Abstract:
A control method comprising: a first step of detecting, by the server module, a failure in the first interface; a second step of executing, by the server module, given recovery processing when a failure is detected in the first interface; a third step of using, by the coupling module, the first end point to detect a failure in the first interface and output a failure notification; a fourth step of converting, by the coupling module, the failure notification into a notification of disconnection of the first interface, and transmitting the disconnection notification generated by the conversion to the storage module from the second end point; and a fifth step of disengaging, by the storage module, coupling to the server module when the disconnection notification is received from the coupling module.

Description:
CLAIM OF PRIORITY 
       [0001]    The present application claims priority from Japanese patent application JP 2013-196829 filed on Sep. 24, 2013, the content of which is hereby incorporated by reference into this application. 
       BACKGROUND 
       [0002]    This invention relates to a technology for accomplishing high-speed data transfer between a server module and a storage module. 
         [0003]    As a computer system in which a server and a storage machine accessed by the server are coupled to each other, the following systems are known. 
         [0004]    One known computer system of this type couples a server and storage via a network such as a SAN (see, for example, Japanese Patent Application Laid-open No. 2012-118973 (Related-art Example 1)). 
         [0005]    In Japanese Patent Application Laid-open No. 2012-118973, there is disclosed a “storage appliance system, which may include at least one application server for locally executing an application, and one or more storage servers in communication with the application server for I/O transmission therebetween”. 
         [0006]    The computer system described above has a utilization mode that is employed by a large-scale computer system. The computer system has an advantage of being highly flexible in system configuration, but has a problem in that the cost of devices constructing the network such as a SAN is high as well as the running cost. 
         [0007]    PCI Express (registered trademark) interfaces are known as high-speed interfaces, and there is a known technology that connects two devices by PCI Express (see, for example, Japanese Patent Application Laid-open No. 2012-128717 (Related-art Example 2)). In Japanese Patent Application Laid-open No. 2012-128717, there is disclosed a technology with which communication between two devices is held through a bridge connection of the two devices with the use of a switch that has a non-transparent port and PCI Express. 
         [0008]    There is also known a technology for transmitting error information by a PCI Express protocol when a failure occurs at an end point in a computer system that uses PCI Express (see, for example, Japanese Patent Application Laid-open No. 2010-238150 (Related-art Example 3)). 
       SUMMARY 
       [0009]    In the case of coupling the server and storage machine of Related-art Example 1 with the use of PCI Express of Related-art Example 2, the server is connected to a link A of the non-transparent port by bridge connection and the storage machine is connected to a link B of the non-transparent port by bridge connection. When a failure occurs in the link A connected to the server, the storage machine at the link B is notified of the failure, which necessitates the execution of PCI Express failure recovery processing in the server and the storage machine both. 
         [0010]    The resultant problem is that, in the case where one storage machine is coupled to a plurality of servers via a non-transparent port, a failure in a link on the side of one of the servers stops access of the other normal servers to the storage machine due to the need to execute failure recovery processing in the storage machine as well. In other words, a failure in one of the server-side links (I/O interfaces) affects all servers through the storage machine. 
         [0011]    In the case where a failure notification is transmitted with the use of Related-art Example 3, the need to expand the PCI Express protocol gives rise to a problem in that existing chip sets and devices cannot be used. 
         [0012]    This invention has been made in view of the problems described above, and an object of this invention is to prevent, in a computer system that couples a storage machine and a plurality of servers by I/O interfaces, the impact of a failure in one of the I/O interfaces from spreading to the overall computer system without expanding a protocol. 
         [0013]    A representative aspect of this invention is as follows. A computer system, comprising: a server module; a storage module; and a coupling module, wherein the server module comprises: a first processor; a first memory; a first interface for coupling to other devices; a storage access part for requesting access to the storage module via the first interface; a failure detecting part for detecting a failure in the first interface; and a failure processing part for executing given recovery processing when the failure detecting part detects a failure in the first interface, wherein the coupling module comprises: a first end point which is connected to the first interface and, when detecting a failure in the first interface, outputs a failure notification; a second end point which is connected to a second interface of the storage module; a data transfer part for transferring data between the first end point and the second end point; and an event imitation part for converting the failure notification into a notification of disconnection of the first interface when the first end point outputs the failure notification, and transmitting the disconnection notification generated by the conversion to the storage module from the second end point, and wherein the storage module comprises: a second processor; a second memory; a storage device; the second interface for coupling to other devices; a storage control part for receiving an access request through the second interface and accessing the storage device; and a disconnection processing part for disengaging coupling to the server module when the disconnection notification is received from the coupling module. 
         [0014]    Thus, in one embodiment of this invention, when the storage module is coupled to a plurality of server modules and a failure occurs in the first interface of one of the server modules, the storage module receives a disconnection notification instead of a failure notification, and disengages the coupling to the server module in which the failure has occurred in the first interface. The impact of the failure in the first interface is prevented from spreading to the overall computer system in this manner. In addition, a protocol of the I/O interfaces does not need to be expanded, which means that the cost of the computer system is kept from rising by using exiting chips and devices. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  shows an embodiment of this invention, and is a block diagram illustrating an example of a computer system. 
           [0016]      FIG. 2  shows the embodiment of this invention, and is a block diagram illustrating an example of the configuration of the server module. 
           [0017]      FIG. 3  shows the embodiment of this invention, and is a block diagram illustrating an example of the configuration of the storage module 
           [0018]      FIG. 4  shows the embodiment of this invention, and is a block diagram illustrating an example of the configuration of the coupling module. 
           [0019]      FIG. 5  shows the embodiment of this invention, and is a block diagram outlining processing that is executed when a failure occurs on the server module side. 
           [0020]      FIG. 6  shows the embodiment of this invention, and is a sequence diagram illustrating an example of processing that is executed when a failure occurs on the server module side. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    An embodiment of this invention is described below with reference to the accompanying drawings. 
         [0022]      FIG. 1  is a block diagram illustrating an example of a computer system according to the embodiment of this invention. 
         [0023]    The computer system of this embodiment is a server apparatus  100 , which includes a plurality of server modules  200 - 1  to  200 - n , a storage module  300 , and a backplane  400  for coupling the plurality of server modules  200 - 1  to  200 - n  and the storage module  300 . 
         [0024]    The server apparatus  100  has the plurality of server modules  200 - 1  to  200 - n , one storage module  300 , and the backplane  400 . In the following description, the server modules  200 - 1  to  200 - n  are collectively denoted by  200 . 
         [0025]    The server modules  200  are computers that provide a given business operation. The storage module  300  is a computer that stores data used by the server modules  200 . In this embodiment, the storage module  300  provides logical units (LUs) to each server module  200 . 
         [0026]    The server module  200 - 1  includes a processor  210 - 1  and a memory  220 - 1 . The rest of the server modules,  200 - 2  to  200 - n , have the same configuration, and a repetitive description is omitted. The processors  210 - 1  to  210 - n  are collectively denoted by  210 . The same symbol notation rule applies to other components as well in the following description. 
         [0027]    The processor  210 - 1  includes, as an I/O interface, a PCI Express interface  230 - 1 , which is hereinafter referred to as PCIe I/F  230 - 1 . The PCIe I/F  230 - 1  includes a root complex  240 - 1 , which is at the top of devices arranged in the tree structure of PCI Express. 
         [0028]    Each processor  210  executes a program stored in the relevant memory  220 . By executing a program stored in the memory  220  with the processor  210 , the server module  200  provides a business operation. 
         [0029]    The memory  220  stores a program executed by the processor  210  and data necessary for the execution of the program. What program and information are stored in the memory  220  is described later with reference to  FIG. 2 . 
         [0030]    The program and information stored in the memory  220  may be stored in an LU provided by the storage module  300 , or other places. In this case, the processor  210  obtains the program and information from the LU or other storage areas where the program and information are stored, and loads the obtained program and information onto the memory  220 . 
         [0031]    The storage module  300  includes a disk controller  310  and storage devices  360 - 1  to  360 - n . The components of the storage module  300  are connected to each other via an I/O interface. 
         [0032]    The disk controller  310  manages storage areas of the storage devices  360 , and controls, among others, the association relations between the server modules  200  and the storage areas. The disk controller  310  includes a processor  320 , a memory  330 , and, as an I/O interface, a PCI Express interface  340  (hereinafter referred to as PCIe I/F  340 ). 
         [0033]    The processor  320  is connected to the PCIe I/F  340  to transfer data to and from the respective server modules  200  via the PCIe I/F  340 . The PCIe I/F  340  includes a root complex  350 , which is at the top of devices arranged in the tree structure of PCI Express. 
         [0034]    The PCIe I/F  340  is connected to a coupling module  410 - 1  via a PCI Express link  510 - 1  to transfer data to and from the server module  200 - 1 . Similarly, the PCIe I/F  340  is connected to a coupling module  410 - 2  via a PCI Express link  510 - 2  to transfer data to and from the server module  200 - 2 . 
         [0035]    The PCIe I/F  340  in this embodiment can be built from a chip set or the like. However, this embodiment is not limited thereto and, as in the server modules  200 , the storage module  300  may be configured so that the processor contains a PCIe I/F. 
         [0036]    This embodiment shows an example in which the storage module  300  includes one disk controller  310 . Alternatively, the storage module  300  may have a redundant configuration in which a single storage module  300  is provided with a plurality of disk controllers  310 . 
         [0037]    The processor  320  executes a program stored in the memory  330 . By executing a program stored in the memory  330  with the processor  320 , functions of the storage module  300  can be implemented. 
         [0038]    The memory  330  stores a program executed by the processor  320  and information necessary for the execution of the program. What program and information are stored in the memory  330  is described later with reference to  FIG. 3 . 
         [0039]    The program and information stored in the memory  330  may be stored in the storage devices  360 - 1  to  360 - n , or other places. In this case, the processor  320  obtains the program and information from the storage devices  360 - 1  to  360 - n  or other places, and loads the obtained program and information onto the memory  330 . 
         [0040]    The storage devices  360 - 1  to  360 - n  are devices for storing data and can be, for example, hard disk drives (HDDs) or solid state drives (SSDs). 
         [0041]    The storage module  300  in this embodiment uses a plurality of storage devices to build a RAID, generates LUs from RAID volumes, and further provides the LUs to the server modules  200 . The LUs store programs such as an OS  221 , which is illustrated in  FIG. 2 , and an application  225 , which is illustrated in  FIG. 2 , and information necessary for the execution of the programs. 
         [0042]    The backplane  400  which couples the server modules  200  and the storage module  300  includes coupling modules  410 - 1  to  410 - n , which are provided respectively for the server modules  200 - 1  to  200 - n . The coupling modules  410 - 1  to  410 - n  have the same configuration, and a repetitive description is omitted. 
         [0043]    The coupling module  410 - 1  has two PCI Express end points, and transfers data between the two end points. The end points of the coupling module  410 - 1  are an end point  420 - 1 , which is connected to the PCIe I/F  230 - 1  of the server module  200 - 1 , and an end point  430 - 1 , which is connected to the PCIe I/F  340  of the storage module  300 . 
         [0044]    The end point  420 - 1  and the server module  200 - 1  are connected by a PCI Express link  500 - 1 . The end point  430 - 1  and the storage module  300  are connected by a PCI Express link  510 - 1 . 
         [0045]    In the example here, the end point  420 - 1  connected to the server module  200 - 1  functions as a host bus adapter (HBA), and the end point  430 - 1  connected to the storage module  300  functions as a target bus adapter (TBA). While the end point  420 - 1  and the end point  430 - 1  use a Fibre Channel (FC) protocol to transfer data in the example of this embodiment, this embodiment is not limited thereto and SCSI, SAS, SATA, or other similar protocols may be employed instead. A detailed configuration of the coupling modules  410  is described later with reference to  FIG. 4 . 
         [0046]    The coupling modules  410  can be installed as a chip (LSI) mounted on a circuit board of the backplane  400 . However, this invention is not limited by how the coupling modules  410  are installed. 
         [0047]    The links  500  and the links  510  include physical paths along which signals are transmitted and logical connections which indicate the hierarchy levels of communication or the like. The server modules  200  and the storage module  300  are loaded in, for example, slots provided in the backplane  400  in a manner that allows the modules to be slotted in and out freely. 
         [0048]      FIG. 2  is a block diagram illustrating an example of the configuration of the server module  200 - 1  according to this embodiment. 
         [0049]    The memory  220 - 1  stores programs for implementing the OS  221  and the application  225 . The OS  221  stored in the memory  220 - 1  includes a storage access part  224 , which accesses the storage module  300 , a PCIe failure processing part  222 , which executes recovery processing when a failure occurs in the PCI Express link  500 - 1  connected to the backplane  400  or in the PCIe I/F  230 - 1 , and an HBA link down processing part  223 , which executes processing of disengaging the coupling to the storage module  300 . 
         [0050]    In this embodiment, where the end point  420 - 1  to which the PCIe I/F  230 - 1  is connected is built from an HBA, the storage access part  224  accesses the end point  420 - 1  via an HBA driver. 
         [0051]    The OS  221  includes the PCIe failure processing part  222  and the HBA link down processing part  223  in the example of this embodiment. However, this embodiment is not limited thereto and the server module  200 - 1  may be configured so that the PCIe failure processing part  222  and the HBA link down processing part  223  run on the OS  221 . 
         [0052]    The OS  221  manages the server module  200 - 1 . The OS  221  has the storage access part  224  which controls access between the server module  200 - 1  and the storage module  300 . The storage access part  224  can be implemented by, for example, a device driver for operating the coupling module  410 - 1 . 
         [0053]    The OS  221  has a file system and other functions (not shown), which are known functions and therefore omitted. The application  225  provides a given business operation. This invention is not limited by what type of application is included in the server modules  200 . 
         [0054]    The processor  210 - 1  operates as function parts that provide given functions by executing processing as programmed by programs of the respective function parts. For instance, the processor  210 - 1  functions as the PCIe failure processing part  222  by executing processing as programmed by a PCIe failure processing program. The same applies to other programs. The processor  210 - 1  also operates as function parts that provide respective functions of a plurality of processing procedures executed by each program. A computer and a computer system are a machine and a system that include these function parts. 
         [0055]    Programs for implementing functions and information such as a table can be stored in the storage module  300 , or in a non-volatile semiconductor memory, or in a storage device such as a hard disk drive or a solid state drive (SSD), or in a computer-readable non-transitory data storage medium such as an IC card, an SD card, and a DVD. 
         [0056]      FIG. 3  is a block diagram illustrating an example of the configuration of the storage module  300  according to this embodiment. 
         [0057]    The memory  330  stores programs that implement a storage control part  333 , a TBA link down processing part  332 , and a PCIe failure processing part  331 . 
         [0058]    The storage control part  333  controls I/O processing between the server modules  200  and the storage module  300 . In this embodiment, the end points  430  to which the PCIe I/F  340  is connected are built from TBAs, and the storage control part  333  therefore accesses the end points  430  via a TBA driver. The storage control part  333  transfers data between the server modules  200  and the storage devices  360  via the end points  430 . 
         [0059]    The TBA link down processing part  332  executes, as described later, processing of disengaging the coupling to the server modules  200 , which are coupled to the storage module  300  by the links  500 . When receiving from one of the coupling modules  410  a notification that the coupling to the relevant server module  200  has been disengaged (a link down or disconnection notification), the disk controller  310  activates the TBA link down processing part (disconnection processing part)  332  to disengage the coupling to the server module  200  along the relevant link  500 , and discards queued I/O (data and commands) of the server module  200  for which the link  500  has just been disconnected. 
         [0060]    The PCIe failure processing part  331  executes given recovery processing when a failure occurs in one of the PCI Express links  510 - 1  to  510 - n  connected to the backplane  400 , or in the PCIe I/F  340 . When a failure occurs in the PCIe I/F  340  or one of the links  510 , the disk controller  310  resets the PCIe I/F  340  to execute the failure recovery processing. 
         [0061]      FIG. 4  is a block diagram illustrating an example of the configuration of the coupling module  410 - 1  according to this embodiment. The same configuration is shared by the coupling modules  410 - 2  to  410 - n , and a repetitive description is omitted. 
         [0062]    The coupling module  410 - 1  includes a data transfer part  440 , a protocol engine  460 , a bridge  450 , the end point  420 - 1 , which functions as an HBA, the end point  430 - 1 , which functions as a TBA, and an event imitation processing part  470 . 
         [0063]    The data transfer part  440  controls data transfer between the memory  220 - 1  of the server module  200 - 1  and the memory  330  of the storage module  300 . The data transfer part  440  in this embodiment includes a DMA controller  441 . 
         [0064]    The DMA controller  441  controls DMA transfer between the memory  220 - 1  of the server module  200 - 1  and the memory  330  of the storage module  300 . 
         [0065]    The protocol engine  460  converts a command used by the server module  200 - 1  and a command used by the storage module  300 . In other words, the protocol engine  460  converts a protocol on the end point  420 - 1  side and a protocol on the end point  430 - 1  side into each other. 
         [0066]    The bridge  450  controls communication between devices that are connected via the end points  420 - 1  and  430 - 1 . For instance, the bridge  450  converts PCI Express signals that differ from each other in lane count. The bridge  450  is used when the DMA transfer described above is unnecessary. 
         [0067]    The end points  420 - 1  and  430 - 1  can be built from, for example, ports for connecting to a device. In this embodiment, the end point  420 - 1  is connected to the PCIe I/F  230 - 1  of the processor  210 - 1 , and the end point  430 - 1  is connected to the PCIe I/F  340  of the disk controller  310 . 
         [0068]    The end point  420 - 1  detects the occurrence of a failure when the link  500 - 1  is reset or shut off, and notifies the protocol engine  460  of the failure. In other words, the end point  420 - 1  outputs a failure notification when a failure occurs in the PCIe I/F  230 - 1  of the server module  200 - 1  or in the link  500 - 1 . 
         [0069]    Receiving the failure notification, the protocol engine  460  activates the event imitation processing part  470 . The event imitation processing part  470  converts the notification of a failure in the link  500 - 1  on the server module  200 - 1  side into a disconnection (link down or hot remove) notification which indicates that the link  500 - 1  has been disconnected. The event imitation processing part  470  transmits the disconnection (link down) notification generated by the conversion, instead of an anomaly notification, to the storage module  300  from the end point  430 - 1 . 
         [0070]    In the case where the coupling module  410 - 1  is built as a chip on the backplane  400 , the coupling module  410 - 1  can be an application-specific integrated circuit (ASIC) which includes a processor and a memory, or a similar chip. 
         [0071]    The end point  420 - 1  in the example given above outputs a failure notification to the protocol engine  460  when detecting a failure on the link  500 - 1  side. Alternatively, the coupling module  410 - 1  may be designed so that the event imitation processing part  470  is activated when the end point  420 - 1  outputs a failure notification. 
         [0072]    The data transfer part  440 , the protocol engine  460 , and the event imitation processing part  470  may be implemented as one control part. 
         [0073]      FIG. 5  is a block diagram outlining processing that is executed when a failure occurs on the server module side. 
         [0074]      FIG. 5  illustrates an example in which the server module  200 - 1  is coupled to the storage module  300  via the coupling module  410 - 1 , and a failure has occurred in the link  500 - 1  on the server module  200 - 1  side. In the illustrated example, the server module  200 - 2  is coupled to the storage module  300  via the coupling module  410 - 2 , and transfers data normally. 
         [0075]    Normal data transfer is described first taking as an example a case where the server module  200 - 2  reads data out of the storage module  300  via the coupling module  410 - 2 . 
         [0076]    The OS  221  of the server module  200 - 2  calls up the storage access part  224  in response to a request to read data stored in the storage module  300  which is received from the application  225 . 
         [0077]    The storage access part  224  transmits the read request to the storage control part  333  of the disk controller  310  via the link  510 - 2 . The read request is a command used in the server module  200 - 2  and is therefore in a different format from that of a command used in the storage module  300 . In short, the server module  200 - 2  and the storage module  300  handle different protocols. 
         [0078]    In the following description, a command used by the server modules  200  is referred to as server command and a command used by the storage module  300  is referred to as storage command. 
         [0079]    The coupling module  410 - 2  receives the read request (server command) from the storage access part  224 , converts the read request into a storage command, and transmits the converted read request (now a storage command) to the storage control part  333 . Specifically, the following processing is executed. 
         [0080]    The data transfer part  440  analyzes the received read request (server command). The data transfer part  440  finds out that the received read request (server command) is a server command to be transmitted to the storage module  300 , and therefore instructs the protocol engine  460  to convert the command. 
         [0081]    The protocol engine  460  converts the received read request (server command) through conversion into a storage command from a server command, and outputs the converted read request (now a storage command) to the data transfer part  440 . 
         [0082]    The data transfer part  440  transmits the input read command (storage command) to the storage control part  333  of the storage module  300 . 
         [0083]    The storage control part  333  receives the read request (storage command), reads data that is requested to be read out of the storage devices  360 - 1  to  360 - n , stores the read data in the memory  330 , and transmits a DMA transfer request to the coupling module  410 - 2 . 
         [0084]    Receiving the DMA transfer request, the coupling module  410 - 2  obtains the address of the destination which is the memory  220 - 2  of the server module  200 - 2 , and the address of the source which is the memory  330  of the storage module  300 . A well-known technology can be employed for the DMA transfer. For example, the DMA controller  441  of the data transfer part  440  obtains the destination address and the source address, and the DMA controller  441  transfers data in the memory  330  of the storage module  300  to the memory  220 - 2  of the server module  200 - 2 . 
         [0085]    The coupling module  410 - 2  accomplishes data transfer through the processing described above. 
         [0086]    A case where a failure has occurred in the link  500 - 1  between the server module  200 - 1  and the coupling module  410 - 1  or in the PCIe I/F  230 - 1  is described next. 
         [0087]    The processor  210 - 1  of the server module  200 - 1  detects that a failure has occurred in the PCIe I/F  230 - 1  or the link  500 - 1 . The detected failure is, for example, a PCI Express bus error. This failure detection may be accomplished by, for example, the monitoring of the PCIe I/F  230 - 1  or the end point  420 - 1  through polling or similar processing performed by the OS  221 , which is executed by the processor  210 - 1 . Alternatively, the failure detection may be accomplished by the monitoring of the PCIe I/F  230 - 1  or the end point  420 - 1  through polling or similar processing performed by the storage access part  224 . An HBA driver provided to the OS  221  may instead monitor the PCIe I/F  230 - 1  or the end point  420 - 1  through polling or similar processing in order to accomplish the failure detection. Software that detects a failure in the link  500 - 1  between the server module  200 - 1  and the coupling module  410 - 1  functions as a failure detecting part. 
         [0088]    Detecting a failure in the link  500 - 1  or the PCIe I/F  230 - 1 , the processor  210 - 1  activates the PCIe failure processing part  222  to execute given failure recovery processing such as resetting the PCIe I/F  230 - 1 . 
         [0089]    In this embodiment, when the I/O interface used is a PCI Express interface, it is sufficient if an error that needs the resetting of the PCIe I/F  230 - 1  is detected as a failure out of errors in the physical layer, the data link layer, and the transaction layer. 
         [0090]    Next, the end point  420 - 1  in the coupling module  410 - 1  notifies the protocol engine  460  of the resetting of the link  500 - 1  or a failure. The protocol engine  460  activates the event imitation processing part  470  on the account that a failure has been detected in the link  500 - 1  or the PCIe I/F  230 - 1 . 
         [0091]    When a failure occurs on the end point  420 - 1  side (the HBA side), the event imitation processing part  470  notifies the disk controller  310  of the storage module  300  of FC disconnection (or link down) from the end point  430 - 1  side (the TBA side). In other words, the event imitation processing part  470  of the coupling module  410 - 1  converts a notification of a detected PCI Express failure into a notification of link down of the FC which is a protocol above PCI Express, and notifies the link down to the storage module  300 . The event imitation processing module  470  discards, in advance, I/O between the server module  200 - 1  and the storage module  300  that has been waiting to be processed in the coupling module  410 - 1 . 
         [0092]    The processor  320  of the disk controller  310  receives the FC disconnection notification and activates the TBA link down processing part  332 . Because FC connection is cut between the server module  200 - 1  and the coupling module  410 - 1 , the TBA link down processing part  332  discards data and commands regarding the server module  200 - 1  that have been waiting to be processed (queued I/O), and finishes, in a normal fashion, processing of disengaging the coupling to the server module  200 - 1 . 
         [0093]    Meanwhile, the PCIe I/F  230 - 1  recovers in the server module  200 - 1  by the resetting. The end point  420 - 1  of the coupling module  410 - 1  notifies the protocol engine  460  of the re-established connection to the server module  200 - 1 . The protocol engine  460  notifies the server module  200 - 1  of the failure in the link  500 - 1  or the PCIe I/F  230 - 1 . 
         [0094]    The storage access part  224  of the server module  200 - 1  receives the failure notification, discards data and commands regarding the storage module  300  that have been waiting to be processed (queued I/O), and completes recovery from the failure. The end point  420 - 1  of the coupling module  410 - 1  detects the recovery of the PCIe I/F  230 - 1  and the link  500 - 1 , and then notifies link up of the link to the server module  200 - 1  to the storage module  300  via the protocol engine  460 . Receiving the link up notification, the storage module  300  rebuilds an environment for data transfer to/from the server module  200 - 1 , and resumes the data transfer. 
         [0095]    In the manner described above, when a PCI Express failure occurs between the server module  200 - 1  and the coupling module  410 - 1 , the coupling module  410 - 1  notifies the storage module  300  of disconnection in a protocol above the protocol of the PCIe I/F, instead of the PCI Express failure, while the PCIe I/F  230 - 1  is reset in the server module  200 - 1 . This enables the storage module  300  to execute link down processing in a normal fashion for the link to the server module  200 - 1  while keeping the PCIe I/F  340  in operation. 
         [0096]    The other server module connected to the PCIe I/F  340  of the storage module  300 , namely, the server module  200 - 2 , can thus maintain access to the storage module  300  without being affected by a failure in the PCIe I/F  230 - 1  of the server module  200 - 1 . 
         [0097]      FIG. 6  is a sequence diagram illustrating an example of processing that is executed when a failure occurs on the server module side. 
         [0098]    In Step S 101 , the processor  210 - 1  of the server module  200 - 1  detects that a failure has occurred in the link  500 - 1  via the PCIe I/F  230 - 1 . In Step S 102 , the processor  210 - 1  activates the PCIe failure processing part  222 . In Step S 103 , the PCIe failure processing part  222  executes given failure recovery processing such as resetting the PCIe I/F  230 - 1 . 
         [0099]    The end point  420 - 1  of the coupling module  410 - 1  notifies the protocol engine  420  of the resetting of the link  500 - 1  or the failure. In Step S 104 , the protocol engine  460  activates the event imitation processing part  470  on the account that a failure has been detected in the link  500 - 1 . 
         [0100]    When a failure occurs on the end point  420 - 1  side (the HBA side) which is connected to the server module  200 - 1 , the event imitation processing part  470  notifies the disk controller  310  of the storage module  300  of FC disconnection (or link down) from the end point  430 - 1  side (the TBA side) (S 106 ). In other words, the event imitation processing part  470  of the coupling module  410 - 1  converts a notification of a detected PCI Express failure into a notification of link down of the FC which is a protocol above PCI Express, and notifies the link down to the storage module  300 . Before notifying the link down, the event imitation processing part  470  discards I/O between the server module  200 - 1  and the storage module  300  that has been waiting to be processed (S 105 ). 
         [0101]    The processor  320  of the disk controller  310  receives the FC disconnection (link down) notification in Step S 107  and activates the TBA link down processing part  332  in Step S 108 . 
         [0102]    In Step S 109 , because FC connection is cut between the server module  200 - 1  and the coupling module  410 - 1 , the TBA link down processing part  332  discards data and commands regarding the server module  200 - 1  that have been waiting to be processed (queued I/O), and finishes, in a normal fashion, processing of disengaging the coupling to the server module  200 - 1 . 
         [0103]    Meanwhile, the PCIe I/F  230 - 1  recovers in the server module  200 - 1  by the resetting (S 110 ). The end point  420 - 1  of the coupling module  410 - 1  notifies the protocol engine  460  of the re-established connection to the server module  200 - 1 . The protocol engine  460  notifies the server module  200 - 1  of the failure in the link  500 - 1  (S 111 ). 
         [0104]    The storage access part  224  of the server module  200 - 1  receives the failure notification in Step S 111 , discards data and commands regarding the storage module  300  that have been waiting to be processed (queued I/O) (S 112 ), and completes recovery from the failure (S 113 ). Thereafter, the end point  420 - 1  of the coupling module  410 - 1  detects the recovery of the link  500 - 1 , and the protocol engine  460  notifies link up of the link to the server module  200 - 1  to the storage module  300  (S 114 ). 
         [0105]    In Step S 115 , the storage module  300  receives the link up notification from the coupling module  410 - 1 , rebuilds an environment for data transfer to/from the server module  200 - 1 , and resumes the data transfer. 
         [0106]    In the manner described above, when a PCI Express failure occurs between the server module  200 - 1  and the coupling module  410 - 1 , the coupling module  410 - 1  notifies the storage module  300  of link down (disconnection) in the FC protocol, which is a protocol above PCI Express, instead of the PCI Express failure, while the PCIe I/F  230 - 1  is reset in the server module  200 - 1 . This enables the storage module  300  to execute link down processing in a normal fashion for the link to the server module  200 - 1  while keeping the PCIe I/F  340  in operation. 
         [0107]    The other server module connected to the PCIe I/F  340  of the storage module  300 , namely, the server module  200 - 2 , can thus maintain access to the storage module  300  without being affected by a failure in the PCIe I/F  230 - 1  of the server module  200 - 1 . The coupling module  410 - 1  issues to the storage module  300  a notification of disconnection of the link  500 - 1  which is converted from a notification of a failure on the server module  200 - 1  side. This prevents the resetting of the PCIe I/F  340  on the storage module  300  side, and accordingly prevents the impact of a failure in the PCIe I/F  230 - 1  of the server module  200 - 1  from spreading to the other server modules  200 . 
         [0108]    Specifically, if a failure in the PCIe I/F  230 - 1  of the server module  200 - 1  (a PCI bus error) is notified to the storage module  300  without modification as in the related-art examples described above, the disk controller  310  undesirably activates the PCIe failure processing part  331 , which resets the PCIe I/F  340 . Then data transfer between the server module  200 - 2  and the storage module  300  along the link  500 - 2  which is connected to the PCIe I/F  340  and which is normal is interrupted. 
         [0109]    In contrast, this invention allows the storage module  300  to execute processing of disengaging the coupling to the server module  200 - 1  (e.g., link down or hot remove) by converting, in the coupling module  410 - 1 , a notification of a failure in the PCIe I/F  230 - 1  on the server module  200 - 1  side into a notification of the disconnection of the link  500 - 1 , and issuing the disconnection notification to the storage module  300 . 
         [0110]    In addition, this invention has no need to expand a PCI Express protocol unlike the related-art examples, and can therefore use existing chips, devices, and software, which means that the cost of the server apparatus  100  where the server modules  200  and the storage module  300  are coupled by PCI Express can be kept from rising. 
         [0111]    While the protocol engine  460  activates the event imitation processing part  470  in the example given above, this invention is not limited thereto and the processing can be implemented by any control part of the coupling module  410 - 1 . 
         [0112]    The embodiment described above gives an example in which the coupling modules  410  are disposed in the backplane  400 . However, this invention is not limited thereto and the coupling modules  410 - 1  to  410 - n  may be placed in, for example, the server modules  200 - 1  to  200 - n , respectively. In this case, the server modules  200  and the storage module  300  may be coupled by a PCIe switch instead of the backplane  400 . 
         [0113]    The embodiment gives an example in which PCI Express interfaces are employed as I/O interfaces that couple the server modules  200  and the storage module  300 . This invention, however, is not limited thereto. 
         [0114]    The embodiment gives an example in which FC is used as a protocol above the I/O interface protocol. Other protocols such as SAS (SCSI) and SATA may be employed instead. A failure in an I/O interface, which is link down of a protocol above the I/O interface protocol in the example discussed in the embodiment, can be substituted by hot remove. 
         [0115]    The invention of this application involves detecting, by the server module  200 - 1 , a failure that necessitates the resetting of an I/O interface that couples the server module  200 - 1  and the storage module  300  via the coupling module  410 - 1 , and resetting the I/O interface by the server module  200 - 1 . The coupling module  410 - 1  detects that a failure has occurred based on the resetting by the server module  200 - 1 , converts a notification of a failure in a communication protocol of the I/O interface into a notification of link disconnection, and transmits the disconnection notification to the storage module  300 . The storage module  300  executes processing of disconnecting its link to the server module  200 - 1 , and hence an I/O interface of the storage module  300  can keep running without being reset. 
         [0116]    Some or all of the computer components, processing parts, processing means, and the like described above in this invention may be implemented by dedicated hardware. 
         [0117]    The various types of software given above as an example in the embodiment can be stored in various recording media including electromagnetic, electronic, and optical recording media (e.g., non-transitory storage media), and can be downloaded onto a computer via a communication network such as the Internet. 
         [0118]    This invention is not limited to the embodiment described above, and encompasses various modification examples. For instance, the above-mentioned embodiment is a detailed description of this invention that is intended for easier understanding, and this invention is not necessarily limited to a mode that includes all of the components described above.