Abstract:
An apparatus, system, and method are disclosed for reinitializing serialization data in a file server. The apparatus includes a failure recognition module, a discard module, and a serialization module. The failure recognition module recognizes a file system serialization failure on a file server. Upon recognition of the serialization failure, the discard module discards existing serialization data located in a first memory address space, such as a file server address space. In certain embodiments, the entire file server address space may be destroyed by the operating system. The serialization module then generates new serialization data from existing connection/position data. The connection/position data is located in a second address space, such as a client address space, that is maintained during the serialization reinitialization process. Containing and rebuilding the serialization data in this manner beneficially prevents system outages, reduces downtime, and decreases the likelihood of subsequent serialization deadlocks.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to file servers and more particularly relates to reinitializing serialization data in a file server in response to a serialization failure. 
     2. Description of the Related Art 
     Serialization of a plurality of data access requests can be extremely complicated for data storage devices that are shared among multiple-processor file system servers. Serialization of the data access requests involves defining which applications are connected to which storage devices, or portions thereof, and what kind of access is provided for each application. For example, some applications are given exclusive access rights for certain write operations, while others may not receive exclusive access. Also, some applications may receive shared access rights for certain read operations on the shared data storage devices. By defining which applications are allowed which type of access at which times, the file system servers are able to prevent many data operation errors that would otherwise occur. 
     However, serialization techniques are not perfect and a serialization implementation may fail. A serialization failure may occur when read or write access to a requested data file or directory is not made available to a requesting application. For example, a serialization failure may occur when two applications are requesting data access rights to data that is exclusively assigned to the other application. 
       FIG. 1   a  shows one example of an application environment  10  in which a serialization conflict might occur. In particular, the illustrated application environment  10  includes a first application  12  and a second application  14 . The first application  12  has exclusive rights (as shown by the solid arrow  16 ) to a first data file  18 . Likewise, the second application  14  has exclusive rights (as shown by the solid arrow  20 ) to a second data file  22 . 
       FIG. 1   a  also shows the first application  12  requesting access rights (as shown by the dashed arrow  24 ) to the second data file  22 . Likewise the second application  14  may request access rights (as shown by the dashed arrow  26 ) to the first data file  22 . In this case, a serialization “deadlock” failure occurs when neither the first application  12  nor the second application  14  can progress until the requested access rights are granted, but the requested access rights cannot be granted because the requested data files  18 ,  22  are already in use by the non-requesting applications  12 ,  14 . When this type of serialization failure occurs, the file system server (not shown) may become nonresponsive and thereby unavailable because the applications  12 ,  14  continue to hold onto their existing access rights while requesting the additional access rights. 
     Although an internal serialization failure, by itself, does not compromise either the integrity of the data stored in the data files  18 ,  22  or the run-time states of the in-flight applications  12 ,  14 , such a serialization failure can have drastic effects on the file system server. For instance, a serious serialization failure may occur where the file system is central to an operating system, such as when the ability to load programs from a file system is necessary for basic operating system functions. Furthermore, serialization failures can result in operating system outages, which can cause the failure of all in-flight application processing, including processing that is not directly related to the corresponding file system. Additionally, serialization failures may lead to excessive costs due to file system server downtime that impacts business-critical applications. 
     With regard to file system serialization failures, the conventional focus is on correcting the underlying causes of all serialization problems. However, this solution is practically infeasible given the complexity of contemporary multitasking, multiprocessing, and clustering environments in which the number of possible serialization problems and causes is overwhelming. 
     From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method automatically handling file system serialization failures in a manner to overcome the disadvantages of conventional technology. Beneficially, such an apparatus, system, and method would allow in-flight applications to remain logically connected to the file system while the file system serialization information is reinitialized. Additionally, such an apparatus, system, and method would be advantageous over conventional systems and methods by preventing system outages and related costs. 
     SUMMARY OF THE INVENTION 
     The present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available file system serialization systems. Accordingly, the present invention has been developed to provide an apparatus, system, and method for reinitializing a file server that overcome many or all of the above-discussed shortcomings in the art. 
     The apparatus to reinitialize a file server is provided with a logic unit containing a plurality of modules configured to functionally execute the necessary steps of reinitializing the serialization data of a file system server. These modules in the described embodiments include a front end module and a back end module. In one embodiment, the front end module resides in a client address space and the back end module resides in a file server address space. 
     In certain embodiments, the front end module may include a connection module and a suspension apparatus. The connection module manages the connection/position information (also referred to as connection/position data) that describes open file connections or other resource connections associated with an application. The suspension apparatus, in one embodiment, suspends data access requests prior to and during reinitialization of the file server serialization. 
     The back end module, in certain embodiments, may include a serialization module, a quiesce module, a discard module, and a failure recognition module. The serialization module manages the serialization data for a given application corresponding to a client address space. The serialization module also generates new serialization data from existing connection/position data as a part of the reinitialization operation. 
     The failure recognition module recognizes a serialization failure. The discard module discards the existing serialization data. For instance, the discard module may request that the operating system destroy the address space in which the existing serialization data is located. In one embodiment, the existing serialization data is located in a file server address space. In a further embodiment, the entire back end module also may be located in the file server address space that is destroyed by the operating system. The suspension module may facilitate the creation of a new file server address space after the existing file server address space is discarded. The quiesce module quiesces the file server prior to and during the reinitialization process. In one embodiment, the quiesce period is coordinated with the suspension apparatus described above. 
     The back end module also may include a completion apparatus and a cluster apparatus. The completion apparatus tracks the progress of a task associated with an application. In one embodiment, the completion apparatus may be used in conjunction with the quiesce module to stabilize the connection/position data during the quiesce period. The connection/position data may reside in the client address space, which is preserved and not discarded during the file system serialization reinitialization. The cluster apparatus manages the necessary rights and negotiation communications among a plurality of file servers within a cluster when the serialization data on one file server is reinitialized. 
     A system of the present invention is also presented to reinitialize the serialization data of a file system server. The system may be embodied in a processing cluster including a plurality of file servers having shared access to one or more shared data storage devices. In particular, one embodiment of the system includes a plurality of file servers, a shared storage device, and a serialization reinitialization apparatus. The system also may include a coupling facility to facilitate global serialization among the plurality of file servers. 
     The system may further include a notification module. In one embodiment, the notification module is configured to notify one or more remote file servers within the processing cluster when a local file server is expected to be reinitialized. Similarly, the notification module notifies the remote file servers after the local file server is reinitialized. 
     A method of the present invention is also presented for reinitializing a file server. The method in the disclosed embodiments substantially includes the steps necessary to carry out the functions presented above with respect to the operation of the described apparatus and system. In one embodiment, the method includes recognizing a file system serialization failure on a file server, discarding the existing serialization data, and generating new serialization data from the existing connection/position data. As mentioned above, the existing connection/position data is stabilized and maintained, for example, in the client address space throughout the reinitialization process. 
     The method also may include quiescing the file server, invoking an operating system function to destroy the file server address space, and invoking an operating system function to create a new file server address space. Additionally, the method may include searching the memory for the existing connection/position data, generating the new serialization data from the existing connection/position data located in the client address spaces, and storing the new serialization data in the new file server address space. 
     A signal bearing medium is also presented. The signal bearing medium is configured to store software instructions to carry out some or all of the functions described above with reference to the method, apparatus, and system. 
     Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussion of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment. 
     Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention. 
     These features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which: 
         FIG. 1   a  is a schematic block diagram illustrating one embodiment of an application environment in accordance with the present invention; 
         FIG. 1   b  is a schematic block diagram illustrating one embodiment of a storage system cluster in accordance with the present invention; 
         FIG. 2  is a schematic block diagram illustrating one embodiment of an electronic memory device in accordance with the present invention; 
         FIG. 3   a  is a schematic block diagram illustrating one embodiment of connection/position data in accordance with the present invention; 
         FIG. 3   b  is a schematic block diagram illustrating one embodiment of serialization data in accordance with the present invention; 
         FIG. 4  is a schematic block diagram illustrating one embodiment of a Co serialization reinitialization apparatus in accordance with the present invention; 
         FIG. 5  is a schematic flow chart diagram illustrating one embodiment of a reinitialization method in accordance with the present invention; and 
         FIG. 6  is a schematic flow chart diagram illustrating one embodiment of a rebuild method in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Many of the functional units described in this specification have been labeled as modules, in order to more particularly emphasize their implementation independence. For example, a module may be implemented as a hardware circuit comprising custom VLSI circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. A module may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like. 
     Modules may also be implemented in software for execution by various types of processors. An identified module of executable code may, for instance, comprise one or more physical or logical blocks of computer instructions which may, for instance, be organized as an object, procedure, or function. Nevertheless, the executables of an identified module need not be physically located together, but may comprise disparate instructions stored in different locations which, when joined logically together, comprise the module and achieve the stated purpose for the module. 
     Indeed, a module of executable code could be a single instruction, or many instructions, and may even be distributed over several different code segments, among different programs, and across several memory devices. Similarly, operational data may be identified and illustrated herein within modules, and may be embodied in any suitable form and organized within any suitable type of data structure. The operational data may be collected as a single data set, or may be distributed over different locations including over different storage devices, and may exist, at least partially, merely as electronic signals on a system or network. 
     Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. 
     Furthermore, the described features, structures, or characteristics of the invention may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of programming, software modules, user selections, network transactions, database queries, database structures, hardware modules, hardware circuits, hardware chips, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. 
       FIG. 1   b  depicts one embodiment of a processing cluster  100  in which certain embodiments of the present invention may be employed. The illustrated processing cluster  100  includes a plurality of file servers  102 , one or more shared storage devices  104 , and a coupling facility  106 . Each file server  102  is configured to manage resources on the processing cluster  100 . For example, the plurality of file servers  102  manages allocation of processing, memory, and data storage resources for each application or other software program executing on the processing cluster  100 . As used herein, references to an “application” may include application software as well as system software, such as an operating system, unless indicated otherwise. 
     The shared storage devices  104  comprise electronic storage devices that are configured to store data per instructions from the plurality of file servers  102 . In one embodiment, the shared storage devices  104  comprise a plurality of hard disk drives. Alternately, the shared storage devices  104  may comprise one or more optical drives, tape drives, and/or other data storage drives. Data stored on the shared storage devices  104  may be read and otherwise accessed by the file servers  102 . In one embodiment, the data on the shared storage devices  104  may be stored within a file system including directories, sub-directories, files, and other directory entries. Each of the directories, sub-directories, files, other directory entries, and similar data structures is a shared storage resource within the processing cluster  100 . 
     Each time an application on one of the file servers  102  requests access to data on one of the shared storage devices  104 , the file server  102  coordinates the data access with other client applications running on the same file server  102  and on the other file servers  102  in the processing cluster  100 . This coordination is referred to as serialization because the file server  102  allows serial, or consecutive, access to the data on the shared storage  104 . Serialization allows each application to have either shared or exclusive access to a particular set of data so that other applications do not interfere with or otherwise disrupt the target set of data. 
     Serialization may be implemented on various levels of granularity within the processing cluster  100  and shared storage devices  104 . For example, serialization may occur at a directory level or a sub-directory level. Additionally, serialization may occur at a file, record, or packet level. The serialization granularity depends on the type of processing cluster  100 , file servers  102 , shared data storage devices  104 , and other hardware used within the processing cluster  100 . The granularity also may depend on the type of data access operations that are requested by an application or an operating system. 
     The coupling facility  106 , in one embodiment, is provided to facilitate serialization among all of the file servers  102  within the processing cluster  100 . In particular, the coupling facility  106  may store serialization information and assist in messaging operations among the many file servers  102 . Alternate embodiments of the processing cluster  100 , however, may perform global serialization without the assistance of a coupling facility  106 . 
       FIG. 2  depicts one embodiment of an electronic memory device  200  that may be used to store serialization programs and data, as well as related information. The illustrated memory  200  is divided into a plurality of address spaces  202 . Each address space  202  comprises a set of legal memory addresses allocated for a given application and represents the amount of memory  200 , either physical or virtual, that is allocated to the application. The illustrated memory  200  specifically includes a client address space  202   a,  a file server address space  202   b,  and additional address space(s)  202   n.  The memory  200  also includes commonly addressable memory  204 . 
     A client address space  202   a  maybe created for each application that interfaces with a given file server  102 . For instance, a memory  200  may include four client address spaces  202   a,  one for each of four clients interfacing with the file server  102 . The client address space  202   a  also may be referred to as the “front end” because it is responsible for interacting directly with the application programs. In general, the client address space  202   a  facilitates data access operations for the requesting software program, such as application software or system software. 
     The illustrated client address space  202   a  includes front end data  210 , generally, and specifically includes connection/position data  212 . Each client address space  202   a  may contain corresponding front end data  210 , including connection/position data  212 , pertinent to the associated client. The connection/position data is descriptive of the data on the shared storage devices  104  that is accessed by the corresponding application. An example of connection/position data  212  is described in more detail with reference to  FIG. 3   a.    
     References throughout this description to “a” or “the” client address space  202   a  in singular form is understood to refer to one or more client address spaces  202   a,  where each client address space  202   a  corresponds to an independent client. Similarly, references to front end data  210  and/or connection/position data  212  is understood to refer to such data for one or more clients interfacing with a given file server  102 . 
     The file server address space  202   b,  in one embodiment, is responsible for serialization within the file server  102  and for data access to the shared storage devices  104 . The file server address space  202   b  also may be referred to as the “back end” because it manages the interface between the file server  102  and the shared storage devices  104 . In particular, the file server address space  202   b  serializes the data access requests for the application corresponding to the associated client address space  202   a.  These data access requests are serialized with other data access requests from other applications serviced by the same file server  102  and other file servers  102  within the processing cluster  100 . 
     The illustrated file server address space  202   b  includes back end data  220 , generally, and specifically includes serialization data  222 . In further embodiments, the back end data  220  also may include completion rights  224 , which may indicate the processing status of a data access request and/or the stability of the connection/position data  212  stored in the client address space  202   a.    
     The additional address space(s)  202   n  may be used for similar programs and data as those stored in the client address space  202   a  and the file server address space  202   b.  The additional address space(s)  202   n  also may include a master address space, and so forth, as is currently known in the art. 
     The commonly addressable memory  204  is a portion of the memory  200  that may be used to store programs and data that are commonly accessible by one or more address spaces  202 . For instance, the commonly addressable memory  204  may be used to store data, such as file names, or metadata that is commonly referenced by both the connection/position data  212  in the client address space  202   a  and the serialization data  222  in the file server address space  202   b.    
       FIG. 3   a  depicts one embodiment of connection/position data  300  that is substantially similar to the connection/position data  212  described with reference to  FIG. 2 . The connection/position data  300  includes several fields that are each configured to store an identifier or other data to describe the connection and position information that is associated with a data access request corresponding to a particular application. The connection/position data  300  also may be referred to herein as connection/position information or connection/position records. 
     The illustrated connection/position data  300  includes an application identifier field  302 , a directory identifier field  304 , a file identifier field  306 , and a position identifier field  308 . In a further embodiment, the connection/position data  300  may include fewer or more data and/or metadata fields. In one embodiment, the application identifier field  302  stores an application identifier that identifies the application for which the client address space  202   a  exists. 
     The directory identifier field  304  stores a directory identifier that identifies a directory on the shared storage devices  104  that is being used for operations associated with the application identified by the application identifier. Similarly, the file identifier field  306  stores a file identifier that identifies a file that is being used for data access operations associated with the same application. In certain embodiments, the file identifier may relate to the directory identifier in that the file is a member of the directory. Given this relationship, the file identifier also may be referred to as a member identifier. The directory identifier and the file identifier may generally be referred to as resource identifiers. In alternate embodiments of the invention, other resource identifier fields and resource identifiers maybe present within the connection/position data  300 . 
     The position identifier field  308 , in one embodiment, stores a position identifier that identifies the position at which the file or storage resource is currently or most recently accessed. In one embodiment, the position identifier may comprise a byte offset that indicates the current read or write position by a number of bytes from the beginning of the file that is being accessed. 
       FIG. 3   b  depicts one embodiment of serialization data  320  that is substantially similar to the serialization data  222  described above with reference to  FIG. 2 . The serialization data  320  includes several fields that are each configured to store an identifier or other data to describe the serialization information that is associated with a data access request corresponding to a particular task. A task is one data access operation that is associated with a particular application. An application may generate one or many tasks. The serialization data  320  also may be referred to herein as serialization information or serialization records. 
     The illustrated serialization data  320  includes a task identifier field  322 , a resource identifier field  324 , and an exclusivity identifier field  326 . In a further embodiment, the serialization data  320  may include fewer or more data and/or metadata fields. In one embodiment, the task identifier field  322  stores a task identifier that identifies the task that is executed within the file server address space  202   b.    
     In one embodiment, the resource identifier field  324  stores a resource identifier that identifies either an input resource or an output resource associated the task identified by the task identifier. In one embodiment, the resource identifier may identify an input resource, such as a shared storage device  104 , from which data may be input into the task operation. For instance, the task operation may read data from a shared storage device  104 . In a further embodiment, the resource identifier may identify an output resource, such as a buffer, to which data may be sent according to the task operation. 
     The exclusivity identifier field  326  stores an exclusivity identifier that identifies the type of resource exclusivity provided for the identified task to the identifier resource. For example, the task may have either shared or exclusive read access to a target data set to be read from the shared storage devices  104 . In many instances, though not all, the exclusivity identifier provides shared access for data read (input) operations. In a further example, the task may have exclusive write access to a target buffer on which data may be written. In many instances, though not all, the exclusivity identifier provides exclusive access for data write (output) operations. 
       FIG. 4  depicts one embodiment of a serialization reinitialization apparatus  400  that may be used in conjunction with various embodiments of the present invention. The illustrated serialization reinitialization apparatus  400  includes a front end module  402  and a back end module  404 . In one embodiment, the front end module  402  and the back end module  404  are software programs that reside in the client address space  202   a  and file server address space  202   b,  respectively. 
     The serialization reinitialization apparatus  400  is configured to reinitialize the serialization data  222  of the file server  102  in response to a serialization error or failure. As described above, a serialization failure may occur when one or more applications cannot properly access stored data that is necessary for completion of an operation. For example, referring back to  FIG. 1 , a file server  102  may be waiting for a first application  12  having exclusive access rights to a data file  18  to conclude an operation before allowing a second application  14  to have access rights to the same data file  18 . 
     When serialization data  222  within a file server  102  or among a plurality of file servers  102  within a processing cluster  100  fails, the file server  102  or processing cluster  100  may become unavailable. For example, a file server  102  may become nonresponsive or “deadlocked” when two applications  12 ,  14  attempt to access data that is exclusively reserved for each other. By reinitializing the serialization data  222  of the file server  102 , the serialization reinitialization apparatus  400  discards the existing serialization information  222  and reconstructs new serialization information from the connection/position data  212 , thereby correcting any serialization failures. 
     Referring back to  FIG. 4 , the front end module  402 , in one embodiment, includes a connection module  410  and a suspension apparatus  412 . The connection module  410  is configured to monitor and record the connection/position data  212  for each task associated with an application. The suspension apparatus  412  is configured, in one embodiment, to suspend data access requests while the serialization data  222  for the file server  102  is being reinitialized. In one embodiment, the suspension apparatus  412  suspends the data access requests during a quiesce period prior to the serialization reinitialization, as well as during the serialization reinitialization. 
     The back end module  404 , as illustrated, includes a serialization module  420 , a quiesce module  422 , a discard module  424 , a failure recognition module  426 , a completion apparatus  428 , and a cluster apparatus  430 . The serialization module  420 , in one embodiment, is configured to manage the serialization data  222  for the file server  102 . Additionally, the serialization module  420  may rebuild the serialization data  222  from the connection/position data  212  in conjunction with a serialization reinitialization of the file server  102 . 
     The quiesce module  422  is configured, in one embodiment, to define and implement a quiesce period prior to a reinitialization of the serialization data  222  of the file server  102 . In certain embodiments, the quiesce period may be a few seconds. Alternately, the quiesce period may be longer or shorter than a few seconds. During the quiesce period, the back end module  404  may deny new data access requests from the front end module  402 . Additionally, the quiesce period may be used to allow ongoing tasks to complete prior to serialization reinitialization. Furthermore, ongoing tasks may be suspended or otherwise postponed during the quiesce period in order to maintain the integrity of the connection/position data  212  stored in the client address space  202   a.    
     The discard module  424 , in one embodiment, is configured to discard the existing serialization data  222  in conjunction with a serialization reinitialization of the file server  102 . In certain embodiments, for example, the discard module  424  may request that the operating system simply destroy all of the information, programs, and data stored in the file server address space  202   b,  or back end. In other words, the operating system may be invoked to delete the back end data  220 , including the existing serialization data  222  and the completion rights  224 . Furthermore, the operating system may entirely discard the back end module  404 , including the serialization module  420 , the quiesce module  422 , the discard module  424 , the failure recognition module  426 , the completion apparatus  428 , and the cluster apparatus  430 . Each of these back end modules, apparatuses, and data maybe rebuilt during the serialization reinitialization. 
     The failure recognition module  426  is configured, in one embodiment, to recognize a serialization failure within the file server  102 . In a further embodiment, the failure recognition module  426  may recognize a global serialization failure, for example in conjunction with the coupling facility  106 . In an alternate embodiment, a human operator may recognize a situation in which the file server  102  is nonresponsive and explicitly issue a command on a system console keyboard (not shown) to initiate the reinitialization process. In this case, the operator may use diagnostic aids to help make such a determination. 
     The completion apparatus  428  is configured, in one embodiment, to track the completion progress of a task. In one embodiment, the completion apparatus  428  may create and use the completions rights  224  within the back end data  220  to track the progress of a task. The cluster apparatus  430 , in one embodiment, is configured to manage communication and operations of the processing cluster  100  during serialization reinitialization of one of the plurality of file servers  102 . 
     The following schematic flow chart diagrams are generally set forth as logical flow chart diagrams. As such, the depicted order and labeled steps are indicative of one embodiment of the presented method. Other steps and methods may be conceived that are equivalent in function, logic, or effect to one or more steps, or portions thereof, of the illustrated method. Additionally, the format and symbology employed are provided to explain the logical steps of the method and are understood not to limit the scope of the method. Although various arrow types and line types may be employed in the flow chart diagrams, they are understood not to limit the scope of the corresponding method. Indeed, some arrows or other connectors may be used to indicate only the logical flow of the method. For instance, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of the depicted method. Additionally, the order in which a particular method occurs may or may not strictly adhere to the order of the corresponding steps shown. 
       FIG. 5  depicts one embodiment of a reinitialization method  500  that maybe performed in conjunction with the serialization reinitialization apparatus  400  described above. The illustrated reinitialization method  500  begins when the failure recognition module  426  recognizes  502  a serialization failure within the file server  102 . Although not described in detail herein, the failure recognition module  426  may, in some embodiments, discriminate between different types of serialization failures. Depending on the type of serialization failure detected  502 , the serialization reinitialization apparatus  400  may determine not to initiate a serialization reinitialization. However, in the described embodiment, the serialization reinitialization apparatus  400  does initiate a serialization reinitialization. 
     After a serialization failure is recognized  502 , the local serialization reinitialization apparatus  400  notifies  504  each of the remote file servers  102  within the processing cluster  100  that the local file server  102  will be reinitialized to correct the serialization failure. In one embodiment, the back end module  404  may include a notification module (not shown) configured to notify  504  the remote file servers  102  of the anticipated serialization reinitialization. In a further embodiment, the notification module may be included within the failure recognition module  426 , the cluster apparatus  430 , or another module or apparatus within the serialization reinitialization apparatus  400 . In certain embodiments, the notification module may communicate with the coupling facility  106  in order to properly notify  504  the remote file servers  102 . 
     Once all of the remote file servers  102  have been notified  504 , the quiesce module  422  initiates  506  a quiesce period prior to the subsequent reinitialization operations. As described above with reference to  FIG. 4 , new tasks and/or ongoing tasks may be denied or suspended during the quiesce period. One advantage of the quiesce period is to allow the connection/position data  212  to stabilize prior to reinitialization. Otherwise, if the connection/position data  212  are not stable when the serialization reinitialization occurs, the new serialization data  222  may be incorrect. Tasks that are not completed or stabilized during the quiesce period may be terminated, in certain embodiments. 
     Once the connection/position information  212  is stable and the quiesce period ends, the discard module  424  discards  508  the existing serialization data  222 . In one embodiment, the discard module  424  may discard  508  only the existing serialization data  222  and nothing more. In another embodiment, the discard module  424  may discard  508  the completion rights  224 , all or part of the back end module  404 , as well as the serialization data  222 . As described above, the discard module  424  may invoke an operating system function to entirely discard  508  the file server address space  202   b.    
     If the back end module  404  is discarded along with the serialization data, the front end module  402  subsequently may rebuild the back end module  404 , including the serialization module  420 . The serialization module  420  then rebuilds  510  the serialization data  222  from the connection/position data  212  that remains stable in the front end data  210  during the serialization reinitialization. The new serialization data  222  is expected to be free from serialization conflicts because it is rebuilt from the stable connection/position data  212 , rather than from the random arrival of data access requests. In this way, the new serialization data  212  is expected to be robust and not lead to a subsequent serialization failure. Rebuilding  510  the serialization data  222  is described in more detail below with reference to  FIG. 6 . 
     With the serialization data  212  rebuilt  510 , the file server  102  notifies  512  the remote file servers  102  within the processing cluster  100  that the serialization reinitialization is complete. In one embodiment, the notification module described above may perform this notification operation. The file server  102  may then resume processing data access requests using the new serialization data  222  to manage the serialized access to the shared data storage devices  104 . The depicted reinitialization method  500  then ends. 
       FIG. 6  depicts one embodiment of a rebuild method  600  that is given by way of example of the serialization rebuild operation  510  of the reinitialization method  500  shown in  FIG. 5 . The illustrated rebuild method  600  begins when a new file server address space  202   a  is created  602  in memory  200 . This, of course, assumes that the previous file server address space  202   b  was destroyed, as described above. The back end module  404  is then reloaded  604  into the newly created file server address space  202   b.  In other words, the serialization module  420 , quiesce module  422 , discard module  424 , and so forth, may be stored in the new file server address space  202   b.    
     The serialization module  420  is then invoked, in one embodiment, to generate the new serialization data  222 . In order to do this, the serialization module  420  may search the memory  200  for the client address spaces  202   a  containing connection/position data  212 . In particular, the serialization module  420  finds  606  each address space  202  and determines  608  if a particular address space  202  contains connection/position data  212 . 
     Once the serialization module  420  identifies a client address space  202   a,  which remains intact during the discard operations  508  described with reference to the reinitialization method  500 , the serialization module  420  may begin to rebuild the serialization data  222 . Specifically, the serialization module  420  may identify  610  connection data located in the application identifier field  302 , directory identifier field  304 , and file identifier field  306  (and other similar identifier fields, if applicable). The serialization module  420  also identifies  612  position data located in the position identifier field  308 . 
     The serialization module  420  then uses the identified connection/position information  212  to create  614  the new serialization data  222  in the new file server address space  202   b.  The serialization module  420  continues to read the connection/position data  212  from the client address spaces  202   a  and write the new serialization data  222  to the file server address space  202   b  until the serialization module  420  determines  616  that there is no more connection/position data  212  to be processed. In one embodiment, the serialization module  420  determines  616  that all of the client address spaces  202   a  have been searched. The depicted rebuild method  600  then ends. 
     In certain embodiments, the total time required to quiesce  506  the file server  102 , discard  508  the existing serialization data  222 , and rebuild  510  the new serialization data  222  may be tens of seconds. Advantageously reinitializing the serialization data  222  in this manner does not require the file server  102  to be powered down. Furthermore, the depicted reinitialization method  500  beneficially does not significantly interrupt in-flight application processing, although a data access request possibly may be suspended for a few or more seconds. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.