Abstract:
A system to isolate a fault to a particular port from among multiple ports in a network. The network typically has a plurality of devices including hosts, storage units, and switch groups that intercommunicate via transceivers. A fault indication is received from one or more of the devices in the network. The fault indication is then processed with a chain of fault indication rules that have been linked together into a binary decision path based on a set of device rules and a data flow model for the network. This permits determining the particular port responsible for the fault, and reporting that port to a user of the network.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention applies to any networking architecture where isolating error occurrences are critical to correctly identifying faulty hardware in the network environment. 
     2. Description of the Prior Art 
     As networks continue to become increasingly sophisticated and complex, qualifying fault indications and isolating their sources is becoming a vexing problem. Some devices have services that indicate faults, either ones occurring in the device itself or observed by the device as occurring elsewhere. Other devices, however, may not indicate faults, due to poor design, prioritizing schemes, pass-thru mechanisms that do not permit the discovery of faults that occurred elsewhere, etc. This is further complicated by the wide variety of devices, vendors, models, hardware versions, software versions, classes, etc. The unfortunate result is that no viable way to evaluate fault indications for determination of their operational relevance and root sources in hierarchical or canonical heterogeneous optical networks exists. 
       FIG. 1  (background art) is a block diagram depicting a generalized storage network infrastructure. This network  10 {XE “network  10 ”} includes blocks representing switch groups  12 {XE “switch groups  12 ”}, hosts  14 {XE “hosts  14 ”}, and storage enclosures  16 {XE “storage enclosures  16 ”}. In a switch group  12 {XE “switch group  12 ”} there can be any number of switches, from 1 to n, containing any number of ports, 1 to m. In some cases these may include a director class switch that all of the other switches are directly connected to, or there may be multiple switches cascaded together to form a pool of user ports, with some ports used for inter-switch traffic and routing (described presently). The hosts  14 {XE “hosts  14 ”} can be of any type from any vendor and having any operating system (OS), and with any number of network connections. The storage enclosures  16 {XE “storage enclosures  16 ”} can be anything from a tape library to a disk enclosure, and are usually the target for input and output (I/O) in the network  10 {XE “network  10 ”}. 
     Collectively, a single switch group  12 {XE “switch group  12 ”} with hosts  14 {XE “hosts  14 ”} and storage enclosures  16 {XE “storage enclosures  16 ”} are “local devices” that are either logically or physically grouped together at a locality  18 {XE “locality  18 ”}. Some of the devices at a locality  18 {XE “locality  18 ”} may be physically located together and others may be separated physically within a building or a site. 
     The hosts  14 {XE “hosts  14 ”} are usually the initiators for I/O in the network  10 {XE “network  10 ”}. For communications within a locality  18 {XE “locality  18 ”}, the hosts  14 {XE “hosts  14 ”} and storage enclosures  16 {XE “storage enclosures  16 ”} are connected to the switch group  12 {XE “switch group  12 ”} via local links  20 {XE “local links  20 ”}. For more remote communications, the switch groups  12 {XE “switch groups  12 ”} are connected via remote links  22 {XE “remote links  22 ”}. 
     In  FIG. 1 , three localities  18 {XE “localities  18 ”} are shown, each having a switch group  12 {XE “switch group  12 ”}. These localities  18 {XE “localities  18 ”} can be referenced specifically as localities  18   a - c {XE “localities  18   a - c ”}. As can be seen, communications from locality  18   a {XE “locality  18   a ”} to locality  18   c {XE “locality  18   c ”} must go via locality  18   b {XE “locality  18   b ”}, hence making the example network  10 {XE “network  10 ”} in  FIG. 1  a multi-hop storage network. 
     All of the devices in the network  10 {XE “network  10 ”} are ultimately connected, in some instances through optical interfaces in the local links  20 {XE “local links  20 ”} and the remote links  22 {XE “remote links  22 ”}. The optical interfaces include multi mode or single mode optical cable which may have repeaters, extenders or couplers. The optical transceivers include devices such as Gigabit Link Modules (GLM) or GigaBaud Interface Converters (GBIC). 
     In Fiber Channel Physical and Signaling Interface (FC-PH) version 4.3 (an ANSI standard for gigabit serial interconnection), the minimum standard that an optical device must meet is no more then 1 bit error in 10^12 bits transmitted. Based on 1 Gbaud technology this is approximately one bit error every fifteen minutes. In 2 Gbaud technology, this drops to 7.5 minutes, and in 10 Gbaud technology, to 1.5 minutes. If improvements to the transceivers are made so that the calculation assumes one bit error in every 10^15 bits, at 2 Gbaud, this is approximately one bit error every week. Also, optical fiber in an active connection is never without light, so bit errors can come inside or outside of a data frame and each optical connection has at lease two transceiver modules which doubles again the probability for a bit error. Furthermore, each interface, junction, coupler, repeater, or extender, has the potential of being unreliable, since there are dB and mode losses associated with these connections that degrade integrity of the optical signal and may result in data transmission losses due to the increased cumulative error probabilities. 
     Unfortunately, determining the sources of errors, and thus determining where corrective measures may be needed if too many errors are occurring in individual sources, can be very difficult. In storage network environments that use cut-through routing technology, an I/O frame with a bit, link or frame level error that has a valid address header can be routed to its destination, forcing an error counter to increment at each hop in the route that the frame traverses. Attempting to isolate where this loss has occurred in a network that may have hundreds of components is difficult and most of the time is a manual task. 
     All the losses that have been described herein are also “soft” in nature, meaning that, from a system perspective, no permanent error has occurred and there may not be a record of I/O operational errors in a host or storage log. The only information available then is the indication of an error with respect to port counter data, available at the time of the incident. 
     As networks evolve, the ability to isolate faults in these networks must also evolve as fast. The ability to adjust to this change in storage networking environments needs to come from an external source and to be applied to the network without the need for interruption by the monitoring system that is employed. 
       FIG. 2  (background art) is a block diagram depicting the generalized multi-hop network  10 {XE “network  10 ”} of  FIG. 1  with errors. An error event has occurred on the remote link  22 {XE “remote link  22 ”} shown emphasized in  FIG. 2 . This could have been a CRC error or other type of optical transmission error. The error here was reported on the two hosts  14 {XE “hosts  14 ”} and the one storage enclosure  16 {XE “storage enclosure  16 ”} which are also shown as emphasized in  FIG. 2 . 
     What is needed is a system able to correlate that these three separately recorded events in the network  10 {XE “network  10 ”} were all caused by a single event. And if the event continues, to notify a user of the fact that it was not a host  14 {XE “host  14 ”} or the storage enclosure  16 {XE “storage enclosure  16 ”} that was faulting but, rather one of the paths in the remote link  22 {XE “remote link  22 ”} in the network  10 {XE “network  10 ”}, aside of the hardware at the endpoints within the localities  18 {XE “localities  18 ”}. The proposed system therefore needs to take fault indications and isolates those to the faulting link. A link is described as the relationship between two devices and is shown in the following  FIG. 3 . 
       FIG. 3  (background art) is a block diagram depicting a single optical link, comprising two optical transceivers  24 {XE “transceivers  24 ”} and the local link  20 {XE “local link  20 ”} or remote link  22 {XE “remote link  22 ”} connecting them. The cable is depicted as twisted to represent that the transmitter  26 {XE “transmitter  26 ”} of one optical transceiver is connected directly to the receiver  28 {XE “receiver  28 ”} of an opposing optical transceiver. All of the hosts  14 {XE “hosts  14 ”}, storage enclosures  16 {XE “storage enclosures  16 ”}, and switch groups  12 {XE “switch groups  12 ”} have optical transceivers  24 {XE “transceivers  24 ”} connecting the local links  20 {XE “local links  20 ”} and remote links  22 {XE “remote links  22 ”}. There can be any number of paths in these links  20 ,  22 {XE “links  20 ,  22 ”} with each path having two directions. For each direction there is one transmitter  26 {XE “transmitter  26 ”} and one receiver  28 {XE “receiver  28 ”}, as represented in  FIG. 3 . 
     It is, therefore, an object of the present invention to provide a system for fault isolation in a storage area network. Other objects and advantages will become apparent from the following disclosure. 
     SUMMARY OF THE INVENTION 
     Briefly, one preferred embodiment of the present invention is a system and a computer program, embodied on a computer readable storage medium, to isolate a fault to a particular port from among multiple ports in a network. The network typically has a plurality of devices including hosts, storage units, and switch groups that intercommunicate via transceivers. A fault indication is received from one or more devices in the network. The fault indication is then processed with a chain of fault indication rules that are linked together into a binary decision path based on a set of device rules and a data flow model for the network. This permits determining the particular port responsible for the fault, and it permits reporting that port to a user of the network. 
     It is an advantage of the fault isolation system that it can determine the root source of a fault indication in a hierarchical or canonical heterogeneous optical network, based on a fault indication from an external service such as a predictive failure analysis (PFA), a performance analysis, a device, a link, or a network soft error notification, etc. 
     It is another advantage of the fault isolation system that it can consider all of the devices and the links between those devices using its fault indication and device rules, to adapt to uniqueness in the various device and counter types provided in a network. 
     It is another advantage of the fault isolation system that it can take into account differences in an underlying network, such as whether it is a storage area network (SAN) using cut-through routing or a local area network (LAN) using a store and forward scheme. 
     It is another advantage of the fault isolation system that it can use proven decision making algorithms and binary forward chaining, albeit in a novel manner, to decide whether to report fault indications and to evaluate the effectiveness of its fault isolation techniques. 
     It is another advantage of the fault isolation system that it can report the results of its fault isolation analysis using different and multiple reporting mechanisms, as desired. 
     It is another advantage of the fault isolation system that embodiments of it can be optimized through the use of sets of the externalized fault indication rules to directly affect its operation. 
     It is another advantage of the fault isolation system that embodiments of it can be implemented in modular form and easily adapted for multiple network applications. 
     It is another advantage of the fault isolation system that embodiments of it can allow loop back or feedback of its fault isolation results to adjust its fault indication and device rules, thus providing for self-optimization. 
     It is another advantage of the fault isolation system that it can aggregate and group data from multiple external fault indications, to provide a correlated response. 
     It is another advantage of the fault isolation system that it can take advantage of historical archives, potentially containing hundreds of data values for hundreds of devices, to further analyze the network. 
     And it is another advantage of the fault isolation system that it can be embodied to handle multiple fault isolations simultaneously, using new instances of its FI rules to follow separate FI chains for each fault isolation case. 
     These and other features and advantages of the present invention will no doubt become apparent to those skilled in the art upon reading the following detailed description which makes reference to the several figures of the drawing. 
    
    
     
       IN THE DRAWINGS 
       The following drawings are not made to scale as an actual device, and are provided for illustration of the invention described herein. 
         FIG. 1  (background art) is a block diagram depicting a generalized storage network infrastructure. 
         FIG. 2  (background art) is a block diagram depicting the generalized multi-hop network of  FIG. 1  with errors. 
         FIG. 3  (background art) is a block diagram depicting a single optical link, comprising two optical transceivers and the local link or remote connecting them. 
         FIG. 4A-B  are diagrams providing an overview of a fault isolation system in accord with the present invention. 
         FIG. 5  is a block diagram depicting a binary forward chaining algorithm employed to provide a fault isolation chain (FI chain) of connected instances of fault isolation rules (FI rules). 
         FIG. 6  is a flow diagram of a default FI chain that is usable to isolate a fault on a fiber channel storage network by applying the above FI rules. 
         FIG. 7  is a hierarchy diagram for an example set of the external rules used to describe device and error attributes. 
       And  FIG. 8  is a flow chart summarizing how the fault isolation system follows a state flow. 
     
    
    
     In the various figures of the drawings, like references are used to denote like or similar elements or steps. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides a system for fault isolation in a network. As illustrated in the various drawings herein, and particularly in the views of  FIG. 4A-B , embodiments of the invention are depicted by the general reference character  100 . 
       FIG. 4A-B  are diagrams providing an overview of a fault isolation system  100 {XE “fault isolation system  100 ”} in accord with the present invention. The fault isolation system  100 {XE “fault isolation system  100 ”} evaluates the storage area network given network counters, topology, and attribute characteristics, to isolate where one or more faults have occurred, no matter where the origin of the fault. 
     In  FIG. 4A  a flowchart shows overall interactions. In a step  102 {XE “step  102 ”} the fault isolation system  100 {XE “fault isolation system  100 ”} reads or receives an external fault indication from one of the externalized hardware or software components in the storage area network. In a step  104 {XE “step  104 ”} the fault isolation system  100 {XE “fault isolation system  100 ”} processes the fault indication to isolate it to a faulting port. In a step  106 {XE “step  106 ”} the fault isolation system  100 {XE “fault isolation system  100 ”} updates its methods with the isolation result, if required. And in a step  108 {XE “step  108 ”} the fault isolation system  100 {XE “fault isolation system  100 ”} sends a notification, if required. 
     In  FIG. 4B  a block diagram shows interactions between the major elements of the fault isolation system  100 {XE “fault isolation system  100 ”}. An externalized rules mechanism  110 {XE “rules mechanism  110 ”} works with a data flow model  112 {XE “data flow model  112 ”} and device rules  114 {XE “device rules  114 ”}, while the data flow model  112 {XE “data flow model  112 ”} and device rules  114 {XE “device rules  114 ”} further work closely together. 
       FIG. 5  is a block diagram depicting a binary forward chaining algorithm employed to provide a fault isolation chain (FI chain  116 {XE “FI chain  116 ”}) of connected instances of fault isolation rules (FI rules  118 {XE “FI rules  118 ”}). The FI chain  116 {XE “FI chain  116 ”} thus is an externalized form of the rules mechanism  110 {XE “rules mechanism  10 ”} and the data flow model  112 {XE “data flow model  112 ”}. As can be seen, each FI rule  118 {XE “FI rule  118 ”} has a binary decision code path  120 {XE “decision code path  120 ”} in the FI chain  116 {XE “FI chain  116 ”} that links it to any other FI rule  118 {XE “FI rule  118 ”}. Each FI rule  118 {XE “FI rule  118 ”} in the FI chain  116 {XE “FI chain  116 ”} describes a specific classification or analysis, such as a counter definition; correlation to another port or counter; classification, such as whether the error was an optical bit level error or frame error; or aggregation across multiple ports, such as the case with inter-switch links. 
     In one exemplary implementation, the FI rules  118 {XE “FI rules  118 ”} are chained together to form the FI chain  116 {XE “FI chain  116 ”} through the use of an externalized form. Examples of that form are serialized Java objects, XML formatted files, etc. The FI rules  118 {XE “FI rules  118 ”} can be integrated beforehand, while the FI chains  116 {XE “FI chains  116 ”} are developed and delivered separately. This allows for delivery of a new FI chain  116 {XE “FI chain  116 ”} that can easily be dropped into place without the need for byte level updates. Each fault isolation can also be performed with a separate thread, providing the fault isolation system  100 {XE “fault isolation system  100 ”} with the ability to handle multiple fault isolations simultaneously. And since every fault isolation can use a new instance of the FI rules  118 {XE “FI rules  118 ”}, each fault isolation can potentially follow a separate FI chain  116 {XE “FI chain  116 ”}. 
     The following is a list of some example FI rules  118 {XE “FI rules  118 ”} for use with optical fiber channel networks: 
     Aggregate Rule: Using multiple possible routing paths, aggregate events across those paths to determine if the fault occurred across one of the remote links  22 {XE “remote links  22 ”}. 
     Classify Rule: Using device rules (discussed presently), determine the classification of the error counter type. 
     Connected Port Rule: Using topology information to identify the active connected port from the current port in the topology. 
     Event Rule: Calculate the number of significant events that have occurred on a port. 
     No Fault Rule: Apply a set of user notifications, and log the case if a fault could not be found. 
     Fault Rule: Apply a set of user notifications, and log the case if a fault could be found. 
     Secondary Counter Rule: Using a contributing counter list defined for a counter as part of the device rules, obtain the next counter in the list for evaluation. 
       FIG. 6  is a flow diagram  200 {XE “flow diagram  200 ”} of an example FI chain  116 {XE “FI chain  116 ”} that is usable to isolate a fault in a SAN that uses fiber channel protocol. This shows the reception of a fault indication from a separate component and the flow that is then taken using the FI rules  118 {XE “FI rules  118 ”}. Each block in the flow diagram  200 {XE “flow diagram  200 ”} represents a separate FI rule  118 {XE “FI rule  118 ”}. 
     The flow through the FI chain  116 {XE “FI chain  116 ”} here starts at a block  202 {XE “block  202 ”}, when a fault indication is received from a service running on a component. For example, with reference again briefly to  FIG. 2 , the indication could be received from the emphasized storage enclosure  16 {XE “storage enclosure  16 ”}. 
     In a block  204 {XE “block  204 ”}, a determination is made whether the fault indication is due to a primary counter exceeding a notify threshold (set as part of a device rule for a particular device, e.g., the emphasized storage enclosure  16 {XE “storage enclosure  16 ”}). If so (“Yes”), in a block  206 {XE “block  206 ”} information about the connected port is received and in a block  208 {XE “block  208 ”} the fact of a faulty link between ports is logged. 
     Otherwise (i.e., “No” at block  204 {XE “block  204 ”}), at a block  210 {XE “block  210 ”} a determination is made whether the primary contributing events equal or exceed an indication event threshold. If so (“Yes”), the flow diagram  200 {XE “flow diagram  200 ”} (i.e., the FI chain  116 {XE “FI chain  116 ”}) again employs block  206 {XE “block  206 ”} and block  208 {XE “block  208 ”}, as described above. 
     Otherwise (i.e., “No” at block  210 {XE “block  210 ”}), at a block  212 {XE “block  212 ”} a determination is made whether the reporting device is directly connected to an endpoint. If so (“Yes”), in a block  214 {XE “block  214 ”} the fact of a faulty endpoint is logged. 
     Otherwise (i.e., “No” at block  212 {XE “block  212 ”}), at a block  216 {XE “block  216 ”} the current indication is examined on all ports of the containing interconnect element. This step is also referred to as the step of getting the first aggregate (“AG 1 ”) containing an interconnect element (ICE) of the current fault indication. At a block  218 {XE “block  218 ”} the current indication is examined on all interswitch link on the connected ICE. This is referred to as the step of getting the second aggregate (“AG 2 ”) of the connected ICE inter-switch link (ISL) of the current fault indication. [An ICE is one of the switches in a switch group  12 {XE “switch group  12 ”} and an ISL is a link that connects two or more switches together in a switch group  12 {XE “switch group  12 ”}.] 
     Then, at a block  220 {XE “block  220 ”}, a determination is made whether the first aggregate (AG 1 ) is greater than the second aggregate (AG 2 ). If so (“Yes”), the flow diagram  200 {XE “flow diagram  200 ”} employs block  206 {XE “block  206 ”} and block  208 {XE “block  208 ”}, as described above. 
     Otherwise (i.e., “No” at block  220 {XE “block  220 ”}), at a block  222 {XE “block  222 ”} a determination is made whether there is another, secondary indicator for the current fault. If so (“Yes”), the flow diagram  200 {XE “flow diagram  200 ”} employs a block  224 {XE “block  224 ”}, where the (old) current indicator is made a previous indicator and the secondary indicator is made the (new) current indicator. The block  204 {XE “block  204 ”} is then again employed in the flow diagram  200 {XE “flow diagram  200 ”}. 
     Otherwise (i.e., “No” at block  222 {XE “block  222 ”}), at a block  226 {XE “block  226 ”} a determination is made whether there is another, secondary indicator for the previous fault. If so (“Yes”), the flow diagram  200 {XE “flow diagram  200 ”} again employs block  224 {XE “block  224 ”}, block  204 {XE “block  204 ”}, etc. 
     And otherwise (i.e., “No” at block  226 {XE “block  226 ”}), at a block  228 {XE “block  228 ”} the flow diagram  200 {XE “flow diagram  200 ”} is done. 
       FIG. 7  is a hierarchy diagram  250 {XE “hierarchy diagram  250 ”} for an example set of the device rules  114 {XE “device rules  114 ”}. The device rules  114 {XE “device rules  114 ”} specify the characterization to, the classification of, and the relationship with a port and the devices it is contained within. With reference again briefly to  FIG. 1 , “devices” are instances of any equipment in the network  10 {XE “network  10 ”}, such as the switch groups  12 {XE “switch groups  12 ”}, hosts  14 {XE “hosts  14 ”}, and storage enclosures  16 {XE “storage enclosures  16 ”}, and the transceivers  24 {XE “transceivers  24 ”} in these. Those skilled in the present art will appreciate that the network and devices illustrated are merely a few representative examples used for discussion purposes, that the choice of these examples should not be interpreted as implying any limitations, and that other networks and devices are encompassed within the spirit of the present invention. 
     The device rules  114 {XE “device rules  114 ”} are used by the different FI rules  118 {XE “FI rules  118 ”} to aid in the decision making processes of the fault isolation system  100 {XE “fault isolation system  100 ”}. The device rules  114 {XE “device rules  114 ”} each include a counter list  252 {XE “counter list  252 ”} and attributes  254 {XE “attributes  254 ”}, as shown. 
     Each device has its own set of device rules  114 {XE “device rules  114 ”}, with the ones chosen to match a particular device by using a best fit model based on a combination of the attributes  254 {XE “attributes  254 ”} (all at first and then decrementing by one until a match is found). For example, the attributes  254 {XE “attributes  254 ”} can include classification, vendor, model, hardware version, and software version. The attributes  254 {XE “attributes  254 ”} thus uniquely identify the device which the device rules  114 {XE “device rules  114 ”} characterize. Preferably all of these attributes  254 {XE “attributes  254 ”} are used, or any number of, and at least one of, to match a device against it&#39;s attributes  254 {XE “attributes  254 ”}. This is not necessarily limited to just the attributes  254 {XE “attributes  254 ”} recited above, but rather, these are an example of possible attributes  254 {XE “attributes  254 ”} that can be used to define or match a device. 
     The counter list  252 {XE “counter list  252 ”} contains a set of error counters  256 {XE “error counters  256 ”}, with each of these also having attributes  258 {XE “attributes  258 ”}, as shown. For example, these attributes  258 {XE “attributes  258 ”} can include a counter classification  260 {XE “counter classification  260 ”}, an indication watermark  262 {XE “indication watermark  262 ”}, a notification threshold  264 {XE “notification threshold  264 ”}, and a list of contributing counters  266 {XE “contributing counters  266 ”}, if there are any. 
     The counter classification  260 {XE “counter classification  260 ”} can be either primary or secondary. Primary counters are considered those directly related to an error that occurred on a device or port. Secondary counters, although possibly being directly related to the error, can have other error counters  256 {XE “error counter  256 ”} which contribute to the counter list  252 {XE “counter list  252 ”} of the present error counter  256 {XE “error counter  256 ”} being incremented. For instance, a bit level error inside of a frame may cause a CRC corruption. A device may then count both the bit level error and the CRC error in its record of errors on the link. The device rules  114 {XE “device rules  114 ”} can therefore define error counters  256 {XE “error counters  256 ”} that contribute to the present error counter  256 {XE “error counter  256 ”}. The fault isolation system  100 {XE “fault isolation system  100 ”} takes this into consideration during fault isolation. Accordingly, the list of contributing counters  266 {XE “contributing counters  266 ”} specifies additional error counters  256 {XE “error counters  256 ”} that could have contributed to the current error counter  256 {XE “error counter  256 ”} to have an event. 
     With reference again to  FIG. 4A-B , we have now covered the rules mechanism  110 {XE “rules mechanism  110 ”} (i.e., the FI chain  116 {XE “FI chain  116 ”} and the FI rules  118 {XE “FI rules  118 ”}) and the device rules  114 {XE “device rules  114 ”}. The other major component of the fault isolation system  100 {XE “fault isolation system  100 ”} is the data flow model  112 {XE “data flow model  112 ”}. The first operation in the data flow model  112 {XE “data flow model  112 ”} is to take the unique identifying port information, which is the world wide port name in the storage area network, and to lookup information about the port using the attribute data provided by the data provider (embodied in the device rules  114 {XE “device rules  114 ”}). The data flow model  112 {XE “data flow model  112 ”} uses this attribute data to lookup the specific external FI rule  118 {XE “FI rule  118 ”} information about the counter, model, and vendor type of the port involved. This provides the fault isolation system  100 {XE “fault isolation system  100 ”} with the classification, propagation, and correlation data needed to isolate the fault, and topology data provided by the data provider (also embodied in the device rules  114 {XE “device rules  114 ”}) can then be used to follow the relationships between the various devices and to locate the root cause of the fault indication, which may be as simple as a bit level optical error or as complex as a multi-hop propagation error. Historical data archives can also be used to lookup information on the port, possibly leading to isolation based on data collected over past time intervals. The final operation in the data flow model  112 {XE “data flow model  112 ”} is to follow the FI chain  116 {XE “FI chain  116 ”} of externalized FI rules  118 {XE “FI rules  118 ”} provided to result in actual fault isolation. 
       FIG. 8  is a flow chart summarizing how the fault isolation system  100 {XE “fault isolation system  100 ”} follows a state flow  300 {XE “state flow  300 ”}. After a successful fault isolation using the FI rules  118 {XE “FI rules  118 ”} (step  302 {XE “step  302 ”}), the fault isolation system  100 {XE “fault isolation system  100 ”} upgrades a fault indication to a fault instance (step  304 {XE “step  304 ”}). Each fault instance is tracked based on the port, counter, and device rule  114 {XE “device rule  114 ”} that triggered the initial fault indication. After an appropriate number of fault instances, as defined by the device rules  114 {XE “device rules  114 ”}, the fault isolation system  100 {XE “fault isolation system  100 ”} upgrades a set of fault instances to a fault notification (step  306 {XE “step  306 ”}) that can be reported (step  308 {XE “step  308 ”}). A fault notification indicates that there is a potential failure occurring at a particular port or device. A fault notification can be cleared (optional step  310 {XE “step  310 ”}), and the cleared fault notification can be upgraded back to a fault notification if the above conditions are again met (i.e., steps  302 - 308 {XE “steps  302 - 308 ”} are repeated). Of course, various notification rules can also be employed with embodiments of the invention. For instance, using the device rules  114 {XE “device rules  114 ”}, such notification rules can be further used to decide if a fault should be updated to notify a user of a potential failure. 
     In summary, fault isolation systems in accord with the present invention permit determination of the root sources of fault indications in hierarchical or canonical heterogeneous optical networks. Given a fault indication from an external service such as a predictive failure analysis (PFA), a performance analysis, a device, a link, or a network soft error notification, etc., the fault isolation system  100  is well suited to fill the current and growing need for fault isolation storage area networks. 
     The fault isolation system can consider all of the devices and the links between those devices using its FI rules and device rules, to adapt to uniqueness in the various device and counter types provided in a network. The fault isolation system can also take into account differences in an underlying network, such as whether it is a storage area network (SAN) using cut-through routing or a local area network (LAN) using a store and forward scheme. For all of this, the fault isolation system can use proven decision making algorithms and binary forward chaining, albeit in novel manner, to decide whether to report fault indications and to evaluate the effectiveness of its fault isolation techniques. The fault isolation system can then report the results of its fault isolation analysis using different and multiple reporting mechanisms, if desired. 
     As a matter of design implementation, the fault isolation system can be optimized through the use of sets of the externalized FI rules to directly affect its operation. It can be implemented in modular form and easily adapted for multiple network applications. It can easily be extended to allow loop back or feedback of its fault isolation results to adjust its FI rules and device rules, thus providing for self-optimization. It can aggregate and group data from multiple external fault indications, to provide a correlated response. It can also take advantage of historical archives, potentially containing hundreds of data values for hundreds of devices, to further analyze the network. Coincidental with all of this, the fault isolation system can be embodied to handle multiple fault isolations simultaneously, using new instances of its FI rules to follow separate FI chains for each fault isolation case. 
     The embodiments of the fault isolation system  100 {XE “fault isolation system  100 ”} described above have primarily been discussed using a storage area network (SAN) as an example, but those skilled in the art will appreciate that the present invention is also readily extendable to networks that serve other purposes. Similarly, fiber channel hardware has been used for the sake of discussion. However, this is simply because of the critical need today to improve the reliability and speed of such networks, and the use of this type as the example here facilitates appreciation of the advantages of the present invention. Networks based on non-optical and hybrid hardware are, nonetheless, also candidates were the fault isolation system  100 {XE “fault isolation system  100 ”} will prove useful. 
     While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the invention should not be limited by any of the above described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.