Abstract:
A method for configuring a computer network that includes a full duplex bi-directional first port and an initiator that can issue a request for the first port to assume a state. The first port, when in a first state, is able to bi-directionally communicate with a full duplex bi-directional second port, and when in a second state, is coupled to itself by having an output thereof coupled to an input thereof. The method comprises inhibiting the initiator from issuing the request, sending data to the initiator describing a desired state of the first port, and enabling the initiator to issue the request for the first port to assume the desired state.

Description:
FIELD OF THE INVENTION 
   The present invention relates to computer networks and, more particularly, to a method and system for configuring a computer network that includes devices with configurable full duplex bi-directional ports. 
   BACKGROUND OF THE INVENTION 
   A computer network organized as a serial storage architecture (SSA) is a collection of nodes interconnected by a full duplex bi-directional serial connection. A standard for SSA is set forth by the American National Standards Institute (ANSI) Task Group X3T10.1 in documents SSA-S2P, SSA-TL1 and SSA-PH1. Additional references are available from the SSA Industry Association in documents SSA-IA/95PH and SSA-IA95SP. 
   In SSA, data is transferred between the nodes in data packets using a store and forward technique sometimes referred to as a bucket brigade. When the segments of an SSA network are organized in a loop, each node is coupled to two other nodes and data can travel throughout the network in a full circle. Alternatively, the nodes can be connected in a string, that is, in a line, that terminates without being connected to a subsequent node. However, in either topology, data communication throughout the network proceeds bi-directionally. 
   Each node has two ports, namely P 1  and P 2 , and each port has an input and an output. Each port is further characterized by a state that can be defined as “on-line”, “wrapped” or “off-line”. In the on-line state the port is able to bi-directionally communicate with a next port located on an adjacent node. In the wrapped state, the port is coupled to itself by having its output coupled to its input. In the off-line state, the port is not able to communicate with another port, and it is not wrapped. 
   An SSA network is often referred to as a web. One web can be partitioned into several smaller webs, or separate webs can be combined to form one larger web. Each web will have at least one initiator, which is a processor for routing data and commands to the nodes in the web. In the case where a web includes more than one initiator, the initiators are ranked from a highest priority to a lowest priority. Based on this priority, the initiators will collectively designate one of the initiators as a master initiator. 
   A master initiator is responsible for handling error conditions that are reported to it by devices on its web. The master initiator is also responsible for setting the state of the ports on its web. 
   An initiator acquires a view of the topology of the network through a process known as “walking the web.” When an initiator walks the web, the initiator examines the ports of the devices in the web of which the initiator is a member, and stores the state of the ports in a topology table. The topology table describes the interconnection between nodes, i.e., the manner in which ports are linked together. It typically includes information such as a node identifier, and the state of each port at the node. Each initiator maintains its own topology table. 
   Each initiator also maintains its own configuration table. A configuration table includes the same information as a topology table, and further includes initiator registration information and port error handling parameters. 
   If a device on a web encounters a fault, the device generates an error message, known as an “Async Alert” in SSA parlance. If the Async Alert indicates a port communications problem, the master initiator of the web responds by performing an automatic error recovery process in which it walks the web to examine and possibly request a change of the state of the ports on the web. The master initiator may also issue a message known as a “Master Alert” to the non-master initiators. In response to a Master Alert, a non-master will walk the web and examine the ports on the web. However, a non-master initiator does not request a change of the state of a port. 
   A master initiator can issue a request for a given port to assume the wrapped state. Provided that the given port is operating normally, the given port will respond by wrapping itself. 
   Alternatively, a master initiator can issue a request for a given port to assume the on-line state. If the given port can establish communication with an adjacent port, then the given port assumes the on-line state. If the given port cannot establish communication with the adjacent port, then the given port assumes the off-line state. This failure to establish communication can occur when (a) there is no adjacent port, such as when the given port is at the end of a string, (b) the adjacent port is in the wrapped state, or (c) the communication link between the given port and the adjacent port has a problem. Note that the port may automatically transition from the on-line state to the off-line state depending on its ability to establish communication with the adjacent port. 
   When the network topology changes, initiator mastership can change, and a new master initiator will be responsible for the state of the ports. However, a first initiator cannot read a topology table from a second initiator. Consequently, in a case where the first initiator becomes a master for a web of which the first initiator has no knowledge, the first initiator has no opportunity to preserve the state of a port located in that web. 
   Note also that the process of walking the web and requesting a particular state for a port is handled exclusively by the initiators. There is no method or means for imposing or even suggesting a desired configuration for the network. 
   Accordingly, it is an object of the present invention to impose a desired configuration on a computer network notwithstanding the presence of an initiator that can examine and request the ports in the network to assume particular states. 
   It is another object of the present invention to impose the desired configuration in a case where the network includes multiple webs and multiple initiators. 
   It is yet another object of the present invention to maintain the desired configuration in a case where the topology of the network changes. 
   SUMMARY OF THE INVENTION 
   The present invention is directed toward a method and system for configuring a computer network that includes full duplex bi-directional ports and one or more processors having an ability to examine and request that each port assume a particular state. The processor, also known as an initiator, maintains a copy of a port information map (PIM) that contains data describing a desired state of all the ports in the network. 
   A control unit imposes a desired configuration by (a) inhibiting all initiators from issuing requests for the ports to change state, (b) sending the PIM describing the desired configuration to the initiators, and (c) enabling the initiators to issue requests for the ports to assume states in accordance with the PIM. 
   The present invention defines and imposes a desired configuration for the entire computer network and synchronizes the configuration among multiple initiators. When the topology of the network changes, the invention provides for the cases of partitioning the network into smaller networks, and for joining networks together. Because the invention affirmatively defines the state of all ports, when a master initiator walks the web, an isolated node remains isolated. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic of a computer network organized in a serial storage architecture loop topology; 
       FIG. 2  is a flowchart of a method for imposing a desired configuring on a computer network in accordance with the present invention; 
       FIG. 3  is a flowchart of a method for an initiator to set the state of a port in a network in accordance with data describing a desired state for the port; and 
       FIG. 4  is a flowchart of a method for an initiator to walk the web and construct a topology table. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention provides a method for configuring a computer network that includes devices with full duplex bi-directional ports and an initiator having an ability to examine and request each port to assume a particular state in accordance with data describing a desired configuration. Each port can assume an on-line, off-line or wrapped state. 
   In brief, a control unit constructs a port information map (PIM) that defines a desired state for each port in the entire computer network. The control unit issues the PIM to the initiator. When the initiator configures the web, it requests the ports to assume desired states in accordance with the PIM. In a case of multiple webs and multiple initiators, the PIM provides all initiators with the desired state of all ports in the network. Therefore a given initiator has knowledge of the desired state of all ports, including those that are not in the same web as the given initiator. This allows an initiator to manage the ports in a case where the network topology changes. 
     FIG. 1  is a schematic representation of a computer network  1  organized in a serial storage architecture loop topology. The principal components of the network are a host processor  5  with a user interface  3 , a control unit  10 , initiators  15 – 17 , and a series of nodes occupied by disk drives  50 – 67 . In a general case, any type of device that can be connected to a computer network, including typical input/output devices can occupy the nodes. 
   User interface  3  enables a user to send commands and data to, and receive data from, computer network  1 . Host processor  5  communicates with control unit  10  over a bus  6 , and control unit  10  communicates with initiators  15 – 17  via a bus  12 . Initiators  15 – 17  and disk drives  50 – 67  are connected to a network comprising three segments  20 ,  21  and  22 . Each of the initiators  15 – 17  and disk drives  50 – 67  include two full duplex bi-directional ports, i.e. P 1  and P 2 , through which data is exchanged. Generally, a device need not be limited to two ports, and the present invention can be applied where the devices have any number of ports. 
   Host processor  5  executes programs using data that is stored on disk drives  50 – 67 . To access data from a disk drive, disk drive  50  for example, host processor  5  issues a command to control unit  10 . Thereafter, control unit  10  issues a corresponding command to initiator  15 , which passes the command to disk drive  50 . The commands from the initiators  15 – 17  to the disk drives  50 – 67  provide for reading data from, and writing data to, disk drives  50 – 67 , and for setting the state of ports on each of disk drives  50 – 67 . 
   Control unit  10  includes a processor  10   a  and memory  10   b  that can be loaded with a program or data from a storage media, such as data memory  8 . When control unit  10  issues a command to any initiator  15 – 17 , the initiator acknowledges the command by returning a status packet indicating whether the initiator successfully completed the command. Although control unit  10  and initiators  15 – 17  are shown here as separate components, they may be integrated into a single housing, or even a single printed circuit board. 
   One of the initiators  15 – 17  must be designated as a master initiator. This designation of mastership occurs during the web walking process. Each of the initiators  15 – 17  has an identifier that also prioritizes the initiators. When a first initiator walks the web and encounters a second initiator, the first initiator reads the identifier of the second initiator. If the identifier of the first initiator indicates a higher priority, then the first initiator assumes mastership. If the identifier of the second initiator indicates a higher priority, then the first initiator concedes mastership. For the description that follows, assume that the initiators are prioritized as  15 ,  16  and  17 , with initiator  15  having the highest priority. 
   Computer network  1  can be organized into segments of smaller webs. For example, assume that devices  53  and  65  are isolated from the network. This would yield (a) a first web, configured as a string that included initiators  15  and  16 , and devices  50 – 52  and  56 – 64 , and (b) a second web, configured as a string that included initiator  17 , and devices  54 ,  55 ,  66  and  67 . Initiator  15  would assume mastership of the first web, and initiator  17  would assume mastership of the second web. 
   A sample Port Information Map is set forth in Table 1, below. Referring again to  FIG. 1 , assume devices  53  and  65  are isolated. Note that in Table 1, device  53 -P 1  and -P 2  are both indicated as “(undefined)”, device  52 -P 1  is “wrapped”, and device  54 -P 2  is “wrapped”. Also, device  65 -P 1  and -P 2  are both indicated as “(undefined)”, device  64 -P 2  is “wrapped”, and device  66 -P 1  is “wrapped”. 
   
     
       
             
           
             
             
             
             
           
         
             
               TABLE 1 
             
           
           
             
                 
             
             
               PORT INFORMATION MAP 
             
             
               DEVICES 53 AND 65 ISOLATED 
             
           
        
         
             
                 
               NODE 
               PORT 
               STATE 
             
             
                 
                 
             
             
                 
               Initiator 15 
               P1 
               On-line 
             
             
                 
               Initiator 15 
               P2 
               On-line 
             
             
                 
               Initiator 16 
               P1 
               On-line 
             
             
                 
               Initiator 16 
               P2 
               On-line 
             
             
                 
               Initiator 17 
               P1 
               On-line 
             
             
                 
               Initiator 17 
               P2 
               On-line 
             
             
                 
               Device 50 
               P1 
               On-line 
             
             
                 
               Device 50 
               P2 
               On-line 
             
             
                 
               Device 51 
               P1 
               On-line 
             
             
                 
               Device 51 
               P2 
               On-line 
             
             
                 
               Device 52 
               P1 
               Wrapped 
             
             
                 
               Device 52 
               P2 
               On-line 
             
             
                 
               Device 53 
               P1 
               (undefined) 
             
             
                 
               Device 53 
               P2 
               (undefined) 
             
             
                 
               Device 54 
               P1 
               On-line 
             
             
                 
               Device 54 
               P2 
               Wrapped 
             
             
                 
               Device 55 
               P1 
               On-line 
             
             
                 
               Device 55 
               P2 
               On-line 
             
             
                 
               Device 56 
               P1 
               On-line 
             
             
                 
               Device 56 
               P2 
               On-line 
             
             
                 
               Device 57 
               P1 
               On-line 
             
             
                 
               Device 57 
               P2 
               On-line 
             
             
                 
               Device 58 
               P1 
               On-line 
             
             
                 
               Device 58 
               P2 
               On-line 
             
             
                 
               Device 59 
               P1 
               On-line 
             
             
                 
               Device 59 
               P2 
               On-line 
             
             
                 
               Device 60 
               P1 
               On-line 
             
             
                 
               Device 60 
               P2 
               On-line 
             
             
                 
               Device 61 
               P1 
               On-line 
             
             
                 
               Device 61 
               P2 
               On-line 
             
             
                 
               Device 62 
               P1 
               On-line 
             
             
                 
               Device 62 
               P2 
               On-line 
             
             
                 
               Device 63 
               P1 
               On-line 
             
             
                 
               Device 63 
               P2 
               On-line 
             
             
                 
               Device 64 
               P1 
               On-line 
             
             
                 
               Device 64 
               P2 
               Wrapped 
             
             
                 
               Device 65 
               P1 
               (undefined) 
             
             
                 
               Device 65 
               P2 
               (undefined) 
             
             
                 
               Device 66 
               P1 
               Wrapped 
             
             
                 
               Device 66 
               P2 
               On-line 
             
             
                 
               Device 67 
               P1 
               On-line 
             
             
                 
               Device 67 
               P2 
               On-line 
             
             
                 
                 
             
           
        
       
     
   
   During the new configuration process, control unit  10  issues commands to the initiators  15 – 17 . The commands include a Freeze Command, Query Configuration Command, Execute Port Information Map (XPIM) Command, Unfreeze Command, and Validate Configuration Command. 
   The Freeze Command inhibits all initiators from responding to an Async Alert by performing an automatic error recovery process. That is, the initiators are inhibited from issuing requests to change the states of the ports when responding to the Async Alert. Note that during regular operation, an initiator may respond to the Async Alert by performing an automatic error recovery process that alters the state of one or more ports. 
   The Query Configuration Command causes an initiator to send data from its Configuration Table to the control unit. After obtaining a Configuration Table from each of the initiators in the network, the control unit can consider the current actual configuration, and develop a desired configuration, for the entire network. 
   When issuing the Execute Port Information Map (XPIM) Command, the control unit also sends the PIM to an initiator. The XPIM causes the initiator to walk the web. If the initiator is a master initiator, it is thus enabled to issue requests for the ports in its web to assume states in accordance with the PIM. 
   The Unfreeze Command enables the initiators to respond to an Async Alert by performing an automatic error recovery process. That is, the initiators are not inhibited from issuing requests to change the states of ports when responding to the Async Alert. 
   The Validate Configuration Command causes an initiator to walk the web and to compare the actual port settings to data in the PIM. The initiator reports the result of this comparison to the control unit. 
     FIG. 2  is a flowchart of a method for imposing a desired configuration on a computer network in accordance with the present invention. This method is applicable to a network having a single initiator, as well as a network having multiple webs and multiple initiators. 
   In step  205 , the control unit (CU) suspends all drive commands by allowing existing drive commands to be completed, and by not issuing new commands. More particularly, the control unit waits for each initiator to acknowledge completion of all commands previously issued by the control unit. The method then advances to step  210 . 
   In step  210 , the control unit issues a Freeze Configuration Command to all initiators. All initiators are inhibited from issuing requests to change the states of the ports when responding to an Async Alert. This step ensures that the occurrence of an Async Alert does not interfere with the present process. The method then advances to step  215 . 
   In step  215 , the control unit determines whether to attempt to establish a new network configuration. This determination allows for a case where, after a predetermined number of attempts, the control unit has not been able to successfully establish communication with all of the initiators. If the control unit determines that it will not attempt to establish a new network configuration, then the method branches to step  275  and terminates. If the control unit determines that it will attempt to establish a new network configuration, then the method advances to step  220 . 
   In step  220 , the control unit issues a Query Configuration Command to each initiator. In response to the Query Configuration Command, an initiator sends data from its Configuration Table to the control unit. The method then advances to step  225 . 
   In step  225 , the control unit establishes a desired configuration for the network, based on the actual configuration reported by each of the initiators in step  220 . The control unit constructs a Port Information Map (PIM) describing the desired configuration for the entire network. The PIM includes a desired setting for all ports in the network. The method then advances to step  230 . 
   As an alternative to steps  220  and  225 , a user of computer network  1  can define a desired configuration via user interface  3 . Accordingly, the PIM would be based on input from the user. 
   In step  230 , the control unit issues an Execute Port Information Map (XPIM) Command to each of the initiators in the network. The control unit sends the command to each initiator in a determined sequence. The sequence starts with the highest-ranking initiator (rank  0 ) and progresses in order of priority to the lowest-ranking initiator (rank n). With each XPIM Command the control unit also sends the PIM to the initiator describing a desired state of the ports. In response to receiving the XPIM command, the initiator walks the web and constructs a topology table and a configuration table. If the initiator is a master initiator, it may also issue requests for the port states to be set in accordance with the PIM. The XPIM process as executed by an initiator is illustrated in  FIG. 3  and described below in greater detail. The method then advances to step  235 . 
   By affirmatively defining a desired state for each port in the network, a network can be partitioned into smaller webs, or similarly, webs can be merged into a larger network. Stated more generally, the method can be applied where a network has M number of webs, each of the M number of webs including a respective initiator and a respective full duplex bi-directional port. After the initiators issue the requests for setting the ports to the desired states, the computer network can have N number of webs, where N is not equal to M. 
   In step  235 , the control unit determines whether all initiators successfully executed the XPIM Commands that were issued in step  230 . An initiator acknowledges a command from the control unit by returning a status packet indicating whether the initiator successfully completed the command. If all initiators successfully executed their respective XPIM Command, then the method advances to step  250 . If all initiators did not successfully executed their respective XPIM Command, then the method advances to step  240 . 
   In step  240 , the control unit issues another XPIM Command to each of the initiators. As before, this is done in sequence starting with the highest-ranking initiator and progressing in order of priority to the lowest-ranking initiator. Each respective initiator executes the process illustrated in  FIG. 3 . The method then advances to step  245 . 
   In step  245 , the control unit determines whether all initiators successfully executed the XPIM Commands that were issued in step  240 . If all initiators successfully executed their respective XPIM Command, then the method advances to step  250 . If all initiators did not successfully executed their respective XPIM Command, then the method loops back to step  215 . 
   In step  250 , the control unit issues an Unfreeze Command to all initiators. The master initiators are thus permitted to request changes in the state of the ports when responding to Async Alerts. The method then advances to step  255 . 
   In step  255 , the control unit issues a Validate Configuration Command to each of the initiators. In response, each initiator compares the actual configuration to data in the PIM. The initiators report the result of these comparisons to the control unit. The method then advances to step  260 . 
   In step  260 , the control unit determines whether the current configuration of the network conforms to the desired configuration of the network. More particularly, the control unit evaluates the reports sent by the initiators in step  255 . If the reports from all initiators indicate that the current configuration matches the PIM, then the method advances to step  265 . If the reports from all initiators do not indicate that the current configuration matches the PIM, then the method loops back to step  210 . 
   In step  265 , the control unit resumes regular operation by issuing disk drive commands to the initiators. The method then advances to step  270 . 
   In step  270 , the method terminates with a successful reconfiguration of the network. 
   In step  275 , the method terminates with a failure. The control unit did not successfully establish the desired network configuration. 
     FIG. 3  is a flowchart a method executed by an initiator, in response to receiving the Execute Port Information Map (XPIM) command from the control unit. The method begins with step  310 . 
   In step  310 , the initiator walks the web and constructs a topology table. This process is illustrated in  FIG. 4 , and described below in greater detail. The method then advances to step  315 . 
   In step  315 , the method considers whether the initiator is a master initiator. This is accomplished by examining the current topology table that was constructed in step  310 . If the initiator is a master, then the method advances to step  320 . If the initiator is not a master, then the method branches to step  335 . 
   In step  320 , the initiator issues a request for each port in the initiator&#39;s web to assume the on-line state. This step ensures that the initiator can communicate with all ports in its web. That is, the initiator can affirmatively access ports that might otherwise be inaccessible because of a previously wrapped port at an intermediate node. The method then advances to step  325 . 
   In step  325 , for each port in the initiator&#39;s web, the initiator issues a request for the port to assume a desired state in accordance with data in the PIM. The method then advances to step  330 . 
   In step  330 , the initiator walks the web and constructs a topology table as shown in  FIG. 4 . The method then advances to step  335 . 
   In step  335 , the initiator constructs a configuration table. The configuration table is first built on the information contained in the topology table. To this topology information, the initiator adds information important to the operation and error handling of the network. This added information includes:
         (a) more detailed port setting information derived from the complete web topology;   (b) Async Alert address information used by all the ports and associated master initiator during error handling; and   (c) identification and access information used for data access between initiators and drives.
 
The method then advances to step  340 .
       

   In step  340 , the method considers whether the initiator is a master initiator. This is accomplished by examining the most current topology table constructed in steps  310  or  330 . Note that a previous master initiator may have lost web mastership as a result of steps  320  and  325 . If the initiator is a master, then the method advances to step  345 . If the initiator is not a master, then the method branches to step  350 . 
   In step  345 , for each port in the initiator&#39;s web the initiator issues a request for the port to assume a final state in accordance with the configuration table. The port&#39;s final state includes not only a setting in accordance with data in the PIM, but also settings important to the operation and error handling of the network. The method then advances to step  350 . 
   In step  350 , the initiator compares the actual configuration of the web, as represented in the initiator&#39;s configuration table, to the PIM. If the configurations match, then the method advances to step  355 . If the configurations do not match, then the method advances to step  360 . 
   In step  355 , the XPIM is declared as a success. The method then advances to step  365 . 
   In step  360 , the XPIM is declared unsuccessful. The method then advances to step  365 . 
   In step  365 , the XPIM method ends. 
     FIG. 4  is a flowchart of a method for an initiator to walk the web and construct a topology table. Initially, the topology table is empty. The method begins with step  410 . 
   In step  410 , the method considers whether the initiator has explored all nodes in the web in which the initiator is located. All nodes are explored when (a) the initiator encounters a given node for a second time, thus indicating that the initiator has explored an entire a loop, or (b) the initiator has explored all nodes that are accessible via all of the initiators&#39; ports. If the initiator has explored all nodes, then the method branches to step  430 . If the initiator has not yet explored all nodes, then the method advances to step  415 . 
   In step  415 , the initiator attempts to establish communication with a next node. The method then advances to step  420 . 
   In step  420 , the method determines whether the attempt to establish communication in step  415  was successful. For example, if the initiator has progressed to the end of a string, then there is no next node and the attempted communication will not be successful. If the attempt to establish communication was not successful, then the method loops back to step  410 . If the attempt to establish communication was successful, then the method advances to step  425 . 
   In step  425 , the initiator updates its topology table. That is, the initiator adds an entry to the topology table to represent the node. The method then loops back to step  410 . 
   In step  430 , the method for walking the web ends. 
   The present invention for configuring a computer network can also be applied in the following circumstances: configuring an SSA web during a power-on sequence, configuring an SSA web during drive replacement or initiator replacement, configuring an SSA web during drive capacity upgrades, fencing a drive, and fencing an SSA initiator. However, the present invention is not limited to SSA, but can be used for any computer network having devices with full duplex bi-directional ports that can be set to an on-line or wrapped state. 
   It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Further, while the procedures required to execute the invention hereof are indicated as already loaded into the memory of the control unit and initiators, they may be configured on a storage media, such as data memory  8  in  FIG. 1 , for subsequent loading into the control unit and initiators. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances that fall within the scope of the appended claims.