Abstract:
A method for transferring information between an iSCSI device operating under an iSCSI protocol within a TCP/IP network and a SCSI over Fiber Channel (FCP) device operating under an FCP protocol within an FC network, including: 
     coupling the TCP/IP and the FC networks via a gateway which conveys data between the networks; 
     generating in the gateway a virtual-FC-address for the iSCSI device; 
     generating in the gateway a virtual-TCP/IP-address for the FCP device; 
     conveying a first FC-data-frame, from the FCP device addressed to the virtual-FC-address of the iSCSI device; 
     translating in the gateway the first FCP-data-frame into a first iSCSI-data-frame, addressed to a TCP/IP address of the iSCSI device; and 
     conveying the first iSCSI-data-frame from the gateway to the iSCSI device responsive to the TCP/IP address. 
     The gateway also transfers data from the iSCSI to the FCP device using the virtual addresses.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to data transfer, and specifically to data transfer between Internet Small Computer System Interface devices and devices operating in a Fibre Channel network. 
     BACKGROUND OF THE INVENTION 
     As requirements for the ability to transfer large amounts of data between computing entities has grown, demand for efficient transfer of the data within and between computing networks has also increased. An ubiquitous protocol used for transferring data is a Transmission Control Protocol/Internet Protocol (TCP/IP) TCP is described by Postel in Request For Comments (RFC) 793 of the U.S. Defence Advanced Research Projects Agency (DARPA), which is incorporated herein by reference. 
     A Small Computer System Interface (SCSI) protocol enables an input/output (I/O) device such as a printer or a scanner, termed a target, to communicate with a client of the I/O device, termed an initiator. The original SCSI was standardized in 1986 by the American National Standards Institute (ANSI) as X3.131-1986, and limited distances between the target and the initiator to relatively small values, of the order of six meters. The current evolving SCSI standard is described in a document titled “SCSI Architecture Model-2 (SAM-2),” produced by T10, Technical Committee of the National Committee on Information Technology Standards, which may be found on the T10 Internet site at ftp://ftp.t10.org/t10/drafts/sam2, and which is incorporated herein by reference. 
     An Internet SCSI (iSCSI) protocol has been developed by the Internet Engineering Task Force (IETF) to enable SCSI clients and I/O devices to communicate with no limitations on distance between the components. A draft of the protocol can be found at http://ietf.org/internet-drafts/draft-ietf-ips-iscsi-08.txt, and is incorporated herein by reference. The iSCSI protocol encapsulates SCSI commands by representing them as serial strings of bytes preceded by iSCSI headers. The strings of bytes with iSCSI headers, termed Protocol Data Units (PDUs), are formed into TCP/IP packets which are transmitted in a TCP/IP network. 
     A number of Fibre Channel (FC) protocols have been issued by the American National Standards Institute, Washington, D.C. A Fibre Channel protocol enables transfer of data-frames via an FC switching fabric controlled by a management facility. An FCP protocol is a mapping of the SCSI protocol into an FC protocol, and is a protocol that supports data transfer between hosts and SCSI I/O devices over FC networks. 
     Cisco Systems, Inc., of San Jose, Calif., produce an SN 5420 storage router which is able to convey SCSI commands from a host operating in a TCP/IP network to a storage device operating in an FC network. The host incorporates a dedicated SN 5420 driver to convert SCSI commands to iSCSI data and transfer the iSCSI data to the SN 5420 router. 
     SUMMARY OF THE INVENTION 
     It is an object of some aspects of the present invention to provide a method and apparatus for transferring data between an Internet Small Computer System Interface device and a Fibre Channel device. 
     In preferred embodiments of the present invention, a gateway couples a network operating under a Transmission Control Protocol/Internet Protocol (TCP/IP) with a network operating under a Fibre Channel (FC) protocol, so as to transfer data between the networks. At least one device in the TCP/IP network is implemented to operate according to an Internet Small Computer System Interface (iSCSI) protocol, such devices herein being termed iSCSI devices. The FC network comprises at least one FC device implemented to operate according to a SCSI protocol, such devices herein being termed FCP devices. 
     The gateway generates an FC “image” of each of the iSCSI devices, each FC image comprising a respective virtual FC address, preferably derived from an FC storage name server. Each iSCSI device is thus “visible” to the FCP devices in the FC network via its respective FC image, and communication between the iSCSI devices and the FCP devices can be implemented via the virtual FC addresses of the iSCSI devices. The gateway also generates a TCP/IP image of each of the FCP devices, each TCP/IP image being visible to the iSCSI devices in the TCP/IP network, and comprising a respective virtual TCP/IP address (preferably derived from an IP name server) with which the iSCSI devices can communicate. To implement communication between a specific iSCSI device and a specific FCP device, a “connection-pair” between the two devices is formed. The connection-pair comprises a first TCP connection between the iSCSI device and the gateway and a second FC connection between the FCP device and the gateway. 
     To transfer data between the two devices, the gateway translates data frames transmitted via the connection-pair between FC protocol data and iSCSI protocol data. Thus, the gateway enables iSCSI devices and FCP devices to communicate bi-directionally in a substantially transparent manner, without requiring software and/or hardware changes to existing iSCSI and FCP devices. 
     Preferably, the gateway performs a synchronization check on iSCSI frames received while a connection-pair is operative. Most preferably, in the event of discovering a synchronization error, the gateway resynchronizes remaining frames and allows missing frames to be recovered at an application level. Alternatively, the gateway closes the connection-pair, and allows the application to reopen it. 
     The gateway is most preferably implemented to translate between each iSCSI task that uses the TCP connection and a corresponding FCP task that uses the FC connection. 
     The gateway is most preferably also implemented to collect FCP data sequences, each of which might be comprised of several FC frames, and then send each sequence as an iSCSI data message. It is also implemented to translate each iSCSI data message into an FCP data sequence, breaking each sequence into one or more FC frames. 
     There is therefore provided, according to a preferred embodiment of the present invention, a method for transferring information between an Internet Small Computer System Interface (iSCSI) device operating under an iSCSI protocol within a Transmission Control Protocol/Internet Protocol (TCP/IP) network and a SCSI over Fibre Channel (FCP) device operating under an FCP protocol within a Fibre Channel (FC) network, including: 
     coupling the TCP/IP and the FC networks via a gateway adapted to convey data between the networks; 
     generating in the gateway a virtual-FC-address compatible with the FC protocol for the iSCSI device; 
     generating in the gateway a virtual-TCP/IP-address compatible with the TCP/IP protocol for the FCP device; 
     conveying a first FC-data-frame, compatible with the FCP protocol and comprising FCP-data, from the FCP device addressed to the virtual-FC-address of the iSCSI device; 
     translating in the gateway the first FCP-data-frame into a first iSCSI-data-frame, compatible with the iSCSI protocol and comprising the FCP-data, addressed to a TCP/IP address of the iSCSI device; 
     conveying the first iSCSI-data-frame from the gateway to the iSCSI device responsive to the TCP/IP address; 
     conveying a second iSCSI-data-frame, compatible with the iSCSI protocol and comprising iSCSI-data, from the iSCSI device addressed to the virtual-TCP/IP-address of the FCP device; 
     translating in the gateway the second iSCSI-data-frame into a second FCP-data-frame, compatible with the FCP protocol and comprising the iSCSI-data, addressed to an FC address of the FCP device; and 
     conveying the second FCP-data-frame from the gateway to the FCP device responsive to the FC address. 
     Preferably, the FCP-data includes a task for the iSCSI device, and translating the first FCP-data-frame includes mapping the task to an iSCSI task; and the iSCSI-data includes a task for the FCP device, and translating the second iSCSI-data-frame includes mapping the task to an FC task. 
     Preferably, translating in the gateway the second iSCSI-data-frame includes performing a synchronization check on the second iSCSI-data-frame. 
     The method preferably further includes resynchronizing a subsequent iSCSI-data-frame responsive to the synchronization check. 
     The method preferably includes generating a connection-pair between the iSCSI device and the FCP device, wherein the connection-pair includes a TCP connection between the iSCSI device and the gateway which is mapped to an FC connection between the gateway and the FCP device. 
     There is further provided, according to a preferred embodiment of the present invention, apparatus for transferring information between an Internet Small Computer System Interface (iSCSI) device operating under an iSCSI protocol within a Transmission Control Protocol/Internet Protocol (TCP/IP) network and a SCSI over Fibre Channel (FCP) device operating under an FCP protocol within a Fibre Channel FC network, including: 
     a gateway, including a central processing unit (CPU) and a memory, wherein the gateway couples the TCP/IP and the FC networks and is adapted to convey data between the networks, wherein the CPU: 
     generates in the memory a virtual-FC-address compatible with the FC protocol for the iSCSI device; and 
     generates in the memory a virtual-TCP/IP-address compatible with the TCP/IP protocol for the FCP device; and wherein the gateway is adapted to: 
     receive a first FCP-data-frame, compatible with the FCP protocol and comprising FCP-data, from the FCP device addressed to the virtual-FC-address of the iSCSI device; 
     translate the first FCP-data-frame into a first iSCSI-data-frame, compatible with the iSCSI protocol and comprising the FCP-data, addressed to a TCP/IP address of the iSCSI device; 
     convey the first iSCSI-data-frame from the gateway to the iSCSI device responsive to the TCP/IP address; 
     receive a second iSCSI-data-frame, compatible with the iSCSI protocol and comprising iSCSI-data, from the iSCSI device addressed to the virtual-TCP/IP-address of the FCP device; 
     translate the second iSCSI-data-frame into a second FCP-data-frame, compatible with the FCP protocol and comprising the iSCSI-data, addressed to an FC address of the FCP device; and 
     convey the second FCP-data-frame from the gateway to the FCP device responsive to the FC address. 
     Preferably, the FCP-data includes a task for the iSCSI device, and the CPU maps the task to an iSCSI task. 
     Further preferably, the iSCSI-data includes a task for the FCP device, and the gateway maps the task to an FCP task. 
     Preferably, the gateway is adapted to perform a synchronization check on the second iSCSI-data-frame. 
     Further preferably, the gateway is adapted to resynchronize a subsequent iSCSI-data-frame responsive to the synchronization check. 
     Preferably, the CPU is adapted to generate a connection-pair between the iSCSI device and the FCP device, wherein the connection-pair includes a TCP connection between the iSCSI device and the gateway which is mapped to an FC connection between the gateway and the FCP device. 
    
    
     The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings, in which: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 which is a schematic diagram illustrating transferring data between an Internet Small Computer System Interface (iSCSI) device in a TCP/IP network and a Fibre Channel (FC) device operating as a SCSI device (FCP device) in an FC network; 
     FIG. 2 is a diagram illustrating a session initiation process sequence of messages between an iSCSI initiator device and an FCP target device, according to a preferred embodiment of the present invention; 
     FIG. 3 is a diagram illustrating a sequence of messages occurring between the iSCSI initiator device and the FCP target device of FIG. 2, when the initiator reads from the target, according to a preferred embodiment of the present invention; and 
     FIG. 4 is a diagram illustrating a sequence of messages occurring between the initiator and the target of FIG. 2, when the initiator writes to the target, according to a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference is now made to FIG. 1, which is a schematic diagram illustrating a system  10  for transferring data between an Internet Small Computer System Interface (iSCSI) device and a Fibre Channel (FC) device implemented to operate as a SCSI device (FCP device). A network  16  operating under a Transmission Control Protocol/Internet Protocol (TCP/IP) comprises one or more generally similar hosts  14 , which may be any host which operates according to a SCSI protocol. At least one of hosts  14  is able to operate as an initiator of SCSI commands. At least one of hosts  14  is able to operate as a target of SCSI commands. The terms initiator and target are described in the Background of the Invention; typically, an initiator comprises a computer which uses a target, and a target comprises a storage drive, a printer, or any other input/output device. Each host  14 , herein also termed iSCSI devices C, D, E, . . . , comprises a converter  18  which is able to convert SCSI data to iSCSI data, and vice versa. The SCSI data transfers between the converter and its host  14 , and the iSCSI data transfers between the converter and TCP/IP network  16 , so that the specific host is able to communicate with other entities within the network. Converters which operate as converter  18  are known in the art, and may take the form of software, hardware, or a combination of software and hardware. An example of such a converter is an 1000x1 iSCSI network interface card (NIC) produced by Alacritech Inc., of San Jose, Calif. As described in the Background of the Invention, transmitting SCSI data to and from SCSI devices in the form of iSCSI data enables the SCSI devices to function in network  16 . Network  16  also comprises an IP name server  38 , which preferably acts as a storage name server. 
     System  10  comprises a network  32  operating under a Fibre Channel (FC) protocol. FC network  32  comprises one or more SCSI devices  34 , which may be any device which operates according to a SCSI protocol and which is able to receive and transmit SCSI data according to an FCP protocol, as described in the Background of the Invention. Devices  34  are herein also termed FCP device A, B, . . . . At least one device  34  is able to operate as an initiator of SCSI commands. At least one device  34  is able to operate as a target of SCSI commands. Network  32  preferably also comprises an FC Simple Name Server  36 . 
     A gateway  12  couples FC network  32  to TCP/IP network  16 , so as to transfer data between the networks. Preferably, gateway  12  acts as a switch within FC network  32 , and comprises a gateway such as the GFS- 8  gateway produced by SANCastle Technologies Inc, of San Jose, Calif. Gateway  12  comprises a central processing unit (CPU)  21  and a memory  20 , the memory preferably also comprising one or more buffers  23  wherein data transferred between networks  12  and  32  is stored. Memory  20  also comprises a task mapping table  25  and a connection mapping table  27 . Most preferably, at installation of gateway  12 , the gateway identifies iSCSI hosts  14  operative in network  16 , using Name Server  38 . Alternatively, the gateway identifies iSCSI hosts  14  by any other means known in the art. For each iSCSI host  14  identified, CPU  21  assigns a virtual FC address in memory  20 , so forming for each respective iSCSI host  14  a virtual FC “image”  24  that is “visible” to entities operating in network  32 . 
     Similarly, most preferably at installation, gateway  12  identifies FCP devices  34  operative in network  32 , using Name Server  36 , or alternatively using any other means known in the art. For each FCP device  34  identified, CPU  21  assigns a virtual TCP/IP address in memory  20 , so forming for each respective FCP device  34  a virtual TCP/IP image  26  that is “visible” to entities operating in network  16 . Each virtual TCP/IP address is formed of a couple (IP address, TCP port) where the IP address corresponds to the IP address of the gateway, and where the TCP port is assigned by CPU  21  in conjunction with Name Server  38 . 
     Thus, all SCSI enabled entities in both networks  16  and  32  are visible to each other, and each SCSI enabled entity in one of the networks is able to communicate with a SCSI enabled entity in the other network via gateway  12 . 
     FIG. 2 is a diagram illustrating a session initiation process sequence of messages between an iSCSI device in network  16  and an FCP device in network  32 , according to a preferred embodiment of the present invention. The sequence of messages occurs when a SCSI host  14  acts as an initiator  50 , and an FCP device  34  acts as a target  52 , for an initial login procedure between the initiator and the target. The initiator has a virtual FC address  56  in gateway  12 , assigned as described above, so that the initiator appears, to FCP device  34 , to “reside” in the gateway. The target has a TCP/IP couple address  58  in gateway  12 , also assigned as described above, so that the target appears, to iSCSI device  14 , also to reside in the gateway. 
     In a first, two-way, communication  53 , a TCP/IP session between initiator  50  and virtual TCP/IP target address  58  is established. Then, in a second communication  54 , initiator  50  sends a Login Command to target  52 , using the target&#39;s virtual TCP/IP address  58 . The Login Command requires target  52  to reply to initiator  50  before full communication between the two can be initiated. The reply comprises parameters of target  52 , such as a type of target and/or specific factors within the SCSI protocol which are to be used in communicating with the target. In addition, initiator  50  may send some more parameters via a Text Command communication  60 . Gateway  12  responds to any communication  60  by sending a Text Response  62  to initiator  50 . Initiator  50  then waits for a Login Response. In a communication  64 , gateway  12  sends a login command to target  52 , using the parameters in communication  54  and communication  60 , the login command being addressed from virtual address  56 . Target  52  responds to communication  64  with a login response  66  to virtual address  56 , the response being received by gateway  12 . The combination of login command  64  and response  66  generate an FC connection between gateway  12  and target  52 . 
     In a final Login Response communication  68 , the gateway sends initiator  50  a reply to communication  54 , using parameters from response  66 , thus completing the initial login procedure. The login procedure generates a “connection-pair” between initiator  50  and target  52 , the connection-pair comprising a TCP connection (between the initiator and the gateway) and an FC connection (between the gateway and the target). The connection-pair is stored as a mapping within connection mapping table  27 , for the duration of the connection. 
     It will be understood that while the process described hereinabove with reference to FIG. 2 applies to the login procedure for an initiator in network  16  and a target in network  32 , a substantially similar process applies for an initial login procedure for an initiator in network  32  and a target in network  16 . In the latter case the login procedure generates a connection-pair comprising an FC connection (between the initiator and the gateway) and a TCP connection (between the gateway and the target). 
     FIG. 3 is a diagram illustrating a sequence of messages occurring between initiator  50  and target  52 , according to a preferred embodiment of the present invention. The sequence applies when initiator  50  reads data from target  52 . In a first message  80 , initiator  50  transmits a read command, in an iSCSI format, to virtual address  58  of target  52 . The message is received by gateway  12 , which generates a new FCP task for this read command, and establishes a mapping between an iSCSI task identity and an FCP task identity (FC OXID) in mapping table  25 . The gateway converts the read command to a translated read command  82 , compatible with the FCP protocol, addressed to target  52  from initiator virtual address  56 . The translation includes translating the SCSI read task identity to the corresponding FCP read task identity (FC OXID), and gateway  12  transmits the translated read command to target  52 . In reply, target  52  transmits a “ready-to-transfer” response  84  to virtual. address  56 . The response is received at gateway  12 , but the gateway takes no action with respect to the response. Target  52  then transmits data in the form of sets of data  86 , consisting of P separate sets of data frames to virtual address  56 . Each set comprises a number N 1 , N 2 , . . . of data frames which target  52  transmits. When target  52  completes sending the P sets of data frames, it sends a final communication FCP_RSP  90  to initiator virtual address  56 , completing the read sequence of commands from the point of view of the target. 
     Gateway  12  collects each FCP set of frames  86  into one message preferably in buffer  23 , and translates the message into an iSCSI data message, using the established mapping between the FCP task identity and the iSCSI task identity. The gateway then sends the message from virtual TCP/IP target  58  to iSCSI initiator  50 , via TCP, by breaking it into several TCP/IP frames  88 . Gateway  12  thus sends P sets of TCP/IP frames, each set comprising a number M 1 , M 2 , . . . of frames. In general, N 1 , N 2 , . . . are respectively different from M 1 , M 2 , . . . . 
     When gateway  12  receives final communication FCP_RSP  90 , it translates it into an iSCSI Response message  92 , and sends the message to initiator  50 . Gateway  12  then removes the iSCSI task/FCP task mapping from its mapping table  25 . 
     FIG. 4 is a diagram illustrating a sequence of messages occurring between initiator  50  and target  52 , according to a preferred embodiment of the present invention. The sequence applies when initiator  50  writes data to target  52 . In a first message  100 , initiator  50  transmits a write command, in an iSCSI format, to virtual address  58  of target  52 . The message is received by gateway  12 , which generates a new FCP task for this write command, and establishes a mapping between the iSCSI task identity and the FCP task identity (FC OXID) in mapping table  25 . The gateway converts the write command to a translated write command  102 . The write command is compatible with the FCP protocol and is addressed to target  52  from initiator virtual address  56 . Gateway  12  then transmits translated write command  102  to target  52 . In reply, target  52  transmits a first FC ready-to-transfer message  104  to virtual address  56 . Gateway  12  translates message  104  to a first iSCSI ready-to-transfer  106 , and transmits message  106  to initiator  50 , causing the initiator to start transmitting Q sets  108  of iSCSI data-out messages to the gateway. Each set comprises a number R 1 , R 2 , . . . of data frames which initiator  50  transmits. As described in more detail below, as each set of data-frames is transmitted, initiator  50  waits for a response before continuing. 
     Gateway  12  collects each iSCSI set of data message frames  108  into one message, and translates it into an FCP sequence, using the established mapping between the FCP task identity and the iSCSI task identity. The gateway then sends the message from virtual FC initiator  56  to iSCSI initiator  50 , via FC, by breaking it into several FC frames  110 . Gateway  12  sends Q sets of FC frames, each set comprising a number S 1 , S 2 , . . . of frames, substantially as described above. In general, R 1 , R 2 , . . . . are respectively different from S 1 , S 2 , . . . . 
     When gateway  12  receives a final communication FCP_RSP  116 , it translates it into an iSCSI Response message  118 , and sends the message to initiator  50 . Gateway  12  then removes the iSCSI task/FCP task mapping from its mapping table  25 . 
     Sequences of instructions described above with reference to FIGS. 3 and 4 have assumed that the initiator of the sequence is an iSCSI device, and the target of the sequence is an FCP device. It will be appreciated that generally similar sets of sequences, mutatis mutandis, apply when the initiator is an FCP device and the target is an iSCSI device. 
     In preferred embodiments of the present invention, gateway  12  is implemented to perform a synchronization check on iSCSI frames received while a connection-pair connecting an initiator and target is operative. As is known in the art, synchronization is checked at the TCP level, but there are cases where a damaged frame may not be detected at this level, for example, a TCP checksum may be valid, but there may be undetected error bits. Preferably, in the event of discovering a synchronization error, gateway  12  resynchronizes subsequent frames and allows missing frames to be recovered at a higher level, corresponding to an application being implemented. Alternatively, gateway  12  is implemented to close the connection-pair, and allow the application to reopen it. 
     It will be appreciated that the preferred embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.