Abstract:
A method and system for automating the creation of a managed data storage system. Specifically the present invention describes an automated method for building, evaluating and repairing a managed set of disk storage devices utilizing a rule based expert system operating on a host computer. The system allocates available disks and controllers according to a predetermined size requirement and a set of rules. The set of rules designates a layout that provides optimum performance. The system also evaluates the layout by utilizing a set of rules to test reliability and comparative analysis to test performance. The system performs self-repairs in the event of a component failure and generates a notification of the failure and an analysis of the degradation of the system resulting from the failure so replacement components might be obtained.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention relate to the field of data storage systems. More particularly, embodiments of the present invention relate generally to the automatic allocation of disks in a data storage system to provide redundant, efficient and reliable storage. 
     2. Related Art 
     Secondary data storage is an integral part of large data processing systems. A typical data storage system in the past utilized a single, expensive magnetic disk for storing large amounts of data. This single disk in general is accessed by the Central Processing Unit (CPU) through a separate Direct Memory Access (DMA) controller. The DMA controller then translates and executes the Input/Output (I/O) requests of the CPU. For single disk memory storage systems, the speed of data transfer to and from the single, large disk is much slower than the processing speed of the CPU and acts as a data processing bottleneck. 
     In response, redundant arrays of independent disks (RAIDs) have evolved from the single disk storage systems in order to match the speed of secondary storage access with the increasingly faster processing speeds of the CPU. To increase system throughput, the RAID architecture of secondary storage allows for the concurrent access of data from multiple disk drives. 
     The concept for the RAID architecture was first formalized in an article written by some members of the Department of Electrical Engineering and Computer Sciences at the University of California at Berkeley, entitled: “A Case for Redundant Arrays of Inexpensive Disks (RAID),” by D. A. Patterson, G. Gibson, and R. H. Katz, ACM SIGMOD Conference, Chicago, Ill., June 1988, hereinafter referred to as “Patterson et al.” 
     Typically, RAID architectures consist of one or more host interface controllers connected to several peripheral interface controllers via a high-speed data bus. Each peripheral interface controller is, in turn, connected to several individual disk drives, which provide the secondary storage for the connected hosts. Peripheral interface controllers, also referred to as array controllers herein, can be connected to the disk drives via common communication interfaces (e.g., SCSI). Generally, the speed of the data bus is greater than the speed of the interface between the disk drives and the peripheral interface controllers. 
     Some RAID storage systems contain spare disk drives. Storage units with additional spare disks are designed to operate continuously over a specified period of time, without requiring any repair of the unit due to failed disks. This is accomplished by carefully identifying and quantifying the components that are expected to fail during a given time period, and incorporating within the system sufficient hot-spare parts or disks. This internal spare disk architecture can automatically switch to the spare disks when a failure is encountered. Spares are incorporated so that compatible disk devices are always at hand upon a disk failure. 
     Prior Art  FIG. 1  depicts a common implementation of a data storage system  100  containing spare disks. The data storage system is arranged in a mirrored configuration  105   a  &amp;  b – 125   a  &amp;  b  with three spares  130 ,  132  &amp;  135 . In the data storage system  100 , a data volume is divided into segments called stripe units. Stripe units are mapped consecutively on a set of physical devices for parallel access purposes. 
     For example, data storage system  100  contains thirteen disks. Ten of the disks (e.g., disks  105   a  &amp;  b ,  110   a  &amp;  b ,  115   a  &amp;  b ,  120   a  &amp;  b , and  125   a  &amp;  b ) contain data and their redundancies. The remaining three disks (e.g., disks  130 ,  132  and  135 ) are spare disks. 
     Further, system  100  stripes its data across groups of data strips. In the redundancy group of stripe  150   a , disk  105   a  contains strip  101   a , disk  110   a  contains strip  102   a , disk  115   a  contains strip  103   a , disk  120   a  contains strip  104   a  and disk  125   a  contains strip  107   a . Mirrored stripe  150   b  contains mirrored strips, e.g. strip  107   b  that mirrors  107   a.    
     A disadvantage of the redundant disk storage array is that it is configured by a system administrator who has the daunting task of building the system. This requires knowing every component in the system and creating the system so that it performs well, is reliable and never loses data. If a component fails and must be replaced, it becomes necessary to reconfigure the system, requiring numerous manipulations in order to have the system working again. 
     In order to build the system, the System Administrator needs to issue many commands, interfacing through a plethora of graphical user interface (GUI) panels to define the disks to be used and to assure that the controllers are different for mirrored disks. He has to define the areas on the disks that will be strung together to define the stripes, and keep track of the configuration. Within the configuration, disks can be mirrored, or spare portions can be spread over a group of disks, or both. If spread out over the array of disks, there are many RAID configurations, depending on how many disks in a group and the amount of redundant storage allocated. All these different configurations require complex and technical settings and parameters to be formulated by the system administrator and programmed into the system using, often times, cumbersome programming tools. All this needs to be done so as to be able to write a maximum amount of data in a minimum amount of time, efficiently and with reliability that if any piece fails, data will not be lost. 
     The system administrator also has to create hot spare pools in order to have sufficient spare components available to replace failed components. He has to track failures and project future failures in order to keep the spare pools sufficiently populated. 
     SUMMARY OF THE INVENTION 
     Accordingly, a need exists for a method and system for reducing the burden on the System Administrator by automating the process of disk allocation and management in a data storage system. 
     Specifically, one embodiment of the present invention provides an automated method and system for disk allocation in a data storage system. The method encompasses automatically creating a managed data storage system from available disk drives and controllers, evaluating the managed data storage system, reporting results of the evaluation, and repairing detected failures as needed. 
     The automated creation of a managed data storage system as described above may be responsive to a function call defining a list of available of disk drives and a requested storage size. The automated method as described may also be in response to a function call defining requested storage size, wherein the available disk drives and controllers would then be assessed. 
     The method for creating and evaluating the managed data storage system may employ a Rule-Based Expert System. The method employs a builder to create a managed data storage system containing a set of disks and controllers configured as mirrored stripes with each side of a mirrored set of disks coupled to a different controller. The mirrored stripes are populated by as many disks as are available. Basically, the builder takes a collection of components and makes a composite device therefrom. 
     The method for evaluating the managed data storage system includes using an evaluator to fail single components in succession and assessing results. The evaluator can be operated on a system constructed using the builder. The automated method further includes failing components in pairs and assessing results. The automated method for repairing detected failures encompasses replacing a failed component with an allocated spare component, generating a notification of replacement and an inventory of remaining replacement components. This can be performed using an immune system. 
     More specifically, an embodiment of the present invention includes a system that contains a builder for automatically configuring a redundant array of storage resources into a storage system, using an available set of resources. The configuration is based on a user parameter set and based on a set of rules. The system also contains an evaluator for automatically evaluating a configuration of the storage system as generated by the builder. The evaluator simulates a response of the configuration to a plurality of failures and generates a report based thereon. Also contained in the system is a fault reaction system for allowing a user to define a prescribed action to take place upon a failure in the storage system. 
     Further embodiments include the above and wherein the storage resources comprise a plurality of disk drives and a plurality of controllers and wherein the set of rules of the builder comprise: placing different sides of a mirror pair on different controllers of the configuration; maximizing the use of available controllers in the configuration; maximizing the number of available disks used in a stripe; using an optimum number of spare disks based on a total number of disks of the configuration as determined by a mean time of failure; and based on a required storage parameter, determining the total number of disks required for the configuration. 
     Further embodiments include the above and wherein the plurality of failures of the evaluator comprise: failing every component individually of the configuration; failing every pair of components individually of the configuration; and failing a controller of the configuration. 
     These and other advantages of the present invention will become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments that are illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention: 
       PRIOR ART  FIG. 1  is a block diagram of a data storage system in a redundant array of independent disks (RAID) in a striped mirror arrangement. 
         FIG. 2  is a logical block diagram of an exemplary host computer upon which an embodiment of the present invention may be practiced. 
         FIG. 3A  is a block diagram illustrating exemplary architecture of a redundant disk storage allocator in accordance with an embodiment of the present invention. 
         FIG. 3B  is a data flow diagram illustrating a system for automatically configuring a redundant array of storage resources into a storage system, evaluating the storage system and prescribing action(s) to be taken in response to failure(s) in accordance with an embodiment of the present invention. 
         FIG. 4  is a flow diagram of a computer-implemented process for managing a data storage system in accordance with an embodiment of the present invention. 
         FIG. 5  is a flow diagram of steps for automating the building of a managed set of disks in accordance with an embodiment of the present invention. 
         FIG. 6  is a flow diagram of steps for automating the evaluating of a managed set disks according to one embodiment of the present invention. 
         FIG. 7  is a flow diagram of a computer-implemented method for repairing a managed set of disks according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present invention. 
     Notation and Nomenclature 
     Some portions of the detailed descriptions that follow are presented in terms of procedures, logic blocks, processing, and other symbolic representations of operations on data bits within a computer memory. These descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. In the present application, a procedure, logic block, process, or the like, is conceived to be a self-consistent sequence of steps or instructions leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, although not necessarily, these quantities take the form of electrical or magnetic information capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system. It has proven convenient at times, principally for reasons of common usage, to refer to these information as transactions, bits, values, elements, symbols, characters, fragments, pixels, or the like. 
     It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the present invention, discussions utilizing terms such as “building,” “creating,” “transmitting,” “receiving,” “evaluating,” “repairing,” “reporting,” “partitioning,” “generating,” or the like, refer to actions and processes of a computer system or similar electronic computing device. The computer system or similar electronic computing device manipulates and transforms data represented as physical (electronic) quantities within the computer system memories, registers or other such information storage, transmission or display devices. 
     Referring to  FIG. 2 , embodiments of the present invention are comprised of computer-readable and computer-executable instructions that reside, for example, in computer-readable media of an electronic system, such as an a host computer system.  FIG. 2  is a block diagram of exemplary embedded components of a host computer system  210  upon which embodiments of the present invention may be implemented. Exemplary host computer system  210  includes an internal address/data bus  220  for communicating information, a central processor  201  coupled with the bus  220  for processing information and instructions, a volatile memory  202  (e.g., random access memory (RAM), static RAM dynamic RAM, etc.) coupled with the bus  220  for storing information and instructions for the central processor  201 , such as instructions for disk storage allocator  212 , and a non-volatile memory  203  (e.g., read only memory (ROM), programmable ROM, flash memory, EPROM, EEPROM, etc.) coupled to the bus  220  for storing static information and instructions for the processor  201 . 
     With reference still to  FIG. 2 , an optional signal Input/Output (I/O) device  208  is shown. The I/O device  208  is coupled to bus  220  for providing a communication link between host computer system  210  and an array network of data storage devices, such as disks. As such, signal I/O device  208  enables the central processor unit  201  to communicate with or monitor other electronic systems blocks that are coupled to the host computer system  210 . In one embodiment of the present invention, the input and output device  208  is a serial communication port, but could also be any number of well known communication standards and protocols, e.g., Universal Serial Bus (USB), Ethernet, FireWire (IEEE 1394), parallel, small computer system interface (SCSI), infrared (IR) communication, Bluetooth wireless communication, etc. Instructions and data from the host computer system  210  travel through the port and onto an external bus  230  that provides for data transfer between components of the data storage system  200 , including between redundant disk storage allocator  205 , processor  201  and an array of disk drives  215 . 
     Optionally, computer system  200  can include a display device  205  that is coupled to bus  220  for displaying graphics and/or video. Furthermore, system  200  can include an optional alphanumeric input device  206  including alphanumeric and function keys coupled to the bus  220  for communicating information and command selections to the central processor  201 . Additionally, the computing device  200  of  FIG. 2  can include an optional cursor control device  207  coupled to the bus  220  for communicating user information and command selections to the central processor  201 . 
       FIG. 3A  is a block diagram illustrating an exemplary architecture  300   a  of a redundant disk storage allocator in accordance with an embodiment of the present invention. Redundant disk storage allocator  212 , resident on host computer system  210 , interfaces with the array of data disks  215  via data bus  230  and a signal I/O device (e.g., signal I/O communication device  208  of  FIG. 2 ), according to one embodiment of the present invention. Allocator  212  comprises three major modules, according to one embodiment. These modules are builder module  320 , repairer module  330  and evaluator module  340 . These modules are discussed below, according to one embodiment, in conjunction with  FIGS. 3B ,  4 ,  5 ,  6  &amp;  7 . 
       FIGS. 3B ,  4 ,  5 ,  6  &amp;  7  below are flow diagrams of computer-implemented processes for creating, evaluating, and repairing a managed data storage system in accordance with embodiments of the present invention. These flow diagrams  300   b ,  400 ,  500 ,  600  and  700  include processes of the present invention which, in various embodiments, are carried out by a processor and electrical components under the control of computer readable and computer executable instructions. The computer readable and computer executable instructions may reside, for example, in data storage features such as volatile memory  202  and/or non-volatile memory  202  or  203  of  FIG. 2 . However, the computer readable and computer executable instructions may reside in any type of readable storage medium. Although specific steps are disclosed in flow diagrams  300   b – 700 , such steps are exemplary. That is, the present invention is well suited to performing various other steps or variations of the steps recited in  FIGS. 3B ,  4 ,  5 ,  6  &amp;  7 . Within the present embodiment, it should be appreciated that the steps of flow diagrams  300   b – 700  may be performed by software, by hardware or by any combination of software and hardware. 
       FIG. 3B  is a data flow diagram  300   b  illustrating a system for automatically configuring a redundant array of storage resources into a storage system, evaluating the storage system and prescribing action(s) to be taken in response to failure(s) in accordance with an embodiment of the present invention. User Interface Parameter Input  310  inputs parameters to a System Builder  320 . These parameters define a data Storage System  215  to be built and may include a name of the set of disks to be built or modified or may include a list of available disks from which to build or modify the storage system. According to one embodiment the input parameters might contain the name of a device to be built and a size in bytes to be made available. There are a wide variety of input parameters that may be used, in addition to those aforementioned, to specify the storage system to be built. 
     System Builder  320 , a Rule Based Expert System (RBES) software module, assesses Available Resources  315  and, using input parameters from User Interface Parameter Input  310  and a set of rules, generates a System Configuration  325 . The Available Resources  315  may include a number and, possibly a variety, of disk drives and controllers. The rules used by the RBES may include such possibilities as; placing different sides of a mirror pair on different controllers of System Configuration  325 , maximizing the use of available controllers in System Configuration  325 , maximizing the number of available disks used in a stripe, using an optimum number of spare disks based on a total number of disks of System Configuration  325  as determined by a mean time between failures and, based on a required storage parameter, determining the total number of disks required for System Configuration  325 . These rules are exemplary and should not be construed as limiting. 
     Once System Configuration  325  is defined, an evaluation is performed by an Evaluator/Failure Simulator  340 . Evaluator  340  may be a software module or a set of software modules employing, according to one embodiment, a RBES. Evaluator  340  simulates failures according to the RBES rules such as, for example; failing every component of System Configuration  325  individually, failing every pair of components individually, and/or failing a controller of System Configuration  325 . Such rules are exemplary and should not be construed as limiting. There are a variety of rules that may be employed for evaluating a system configuration. Evaluator  340  simulates a response to the simulated failures and generates a Report  350 . Report  350  may contain assorted relevant information, including, according to one embodiment, an indication as to whether or not data would be lost in response to any failure or combination of failures. 
     A User, such as a System Administrator charged with the task of building a data storage system, decides, according to one embodiment, based on the report from step  350 , whether System Configuration  325  is adequate. If so, in accordance with one embodiment, he requests via User Interface  310  that Builder  320  build Storage System  215  as configured. In accordance with one embodiment, if System Configuration  325  is not adequate, input parameters are modified and a new System Configuration  325  is generated and so forth until a satisfactory configuration is defined at which time Builder  320  is requested to build Storage System  215 . 
     Once Storage System  215  is built, Immune/Fault Reaction System  330  (e.g., Repairer  330  of  FIG. 3A ) monitors Storage System  215  and, if a failure is detected, responds according to user-prescribed actions. Such user-prescribed actions may, according to one embodiment, include automatically replacing a failed disk with a hot spare. User prescribed actions may, in accordance with an embodiment, include notifying a System Administrator of a failure, via a predefined mode, so that the System Administrator might take action. 
       FIG. 4  is a flow diagram  400  of a computer-implemented process for managing a data storage system in accordance with an embodiment of the present invention. The data storage system is made up of a collection of disks managed by a Solaris™ Volume Manager (SVM) as provided by Sun Microsystems, and the storage system&#39;s base configuration is designed to correspond to the heap portion of random access memory. In step  410 , according to one embodiment, the process begins when a System Administrator or a qualified user uses a user interface to input a command or commands defining a data storage system to be built or modified. The command might contain, according to one embodiment, the name of the set of disks to be built or modified and a list of the disks from which to build or modify the set. According to one embodiment, the command might contain the name of the device to be built and a size in bytes, and the builder (e.g., builder  320  of  FIG. 3 ) portion of the allocator (e.g., allocator  212  of  FIG. 3 ) assesses the available hardware for building the device. The builder  320  then, as illustrated in step  420 , builds or modifies the system using a rule-based expert system based on the input values received and a set of rules. The process may then move to the evaluation phase if indicated, as shown by step  430 , or the process might end with the built system, provided no failures have occurred. If an evaluation is not indicated, the process proceeds to step  460  and checks for failures. 
     At step  440  of  FIG. 4 , according to one embodiment of the present invention, the evaluator (e.g., evaluator  340  of  FIG. 3 ) portion of allocator  212  evaluates the system&#39;s reliability. The evaluation occurs in response to a command, based on applying a set of rules. The set of structured rules, generally, calls for failing components of the data storage system, both singly and in pairs, and assessing the results. The evaluator may also be employed, according to one embodiment, independent of the builder and repairer. That is, evaluator  340  may be employed to evaluate an existing data storage system. The evaluation is performed, according to one embodiment, utilizing a rule-based expert system. Following the evaluation, the evaluator may issue a report containing the results of the evaluation. 
     According to one embodiment, if the evaluation results indicate a need for improvement, as shown in step  450 , the process moves to step  410  so that the System Administrator may modify the input requirements accordingly and call on builder  320  to modify the data storage system. If no improvement is needed, the allocator monitors the data storage system for failures, as illustrated by step  460 . If no failures are detected, the allocator continues to monitor the system. 
     At step  470  of  FIG. 4 , according to one embodiment, allocator  212  detects a failure of one or more components in the system and calls on the repairer (e.g., repairer  330  of  FIG. 3 ). Repairer  330  may, in one embodiment, incorporate a method such as described in the following co-pending U.S. patent application assigned to the present assignee, Ser. No. 09/955,527, entitled “METHOD AND SYSTEM FOR LEVERAGING SPARES IN A DATA STORAGE SYSTEM INCLUDING A PLURALITY OF DISK DRIVES,” by Ebrahim Hashemi, the disclosure of which is hereby incorporated by reference. Repairer  330  repairs the system by substituting a spare component for the failed component and sends notification to one or more designated devices, as illustrated by step  470 . The notification might be, according to various embodiments, a log generated at a system log printer, an e-mail message to a System Administrator&#39;s personal computer or PDA, a call to a System Administrator&#39;s phone, a message to a pager, an icon on a system manager console that becomes a display that highlights the failure. The notification might also be a combination of any of the foregoing or of any other message medium that would serve to notify a System Administrator that the reliability of the system is becoming degraded so that replacement spares might be added back to the system to restore its original degree of reliability. 
       FIG. 5  is a flow diagram  500  of steps for automating the building or modification of a managed set of disks in accordance with an embodiment of the present invention. In step  510 , the allocator receives a function call requesting that it build or modify a managed set of disks based on input values. The input values may include, but are not limited to, those described in the following paragraphs and associated tables. 
     Table 1 below illustrates one example of pseudo code that may be used in a Solaris™ operating environment as provided by Sun Microsystems for creating a managed set of disks named set_name that manages the set of disks listed in disk_list, or adds the set of disks listed in disk_list to the set of disks already managed in the set named set_name. 
     
       
         
               
               
             
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                 int result svm_manage_disks(char *set_name, char 
               
             
          
           
               
                   
                 *disk_list[ ]); 
               
               
                   
                   
               
             
          
         
       
     
     Table 2 below illustrates one example of pseudo code that may be used in a Solaris™ operating environment as provided by Sun Microsystems for allocating a size, in bytes, from the managed set named set_name and returning a reference to the device to which the space was allocated in ★device_name. 
     
       
         
               
               
             
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
             
               
                   
                 Int result svm_alloc(char *set_name uint64_t 
               
             
          
           
               
                   
                 size_in_bytes,char **device_namep); 
               
               
                   
                   
               
             
          
         
       
     
     Table 3 below illustrates one example of pseudo code that may be used in a Solaris™ operating environment as provided by Sun Microsystems for changing the amount of space allocated to device_name in set_name to size_in_bytes. 
     
       
         
               
               
             
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
             
             
               
                   
                 int result svm_realloc(char *set_name, char 
               
             
          
           
               
                   
                 *device_name, uint64_t size_in_bytes; 
               
               
                   
                   
               
             
          
         
       
     
     Table 4 below illustrates one example of pseudo code that may be used in a Solaris™ operating environment as provided by Sun Microsystems for freeing the amount of space allocated to device_name in set_name. 
     
       
         
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
             
             
               
                   
                 int result svm_free(char *set_name, char *device_name) ; 
               
               
                   
                   
               
             
          
         
       
     
     According to one embodiment, the builder (e.g., builder  320  of  FIG. 3 ) portion of the allocator (e.g., allocator  212  of  FIG. 3 ) assesses available hardware as illustrated in step  520  of  FIG. 5  for building the managed set of disks. An ideal collection of hardware contains disks of identical type and size, but collections of disks of varying sizes may be used. Builder  320  uses the Solaris™ format utility to divide each disk that it manages into partitions. If a collection contains disks of varying sizes, builder  320  makes all partitions the same size even though doing so may not fully utilize the available space on the larger disks. This arrangement enables any disk to replace any other disk in the configuration should the other disk fail. 
     Some of the disks in the collection are used as hot spares. In one embodiment the allocator may use partitions of disk space as hot spares. The software automatically replaces failed disks with hot spare disks. As illustrated in step  530 , Builder  320  calculates the number of hot spare disks needed to ensure that a hot spare disk is available whenever a disk used to store data fails. In one embodiment, it bases its calculation on the percent availability it determines is feasible (using “mean time between failures” data) for the set of disks it is building. An odd number of disks is always reserved as hot spares, leaving an even number of disks for data storage. 
     Step  540  illustrates the creating of mirrored stripes according to one embodiment of the present invention. Following a set of provided rules, the builder combines the data storage slices into a single striped and mirrored volume. The slices are arranged in the volume to provide the maximum redundancy possible in the collection of disks that allocator  212  is managing. This may be accomplished, as illustrated by step  550 , by making the stripes and mirrors as populated with disks as possible. This may follow a rule for using all the available disks. The striped mirror configuration is believed to provide the best performance and reliability for separate disk drives. 
     At step  560 , according to one embodiment, another rule may be followed which is to use all available controllers. This would also add to the reliability of the storage system device being built. Step  570  illustrates another rule that may be followed, which is to assign different sides of a mirror to different controllers. This assures redundancy in the case a controller should fail. 
     Steps  510  through  570  have provided an example of the steps that may be taken and rules that may be imposed in a rule-based expert system for building a single volume managed disk storage system according to one embodiment of the present invention. It should be understood that although specific steps are disclosed in flow diagram  500 , such steps are exemplary. That is, the present invention is well suited to performing various other steps or variations of the steps recited in  FIG. 5 . 
       FIG. 6  is a flow diagram  600  of steps for automating the evaluating of a managed set disks according to one embodiment of the present invention. This step may be performed by an evaluator (e.g., evaluator  340  of  FIG. 3 ) portion of allocator  212 . The evaluator would respond to a function call, as illustrated by step  610  of  FIG. 6 , requesting the evaluation of a set or volume of managed disk storage. The managed disk storage to be evaluated may be a newly built set, a newly modified set or an existing set for which an evaluation is desired. The evaluation may, according to one embodiment of the present invention, be based on a rule-based expert system. 
     Step  620  illustrates one rule that evaluator  340  may follow in evaluating a managed disk storage system, according to one embodiment. In this step, evaluator  340  systematically fails every component of the system, singly, and obtains information on performance and reliability (e.g., has data been lost?). 
     Step  630  illustrates a subsequent rule that evaluator  340  may follow in the evaluation process. In step  630  the evaluator systematically fails components in predetermined pairs and obtains information on performance and reliability. 
     At step  640  the evaluator generates a report containing the information obtained in steps  620  and  630  of the evaluation process. It should be understood that although specific steps are disclosed in flow diagram  600 , such steps are exemplary. That is, the present invention is well suited to performing various other steps or variations of the steps recited in  FIG. 6 . 
       FIG. 7  is a flow diagram  700  of a computer-implemented method for repairing a managed set of disks according to one embodiment of the present invention. The system repairer (e.g., repairer  330  of  FIG. 3 ) portion of allocator  212  monitors the managed set of disks according to one embodiment of the present invention. Step  710  of  FIG. 7  illustrates repairer  330  detecting a failure in the managed set of disks. According to one embodiment, as shown in step  720 , repairer  330  checks to see if the failure has occurred in a controller. If so, the repairer sends notification to the System Administrator&#39;s console and/or to a designated device such as a pager, a cell phone or a personal computer, advising of the failure and the need to replace the controller. In one embodiment, the system may be configured to have spare controllers and to automatically repair the system by substituting a spare controller for the one that has failed. The process then proceeds to step  760 , according to one embodiment, and generates a log entry for the failure. 
     In step  740 , if the failure was not determined to be a controller, it may be assumed to be a disk failure, according to one embodiment. The system may automatically replace a failed disk with one of the hot spare disks, employing a method such as described in co-pending U.S. patent application assigned to the present assignee, Ser. No. 09/955,527, entitled “METHOD AND SYSTEM FOR LEVERAGING SPARES IN A DATA STORAGE SYSTEM INCLUDING A PLURALITY OF DISK DRIVES,” by Ebrahim Hashemi, as disclosed above. 
     Having replaced a disk, according to one embodiment, the system repairer  330  notifies the System Administrator of the action taken as illustrated in step  750  of  FIG. 7 . The notification may include guidance for restoring the system to its original degree of reliability. This guidance may include instructions for replacing a particular spare disk or disks. 
     The repairer then may proceed to step  760  of  FIG. 7  and generate a log entry for the failure that occurred, thus ending the response to the failure. The process then returns to a monitoring mode and flow diagram  700  is exited. 
     The foregoing descriptions of specific embodiments have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.