Abstract:
Many 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 Fiber Channel (FC) switch. However, the conventional use of a separate FC switch to couple the storage router makes it difficult and time consuming to restore zone configuration of the FC switch. Accordingly, the present inventor devised, among other things, an exemplary method of automatically maintaining and synchronizing a copy of zone configuration data for an FC switch. Through these and/or other features, the exemplary embodiment ultimately reduces the cost and complexities associated with implementing storage-area networks.

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, which allows users to exploit economies of scale. Moreover, a group of storage devices can be logically partitioned into private storage areas, called zones, with the access to each zone restricted to certain users or computer systems. 
     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 Fibre Channel-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. 
     However, the present inventor has recognized that conventional storage-area networks, such as those that use separate FC switches and storage routers, present increased complexities and costs related to maintaining and restoring a zoning configuration. For example, administrators of these networks may be forced to manually and separately reconfigure the zoning defined in a FC switch in the event of a system failure. This can be problematic because the zoning configuration 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 inventor has recognized a need to reduce the cost and complexities associated with maintaining storage-area networks, particularly restoring zoning configurations. 
     SUMMARY 
     To address this and other needs, the present inventor devised methods, software, and related devices and systems that automatically maintain and synchronize a copy of a zone configuration for at least one FC switch in another device, such an iSCSI storage router, to facilitate restoration of the zone configuration. In one embodiment, the FC switch is integrated onto a common circuit board with the iSCSI 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  corresponding to one or more embodiments of the present invention. 
         FIG. 2A  is a prospective view of an exemplary integrated storage router-switch  200  corresponding 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  and corresponding to one or more embodiments of the present invention. 
         FIG. 3  is a flow chart corresponding to one or more embodiments of the present invention. 
         FIG. 4  is a flow chart showing an exemplary method of exemplary method of operating a synchronization module in accord with one or more embodiments of the present invention. 
         FIG. 5  is a flow chart showing an exemplary method of restoring a zone configuration I accord with 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 , a management station  114 , 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 respective features such as displays, user interfaces, processors, memories, operating systems, and host bus adapters. 
     The exemplary host bus adapters 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. In the exemplary embodiment, each 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. In some embodiments, the host bus adapters are virtual in the sense that iSCSI drivers are provided to effectively enable non-iSCSI network interface cards to function as iSCSI-compliant devices. 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 entitled System, Method, and Software for Target ID Binding in a Storage-area Network and U.S. patent application Ser. No. 10/143,456 entitled System, Method, and Software for a Virtual Host Bus Adapter in a Storage-area Network. Both of these applications were filed on May 9, 2002 and are incorporated herein by reference 
     Management station  114  includes user interfaces  114 . 1 , such as a graphical-user interface and/or a command-line interface (neither shown separately), that facilitate monitoring, configuring, and control of router-switches  130  and  132 . 
     Integrated storage router-switches  130  and  132 , which communicate with hosts  110  and  112  and management station  114  via IP network  120 , 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 . 
     More particularly, GE ports  130 . 1 ,  130 . 2 ,  132 . 1  and  132 . 2  are coupled to IP network  120 . 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  include 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. FC ports in port sets  130 . 5  and  132 . 5  are coupled via FC-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 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 5  and FE. And, FC host  155  includes FC ports FT and FU, with port FT coupled to port F 6  of switch-router  130  and port FU coupled to port FF 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 the exemplary embodiment, the storage devices are logically organized into one or more zone, such as zones A and B, with components within zone A accessible by iSCSI-compliant host  110  and components within zone B accessible by iSCSI-compliant host  112 . As described in further detail below, the router-switches each maintain one or more sets of zone configuration data (not shown in this figure), which are subject to modification by authorized modifiers, such as management station  114 , iSCSI-compliant hosts  110 ,  112 , and/or FC hosts  154 ,  155 . 
     Operation of the router-switch includes system initialization. In the exemplary embodiment, system initialization includes executing start-up diagnostics, starting and initializing applications, initializing 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 through the respective HBA, 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 IP network  120  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. 
       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 which 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 one or more backup copies of zone configuration for the FC switch, detects zone configuration changes, and updates or synchronizes one or more of the backup copies of the zone configuration data, such as backup zone data  216 . 2 . In the exemplary embodiment, backup zone data  216 . 2  takes the form of XML files in a backup-zone directory structure and includes zone configuration data that specifically concerns switch portion  220  and that is defined or modified through one or more of ports  211 . 1 ,  211 . 2 ,  212 , and  213  (non-storage-side ports). However, in other embodiments, the backup zone data includes zone configuration data for one or more FC switches other than that in switch portion  220  and/or zone configuration data that is defined or modified through one or more non-storage-side ports, but also through one or more storage-side ports, such as the FC ports. Examples of zone configuration data include zone, zoneset, and alias listings or definitions. Generally, a zone definition generally includes ports, FC addresses, device WWN, and aliases; a zoneset includes a listing of zones; and an alias is a convenient grouping of ports, FC addresses, and device WWN. However, some embodiments may restrict the items that may be used or included within a zone, zoneset, or alias. For example, one embodiment may prevent use of FC addresses or ports in an alias or zone definition. 
     Various embodiments may store the backup zone 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  114  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 zone configuration of the switch-router to a persistent memory inside or outside the switch-router, or to restore the zone configuration for the switch-router based on the all or a portion of the backup zone data. 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 port 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 an 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: Aribtated Loop (AL) Fairness; Interface enable/disable; Linkspeed settable to 1 Gbps, 2 Gbps, or Auto; 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 which 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 implements a 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 (MB)). 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 requestor.) 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 method of operating synchronization module  216 . 1  (in  FIG. 2 .) Flow chart  400  includes process blocks  410 - 430 . Though these blocks (and those of other flowcharts in this document) are described 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 devices, circuits, 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  410 , which entails detecting a zone change. In the exemplary embodiment, this detection occurs as a result of detecting receipt of a command to create or modify zone data, such as a zone, a zoneset, or an alias, and receiving acknowledgment that the command was successfully executed. (Note that commands that are successfully executed result in changes to the relevant portion of the zone configuration data on the FC switch; commands that fail result in transmission of a error message to the command sender.) A zone change can also be detected independently of any received zone-changing commands by comparing zone data stored on one or more FC switches (or in memories associated with FC switches) to a reference set of zone data, such as backup zone data  216 . 2 . For example, some embodiments schedule regular comparisons of zone data (or portion thereof) to the backup zone data. Still other embodiments perform such comparisons based on a set of events, for example, receipt of zone merge commands. With detection of a zone change, exemplary execution advances to block  420 . 
     Block  420  entails determining whether to update the backup zone data based on the detected change. In the exemplary embodiment, this determination entails determining whether the detected zone change was an authorized type of change and whether the change was made or initiated by an authorized changer. For example, some embodiments treat any zone changes made to FC switch  222  through use of the graphical user interface or command line interface for the router-switch as being authorized types of changes and as being by an authorized changer. In some embodiments, any changes to FC switch  222  made by or through one or more of ports  211 . 1 ,  211 . 2 ,  212 ,  213 , and  214  are deemed to be authorized changes by an authorized changer. In still other embodiments, changers, such as other FC switches, acting through one or more of the FC ports on switch-router  200  are authorized to make one or more types of changes. For example, in one embodiment, another FC switch acting through one of FC ports  223  on switch-router  200  can clear the zone configuration for FC switch  222 , which would in turn result in clearing of the backup zone data. However, other embodiments may be more or less restrictive in defining the sets of authorized changes and changers. For example, some embodiments consider changes made to the zone configuration data for other FC switches or components to be authorized changes. 
     If the update determination is negative, then execution branches back to block  410  to await detection of another zone change. However, if the update determination is affirmative, execution advances to block  430 . 
     Block  430  updates the backup zone data. In the exemplary embodiment, this update entails updating the backup zone data by appending or overwriting a complete, date-stamped copy of the zone configuration data from FC switch  222  to any existing backup zone data. The copy may be in the form of a date-stamped file added to a backup zone directory structure. In some embodiments, this zone configuration data includes not only the zone configuration data for FC switch  222 , but also the (or at least a version of the) zone-configuration data of other FC switches that may be coupled to FC switch  222 . 
     However, other embodiments append a date-stamped copy of zone changes, which when applied to the previous backup zone data, yield complete zone data. This form of update creates a form of audit trail that facilitates restoration of the zone configuration to any previous state represented in the backup zone data. 
     Still other embodiments append both changes and a complete zone data set to any previous local backup zone data. 
     Update in some instances, such as one made in response to a clearing of zone configuration data on the switch, entails erasing or deleting the contents of the backup zone configuration. (If the clearing is the result of a command from one of a predetermined set of authorized changers, for example, a clear command issued through the graphical user interface or command line interface for the router-switch, then FC switch  222  will be isolated from the fabric.) (Note that the exemplary embodiment automatically creates an “iscsi” alias in the backup zone data if it contains no zone configuration data. Creation of the “iscsi” alias ensures that both internal Fibre Channel ports are added to a zone and that the IP side of the network does not become isolated from the Fibre Channel devices.) After update of the backup zone data, execution returns to block  410  to await detection of another zone change. 
       FIG. 5  shows a flow chart  500  of an exemplary method of restoring a zone configuration of a FC switch, such as FC switch  222  in router-switch  200 . Flow chart  500  includes process blocks  510 - 540 . 
     The exemplary restoration method begins at block  510 , which entails receipt of a restoration command. In the exemplary embodiment, this command is received from the command-line or graphical user interface on a management station, such as management station  114  in  FIG. 1  and specifies a particular portion (such as a file) of the backup zone data to use as basis for the restoration. (The graphical- and command-line interfaces provide features for allowing an admininstrator to view the directory structure containing the backup zone data and thus facilitates selection or specification of the desired backup zone data). However, other embodiments may accept the command from other authorized changers. Execution continues at block  520 . 
     Block  520  entails isolating the FC switch that is the target of the restoration. In the exemplary embodiment, this entails clearing the current zone configuration data on the FC, using a “clear FC zones” command, which results in isolation of the FC switch. Execution proceeds to block  530 . 
     Block  530  entails writing entries from the backup zone data to the FC switch. In the exemplary embodiment, this entails writing the specified set of backup zone data to the FC switch and updating the backup zone data pursuant to the method outlined in  FIG. 4 . In some embodiments, for example, those that store differential backup zone data as opposed to complete backup zone data, several sets of differential data files may need to consolidated to form a Block  540  concludes the restoration process by resetting the FC ports on the FC switch and rejoining the switch to the switch fabric. 
     CONCLUSION 
     In furtherance of the art, the inventor has presented various exemplary systems, methods, and software related to creating, maintaining, and synchronizing backup zone configuration data for one or more components in a storage-area network. 
     The embodiments described above and in the following claims 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.