JP2006260223A - iSCSI STORAGE SYSTEM AND PASS MULTIPLEX METHOD FOR THE SYSTEM - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a redundant configuration in a storage system using multi-connection/session in an iSCSI (internet small computer system interface). <P>SOLUTION: An iSCSI initiator device 1 establishes a session by multi-connection/session based on IP addresses of iSCSI pass multiplexers 13 and 14 received from the iSCSI pass multiplexer 13 set as the first order. An iSCSI/SCSI protocol control part 8 in the iSCSI pass controller 13 set as the first order, extracts CDB of an SCSI from PDU of an iSCSI received from the iSCSI initiator device 1, and gives a command to a fiber channel storage unit 12 based on the extracted CDB. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an iSCSI storage system in which data is transferred using iSCSI, and a path multiplexing method in the iSCSI storage system.

  With the spread of IP (Internet Protocol) networks such as the Internet, there is an increasing demand for data transfer from a server or the like to a storage device via an IP network. As a method for realizing such data transfer, there is a method using iSCSI (Internet Small Computer System Interface). In iSCSI, SCSI commands and responses are encapsulated in TCP (Transmission Control Protocol) packets and transferred.

  When data transmission / reception is performed between a server (corresponding to an iSCSI initiator) and a storage device (for example, consisting of a magnetic disk and a control device; corresponding to an iSCSI target) mounted with iSCSI via a wide area network such as an IP network, In general, the distance between the server and the storage device is large. In such a situation, concerns about the reliability of the storage device and the reliability of data transfer to the storage device are high compared to the local SCSI environment.

  Therefore, some redundant configuration (duplex configuration) needs to be taken. For example, there is a storage system in which two iSCSI controllers are installed between an IP network and a storage device (see, for example, Patent Document 1). In such a storage system, two iSCSI controllers are communicatively connected, each monitoring the other iSCSI controller. When a failure occurs in one iSCSI controller, a command issued to the iSCSI controller is taken over by the other iSCSI controller.

JP 2003-203019 (paragraph 0005-0010, FIG. 1)

  However, the iSCSI storage system described in Patent Document 1 is merely a standby system in which an existing redundancy technology is diverted to make the other iSCSI controller stand by.

  iSCSI defines a multi-connection / session in which a plurality of connections can be established in one session. An object of the present invention is to provide an iSCSI storage system capable of realizing a redundant configuration in a storage system using multi-connection / session in iSCSI and a path multiplexing method in the system.

  In the iSCSI storage system according to the present invention, a plurality of iSCSI path control devices are provided between an iSCSI initiator and a target device (for example, consisting of a magnetic disk and a control device), and the iSCSI initiator is connected to each of the plurality of iSCSI path control devices. A connection / session control means for establishing a session with a multi-connection / session, and an iSCSI layer control means for performing control in the iSCSI layer, and each of the plurality of iSCSI path control devices includes other iSCSI path control devices. Status setting means for setting each other's order, and when the connection / session control means executes the discovery process when it is set to the first order, its own address and other iSCSI paths Control unit Address response means for responding to the iSCSI initiator, and an iSCSI / SCSI protocol control unit having a function of giving a command (command or data) received from the iSCSI initiator to the target device, and a connection / session control means, A session is established based on a plurality of addresses received from the iSCSI path control device set in the first order, and the iSCSI / SCSI protocol control unit in the iSCSI path control device set in the first order is sent from the iSCSI initiator. A SCSI CDB is extracted from the received iSCSI PDU, and an input / output request is given to the target device based on the extracted CDB.

  The iSCSI path control device includes a PDU route control means having a function of transferring information (for example, ITT) included in the iSCSI PDU received from the iSCSI initiator to another iSCSI path control device, and is in a rank other than the first rank. When the PDU route control means of the set iSCSI path control device receives the iSCSI PDU from the iSCSI initiator, the information is transferred to the iSCSI path control device set in the first order, The PDU route control means of the set iSCSI path control device is configured to output the data input from the target device to the iSCSI path control device to which the information is transferred when receiving the information transfer. May be.

  When the iSCSI layer control means determines that an error has occurred due to a failure in the transmission path between the iSCSI initiator and the iSCSI path control device, the connection / session control means executes retransmission control of the iSCSI command. It may be configured.

  When another iSCSI path control device determines that a failure has occurred in the iSCSI path control device set in the first order, the status setting means of the other iSCSI path control device sets the first iSCSI path control device as the first. It may be configured to set the rank. According to such a configuration, even if a failure occurs in one iSCSI path control device, data transfer between the iSCSI initiator and the target device is not disabled.

  When the status setting unit of the iSCSI path control device set in the first order determines that a failure has occurred in the transmission path between the own iSCSI path control device and the target device, the iSCSI path control device is replaced with the own iSCSI path control device. The other iSCSI path control device may be configured to perform control for setting to the first order. According to such a configuration, since a redundant configuration is maintained between the iSCSI initiator and the iSCSI path control device, it is a single point of failure (the system is stopped due to only one component). It will not be.

  In the path multiplexing method according to the present invention, a plurality of iSCSI path control devices are provided between the iSCSI initiator and the target device, and each of the plurality of iSCSI path control devices communicates with other iSCSI path control devices. When a plurality of iSCSI path controllers are set to the first rank, when the iSCSI initiator executes the discovery process, the addresses of other iSCSI path controllers are set. In response to the iSCSI initiator, the iSCSI initiator establishes a multi-connection / session session based on the plurality of addresses received from the iSCSI path control device set in the first order, and the iSCSI set in the first order. The path control device starts from the iSCSI initiator Extract the CDB of a SCSI from Shin has been the iSCSI PDU, it is characterized in providing an output request to the target device based on the extracted CDB.

  According to the present invention, an iSCSI target (iSCSI path control device) spanning a plurality of pieces of hardware can be included in one session only by the iSCSI initiator establishing a session by multi-connection / session. As a result, the business can be continued even if a failure occurs in any one iSCSI target.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration example of an iSCSI storage system according to the present invention. In the example shown in FIG. 1, the iSCSI storage system includes an iSCSI initiator device 1 having an iSCSI and TCP / IP protocol control unit (hereinafter referred to as a protocol control unit) 2, an iSCSI initiator device 1, and two iSCSI path multiplexing devices ( (iSCSI path control device) 13 and 14 are communicably connected to each other and receive data from the two iSCSI path multiplexers 13 and 14 via fiber channel and to the iSCSI path multiplexers 13 and 14 via fiber channel. And a fiber channel storage unit (target device) 12 for outputting data.

  Note that the iSCSI initiator device 1 is a server connected to another server device or a terminal device by, for example, a LAN (not shown). Therefore, the iSCSI initiator device 1 includes a CPU that operates according to a program. In addition, at least two communication paths are provided between the iSCSI initiator device 1 and the IP network 3.

  The protocol control unit 2 is hardware and software that controls each layer in the iSCSI hierarchical model shown in FIG. For example, in the control of the iSCSI layer, the protocol control unit 2 encapsulates a SCSI command and data from the SCSI layer to create an iSCSI PDU (Protocol Data Unit) and passes it to the TCP / IP layer. Also, the SCSI response and data are extracted from the iSCSI PDU from the TCP / IP layer and passed to the SCSI layer. Accordingly, the connection / session control means for establishing a session with each of the iSCSI path control apparatuses and the iSCSI layer control means for performing control in the iSCSI layer are realized by the protocol control unit 2.

  Each of the iSCSI path multiplexing devices 13 and 14 includes a function as an iSCSI target. The iSCSI path multiplexer 13 is a remote direct memory access (used for communication with a main storage device (not shown), a NIC (Network Interface Card) 4 connected to the IP network 3, and the iSCSI path multiplexer 14). State / PDU route control mechanism (state setting means, PDU route control means) 6 for setting the path of the iSCSI PDU according to the state of the RNIC (Remote NIC) 10 having the RDMA) function and the iSCSI path multiplexing devices 13 and 14 And an iSCSI / SCSI protocol control unit 8. The iSCSI path multiplexing device 13 is equipped with a CPU (not shown) that performs control according to a program, and the entity of the state / PDU route control mechanism 6 is software.

  In the iSCSI path multiplexing devices 13 and 14, between the NICs 10 and 11 and the state / PDU route control mechanisms 6 and 7, protocol control of the TCP / IP protocol or iSCSI discovery session (i.e., the iSCSI initiator uses the SendTagets command to perform iSCSI control). There is a control unit (not shown) that performs control in the case of a session for inquiring a target. Therefore, such a control unit realizes an address response means for responding an address to the iSCSI initiator.

  The iSCSI path multiplexer 14 is configured in the same manner as the iSCSI path multiplexer 13. That is, depending on the state of the RNIC 11 having the remote direct memory access (RDMA) function used for communication with the main storage device, the NIC 5 connected to the IP network 3, and the iSCSI path multiplexer 13, and the iSCSI path multiplexers 13 and 14. And a state / PDU route control mechanism 7 for setting the route of the iSCSI PDU and an iSCSI / SCSI protocol control unit 9.

  Note that the communication path 15 between the iSCSI path multiplexers 13 and 14 is duplicated, and communication between the iSCSI path multiplexers 13 and 14 is continued even if one path is disconnected. The communication path 15 is also used for life and death monitoring. In other words, the iSCSI path multiplexers 13 and 14 perform, for example, heartbeat transmission / reception on the communication path 15. Further, the iSCSI / SCSI protocol control units 8 and 9 control the iSCSI layer and the SCSI layer.

  The fiber channel storage unit 12 as a storage device provides the same logical unit to the iSCSI path multiplexers 13 and 14. That is, the fiber channel storage unit 12 appears to be the same when viewed from the iSCSI path multiplexer 13 and from the iSCSI path multiplexer 14.

  The state / PDU route control mechanisms 6 and 7 communicate with each other by the RNICs 10 and 11, and information indicating whether the iSCSI path multiplexers 13 and 14 are in the first state (first order) or the second state. Is set in the main memory. Specifically, it is assumed that one of the iSCSI path multiplexers 13 and 14 is in the first state and the other is in the second state. When the iSCSI path multiplexers 13 and 14 are both in a state where they can operate normally, the predetermined iSCSI path multiplexer is set to the first state. The state / PDU route control mechanism in the iSCSI path multiplexer in the second state uses the RNICs 10 and 11 to send the iSCSI PDU by remote direct memory access, and the main memory in the iSCSI path multiplexer in the first state. Forward to department. The state / PDU route control mechanism in the iSCSI path multiplexing apparatus in the first state sends the iSCSI PDU to the iSCSI / SCSI protocol control unit.

  Next, the operation of the iSCSI storage system will be described with reference to the flowcharts of FIGS. FIG. 3 is a flowchart showing the operation in the case of an iSCSI discovery session. In the following description, it is assumed that the iSCSI path multiplexer 13 is set in the first state and the iSCSI path multiplexer 14 is set in the second state.

  When the iSCSI initiator device 1 executes the discovery process, the iSCSI path multiplexing devices 13 and 14 extract the discovery session information from the IP packet transmitted by the iSCSI initiator device 1 (step S11). As a response to the discovery session, the iSCSI path multiplexer 13 in the first state receives its own IP address, the IP address of the iSCSI path multiplexer 14 in the second state, the target portal group tag, and The target name is returned to the iSCSI initiator device 1 (steps S12 and S13). The iSCSI path multiplexing device 14 in the second state does not respond in the discovery session (steps S12 and S14).

  The iSCSI initiator device 1 establishes a session by multi-connection / session for a plurality of IP addresses obtained by the iSCSI discovery session (step S15). One connection is a connection for the iSCSI path multiplexer 13 and the other connection is a connection for the iSCSI path multiplexer 14.

  4 and 5 are flowcharts showing the operation of the iSCSI path multiplexers 13 and 14. The iSCSI path multiplexing device 13 or the iSCSI path multiplexing device 14 extracts an iSCSI PDU from the IP packet transmitted by the iSCSI initiator device 1 (step S21).

  When an iSCSI command is issued from the iSCSI initiator device 1 using the connection of the iSCSI path multiplexing device 13 in the first state, the state / PDU route control mechanism 6 of the iSCSI path multiplexing device 13 The initiator task tag (ITT) of the iSCSI PDU is extracted. Then, the main storage device address is generated from the ITT, and the iSCSI PDU is stored in the generated address. That is, the state / PDU route control mechanism 6 maps the received iSCSI PDU to the address of the main storage device according to ITT (steps S22 and S23).

  When an iSCSI command is issued from the iSCSI initiator device 1 using the connection of the iSCSI path multiplexing device 14 in the second state, the status / PDU route control mechanism 7 of the iSCSI path multiplexing device 14 The initiator task tag (ITT) of the iSCSI PDU is extracted, the address of the main storage device is generated from the ITT, and the received iSCSI PDU is stored in the generated address (steps S22 and S26). The iSCSI PDU thus transferred is transferred to the main storage device of the iSCSI path multiplexer 13 via the RNIC 11 and the communication path 15 (step S27). Note that the iSCSI path multiplexing device in the first state is referred to as a first iSCSI path multiplexing device, and the iSCSI path multiplexing device in the second state is referred to as a second iSCSI path multiplexing device. .

  The state / PDU route control mechanism 6 of the iSCSI path multiplexer 13 extracts the ITT from the iSCSI PDU stored in the main storage device when the iSCSI PDU is transferred from the iSCSI path multiplexer 14. The extracted ITT is stored as the second ITT (step S24). If no iSCSI PDU is transferred from the iSCSI path multiplexing device 14, the process of step S24 is not executed.

  Then, the iSCSI / SCSI protocol control unit 8 of the iSCSI path multiplexing device 13 extracts a CDB (Command Description Block) as a SCSI command from the iSCSI PDU (step S25), and via the fiber channel (FC), The extracted command is executed for the fiber channel storage unit 12. That is, for example, an input / output request is given to the fiber channel storage unit 12.

  As described above, when the iSCSI initiator device 1 executes the iSCSI task using the connection of the iSCSI path multiplexing device in the first state, the processing is performed in the order of steps S21, S22, S23, and S25. Executed. Further, when the iSCSI initiator device 1 executes the iSCSI task using the connection of the iSCSI path multiplexing device in the second state, the processing is performed in the order of steps S21, S22, S26, S27, S24, and S25. Is executed. In iSCSI, an iSCSI initiator can issue an iSCSI command from any connection in the iSCSI, but an iSCSI response needs to be returned on the connection from which the iSCSI command is issued.

  In this embodiment, a plurality of iSCSI paths are set to be usable at the same time. However, for example, the iSCSI initiator device 1 basically uses the connection of the iSCSI path multiplexing device in the first state. To execute the iSCSI task. In addition, between the iSCSI path multiplexers 13 and 14 and the fiber channel storage unit 12, data is input / output between the iSCSI path multiplexer and fiber channel storage unit 12 in the first state. Is called.

  As shown in FIG. 5, when the iSCSI response is output from the fiber channel storage unit 12 (step S31), only the iSCSI path multiplexing device 13 in the first state receives the iSCSI response.

  The iSCSI / SCSI protocol control unit 8 of the iSCSI path multiplexing device 13 in the first state converts the SCSI CDB into an iSCSI PDU and stores it in the main storage device (step S32). Further, the iSCSI / SCSI protocol control unit 8 of the iSCSI path multiplexing device 13 extracts ITT from the converted iSCSI PDU. Then, it is determined whether or not the extracted ITT matches the stored second ITT (step S33).

  If they match, the iSCSI response from the Fiber Channel storage unit 12 is a response to the iSCSI command issued by the iSCSI initiator device 1 using the connection of the iSCSI path multiplexing device 14 in the second state. It will be. Therefore, the state / PDU route control mechanism 6 of the iSCSI path multiplexer 13 transfers the data to the main storage device of the iSCSI path multiplexer 14 via the RNIC 10 and the communication path 15 (step S34). In this case, the iSCSI path multiplexing device 14 in the second state returns an iSCSI PDU to the iSCSI initiator device 1 (step S36).

  If they do not match, no transfer is performed via the RNIC 10 and the communication path 15 (step S35). In this case, the iSCSI path multiplexing device 13 in the first state returns an iSCSI PDU to the iSCSI initiator device 1 (step S36).

  FIG. 6 is a flowchart showing a recovery method when a failure occurs in the iSCSI path. When the protocol control unit 2 of the iSCSI initiator device 1 detects that an error has occurred in the running iSCSI task (step S41), it performs the following processing. Note that errors in the iSCSI task include that there is no iSCSI response to the iSCSI command, that there is an inconsistent field in the PDU, and a data error (digest error) in the PDU. In addition, an error may occur in the TCP layer or the like.

  The protocol control unit 2 of the iSCSI initiator device 1 determines whether or not the error that has occurred is due to a failure in the transmission path between the iSCSI initiator device 1 and the iSCSI path multiplexing devices 13 and 14 (step S42). Specifically, there is an iSCSI response to the iSCSI command, but when a data error has occurred, it is determined that an error has occurred due to a failure in the transmission path. When an error occurs due to a failure in the transmission path, the protocol control unit 2 of the iSCSI initiator device 1 retransmits the iSCSI command in accordance with the recovery method defined in iSCSI (step S43).

  If it is determined that the cause of the error is not a failure in the transmission path, the protocol control unit 2 of the iSCSI initiator device 1 makes an error inquiry to the iSCSI path multiplexing devices 13 and 14. Whether the state / PDU route control mechanisms 6 and 7 of the iSCSI path multiplexers 13 and 14 are responding to the heartbeat in the interconnect (through the communication path 15) of the iSCSI path multiplexers 13 and 14 in response to the inquiry. It is confirmed whether or not (step S44).

  When the state / PDU route control mechanism 6 of the iSCSI path multiplexer 13 confirms that there is no heartbeat response, it is determined that a hardware failure has occurred in the iSCSI path multiplexer 14. If the state / PDU route control mechanism 7 of the iSCSI path multiplexer 14 confirms that there is no heartbeat response, it is determined that a hardware failure has occurred in the iSCSI path multiplexer 13.

  When the state / PDU route control mechanism 7 of the iSCSI path multiplexing device 14 determines that a hardware failure has occurred in the iSCSI path multiplexing device 13 in the first state, the iSCSI initiator device 1 closes the session. (Steps S45 and S46). Then, the state / PDU route control mechanism 7 of the iSCSI path multiplexing device 14 sets information indicating that it is in the first state in the main storage unit (step S47). Further, the iSCSI initiator device 1 reestablishes the session with a single connection / session and performs session recovery (step S48). Then, the iSCSI initiator device 1 executes again the iSCSI task in which the error has occurred (step S49). When the iSCSI initiator device 1 executes a discovery session, the iSCSI path multiplexing device 14 returns only its own IP address.

  If the state / PDU route control mechanism 6 of the iSCSI path multiplexer 13 determines that a hardware failure has occurred in the iSCSI path multiplexer 14 in the second state, for example, the iSCSI initiator device 1 To that effect. In that case, the protocol control unit 2 of the iSCSI initiator device 1 retransmits the iSCSI command in accordance with the recovery method defined in iSCSI (step S43).

  State of iSCSI path multiplexers 13 and 14 / If both PDU route control mechanisms 6 and 7 determine that there is a heartbeat response, the iSCSI path multiplexer 13 and the fiber channel that are in the first state It is determined that a failure has occurred in the transmission path to the storage unit 12. In that case, the state / PDU route control mechanism 7 of the iSCSI path multiplexing device 14 in the second state prompts the iSCSI initiator device 1 to close the session (step S50). Note that the iSCSI path multiplexing apparatus 13 may prompt the session to be closed.

  Then, the state / PDU route control mechanism 6 of the iSCSI path multiplexing device 13 sets information indicating that it is in the second state in the main storage unit. Further, the state / PDU route control mechanism 7 of the iSCSI path multiplexing device 14 sets information indicating that it is in the first state in the main storage unit (step S51). The iSCSI initiator device 1 establishes a session by multi-connection / session by the method as shown in FIG. 3 (step S52). Further, the protocol control unit 2 of the iSCSI initiator device 1 executes again the iSCSI task in which the error has occurred (step S53).

  As described above, when the iSCSI initiator device 1 determines that an error has occurred due to a failure in the transmission path between the iSCSI initiator device 1 and the iSCSI path multiplexing devices 13 and 14, the iSCSI initiator device 1 The iSCSI command is retransmitted in accordance with the recovery method being used. When it is determined that a failure has occurred in the iSCSI path multiplexing device in the first state, the iSCSI task is set in the first state to the iSCSI task. Run again. Further, when it is determined that a failure has occurred in the transmission path between the iSCSI path multiplexing apparatus in the first state and the fiber channel storage unit 12, the iSCSI path set in the first state The multiplexing task and the iSCSI path multiplexing device set to the second state are switched, and the iSCSI task is executed again.

  Note that iSCSI path multiplexing is realized in an environment in which an iSCSI target (corresponding to the iSCSI path multiplexers 13 and 14) having the same logical unit (for example, Fiber Channel storage unit 12) as a target device spans multiple hardware. In the past, software that enables multiplexing on the operating system (OS) on which the iSCSI initiator is operating has been used.

  However, in such a configuration, the path multiplexing method defined by iSCSI cannot be used. This is because a target device that spans multiple hardware cannot be included in one SCSI session, and multiple logical units can be seen from the OS on which the iSCSI initiator is operating. Also, in order to realize path multiplexing, software for realizing the multiplexing function must be used, which increases the price of the system.

  In the above embodiment, two pieces of hardware are provided as the iSCSI path multiplexing device, but more pieces of hardware may be provided. When more hardware is provided, the other iSCSI path multiplexer transfers the received iSCSI PDU to the iSCSI path multiplexer set in the first state.

  The present invention is suitably applied to a system that writes data to a storage device via an IP network and reads data from the storage device.

It is a block diagram which shows the structural example of the iSCSI storage system by this invention. It is explanatory drawing which shows an iSCSI hierarchical model. It is a flowchart which shows the operation | movement in the case of an iSCSI discovery session. It is a flowchart which shows operation | movement of an iSCSI path multiplexing apparatus. It is a flowchart which shows operation | movement of an iSCSI path multiplexing apparatus. It is a flowchart which shows the recovery system when a failure generate | occur | produces in an iSCSI path.

Explanation of symbols

1 iSCSI initiator 2 TCP / IP protocol control unit 3 IP network 4, 5 NIC
6, 7 Status / PDU route controller 8, 9 iSCSI / SCSI protocol controller 10, 11 RNIC
12 Fiber Channel storage unit 13, 14 iSCSI path multiplexer 15 Communication path

Claims (6)

In the iSCSI storage system in which the path between the iSCSI initiator and the target device is multiplexed,
A plurality of iSCSI path control devices are provided between the iSCSI initiator and the target device,
The iSCSI initiator includes a connection / session control means for establishing a session with each of the plurality of iSCSI path control devices by a multi-connection / session;
iSCSI layer control means for performing control in the iSCSI layer,
Each of the plurality of iSCSI path control devices includes:
Status setting means for setting the mutual ranking with other iSCSI path control devices;
Address response means for responding to the iSCSI initiator with its own address and the address of another iSCSI path control device when the connection / session control means executes discovery processing when it is set in the first order. When,
An iSCSI / SCSI protocol control unit having a function of giving a command received from the iSCSI initiator to the target device;
The connection / session control means establishes a session based on a plurality of addresses received from the iSCSI path control device set in the first order,
The iSCSI / SCSI protocol control unit in the iSCSI path control device set in the first order extracts the SCSI CDB from the iSCSI PDU received from the iSCSI initiator, and enters the target device based on the extracted CDB. An iSCSI storage system characterized by providing an output request. The iSCSI path control device includes a PDU route control means having a function of transferring information included in the iSCSI PDU received from the iSCSI initiator to another iSCSI path control device,
The PDU route control means of the iSCSI path control device set to a rank other than the first rank receives the information when the iSCSI PDU is received from the iSCSI initiator, and the iSCSI path control apparatus is set to the first rank. Forward to
When receiving the information transfer, the PDU route control means of the iSCSI path control device set in the first order outputs the data input from the target device to the iSCSI path control device that transferred the information. The iSCSI storage system according to claim 1. The iSCSI layer control means executes retransmission control of an iSCSI command when the connection / session control means determines that an error has occurred due to a failure in a transmission path between the iSCSI initiator and the iSCSI path control device. The iSCSI storage system according to claim 1 or 3. When another iSCSI path control device determines that a failure has occurred in the iSCSI path control device set in the first order, the status setting means of the other iSCSI path control device refers to its own iSCSI path control device. The iSCSI storage system according to any one of claims 1 to 3, wherein the iSCSI storage system is set to one rank. If the status setting means of the iSCSI path control device set in the first order determines that a failure has occurred in the transmission path between the own iSCSI path control device and the target device, it replaces the own iSCSI path control device. The iSCSI storage system according to any one of claims 1 to 4, wherein control for setting another iSCSI path control device to the first order is performed. In a path multiplexing method for multiplexing a path between an iSCSI initiator and a target device,
A plurality of iSCSI path control devices are provided between the iSCSI initiator and the target device,
Each of the plurality of iSCSI path control devices sets the order of each other with other iSCSI path control devices,
When the plurality of iSCSI path control devices are set to the first order, when the iSCSI initiator executes the discovery process, its own address and the addresses of other iSCSI path control devices are sent to the iSCSI initiator. Respond,
The iSCSI initiator establishes a session with a multi-connection / session based on a plurality of addresses received from the iSCSI path control device set in the first order,
The iSCSI path control device set in the first order extracts the SCSI CDB from the iSCSI PDU received from the iSCSI initiator, and gives an input / output request to the target device based on the extracted CDB. Path multiplexing method.

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