifically, zone  150  can be set on the basis of the protocol type of the disk drive  114  or in units of the RAID group  140 , for example. 
     The zone  150   a  exemplified by  FIG. 1  comprises physical links  108   a ,  108   b , physical links  108   d  and  108   e , and physical links  108   h  and  108   i . In this case, when the storage controller  200  accesses the RAID group  140 , either of the physical links  108   a  and  108   b  in the wide link  120   a  is used and the physical link  108   c  not contained in zone  150   a  is not used. 
     Meanwhile, zone  150   b  exemplified by  FIG. 1  contains physical links  108   c  and  108   g . As a result, when the storage controller  200  accesses the disk drive  114   a , only physical link  108   c  is adopted by the wide link  120   a  and the physical links  108   a  and  108   b  that are not contained in zone  150   a  are not used. 
       FIG. 2  is a block diagram showing a constitutional example of the storage controller  200 . 
     The storage controller  200  comprises a host I/F controller  210 , a management terminal I/F  211 , a RAID controller  212 , a memory  213 , and an SAS controller  214 . At least one of the host I/F controller  210 , SAS controller  214 , RAID controller  212  and memory  213  may be limited to one or may be provided in a plurality. 
     The host I/F controller  210  is communicably connected to a host  101  via the SAN  102  by means of the interface  103  in  FIG. 1 . The host I/F controller  210  is capable of controlling the conversion of the protocol for communications between the host computer  101  and RAID controller  212 . 
     The management terminal I/F  211  is communicably connected to the management terminal  104  via the management network  106  of  FIG. 1 . The management terminal I/F  211  is capable of controlling the conversion of the protocol for communications between the management terminal  104  and RAID controller  212 . 
     The host I/F controller  210 , management terminal I/F  211 , memory  213 , and the SAS controller  214  are connected to the RAID controller  212  by buses  220   a ,  220   b ,  220   c , and  220   d . Bus  220  is a PCI or PCI-Express or the like, for example. 
     The memory  213  stores a control program  300  and is read to and executed by the RAID controller  212 . Details on the control program  300  will be provided subsequently. 
     The SAS controller  214  is capable of controlling conversion of the protocol for communications between the SAS expander  130  and the RAID controller  212 . The SAS expander  214  comprises a wide port  250 . The wide port  250  is a port constituted by two or more physical phys and is connected to the SAS expander  130   a  via the wide link  120   a . The SAS controller  214  may comprise a plurality of wide ports  250 . In other words, when a plurality of SAS expanders  130  are connected to the SAS controller  214 , the SAS controller  214  comprises a plurality of wide ports  250 . 
     The RAID controller  212  can comprise a microprocessor, a bridge for data transfers (LSI (Large Scale Integration), for example), and a RAID control logic circuit (an exclusive OR X-or engine, for example), for example. The processor, bridge, and RAID control logic circuit and so forth in the RAID controller  212  may be divided between a plurality of chips. 
     Upon receipt of a write command from the host computer  101 , the storage controller  200  is capable of temporarily storing data corresponding with the write command in the memory  213  and writing the data stored in the memory  213  to the disk drive  114 . On the other hand, when the storage controller  200  receives a read command from the host computer  101 , the storage controller  200  is able to read data corresponding with the read command from the disk drive  114 , store the data thus read temporarily to the memory  213 , and transmit the data stored in the memory  213  to the host computer  101 . 
       FIG. 3  shows a constitutional example of the control program  300 . 
     The control program  300  comprises an SAS expander control program  320 , an RG/LU setting program  330 , a zone configuration control program  340 , a performance monitoring program  350 , a background control program  360 , and a fault processing program  370 , for example. 
     The SAS expander control program  320  issues an inquiry to the direct device table  195  in the SAS expander  130  and, as a result, is able to acquire the physical mount positions of the disk drive  114  and SAS expander  130 . 
     Furthermore, the SAS expander control program  320  is able to register the addresses of devices that are indirectly attached downstream and set route information in the expander route table  196 . In the case of the expander route table  196   a  of the SAS expander  130   a , an indirectly attached device is a device that is not directly attached to the respective physical phys of the SAS expander  130   a  and is capable of access from this physical phy via at least one other physical phy. More specifically, stated with respect to the example in  FIG. 1 , the indirectly attached devices of phy identifiers  0  and  1  are disk drives  114   b  and  114   c  and the indirectly attached device of phy identifier  2  is disk drive  114   a . Therefore, in order to establish a connection with the disk drives  114   b  and  114   c , for example, potential pathway information for reaching the disk drives  114   b  and  114   c  must be registered in the expander route table  196   a  of the SAS expander  130   a . ‘Potential pathway’ is a set of physical links between a SAS initiator phy and a SAS target phy. 
     The SAS expander control program  320  is also capable of acquiring the number of the plurality of physical links  108  constituting the wide link  120  and an ID for identifying each physical link (for identifying the phy identifier of the SAS expander) and registering the number and ID in the direct device table  195 . In other words, the SAS expander  130  is able to hold the wide link  120 , the number of physical links  108  constituting the wide link  120  and the ID for identifying the physical links in the direct device table  195  of the SAS expander. 
     The RG/LU setting program  330  is a program for setting the RAID group  140  and setting an LU (logical unit) in the RAID group  140 . The LU is also called the logical volume. The host computer  101  issues an I/O command for designating the LUN (logical unit number) which is an ID for identifying the LU. The storage controller  200  is able to use the LUN designated by the host computer  101  to specify the RAID group  140  corresponding with the LUN and access the specified RAID group  140 . 
     The zone configuration control program  340  is a program for changing the settings of the zone  150 . The zone configuration control program  340  is capable of determining settings for logically allocating a physical link  108  constituting the wide link  120  to the disk drive  114  or RAID group  140  and issuing a request for a zone change to the zone setting program  190  of the SAS expander  130 . Further, because the zone configuration control program  340  co-operates with the storage system management program  105  operated by the administrator, the settings of the zone  150  can also be changed by means of manual operation by the administrator. 
     The performance monitoring program  350  is a program for estimating the I/O requests of the host computer  101  or background control program  360  and generating statistical information on performance. The performance monitoring program  350  is capable of generating performance statistical information by means of the history of past I/O characteristics and the estimated performance. 
     The background control program  360  is a computer program executed by the backend. The background control program  360  is a program that executes a correction copy of the RAID group  140 , and data transfers and copies between disk drives  114 , and so forth, for example. The background control program  360  is a generic term for a program related to I/O processing that is executed in storage. Subsequently, because an I/O executed by the background control program  360  is not an I/O that is performed in accordance with an I/O request from the host computer  101 , this I/O is known as an internal I/O. Further, the copying or movement of data is not limited to copying or movement within the storage system  100 . Copying (so-called remote copying) to a disk drive within the external storage system or movement if possible, for example, is also acceptable. 
     The fault processing program  370  is a program for detecting various faults of the storage system  100 . More specifically, for example, the fault processing program  370  is constituted to detect a fault when a fault occurs in a physical link  108  constituting the wide link  120  and to execute processing that corresponds with the fault. 
     The direct device table  195  and expander route table  196  will be described next and zone control will be described at such time. 
       FIG. 4  shows a constitutional example of the direct device table  195   a  in the SAS expander  130   a  and information that is registered in the table  195   a .  FIG. 5  shows a constitutional example of the direct device table  195   b  in the SAS expander  130   b  and information that is registered in the table  195   b .  FIG. 6  shows a constitutional example of an expander route table  196   a  in the SAS expander  130   a  and information that is registered in the table  196   a .  FIG. 7  shows a constitutional example of an expander route table  196   b  in the SAS expander  130   b  and information that is registered in the table  196   b.    
     The direct device table  195  is a table for associating devices that are directly attached to the SAS expander  130  (drives and SAS controllers and so forth) with the phy identifier of the SAS expander  130 . Further, information for managing the zone setting is also saved in the direct device table  195 . 
       FIG. 4  will now be described. A plurality of phy identifiers that correspond with each of the plurality of physical phys of the SAS expander  130   a  are recorded in fields  410  of the direct device table  195   a . The SAS-compliant addresses (‘SAS addresses’ hereinbelow) of the devices that are directly attached to the physical phy are recorded for each of the physical phys of the SAS expander  130   a  in fields  420 . The SAS addresses of devices that permit transmission (‘permitted devices’ hereinbelow) are recorded for each physical phy of the SAS expander  130   a  in field  430 . The permitted devices are the access source of the backend of the storage system  100 . The access source is different depending on whether data is sent from upstream to downstream or from downstream to upstream. In the former case, the access source is the SAS controller  214  and, in the latter case, the access source is the device drive  114 . Consequently, in this embodiment, the permitted device is either the SAS controller  214  or disk drive  114 . 
     In the case of the connection configuration exemplified by  FIG. 1 , a device that is directly attached to the physical phy of phy identifier  0  of the SAS expander  130   a  is the SAS controller  214 . Accordingly, the SAS expander  130   a  registers the SAS address of the SAS controller  214  in a field corresponding with a phy identifier  0  in fields  420 . The SAS expander  130  also registers information representing the connection configuration exemplified by  FIG. 1  also for the other phy identifiers. 
     Further, in the case of zone  150   a  in  FIG. 1 , the device using phy identifier  0  of the SAS expander  130   a  is either disk drive  144   b  or  144   c . Accordingly, the zone configuration control program  340  registers the SAS addresses of the disk drives  144   b  and  144   c  in field  430  as permitted devices corresponding with phy identifier  0 . The zone configuration control program  340  likewise registers the SAS address of the permitted device corresponding with each phy identifier in accordance with zone  150   a  and zone  150   b  in  FIG. 1  also for the other phy identifiers. Further, NULL in field  430  signifies that there is no permitted device. Hence, when there is no permitted device at all as per the phy identifier  6  of the SAS expander  130   a  (See  FIG. 1 ), all NULL are recorded in the fields of the permitted devices (fields of field  430 ). 
     Moreover, a wide link and a plurality of physical links constituting the wide link can be associated in the direct device table  195   a . Thereupon, information representing whether the wide link is upstream from the perspective of the SAS expander  130   a  having the table  195   a  can be established. As a result, the SAS expander  130   a  is able to distinguish via which wide link data from the disk drive  140  may flow upstream. According to table  195   a , when an I/O for disk drive  144   a  is received from the physical phy of phy identifier  2  on the upstream side, the SAS expander  130   a  is capable of outputting the I/O from the physical phy of phy identifier  3  because it can be seen from table  195   a  that the disk drive  144   a  is directly attached to the physical phy of phy identifier  3 . 
       FIG. 5  will be described next (a description of the points in common with the description of  FIG. 4  will be omitted or simplified here). 
     Information representing the connection configuration exemplified by  FIG. 1  is also registered in the table  195   b  in  FIG. 5 . That is, because the SAS expander  130   a  is directly attached to the physical phy of phy identifier  0  of the SAS expander  130   b , for example, the SAS address of the SAS expander  130   a  is registered in a field of fields  410  that corresponds with phy identifier  0 . Further, because a device that is directly attached to the physical phys of phy identifiers  5  and  6  of the SAS expander  130   b , for example, does not exist, NULL is registered in fields of fields  410  that correspond with phy identifiers  5  and  6 . According to table  195   a , when an I/O for disk drive  144   b  is received from the physical phy of phy identifier  1  on the upstream side, the SAS expander  130   b  is capable of outputting the I/O from the physical phy of phy identifier  3  because it can be seen from table  195   b  that disk drive  144   b  is directly attached to the physical phy of the phy identifier  3 . 
     As described hereinabove, in this embodiment, a phy identifier (may be an ID of another type), an SAS address (may also be information of another type) representing a device that is directly attached to the physical phy, and an SAS address (may also be information of another type) representing an access source device that allows its physical phy to be bypassed are recorded in the direct device table  195  for each physical phy of the SAS expander  130  comprising the table  195 . 
     The expander route table  196  will be described next. The expander route table  196  is a table that holds information on devices that are indirectly attached to the downstream side of the SAS expander  130  that comprises the table  196  (connected with at least one physical phy isolated). The wide port  250  (Logical port) of the SAS expander  130  that designates the Subtractive attribute of the SAS standard is called the ‘downstream port’ hereinbelow and the wide port of the SAS expander  130  that designates the Table attribute of the SAS standard will be called the ‘upstream wide port’ hereinbelow. Where the registered content of the expander route table  196  is concerned, per an expander route table of the SAS standard, when another SAS expander  130  is connected to the downstream wide port of a certain SAS expander  130  and an indirectly attached device is connected to the other SAS expander  130 , the SAS expander control program  320  must register the SAS address of the indirectly attached device in the expander route table  196  of the upstream SAS expander  130 . 
       FIG. 6  will now be described. Because the SAS expander  130   b  is connected to the downstream wide port of the SAS expander  130   a  in  FIG. 1 , the SAS expander control program  320  registers the SAS address of the indirectly attached device (disk drive  144   b  or  144   c ) that performs access via the wide link  120   a  in  FIG. 1  in fields  510  that correspond with the numbers of each physical phy constituting the wide link  120   a  of the expander route table  196   a  (further, ‘Physical Phy’ in  FIG. 6  represents a physical phy). According to Table  196   a , when an I/O for disk drive  144   b  is received from upstream, the SAS expander  130   a  is able to output the I/O from the physical phys of phy identifiers  4  or  5  because it can be seen from Tables  195   a  and  196   a  that the disk drive  144   b  is an indirectly attached device that is allocated to downstream phy identifier  4  or  5 . 
       FIG. 7  will now be described. In  FIG. 1 , where the SAS expander  130   b  is concerned, another SAS expander  130  is not connected to the downstream wide port of the SAS expander  130   b . As a result, the fields  510  of the expander route table  196   b  are all unregistered. 
     As a result of the constitution of the respective tables exemplified in  FIGS. 4 to 7 , control of access to each of the disk drives  114  can be performed by the storage controller  200 , for example. Control in each case will be described hereinbelow with reference to  FIG. 21  and also suitably with reference to  FIGS. 1 ,  2 , and  4  to  7 . 
     Upon gaining access to a desired disk drive  114 , the storage controller  200  is able to issue a predetermined frame for establishing a connection (‘open address frame’ hereinbelow) and, when, thereafter, a response representing the establishment of a connection is received, the storage controller  200  is able to access the desired disk drive  114 . 
     More specifically, for example, when the storage controller  200  writes data to disk drive (hereinbelow ‘SAS target device’)  114   b , the control program  300  first transmits a request to transmit a frame (frame including a write request and write target data) to the SAS controller (‘SAS initiator device’ hereinbelow)  214  (S 0 ). The SAS initiator device  214  receives the request and attempts to establish a connection by issuing an open address frame for an SAS target device  114   b  from the physical phy of an optional phy identifier of the wide port  250  (S 1 ). At this stage, the SAS initiator device  214  designates a phy identifier in accordance with a predetermined rule and is unable to select the phy identifier by means of a method that does not comply with the rules due to the restrictions of the SAS protocol. For example, the rules dictate that, if the phy identifiers are designated in order of how young they are, the SAS initiator device  214  should first issue an open address frame from the physical phy of phy identifier  0  and cannot issue an open address frame from the physical phy of the phy identifier  2  in a state where the physical phys  0 ,  1  have not established a connection, for example, from the outset by ignoring the rules. 
     Upon receipt of an open address frame, the SAS expander  130   a  references the expander route table  196   a  and checks the path for establishing a connection with the SAS target device  114   b  (S 2 ). Here, when the SAS expander  130   a  comprises a plurality of physical phys in the form of a wide port, a young number is selected from among the available physical phys excluding the physical phys that cannot be used as a result of other connection and zone settings. 
     When, as a result of referencing the direct device route table  195   a  and the expander route table  196   a , and so forth, any one of path not found, no target, and connection not possible due to zone non-registration applies, the SAS expander  130   a  sends back an OPEN REJECT error to the SAS initiator device  214 . Upon receipt of the OPEN REJECT error (S 4 ), the SAS initiator device  214  transmits information contained in the error, for example, an address error of the SAS target device, or a connection establishment not possible due to zone non-allocation to the control program  300  and the control program  300  receives this information (S 6 ). When the establishment of a connection fails due to the zone non-allocation, a Primitive, which signifies the failure of connection establishment due to zone non-allocation is newly defined for the SAS signal called ‘Primitive’ and, by issuing the Primitive for which the SAS expander has been newly defined, the impossibility of the establishment of a connection due to zone non-allocation can also be identified. When the OPEN_REJECT error is happened due to the zone non-allocation, an OPEN_REJECT error, which signifies the OPEN_REJECT error due to zone non-allocation can be newly defined for the SAS control signal called ‘Primitive’. In case of the zone non-allocation, the failure of connection establishment due to zone non-allocation can be categorized an other error cause by transmitting a response to the connection request by way of the defined OPEN_REJECT-Primitive. 
     The serial processing of this stage is performed when the SAS expander  130   a  receives an open address frame via the physical phy of the phy identifier  2 , for example. This is because the SAS address of the disk drive  114   b  is not registered in the field corresponding with the phy identifier  2  in the direct device table  195   a  and the SAS address of the disk drive  114   b  is not registered in the field corresponding with the phy identifier  2  in the expander route table  196   a  either. 
     In S 2 , when any of path not found, no target, and connection not possible due to zone non-registration applies but all the physical phys constituting a wide port are being used by another connection, the SAS expander  130   a  sends back OPEN REJECT to the SAS initiator device  214 . Upon receipt of the OPEN REJECT error (S 5 ), the SAS initiator device  214  performs S 1  once again. The number of retries and the time required for the retries are managed by the SAS initiator device  214  and failure of the retries when a threshold value is reached is reported to the control program. 
     When, in S 2 , any of path not found, no target, and connection not possible due to zone non-registration does not apply and there is an available physical phy of a path that has been found, the SAS expander  130   a  selects the available physical phy, defines the paths of the available physical phy and the physical phy of the SAS expander on the address-frame input side (internal switching of SAS expanders is defined), and transfers the address frame to the downstream SAS expander  130   b  via the selected available physical phy (S 3 ). As a result, the same S 2  processing as for the SAS expander  130   a  is performed for the SAS expander  130   b  and, when the SAS target device  114   b  is found, communications are performed between the SAS expander  130   b  and SAS target device  114   b  to establish a connection (S 7 ). The SAS target device  114   b  issues an OPEN Accept, whereupon the OPEN Accept passes through the connection (path) established between the SAS initiator device  214  and SAS target device  114   b  before returning to the SAS initiator device  214  (S 8 ). The SAS initiator device  214  responds to receiving the OPEN Accept and transfers the frame corresponding with the frame transmission request received in S 1  to the SAS target device  114   b  (S 9 ). When the frame is received (S 10 ), the SAS target device  114   b  sends back an ACK. The SAS initiator device  214  receives the ACK (S 11 ) and, when a frame transfer is not required, performs a connection end sequence (S 12 ) to end the connection by releasing the physical phys of all the SAS expanders. 
     An example of the flow of processing performed when a connection is established was described above. When data is sent from the SAS target device to the SAS initiator device, the SAS target device above outputs a connection request to the SAS initiator device and transfers the frame from the SAS target device to the SAS initiator device. Because the processing sequence is the same as the sequence in  FIG. 21  except for the fact that the connection request is implemented by the SAS target device, a description is omitted here. 
     An example of the flow of processing that is performed by the storage system  100  according to this embodiment will be described hereinbelow. 
       FIG. 8  shows an example of the flow of processing that is performed when the storage system is booted. Further, in  FIG. 8 , ‘RG’ signifies a RAID group. 
     The RG/LU setting program  330  acquires information on set RAID groups  140  (step  400 ). This information can be acquired by a RAID group management table  509 , for example. The RAID group management table  509  records, for each RAID group, the numbers representing the RAID groups and the protocol types of the disk drives  114  constituting the RAID groups. Although not illustrated, a variety of other types of information such as numbers representing the disk drives constituting the RAID groups and LUN and so forth of the LU established on the RAID groups may also be recorded for each of the RAID groups. 
     The zone configuration control program  340  initializes the zone  150  corresponding with all the RAID groups  140  (one zone  150  is set for each RAID group, for example) (step  410 ) and a physical link is allocated to each zone  150  (step  415 ). 
     Further, when, during booting, an instruction to divide the physical links used according to the protocol classification is issued beforehand by the management  104 , in step  415 , the zone configuration control program  340  divides the zone  150  according to the protocol classification so that there is no overlap. In the example in  FIG. 1 , zone  150  is established so that zone  150   a  includes physical links  108   a  and  108   b  that constitute the wide link  120   a  and zone  150   b  includes the physical link  108   c  constituting the wide link  120   a  and there is no mutual sharing of the physical links  108  by the zones. The number of physical links constituting the wide link  120  can be calculated by using various conditions, and statistical information such as the drive types constituting the RAID groups  140 , the performance of the drives, the number of drives, and the I/O request performance of the RAID group  140  monitored by the performance monitoring program  350 , for example. 
       FIG. 9  shows an example of the flow of processing for changing the number of physical links  108  allocated to zone  150 . 
     The performance monitoring program  350  starts the execution in accordance with an instruction from the management terminal  104 . When an instruction for performance monitoring arrives, the performance monitoring program  350  starts to execute the acquisition of statistical information on performance for each of the RAID groups  140  and moves to step  520 . When an instruction does not arrive, the performance monitoring program  350  waits for an instruction as is in step  510 . Further, ‘performance’ as it is meant here is the data size transferred for each unit of time. 
     In step S 520 , if an instruction to end performance monitoring arrives from the management terminal  104 , the performance monitoring program  350  ends the execution and ends the flow. When there is no end instruction, the processing moves to step  530 . 
     In step  530 , when, based on the statistical information on performance, the performance threshold value of a certain RAID group  140  being monitored is exceeded, the processing moves to step  600  and, when step  600  is complete, the processing returns to step  520 . The performance threshold value used in step  530  is a value that is decided on the basis of the number of physical links  108  included in zone  150 , for example. 
       FIG. 10  shows an example of the flow of processing that is performed in step  600  in  FIG. 9 . 
     In step  610 , the performance monitoring program  350  calculates the required number of physical links  108  on the basis of the statistical information on performance. Specifically, the number of physical links  108  in a number suited to the performance at which the performance threshold value is exceeded or a number suited to the maximum performance hereafter that is estimated from the statistical information on performance is calculated. 
     In step  630 , the zone configuration control program  340  judges whether further physical links  108  can be added to the zone  150  to be changed. When further physical links can be added, the processing moves to step  640  and, when no further physical links can be added, the processing moves to step  650 . Here, a case where further physical links can be added is, for example, a case where a physical link that is not allocated to any zone (or a physical link that has already been allocated to a zone and may not be allocated further to the other zone) exists and a case where physical links cannot be added is a case where physical links that have not been allocated to a zone (or physical links that have been allocated to a zone and have not been added to the other zone) do not exist. 
     In step  640 , the zone configuration control program  340  considers performance information related to other RAID groups  140  (or disk drives  114 ) when the wide link  120  of the zone to be changed is shared with another zone  150  (when one wide link  120   a  is shared with two zones  150   a  and  150   b  as exemplified by  FIG. 1 , for example) and calculates the number of physical links  108  that can be added to the wide link  120  of the zone  150  to be changed so that there is no adverse effect on the performance of the other RAID groups  140  (or disk drives  114 ). 
     In step  650 , the zone configuration control program  340  judges whether the other zone  150  is sharing a physical link  108  with zone  150  to which a physical link  108  is to be allocated. When such sharing exists, the zone configuration control program  340  checks whether the number of physical links  108  of the other zone  150  is a minimum value (other zone  150  comprises only one physical link  108 ). When the number of physical links  108  that the other zone  150  comprises is not the minimum value, the zone configuration control program  340  moves to step  660  because a margin exists for reducing the number of physical links  108  of the other zone  150 . When the number of physical links  108  that the other zone  150  comprises is the minimum value, it is not possible to change all the zones  150  and the processing moves to step  680 . 
     In step  660 , the zone configuration control program  340  calculates the number of physical links that can be reduced in the other zone  150  and proceeds with step  670 . 
     In step  670 , the zone configuration control program  340  changes the number of physical links  108  in zone  150 . 
     A case where physical links are added to zone  150  in step  670  will be described by way of example. For example, in  FIG. 1 , if, when a physical link  108   a  is not allocated to a RAID group  140  (set of disk drives  114   b  and  114   c ), the physical link  108   a  is allocated to the RAID group  140 , the zone configuration control program  340  issues a physical link addition instruction to the SAS expander  130   a . The physical link addition instruction contains phy identifier  0  of the SAS expander  130   a  and the addresses of the devices to be allocated (respective SAS addresses of the disk drives  114   b  and  114   c ). A zone setting program  190   a  records the addresses of the device to be allocated (the SAS addresses of the disk drives  114   b  and  114   c ) in fields of fields  430  that correspond with the phy identifier  0  of the direct device table  195   a  in accordance with the physical link addition instruction. In addition, the zone setting program  190   a  records the respective SAS addresses of the disk drives  114   b  and  114   c  in the fields corresponding with the phy identifier  0  of the expander route table  196   a.    
     A case where allocated physical links are eliminated from zone  150  in step  670  will now be described by way of example. For example, if the allocation of physical link  108   a  is released when the physical link  108   a  in  FIG. 1  has been allocated to the RAID group  140  (set of disk drives  114   b  and  114   c ), the zone configuration control program  340  issues a physical link elimination instruction to the SAS expander  130   a . The physical link elimination instruction contains the phy identifier  0  of the SAS expander  130   a  and the addresses of the devices to be allocated (the respective SAS addresses of the disk drives  114   b  and  114   c ). The zone setting program  190   a  eliminates the respective SAS addresses of the disk drives  114   b  and  114   c  from the fields of fields  430  that correspond with phy identifier  0  of the direct device table  195   a  in accordance with the physical link elimination instruction and records NULL in these fields. In addition, the zone setting program  190   a  eliminates the addresses of the devices for which allocation is to be released from the fields corresponding with phy identifier  0  of the expander route table  196   a  (the respective SAS addresses of the disk drives  114   b  and  114   c ) to establish non-registration. 
     As detailed earlier, the processing to allocate a physical link and to release the allocation thereof involves the addition of information on the devices (SAS targets) targeted for the allocation of the physical link to at least one of the direct device table  195  and expander route table  196  in the SAS expander  130  comprising the physical link to be allocated or whose allocation is to be released or the elimination of information on the devices whose physical link allocation is to be released. The control program  300  grasps the respective SAS expanders  130  that exist downstream of the storage controller  200  and the phy identifiers of each SAS expander  130  (holds the SAS addresses of all the SAS expanders  130  and the phy identifiers of the respective SAS expanders  130 , and so forth, for example). The control program  300  is able to designate phy identifiers for the physical phys to which the physical links are connected and SAS addresses that are newly associated with the phy identifiers or eliminated from the phy identifiers, for the SAS expanders  130  having the physical links to be allocated or whose allocation is to be released. When all the SAS addresses are eliminated, a designation to that effect may be made instead of the SAS addresses. 
     Further, in step  680 , the zone configuration control program  340  issues a report to the management terminal  104  to the effect that the zone  150  cannot be changed because physical links  108  cannot be changed for the zone  150  whose performance is judged to be required and for any kind of zone  150  that is shared with zone  150 . 
       FIG. 11  shows a constitutional example of the zone state management table  700 . Further, in  FIG. 11 , ‘RG’ represents a RAID group, ‘WL’ represents a wide link, and ‘phy’ represents a physical phy. 
     The zone state management table  700  is a table for holding the control program  300 , for example, and contains the following information. Each of the information items therein will now be described. 
     The RG number  710  is an identification number of the RAID group  140 . The drive classification  720  is the classification of the drives constituting the RAID group  140  (may contain various information such as the protocol classification and whether there is a performance difference between the drives, for example). The LU number  730  is a list of the numbers of logical units for storing data corresponding with the RG number  710 . The zone number  740  is an identification number of the zone  150  that corresponds with the RAID group  140 . The performance statistical information  750  holds statistical information on the performance that is acquired by the performance monitoring program  350 . The performance threshold value  760  is a value (threshold value) that is the product of a calculation based on information  790  on overlapping zones  150 . When an I/O request exceeding this value arrives from the host, the threshold value is exceeded in step  530  in  FIG. 9  and the flow  600  for changing the zone  150  is executed. The phy identifier  770  constituting the WL stores the phy identifier of the SAS expander  130  constituting the wide link  120 . Wide link part fault production  780  is a list that registers the particular physical link  108  in which a fault occurs when a fault occurs in a portion of the physical links  108  constituting the wide link  120 . ‘Unregistered’ is registered when a normal state prevails or the physical link  108  has recovered from a fault. 
     The control program  300  is able to provide the management terminal  104  with the table  700  in response to a request from the storage system management program  105  of the management terminal  104 , for example. The storage system management program  105  is able to display information represented by the table  700  on the display device of the management terminal  104 . 
     Further, several examples of cases where a change is made to the allocation of physical links in the present embodiment will be described hereinbelow. Further, as can be seen from the above description, a plurality of physical links constituting one wide link can be distributed among a plurality of zones but one or more physical links in one wide link in one zone is called a ‘Sub Wide Link’ hereinbelow. 
       FIG. 12A  shows the allocation of physical links prior to changing the allocation in a first case where the allocation of physical links is changed and  FIG. 12B  shows the allocation of physical links after the allocation has been changed. 
     Suppose that, prior to changing the allocation of physical links, one zone  150  is allocated to one RAID group  140 , as exemplified by  FIG. 12A  ( 150   a  is allocated to  140   a  and  150   b  is allocated to  140   b , for example). Further, the classifications of drives constituting the RAID groups  140   a  and  140   b  respectively are different (suppose, for example, that  140   a  is a set of SAS drives and  140   b  is a set of SATA drives). Suppose that one wide link  120  is constituted by four physical links. Further, there are two physical links in the Sub Wide Link of zone  150   a  and two physical links in the Sub Wide Link of zone  150   b.    
     In this case, suppose that the performance monitoring program  350  judges that an I/O request from the host computer  101   a  requires a sustain performance in comparison with an I/O request from the host computer  101   b . In this case, the performance monitoring program  350  judges that a large number of physical links  108  constituting the wide link  120  must be established for zone  150   a.    
     Therefore, as shown in  FIG. 12B , the zone configuration control program  340  reduces the physical links in the Sub Wide Link of the zone  150   b  by one and one physical link is added to the Sub Wide Link of zone  150   a . Here, the zone configuration control program  340  changes the allocation of physical links so that there is no overlap between zone  150   a  and zone  150   b . This is because it is judged, in view of the difference in drive classification between RAID group  140   a  and RAID group  140   b , that zone  150   a  and zone  150   b  are overlapping. 
     As a result, the control program  300  is able to allocate a plurality of physical links constituting the wide link  120  to a drive or RAID group. The number of physical links allocated makes it possible to implement bandwidth assurance within the storage system by monitoring increases in the request performance (in other words, the load) of I/O requests from the host and controlling the allocation of physical links. Further, the effect on the throughput performance produced by differences in the drive classifications can be alleviated. 
       FIG. 13  shows the allocation of physical links prior to changing the allocation in a second case where changes to the allocation of physical links are made.  FIG. 14  shows the allocation of physical links after the allocation has been changed. 
     Suppose that, prior to changing the allocation of physical links, one zone  150  is allocated to one RAID group  140  as exemplified by  FIG. 13 . Suppose that one wide link  120  is constituted by five physical links. Further, suppose that there is one physical link in the Sub Wide Link of zone  150   a , two physical links in the Sub Wide Link of zone  150   b  and two physical links in the Sub Wide Link of zone  150   c . Suppose that data is copied from RAID group  140   b  to RAID group  140   c  by means of the background control program  360  (that is, suppose that processing to read data from the RAID group  140   b  and write the data thus read to the RAID group  140   c  is performed). 
     In this case, suppose that the performance monitoring program  350  judges that there has been an I/O request for the RAID group  140   a  from the host computer  101  as shown in  FIG. 14  (or the request performance of the I/O requests exceeds the predetermined threshold value). 
     Therefore, as shown in  FIG. 14 , the zone configuration control program  340  reduces the physical links in the Sub Wide Link of zone  150   b  by one and reduces the physical links in the Sub Wide Link of zone  150   c  by one and adds the same number of physical links to the Sub Wide Link of zone  150   a.    
     As a result, bandwidth assurance to satisfy the performance of the I/O requests from a host as far as possible can be implemented in the storage system. Further, although the number of physical links from both the Sub Wide Links of zones  150   b  and  150   c  is reduced, if performance of the same level as that of the I/O request from the host computer  101  is also required by the internal I/O, the physical links need not be taken from both Sub Wide Links. As mentioned earlier, the number of physical links taken away or added can be a suitable value according to the performance required by the I/O or the drive classification. 
       FIG. 15A  shows the allocation of physical links prior to changing the allocation in a third case in which a change to the allocation of physical links is performed and  FIG. 15B  shows the allocation of physical links after changing the allocation. 
     Suppose that, prior to changing the allocation of physical links, one zone  150  is allocated to one RAID group  140  as exemplified by  FIG. 15A . Suppose that one wide link  120  is constituted by four physical links. Further, suppose that there are three physical links in the Sub Wide Link of zone  150   a  and one physical link in the Sub Wide Link of zone  150   b . As a result, the I/O request for the RAID group  140   a  from the host computer  101   a  and the I/O request for the RAID group  140   b  from the host computer  101   b  can be processed. 
     In this case, suppose that the fault processing program  370  detects the occurrence of a fault in the physical link constituting the Sub Wide Link of zone  150   b . Access cannot be made to the RAID group  140   b  by the storage controller  200  without further processing and, consequently, an I/O request from the host computer  101   b  cannot be processed. 
     Therefore, the zone configuration control program  340  makes changes to the allocation of physical links so that the Sub Wide Link of the zone  150   b  returns to the same state as prior to the occurrence of the fault. More specifically, the zone configuration control program  340  reduces the physical links in the Sub Wide Link of zone  150   a  by one and adds one physical link to the Sub Wide Link of zone  150   b , as shown in  FIG. 15B . 
     As a result, even when a fault occurs in a physical link constituting the wide link, an access path to the disk drive or RAID group can be maintained by correcting the allocation of the number of physical links. 
     Further, the following may be performed in the above embodiment. 
     For example, as exemplified by  FIG. 16 , a plurality of RAID groups  140   a  and  140   b  may be associated with one zone  150   a . In this case, the storage controller  200  may change the allocation, within the range of the Sub Wide Link of another zone  150   a , of the number of physical links for the RAID group  140   a  and the number of physical links for the RAID group  140   b  in the wide link  120  and add physical links in the Sub Wide Link of the other zone  150   b  to the Sub Wide Link of the zone  150   a . Further, the number of physical links allocated to the RAID group  140   a  can be adjusted within a range such that there is no adverse effect on the other RAID group  140   b  that belongs to the zone  150   a  when the allocation is changed within the range of the Sub Wide Links of zone  150   a . As the lower limit for a range that does not produce an adverse effect, for example, a number that must satisfy the request performance for the RAID group  140   b  can be adopted as the lower limit. 
     Furthermore, as probably mentioned earlier, a plurality of zones  150   a  and  150   b  may be overlapped in the wide link  120  as exemplified by  FIG. 17 . That is, according to the example in  FIG. 17 , the storage controller  200  makes it possible to access the RAID group  140   a  and the other RAID group  140   b  from the wide link  120 . 
     Further, as exemplified by  FIG. 18 , the zone concept may be dispensed with. According to the example in  FIG. 18 , the allocation of a particular physical link among the plurality of physical links in the wide link  120  to a particular RAID group  140  (or disk drive) is controlled. 
     Moreover, as exemplified by  FIG. 19 , a priority is set for access sources  1000   a  and  1000   b  outside the storage system  100  and the number of physical links allocated to a RAID group (or disk drive) may be determined on the basis of the priority level of the external access source of the access destination RAID group (or disk drive). More specifically, when there are two types of priority which are high and low, for example, the storage controller  200  is able to allocate two times the number of physical links in comparison with the access destination RAID group  140   b  from the external access source  1000   b  of low priority to the access destination RAID group  140   a  from the external access source  1000   a  of high priority in the wide link  120  (four physical links can be allocated to  140   a  and two physical links can be allocated to  140   b , for example). Further, in this modified example, the external access source is the host computer  101   
     or an application program in the host computer  101  (a computer program running on the operating system). The storage controller  200  is able to store information representing the priority level of the external access source in the memory for each external access source. The storage controller  200  specifies the external access source upon establishing a connection with the external access source or upon receiving an I/O request, for example, and, by detecting the priority level corresponding with the specified external access source from the memory, is able to execute a change to the number of physical links allocated to the access destination of the external access source thus specified. 
     Furthermore, as exemplified by  FIG. 20 , the storage controller  200  may make the number of physical links allocated to the RAID group  140   b  (or disk drive) in the wide link  120  zero. In so doing, it is possible to ensure that, although the RAID group  140   b  (or disk drive) cannot be accessed by the storage controller  200 , data in the RAID group  140   b  can be updated and data cannot be read from the RAID group  140   a . That is, when a high security level is required of the RAID group  140   b , data in the RAID group  140   b  can be protected by making the number of physical links zero as mentioned above. Further, although the allocation of physical links connecting the RAID group  140   b  and SAS expander  130  may be released instead of this method, it is considered desirable to establish zero physical links in the wide link  120  and that the number of physical links that can be allocated to the other RAID groups (or disk drives) should increase to the same extent as mentioned earlier. Further, although this is said to be the security level of the RAID group in the above description, this may be the security level of the disk drives constituting the RAID group or of the LU. 
     Preferred embodiments of the present invention as well as a few modified examples thereof were described hereinabove but these are examples serving to illustrate the present invention. There is no intention to limit the scope of the present invention to these embodiments and modified examples. The present invention can also be implemented by a variety of other embodiments. 
     For example, the above storage system can also be applied to a server system. Here, it can be assumed that the storage controller  200  is a server machine (a so-called blade server, for example), for example. 
     Furthermore, for example, a plurality of disk drives can be installed in an enclosure and the performance monitoring program  350  may monitor the resources at fixed intervals by issuing a resource monitoring command for monitoring the resources of the enclosure (disk drives, for example) at fixed intervals to a predetermined destination at fixed intervals. Here, a zone dedicated to resource monitoring commands may be provided. As a result, physical links that are used when processing I/O requests for disk drives and physical links that are used in the issuing of resource monitoring commands can be separated, whereby resource monitoring can be performed so that there is no effect on I/O requests from host computers. 
     Further, although the premise is that the computer system (storage system, for example) of the embodiment of the present invention uses an SAS I/F, for example, the embodiment of the present invention can also be applied to future I/Fs with a function that is equivalent to an SAS wide link. 
     Moreover, for example, in the above description, the allocation-controlled ‘physical links’ may be ‘logical links’. Logical links can be managed by means of a direct device table and expander route table and so forth as per the abovementioned physical links. Logical links are links formed by time-dividing one physical link. More specifically, in the case of a transfer of a connection in which a low transfer rate (1.5 Gbps, for example) and a high transfer rate (3 Gbps, for example), for example, are mixed, a high-speed physical link (3 Gbps, for example) is time-divided to establish the transfer state at a certain time and establish a no transfer state at another time at which a transfer was originally possible. More specifically, as exemplified by  FIG. 22 , for example, an increase in the transfer speed of the whole system can be implemented simultaneously establishing a plurality of low-speed connections at the same time by means of an environment in which a multiplicity of disk drives are connected at low speed by time-dividing a physical link into two or four and bundling a plurality of logical links of a low transfer rate to form one physical link. The abovementioned zoning control (control of the allocation of logical links to the respective zones) can be established by making a logical phy table of indexes indicating the physical phys (phy) of the direct device table and expander route table  196  for each logical link.