Abstract:
Many storage-area networks (SANs) were developed to facilitate high-speed storage of large quantities of digital data. However, at least some conventional SANs present increased maintenance costs and complexities that can discourage their use. For example, in some SANs, its difficult and time consuming to properly reconfigure a Fiber Channel switch after a system failure since the switch is configurable by multiple entities. Accordingly, the present inventors devised, among other things, a method and systems for automatically maintaining and synchronizing one or more backup copies of configuration data.

Description:
TECHNICAL FIELD 
     Various embodiments of the present invention concern storage-area networks, especially storage routers and Fibre Channel switches suitable for such networks. 
     BACKGROUND 
     In recent years, the rapid growth of the Internet and other computer networks has fueled an equally fantastic growth in the use of computers as everyday communications devices for both individuals and businesses. Such widespread and growing use has led to the generation and accumulation of vast amounts of digital data. This, in turn, has spurred scientists and engineers to develop specialized subsystems, such as storage-area networks, for managing and storing data. 
     A storage-area network (SAN) is a high-speed subnetwork of shared data-storage devices, such as disk and tape drives. These networks are particularly advantageous not only because they spare other servers in a larger network, such as corporate intranet, from the burden of storing and managing large amounts of data, and thus allow use of these servers for other higher priority uses, but also because they facilitate data consolidation. Consolidation promotes manageability and scalability by for example simplifying backup and restore procedures and facilitating expansion of storage capacity. 
     Some storage-area networks (SANs) are structured so that an end-user or client-computer can access data on one or more target storage devices through a storage router and a separate Fibre Channel switch. (Fibre Channel generally refers to a serial data-transfer architecture and communications standard developed by a consortium of computer and storage-device manufacturers for use with high-speed mass-storage devices and other peripherals, particularly via optical fiber interconnects.) The Fibre Channel (FC) switch converts data received from the storage router to a FC-compliant protocol, such as FC-AL (Fibre Channel Arbitrated Loop) standard, and directs the converted data via high-speed electrical or optical fiber lines to the proper target devices. The FC switch, high-speed lines and related hardware are sometimes called a “fabric.” 
     One problem that the present inventors have recognized with conventional storage-area networks, such as those that use separate FC switches and storage routers, is that these networks present increased maintenance complexities and costs that discourage their use by many companies and organizations. For example, administrators of these networks may be forced to manually and separately reconfigure the storage router and the FC switch in the event of a system failure. Moreover, the FC switch may be configured by different entities independently of the administrator, making it even more difficult, time-consuming, and costly to perform the restoration. 
     Accordingly, the present inventors have recognized a need to reduce the cost and complexities associated with maintaining storage-area networks. 
     SUMMARY 
     To address this and/or other needs, the present inventors devised methods, software, and related devices and systems that automatically maintain and synchronize one or more backup copies of configuration data for a Fibre Channel (FC) switch in a storage-area network. One exemplary method entails detecting a configuration change in a FC switch, and in response to detecting the change, updating a backup copy of configuration data stored in a memory external to the FC switch. One embodiment integrates the FC switch onto a common circuit board with an iSCSI-compliant storage router. Through these and other features, the exemplary embodiment ultimately reduces the cost and complexities associated with maintaining storage-area networks. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of an exemplary system  100  that corresponds to one or more embodiments of the present invention. 
         FIG. 2A  is a perspective view of an exemplary integrated storage router-switch  200  that corresponds to one or more embodiments of the present invention. 
         FIG. 2B  is a block diagram showing further details of the integrated storage router-switch  200  that corresponds to one or more embodiments of the present invention. 
         FIG. 3  is a flow chart showing details of an exemplary management communications method that corresponding to one or more embodiments of the present invention. 
         FIG. 4  is a flow chart showing details of an exemplary synchronization method that corresponds to one or more embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     This description, which references and incorporates the above-identified figures and the appended claims, describes one or more specific embodiments of one or more inventions. These embodiments, offered not to limit but only to exemplify and teach the one or more inventions, are shown and described in sufficient detail to enable those skilled in the art to implement or practice the invention. Thus, where appropriate to avoid obscuring the invention, the description may omit certain information known to those of skill in the art. 
       FIG. 1  shows an exemplary computer system  100 , which incorporates teachings of the present invention. System  100  includes iSCSI-compliant hosts  110  and  112 , an IP network  120 , integrated storage router-switches  130  and  132 , Fibre Channel-compliant communications channels  140 , and Fibre Channel (FC) hosts and devices  150 . 
     iSCSI-compliant hosts  110  and  112 , which take the exemplary forms of servers or other computer systems, and are substantially identical in this embodiment, include not only conventional features such as processors, memory, and an operating system (not shown), but also respective hardware or virtual host bus adapters  111  and  113 . 
     Host bus adapters  111  and  113  comply with a version of the Internet Small Computer System Interface (iSCSI) protocol for storage of data over an IP network. The host bus adapters facilitate encapsulation and communication of Small Computer System Interface (SCSI) input-output commands using an Internet Protocol, such as TCP/IP. For details regarding a virtual host bus adapter and related software modules, see co-pending and co-owned U.S. patent application Ser. No. 10/143,561 (Cisco seq. no. 6122) entitled System, Method, and Software for Target ID Binding in a Storage-area Network and U.S. patent application Ser. No. 10/143,456 (Cisco Seq. No. 6126) entitled System, Method, and Software for a Virtual Host Bus Adapter in a Storage-area Network. Both of the applications were filed on May 9, 2002 and are incorporated herein by reference. 
     In the exemplary embodiment, the host bus adapter includes a network interface card or a Gibabit Ethernet server card, which includes a Gigabit Ethernet driver. Other embodiments use any IP-capable interfaces, for example, 10/100 Ethernet, wireless local-area network (LAN), Asynchronous Transfer Mode (ATM), etc. Host bust adapters  111  and  113  support communications via IP network  120  with integrated storage router-switches  130  and  132 . 
     Integrated storage router-switches  130  and  132  are substantially identical in the exemplary embodiment. Router-switch  130  includes GE ports  130 . 1  and  130 . 2 , a management (M) port  130 . 3 , a high-availability (HA) port  130 . 4 , and a FC port set  130 . 5 . Router-switch  132  similarly includes GE ports  132 . 1  and  132 . 2 , a management (M) port  132 . 3 , a high-availability (HA) port  132 . 4 , and a FC port set  132 . 5 . 
     GE ports  130 . 1  and  130 . 2  are coupled respectively to GE switches  120  and  122 , and GE ports  132 . 1  and  132 . 2  are similarly coupled to the GE switches. M ports  130 . 3  and  132 . 3  are coupled to each other, and HA ports  130 . 4  and  132 . 4  are also coupled to each other. 
     FC port set  130 . 5  includes ports F 1 -F 8 , which are operatively coupled via router-switch interface  130 . 6  to GE ports  130 . 1  and/or  130 . 2 . FC port set  132 . 5  includes optical ports FA-FH, which are operatively coupled via router-switch interface  132 . 6  to GE ports  132 . 1  and/or  132 . 2 . 
     In the exemplary embodiment, all the Fibre-Channel ports are general ports, which can function as fabric, fabric-looped, or N ports. Router-switch interface  130 . 6  includes software for making GE ports  132 . 1  and  132 . 2  and FC port set  130 . 5  appear to hosts  110  and  112  as a single integrated device. Fibre-Channel ports in port sets  130 . 5  and  132 . 5  are coupled via Fibre-Channel compliant communication channels  140 , for example, optical fiber cables, to FC hosts and devices  150 . In the exemplary embodiment, router-switches  130  and  132  conform to a version of the Fibre-Channel standard, such as Fibre Channel Arbitrated Loop (FC-AL) standard. 
     FC hosts and devices  150 , which together with router-switches  130  and  132  and channels  140  constitute a FC-compliant storage-area network, includes disk arrays  151  and  152 , a tape library  153 , and FC hosts  154  and  155 . Disk array  151  is accessible via FC ports FJ and FK, which are coupled respectively to ports F 1  and FA of router-switches  130  and  132 . Disk array  152  is accessible via FC ports FL, FM, FN, FO, which are coupled respectively to ports F 2 , FB, F 3 , and FC. (Disk arrays  151  and  152  are RAIDs (Redundant Array of Independent (or Inexpensive) Disks) or JBODs (Just a Bunch of Disks.) Tape library  153  is accessible via FC ports FP and FQ, which are coupled respectively to ports F 4  and FD. Each of the target storage devices has an associated logical unit number (not shown.) 
     FC host  154  includes FC ports FR and FS, which are coupled respectively to port F 7  and FG. And, FC host  155  includes FC ports FT and FU, with port FT coupled to port F 8  of switch-router  130  and port FU coupled to port FH of switch-router  132 . FC hosts  154  and  155  can access disk arrays  151  and  152  and a tape library  153  through router-switch  130  and/or  132 . In this embodiment, access control between the FC host and the storage device is not provided; thus, any host using one of the router-switch&#39;s FC interfaces can access any device coupled to router-switches  130  and  132 . However, some other embodiments include access control. 
     Normal operations of the router-switch include system initialization. In the exemplary embodiment, system initialization includes executing start-up diagnostics, starting and initializing applications, initializing or configuring the switch, and verifying switch operation. The initialization of the switch and the router portion are synchronized so that the entire system is made operational in a controlled fashion. 
     After initialization, host  110  or  112  accesses one or more of target storage devices  151 ,  152 , and/or  153  through its operating system. The operating system forwards a block-level input-output command to HBA  111  or  113 , which in turn communicates the command and any associated data in an appropriate format (with target and LUN addresses or names) through a TCP/IP socket and GE switch  120  or  122  to one of GE ports  130 . 1 ,  130 . 2 ,  132 . 1  and  132 . 2 . The router portion of switch-router  130  or  132  strips off the TCP/IP and iSCSI headers, maps the logical iSCSI targets to SCSI addresses, adds FC and FCP headers, and routes the logical command and data onto the switch portion that includes FC port set  130 . 5  (or  132 . 5 ). The switch portion then transfers the logical command and data via one of its FC ports and a Fibre Channel link to one or more of FC hosts and devices  150  based on the SCSI addresses. 
     In response to the command and any associated data, the appropriate target storage device communicates data and/or status information through the appropriate channel and through one of the FC ports of switch-routers  130  and  132 . The receiving switch-router formats the data and status according to the iSCSI and TCP/IP protocols and transmits across an IP network to the host bus adapter of the iSCSI host ( 110  or  112 ) that initiated the input-output command. 
     Exemplary Router-Switch Architecture 
       FIGS. 2A and 2B  shows details of an exemplary storage router-switch  200  which may be substituted for one or both of the integrated router-switches in  FIG. 1 . 
       FIG. 2A , a perspective view of router-switch  200 , shows its 1U rack-mountable chassis or case  202 , which includes a front panel  204 . Front panel  204  includes GE port connectors  211 . 1  and  211 . 2 , a console-port connector  212 , a management-port connector  213 , an HA-port connector  214 , and FC port connectors (interfaces)  223 . 1 - 223 . 8 . Each FC port has two associated LEDs (Light Emitting Diodes): one indicates whether the port is active and the other indicates whether the port is faulty. In the exemplary embodiment, each of connecters  212 ,  213 , and  214  is a female RJ-45 (registered-jack  45 ) connector, and FC port connectors  223 . 1 - 223 . 8  take the form of female LC, MU, MTP, or MTRJ connectors. Other embodiments, however, use other types of connectors. 
       FIG. 2B , a block diagram, shows that router-switch  200  includes a router portion  210  and a switch portion  220  on a common motherboard  230 . The motherboard is powered by a power supply (not shown) and cooled by common cooling system, such as a fan (also not shown). 
     Router portion  210  includes GE ports  211 . 1  and  211 . 2 , console port  212 , management port  213 , high-availability (HA) port  214 , bridge-and-buffer module  215 , software  216 , router processor  217 , and router-to-switch interface  218 . In the exemplary embodiment, router portion  210  complies with a version of the iSCSI protocol, such as draft 08 or later, and incorporates commercially available router technology, such as the 5420 Storage Router from Cisco System, Inc. of San Jose, Calif. 
     More particularly, GE ports  211 . 1  and  211 . 2  couple the router switch to an IP network for access by one or more servers or other computers, such as servers or iSCSI hosts (in  FIG. 1 ). In some embodiments, GE ports  211 . 1  and  211 . 2  have respective MAC (Media Access Control) addresses, which are determined according to: base MAC address for the switch-router plus 31 minus the respective port number. (Two Gigabit Ethernet interfaces are available. Each ScsiRouter supports one or more IP addresses. The ScsiRouter IP address may be tied to any VLAN (virtual local-area network) on either GE interface.) 
     Console port  212  couples to a local control console (not shown). In the exemplary embodiment, this port takes the form of an RS-232 interface. 
     Management port  213  provides a connection for managing and/or configuring router-switch  110 . In the exemplary embodiment, this port takes the form of a 10/100 Ethernet port and is assigned the base MAC address for the router-switch. As such, this port communicates via an IP protocol, for example, TCP/IP. 
     HA port  214  provides a physical connection for high-availability communication with another router-switch. In the exemplary embodiment, this port takes the form of a 10/100 Ethernet port, and is assigned the base MAC address plus 1. A failover occurs in the exemplary embodiment when: all devices used by the router-switch are inaccessible; the GE port used by the router-switch fails; router-to-switch interface  218  fails; or a switch failure is detected. A switch failure may cause the entire system, that is, the router-switch, to reboot. 
     Bridge-and-buffer module  215 , which is coupled to GE ports  211 . 1  and  211 . 2 , provides SCSI router services, which are compliant with a version of the iSCSI protocol. In the exemplary embodiment, module  215  incorporates a Peripheral Component Interface (PCI) bridge, such as the Galileo GT64260 from Marvell Semiconductor, Inc., of Sunnyvale, Calif. Also module  215  includes a 64-megabyte flash file system, a 1-megabyte boot flash, and a 256-megabyte non-volatile FLASH memory (not shown separately.) In addition to data and other software used for conventional router operations, module  215 , in this exemplary embodiment, includes router-switch interface software  216 . 
     Software  216  performs iSCSI routing between servers and the storage devices. In the exemplary embodiment, the software includes not only an integrated router-switch command-line-interface module CLI and a web-based graphical-user-interface module GUI that facilitate operation, configuration, administration, maintenance, and support of the router-switch. Both the command-line interface and the graphical user interface are accessible from a terminal via one or both of the ports  212  and  213 . 
     Additionally, software  216  includes a synchronization module  216 . 1  which maintains backup copies of configuration and firmware data for the router and the FC switch, detects configuration and firmware changes, and updates or synchronizes one or more of the backup copies of the switch configuration data, such as a primary backup copy  216 . 2  (primary data) and a secondary backup copy  216 . 3  (secondary data), which are stored in a memory. FC switch configuration data includes both global and port-specific configuration data. The global configuration data includes domain-identification data, domain-identification lock status, buffer-to-buffer credit, a distributed-services-timeout setting, fabric-services-timeout setting, an error-detect-timeout setting, a resource-allocation timeout setting, a zoning merge, zoning default, zoning autosave, and device-discovery timeout. Port-specific configuration data includes inputs for enabling the port, AL-fairness, fabric-address notification (FAN), in-band-management (MS), multi-frame sequence (MFS) bundling, and for setting port-transfer rate, port type, and TL-port mode. 
     Various embodiments may store these sets of switch configuration data in any convenient storage device or location, including, for example, in a volatile or non-volatile memory on router portion  210  or in a non-volatile memory on a management station, such as management station  116  in  FIG. 1 . The command-line-interface module and the graphical-user-interface module include command features (not shown) which allow a user to save a configuration of the switch-router to a persistent memory inside or outside the switch-router, or to restore the switch-router to a configuration stored in the persistent memory. Further details regarding exemplary operation and architecture of synchronization module  216  are described in a separate section below. 
     Router Processor  217 , in the exemplary embodiment, is implemented as a 533-MHz MPC7410 PowerPC from Motorola, Inc. of Schaumburg, Ill. This processor includes 1-megabyte local L2 cache (not shown separately). In the exemplary embodiment, router processor  217  runs a version of the VX Works operating system from WindRiver Systems, Inc. of Alameda, Calif. To support this operating system, the exemplary embodiment also provides means for isolating file allocations tables from other high-use memory areas (such as areas where log and configuration files are written.) 
     Coupled to router processor  217  as well as to bridge-and-buffer module  215  is router-to-switch (RTS) interface  218 . RTS interface  218  includes N/NL switch-interface ports  218 . 1  and  218 . 2  and management-interface port  218 . 3 . 
     Switch-interface ports  218 . 1  and  218 . 2  are internal FC interfaces through which the router portion conducts input-output (I/O) operations with the switch portion. When a mapping to a FC storage device is created, the router-switch software automatically selects one of the switch-interface ports to use when accessing the target device. The internal interfaces are selected at random and evenly on a per-LUN (logical unit number) basis, allowing the router-switch to load-balance between the two FC interfaces. The operational status of these internal FC interfaces is monitored by each active SCSI Router application running on the switch-router. The failure of either of these two interfaces is considered a unit failure, and if the switch-router is part of a cluster, all active SCSI Router applications will fail over to another switch-router in the cluster. Other embodiments allow operations to continue with the remaining switch-interface port. Still other embodiments include more than two switch-interface ports with various allocation algorithms. 
     In the exemplary embodiment, the N/NL switch-interface ports can each use up to 32 World Wide Port Names (WWPNs). The WWPNs for port  218 . 1  are computed as 28+virtual port+base MAC address, and the WWPNs for port  218 . 2  are computed as 29+virtual port+base MAC address. Additionally, management of switch-interface ports  218 . 1  and  218 . 2  is hidden from the user. One exception is the WWPN of each internal port. The internal WWPNs are called “initiator” WWPNs. Users who set up access control by WWPN on their FC devices set up the device to allow access to both switch-router initiator WWPNs. 
     Switch-interface port  218 . 3  is used to exchange configuration data and get operational information from switch portion  220  through its management-interface port  224 . In the exemplary embodiment, switch-interface port  218 . 3  is a 10/100 Ethernet port. In the exemplary embodiment, this exchange occurs under the control of a switch management Application Program Interface (API) that is part of interface software  216 . One example of a suitable commercially available API is from QLogic Corporation of Aliso Viejo, Calif. Ports  218 . 1 ,  218 . 2 , and  218 . 3  are coupled respectively to FC interface ports  221 . 1  and  221 . 2  and interface port  224  of switch portion  220 . 
     Switch portion  220 , which in the exemplary embodiment incorporates commercially available technology and supports multiple protocols including IP and SCSI, additionally includes internal FC interface ports  221 . 1  and  221 . 2 , an FC switch  222 , external FC ports (or interfaces)  223 , a management interface port  224 , and a switch processor module  225 . 
     FC interface ports  221 . 1   221 . 2  are coupled respectively to ports of  218 . 1  and  218 . 2  of the router-to-switch interface via copper traces on or within board  230  or internal optical fiber links, thereby forming internal FC links. (In the exemplary embodiment, each external FC interface supports auto-negotiation as either an F or FL port, and the internal FC interfaces are fixed as either an F or FL port.) 
     FC switch  222 , in the exemplary embodiment, incorporates a SANbox2-16 FC switch from QLogic Corporation. This SANbox2 switch includes QLogic&#39;s Itasca switch ASIC (application-specific integrated circuit.) Among other things, this switch supports Extended Link Service (ELS) frames that contain manufacturer information. FC switch  222  also includes one or more sets of switch configuration data  222 . 1 , which are subject to modification not only via commands from “storage-side” components, such as FC servers, hosts, and controllers, but also via commands from “router-side” components, such as a management station, command-line interface, or graphical user interface. Various embodiments may store these sets of switch configuration data in any convenient storage location, including for example, in one of the target storage devices or in a volatile or non-volatile memory anywhere on switch portion  220 . 
     FC ports  223 . 1 - 223 . 8 , which adhere to one or more FC standards or other desirable communications protocols, can be connected as point-to-point links, in a loop or to a switch. For flow control, the exemplary embodiment implements a FC standard that uses a look-ahead, sliding-window scheme, which provides a guaranteed delivery capability. In this scheme, the ports output data in sets of operatively related frames called sequences, with each frame having a header, a checksum, and a maximum length, such as 2148 bytes. 
     Moreover, the FC ports are auto-discovering and self-configuring and provide 2-Gbps full-duplex, auto-detection for compatibility with 1-Gbps devices. For each external FC port, the exemplary embodiment also supports: Arbitrated Loop (AL) Fairness; Interface enable/disable; Linkspeed settable to 1 Gbps, 2 Gbps, or Auto-sensing; Multi-Frame Sequence bundling; Private (Translated) Loop mode. 
     Switch processor module  225  operates the FC switch and includes a switch processor (or controller)  225 . 1 , and associated memory that includes a switch management agent  225 . 2 . In the exemplary embodiment, switch processor  225 . 1  includes an Intel Pentium processor and a Linux operating system. Additionally, processor  225  has its own software image, initialization process, configuration commands, command-line interface, and graphical user interface (not shown). (In the exemplary embodiment, this command-line interface and graphical-user interface are not exposed to the end user.) A copy of the switch software image for the switch portion is maintained as a tar file  226  in bridge-and-buffer module  215  of router portion  210 . 
     Exemplary Management Communications 
     The exemplary router-switch implement a novel communications method to make router portion  210  and switch portion  220  appear as an integrated device, particularly as viewed through management interface  213 . To this end, software  216  includes an SNMP router-management agent and an MIB router handler (not shown.) (SNMP denotes the Simple Network Management Protocol, and MIB denotes Management Information Base (MIB)). The agent and handler cooperate with counterparts in switch portion  220  (also not shown) to provide integrated management and control of router and switching functions in router-switch  200 . 
     Specifically, the exemplary embodiment implements or supports Fibre Alliance MIB 3.0, which entails loading MIB objects as separate modules, and adding them to a global MIB database that the SNMP router-management agent uses when resolving objects to a particular set of MIB handlers. In the exemplary embodiment, the SNMP router-management agent is based on the Wind River WindNet v1/v2c SNMP Agent code base, and an SNMP switch-management agent is based on the Linux UCD-SNMP code base. 
     More specifically,  FIG. 3  shows a flow chart  300  illustrating an exemplary method of using these agents and associated handlers. (The exemplary method is also applicable to management functions invoked via a graphical-user or command-line interface.) Flow chart  300  includes process blocks  310 - 399 , which are arranged and executed in a particular order in the exemplary embodiment. However, other embodiments of the invention may reorder the execution of two or more blocks or portions thereof and/or execute two or more blocks or portions thereof in parallel. Moreover, the exemplary process flow applies to software, firmware, and hardware implementations. 
     Block  310  shows that the exemplary method begins with router-management agent AGT (in  FIG. 2 ) receiving a management inquiry in the form of SNMP get or getNext request via management port  213  from an SNMP management station (not shown) connected to a management network (not shown). Execution continues at block  320 . 
     In block  320 , the router-management agent processes the management inquiry, which in the exemplary embodiment takes the form of an SNMP get or get-next request, by generating at least one SNMP management-request object. 
     In block  330 , the router-management agent determines whether the management-request object relates to router or switch functions. If the object concerns router functions or can otherwise be fulfilled by the router-management agent, execution branches to block  340 , which entails the router-management agent processing the request object, and then to block  380 . 
     If, at block  330  the request object is determined to concern switch functions or otherwise cannot be fulfilled by the router-management agent, execution branches first to block  350  which entails mapping the request to a switch request and then sending the request object to the switch management agent, second to block  360  which entails the switch-management agent processing the request object, and third to block  370 , which entails sending the response to the request back to the router-management agent. In some embodiments, the router-management agent, at block  360 , may also perform other scheduled maintenance tasks, such as retrieve all or one or more portions of a set (or sets) of switch configuration data stored on the FC switch. 
     In the exemplary embodiment, the request object and its response are communicated between the router-management agent and the switch-management agent via the internal Ethernet link defined by ports  218 . 3  and  224 . Also note that in the exemplary embodiment, the FC-management handler will try as many as three times to get a valid response from the switch-management agent, with a timeout of 0.3 seconds per request. If it does not get a valid response after three tries, an SNMP error signal is passed back to the router-management agent and ultimately onto the management station. Additionally, entries for non-user (internal) FC ports are filtered out from any responses passed back to the router-management agent. 
     The exemplary embodiment uses two data structures to facilitate communications between the FC-management handler and the switch-management agent. For each group of MIB objects, the exemplary embodiment maintains a branch information table, and for each object within a group, there also exists a leaf information object. The exemplary branch information data structure (FcSwSnmpBranchInfo) includes the following fields:
         oidCount—specifies number of elements in oidList.   oidList—pointer to SNMP Object ID for group.   leafCount—specifies number of elements in leafInfo.   leafInfo—pointer to leaf information table for group.   preInstFilter—function pointer that allows filtering and adjustment on SNMP instance value before request is sent to FC Switch SNMP Agent.   postInstFilter—function pointer that allows filtering and adjustment on SNMP instance value after response is received from FC Switch SNMP Agent.   valueFilterLastmatch—specifies last component of SNMP object ID, used to return an additional object with request.   postValueFilter—function pointer that allows filtering based on an object value.   copyValue—function pointer that allows for overriding of an object value in response.
 
And, the exemplary leaf information data structure (FcSwSnmpLeafInfo) includes the following fields:
   lastmatch—specifies last element of SNMP Object ID within group.   type—specifies SNMP object type.   requestLastmatch—specifies an optional value used to override lastmatch value.
 
The branch and leaf data structures allow the FC management module to handle the following:
   Mapping of the port index from 1 through 8 on the Storage Router to actual FC Switch ports, while filtering non-user ports.   Filtering of entries from the connUnitLink table and connUnitSns table based on the value of an object within a particular entry.   The overriding of response values returned by the FC Switch SNMP Agent.   The ability to return a response value for an object that does not exist in a particular table, due to an error in the FC Switch SNMP Agent.       

     After execution of block  370  as well as block  340 , exemplary execution continues with block  380 . In block  380 , the router-management agent, which may be regarded as a master management agent to the switch- or slave-management agent for the switch, sends the response back to the management station (or other requester.) The exemplary embodiment sends the response back via management port  213 . In some embodiments, the router-management agent may also perform scheduled or event-driven maintenance-related tasks, such as retrieving one or more portions of a source set (or sets) of switch configuration data stored on the switch. 
     Next, block  390  determines whether there are further requests to be answered. If there are additional requests, execution of the exemplary method branches back to block  310 . And, if there are no additional requests execution branches to block  399 , which generally represents any other operations. 
     Exemplary Operation of Synchronization Module 
       FIG. 4  shows a flowchart  400  illustrating an exemplary architecture and method of operating synchronization module  216 . 1  (in  FIG. 2 .) Flow chart  400  includes process blocks  402 - 430 . Though these blocks (and those of other flow charts in this document) are arranged serially in the exemplary embodiment, other embodiments may reorder the blocks, omit one or more blocks, combine two or more blocks, and/or execute two or more blocks in parallel using multiple processors or a single processor organized as two or more virtual machines or subprocessors. Moreover, still other embodiments implement the blocks as one or more specific interconnected hardware or integrated-circuit modules with related control and data signals communicated between and through the modules. 
     The exemplary method begins at block  402 , which entails determining whether a backup copy of switch configuration data has been created. In the exemplary embodiment, this entails examining a size or date stamp associated with primary backup data  216 . 2  and comparing it to the current date if a backup data file exists. If the determination indicates that no primary backup data exists (or that it is corrupted or otherwise invalid), then execution branches to block  404 . However, if the determination indicates that primary backup data has been saved in a predetermined area or directory of storage-router memory (or other storage location), then execution branches to block  404 ; otherwise, execution continues at block  406 . 
     Block  404  entails initializing the FC switch using a default configuration. In the exemplary embodiment, this default configuration is provided in memory of the router-switch during manufacture or during download of firmware for the router-switch; however, other embodiments may allow a user to define a default configuration. Some embodiments may copy this default configuration to the primary backup data or otherwise update the primary backup data to indicate the implementation of the default configuration. 
     Block  406  entails retrieving one or more set of switch configuration data from switch portion  220 , or more precisely FC Switch  222 . In the exemplary embodiment, the retrieval entails sending a management request to the switch and retrieving a set of switch configuration values or parameters that correspond to a selected one of a number of sets of switch configuration data, for example, a backup or current set of switch configuration data. However, other embodiments select the most recently updated set of switch configuration data. This notification can occur in response to the storage router registering with the FC switch to receive notification of specific types of changes. 
     In the exemplary embodiment, the retrieved switch configuration data includes one or more of the following parameters and/or associated identifiers: domain-identification data, domain-identification lock status, buffer-to-buffer credit, a distributed-services-timeout setting, fabric-services-timeout setting, error-detect-timeout setting, resource-allocation-timeout setting, a zoning merge, zoning default, zoning autosave, device-discovery-timeout setting, port enablement setting, AL-fairness, fabric-address notification, in-band-management, multi-frame-sequence bundling, port-transfer rate, port type, and TL-port mode. (The switch configuration data is subject to change via the router-switch management interface or via FC hosts.) 
     Block  408  determines whether the retrieved switch configuration data has been changed relative to the primary backup data stored on the router side of the FC switch. To this end, the exemplary embodiment compares each item in the retrieved switch configuration data to each corresponding item in the primary backup data and records results of the comparisons. If the determination indicates that primary backup data differs from the retrieved switch configuration data, execution branches to block  410 . 
     Block  410  entails determining whether the retrieved switch configuration data was changed externally, for example by FC hosts or other entities on the storage-side of the FC switch. The exemplary embodiment can make this determination based on a log of commands it receives from the router-switch management interface. If the change was made externally (that is, not through the router-switch management port), execution advances to block  412 , which updates the primary backup data to reflect the changes made to the switch configuration data. In some embodiments, the update entails replacing the existing primary backup data with the retrieved switch configuration data; other embodiments update the existing backup data by simply adding or appending the retrieved switch configuration data to a directory structure associated with the primary backup data, or by adding differential data that represents the difference in the current primary backup data and the retrieved switch configuration data. 
     However, if the change was not made externally, execution advances to block  414 , which updates the secondary (or temporary) backup copy of the switch configuration data to reflect the switch-configuration changes. (Examples of non-external switch-configuration changes include those made through use of management or configuration commands in the graphical user interface or the command-line interface.) In some embodiments, the update entails replacing the existing secondary backup data with the retrieved switch configuration data; other embodiments update the existing secondary backup data by simply adding or appending the retrieved switch configuration data to a directory structure associated with the secondary backup data, or by adding differential data that represents the difference in the current secondary backup data and the retrieved switch configuration data. From blocks  412  and  414 , execution continues at block  416 . 
     In block  416 , the router processor determines whether a shutdown mode has been invoked. In the exemplary embodiment, a shutdown mode is invoked by events, such as receipt of a command from a management interface or through a detected loss of power. (Other embodiments broaden the shutdown determination to include a standby mode or a power-conservation mode.) If the determination indicates that no shutdown or other analogous mode has been invoked, execution returns to block  406 , which entails retrieving switch configuration data stored on the FC switch. 
     In the exemplary embodiment, this further retrieval occurs during normal operation of the router-switch. Specifically, during any management-related accesses of the FC switch (through internal management port  224 , such as described in  FIG. 3 ), the exemplary embodiment also retrieves a copy of one or more versions of the FC switch configuration data. In other embodiments, the switch configuration query or retrieval may occur in response to a request (from the command-line or graphic user interface, for example) to display the current switch configuration, or in response to a notification message or signal from the FC switch that its configuration is changed. In some embodiments, this notification procedure is established through process of the router processor registering to receive notice of specific types of changes from the FC switch. However, in other embodiments, the retrieval occurs on scheduled or other event-driven basis, for example, every 30, 60, or 90 minutes or during other predetermined types of management activities. 
     Block  418 , which is executed if block  416  determines that a shutdown mode has been invoked, entails disabling or preventing external (storage-side) changes to the switch configuration data stored on the FC switch. To this end, the exemplary embodiment changes the setting of the “management server enable” feature to disabled. Other embodiments may disable switch hardware, such as the FC ports. Exemplary execution proceeds to block  420 . 
     Block  420  entails determining whether the primary and secondary backup data and the switch configuration data match each other. In the exemplary embodiment, this determination entails retrieving switch configuration data from the FC switch and from the router memory and then comparing them item by item to identify any differences. If the determination is that the primary, secondary, and retrieved switch data match each other, then execution branches to block  422 , which shuts down the router-switch or selected portions of it. In the exemplary embodiment, this is done via a reset command or via hardware reset of the switch. However, if the determination is that the three data sets do not match each other, execution branches to block  424 . 
     In block  424 , the router processor determines whether the primary backup data matches the secondary backup data. The exemplary embodiment determines this by performing an item-by-item comparison of the primary and secondary backup data. However, other embodiments may set a flag representative of a difference at the time a change is made to one or both of the data sets after they are synchronized and examine the status of the flag to make the determination. If the determination is that the primary and secondary data do not match each other, then execution progresses to block  426 . 
     In block  426 , the router processor determines whether the secondary set of switch configuration data matches the operative set of switch configuration data. If a match is determined, exemplary execution branches to block  428 , which entails synchronizing or updating the primary backup data based on the secondary backup data. However, if a match is not determined, execution branches to block  440 , which entails synchronizing or updating the primary backup data based on the retrieved switch configuration data. 
     From block  428  and block  440 , execution advances to block  422 , which entails shutting down the router-switch. The shutdown procedure may include ensuring the components are shutdown is a serial fashion or prepared to shutdown to minimize data loss in components which may not have been previously synchronized to non-volatile storage. Some embodiments allow isolation of the shutdown to the router portion or the switch portion, and leave the other portion operating. 
     CONCLUSION 
     The embodiments described in this document are intended only to illustrate and teach one or more ways of practicing or implementing the present invention, not to restrict its breadth or scope. The actual scope of the invention, which embraces all ways of practicing or implementing the teachings of the invention, is defined only by the following claims and their equivalents.