Abstract:
Secondary or augmented control of a storage array in a cost effective manner is accomplished by connecting a host to the storage array via a storage adapter independent of a RAID controller. The RAID controller provides primary control for services standard to the RAID controller. Augmented or enhanced services as well as backup control are provided by a control module executing on the host, communicating to one or more selected storage devices within the storage array via the storage adapter. In one embodiment, the control module detects faults or failures in the RAID controller, selectably directs storage commands to the RAID controller, emulates a storage controller including a RAID controller, and provides enhanced or augmented services such as conducting diagnostic, firmware update, or disaster recovery operations.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. The Field of the Invention  
           [0002]    The invention relates to apparatuses, methods, and systems for controlling arrays of storage devices. Specifically, the invention relates to apparatus, methods, and systems for redundantly controlling a storage array.  
           [0003]    2. The Relevant Art  
           [0004]    RAID systems (i.e., systems using Redundant Arrays of Independent Disks) are used to store large quantities of data within computer and storage networks. RAID systems are designed to be fault resistant and fault tolerant by distributing data among redundant arrays of independent disks usually with some form of error coding. Storage device redundancy and redundant data encoding facilitate continued operation and/or data recovery in the event of a failure within a particular storage device.  
           [0005]    In addition to redundant storage devices, RAID systems often deploy redundant controllers to facilitate continued operation after a particular controller becomes inoperable. In addition to handling failures and controller redundancy properly, RAID controllers are typically required to receive write requests and associated data from a host computer, acknowledge reception of the data, stripe the data over a plurality of drives, and send the data to a storage array at a high throughput rate. As a result, RAID controllers are highly specialized and complex devices.  
           [0006]    The specialized nature of RAID controllers, particularly redundant RAID controllers presents several challenges. In many redundant configurations, a secondary RAID controller waits in a standby or load sharing mode, ready to receive commands from the host computer in case a primary RAID controller is busy or fails. In some configurations, the secondary RAID controller performs no other function than waiting to take control in case of failure. The secondary RAID controller, although useful, adds significant cost to the RAID system.  
           [0007]    RAID controllers are typically quite reliable in that they are typically solid state solutions with highly reliable components. In an attempt to reduce system cost, some administrators may forego using a redundant controller. Foregoing a controller is a risky proposition in that losses from downtime frequently exceed the cost of an entire system. Nevertheless, a demand for single controller solutions currently exists within data processing systems.  
           [0008]    Furthermore, as specialized devices with specialized hardware to increase throughput, RAID controllers tend to fall out of date quickly—particularly as a system is updated and upgraded. Updating redundant RAID controllers requires purchasing the controllers in pairs. The added cost of the secondary RAID controller may hinder RAID system users from purchasing new controllers that could add significant functionality to their RAID systems. In addition, prolonging upgrades of old RAID controllers may place the controllers at additional risk for obsolescence or failure.  
           [0009]    Another disadvantage of currently available storage control solutions is that, as solid state devices, RAID controllers are often fixed in their feature set at the time of manufacture and typically provide no facility for enhanced or augmented services such as advanced data recovery services, diagnostic services, firmware update services, and the like.  
           [0010]    Given the disadvantages of currently available storage control solutions, what is needed is a cost-effective apparatus, method, and system for redundant control of a RAID system without using a dedicated secondary controller. Such an apparatus and method would reduce the cost of providing, upgrading, and augmenting RAID functionality within storage systems.  
         SUMMARY OF THE INVENTION  
         [0011]    The various elements of the present invention have 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 redundantly controlled storage systems. Accordingly, the present invention provides an improved apparatus, method, and system for storage control of storage devices.  
           [0012]    The present invention eliminates the need for a dedicated secondary controller by using a host-based adapter and associated control and emulation software executing on a host. In the context of the present specification, the term “dedicated controller” refers to a storage controller, particularly a RAID controller, with dedicated resources such as a CPU, logic unit, or the like. In particular, the present invention uses the shared resources of the host to reduce the cost and complexity of provided redundant control of a storage array or the like, while offering the additional advantage of augmented or enhanced services typically not found on currently available controllers.  
           [0013]    In a first aspect of the present invention, an apparatus for storage control of a storage array includes a RAID controller operably connected to a storage array, a storage adapter residing on a host computer that is also operably connected to the storage array independent of the RAID controller, and a control module residing on the host computer. Due to the unique configuration of the present invention, the storage adapter is able to transmit storage commands to a selected storage device within the storage array.  
           [0014]    In one embodiment, the control module selectively directs storage commands to the RAID controller and the storage adapter. During normal operation, the control module may direct commands supported by the RAID controller to the RAID controller and direct commands related to augmented or enhanced services to the storage adapter. In response to an inoperable RAID controller, the control module may also emulate the RAID controller and conduct operations corresponding to storage commands on one or more selected storage devices within the storage array.  
           [0015]    As described in the present invention the storage adapter is an electrical interface between the control module and the storage devices. Possible implementations of the storage adapter include a SCSI adapter, an SSA adapter, a fiberchannel adapter, an IDE adapter, or the like. Using a standard storage adapter such as the aforementioned adapters often facilitates using the present invention without purchasing additional hardware.  
           [0016]    A controller storage adapter may also provide an interface between the control module and the RAID controller. However, in certain embodiments, the RAID controller does not interface with a storage adapter, but rather resides on the host computer. By including the RAID controller on the host computer, the present invention may provide improved performance in a more cost-effective manner than previous solutions.  
           [0017]    There are many possible different implementations for the RAID controller. Some implementations include a SCSI RAID controller, an SSA RAID controller, a fiberchannel RAID controller, an IDE RAID controller, or the like. Those skilled in the art may also derive other implementations for the RAID controller.  
           [0018]    In certain embodiments, the control module selectively emulates a RAID controller. By emulating a RAID controller, the control module may conduct RAID operations as well as non-RAID operations on the storage devices via the storage adapter. In one embodiment, the supported operations include read operations, write operations, recovery operations, diagnostic operations, formatting operations, and firmware update operations. In one embodiment, the control module is a device driver that translates operating system calls to storage device commands.  
           [0019]    In one embodiment, the control module also includes a multipath software layer that selects a control path through either the RAID controller or the storage adapter. The multipath software layer may also select multiple control paths in parallel to allow the control module to perform augmented services on the storage devices while the RAID controller is performing standard services on the storage devices. Thus, the present invention provides cost-effective enhanced functionality to the RAID system.  
           [0020]    In another aspect of the present invention, a method for controlling a storage array includes transmitting storage commands to a RAID controller that conducts operations on a storage array, transmitting storage commands via a storage adapter to a selected storage device of the storage array, and selectively directing storage commands to the RAID controller and the storage adapter.  
           [0021]    In one embodiment, the method further includes emulating a RAID controller. By emulating the RAID controller, the method may provide alternate control of the storage array to a host computer or the like. In addition, enhanced or augmented services as well as backup or secondary control of the storage devices may be provided by the aforementioned method.  
           [0022]    Various elements of the present invention are combined into a storage system of the present invention including a host computer, a storage array, a RAID controller operably connected to the storage array, a storage adapter operably connected to the storage array independent of a storage controller, and a control module residing on the host computer.  
           [0023]    The control module of the present invention selectively directs storage commands to the RAID controller and the storage adapter. In response to receiving storage commands from the control module, the RAID controller executes corresponding operations on the storage array. Additionally, the control module may transmit storage commands from the control module to a selected storage device within the storage array via the storage adapter.  
           [0024]    In another aspect of the present invention, a method for servicing a storage array includes operably connecting a storage array to a storage adapter independent of a RAID controller and installing a control module on the host computer. The method for servicing a storage array enables a technician or the like to provide diagnostic operations, data recovery, firmware updates and other services related to storage arrays.  
           [0025]    The method for servicing a storage array may also include operably connecting a storage adapter to a storage array, and transmitting storage commands to one or more selected storage devices within the storage array. The method may also include disabling or quiescing the RAID controller and transferring control of the storage array to the storage adapter. Transferring control to the storage adapter allows the method to use an alternate control path to communicate with the storage devices. In communicating with the storage devices, the method may update firmware within a storage device, conduct diagnostic operations, conduct recovery operations or the like.  
           [0026]    The various elements and aspects of the present invention provide a cost-effective alternative to a dedicated redundant RAID controller. Additionally, the present invention provides augmented services and features not found in currently available RAID storage systems. These and other 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  
       [0027]    In order that the manner in which the advantages and objects of the invention are obtained will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof, which 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:  
         [0028]    [0028]FIG. 1 is a schematic block diagram illustrating a typical prior art storage system;  
         [0029]    [0029]FIG. 2 is a schematic block diagram illustrating one embodiment of an alternate control storage system of the present invention;  
         [0030]    [0030]FIG. 3 is a schematic block diagram illustrating an additional embodiment of the alternate control storage system of the present invention;  
         [0031]    [0031]FIG. 4 is a schematic block diagram illustrating one embodiment of a storage control apparatus of the present invention;  
         [0032]    [0032]FIG. 5 is a flow chart diagram illustrating one embodiment of a storage control method of the present invention;  
         [0033]    [0033]FIG. 6 is a flow chart diagram illustrating a storage system service method of the present invention; and  
         [0034]    [0034]FIG. 7 is a schematic block diagram illustrating selected embodiments of an interconnection network in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]    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.  
         [0036]    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.  
         [0037]    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.  
         [0038]    [0038]FIG. 1 is a schematic block diagram illustrating a typical prior art storage system  100 . The depicted storage system  100  includes a host  110 , an adapter  114 , a redundant set of RAID controllers  120 , an interconnection network  132 , and an array of storage devices  134 . In the depicted storage system  100 , the host  110  sends commands to the RAID controllers  120 . In turn the RAID controllers  120  may communicate with the storage devices  134  via the interconnection network  132 .  
         [0039]    In one redundant arrangement, a primary RAID controller  120   a  executes operations on the storage devices  134  in response to commands issued by the host  110 . In the aforementioned arrangement, a secondary RAID controller  120   b  may be activated in response to a failure by the primary RAID controller  120   a.  By activating the secondary RAID controller  120   b  in response to failure of the primary RAID controller  120   a,  reliability and availability of the storage system  100  is improved.  
         [0040]    The cost of achieving the improved reliability of the storage system  100  may be substantial. The RAID controllers  120  are typically non-commodity specialized devices that are expensive to purchase, install, and maintain. For example, the RAID controllers often contain components that are highly specialized, quickly out-dated, and more expensive than general purpose storage controllers.  
         [0041]    [0041]FIGS. 2 and 3 are schematic block diagrams illustrating selected embodiments of an alternate control storage system  200  of the present invention. As depicted, the alternate control storage system  200  includes a host  110 , a primary RAID controller  120   a,  an interconnection network  132 , one or more storage devices  134 , a control module  212 , one or more adapters  214 , an internal bus  216 , and multiple interface ports  218 . The alternate control storage system  200  is a low-cost, resource-efficient alternative to currently available redundant storage systems.  
         [0042]    [0042]FIG. 2 depicts a particular embodiment of the alternate control storage system  200 , namely an alternate control storage system  200   a,  wherein the primary RAID controller  120   a  is external to the host  110 . Likewise, FIG. 3 depicts a particular embodiment of the alternate control storage system  200 , namely an alternate control storage system  200   b,  wherein the primary RAID controller  120   a  resides on the host  110 .  
         [0043]    The host  110  may interface to the primary RAID controller  120   a  via the internal bus  216  as depicted in FIG. 2, or via one of the interface ports  218  as depicted in FIG. 3. In turn, the primary RAID controller  120   a  communicates with the storage devices  134  via the interconnection network  132 . To facilitate communication with the interconnection network  132 , the primary RAID controller  120   a  may include one or more interface ports  218  that provide a storage interface or storage network interface such as a SCSI interface, an SSA interface, a fiberchannel interface, an IDE interface, an ethernet interface, or the like.  
         [0044]    In the depicted alternate control storage system  200   a,  the control module  212  and the adapters  214  reside on the host  110 . One of the adapters  214  may be a controller adapter  214   a  while another may be a storage adapter  214 b. During normal operation, the control module  212  directs standard storage commands to the primary RAID controller  120   a  via the controller adapter  214   a.  In turn, the primary RAID controller  120   a  executes operations on the storage devices  134 .  
         [0045]    In one embodiment, in response to failure of the primary RAID controller  120   a,  the control module  212  emulates the primary RAID controller  120   a  by receiving commands from the host and executing corresponding operations on the storage devices  134  via the storage adapter  214   b  and the interconnection network  132 . Thus, the control module  212  and the storage adapter  214   b  essentially emulate a RAID controller  120 , eliminating the need to include an expensive secondary RAID controller  120   b.    
         [0046]    In one embodiment, the adapters  214 , including the controller adapter  214   a  and the storage adapter  214   b,  may be SCSI adapters, SSA adapters, fiberchannel adapters, IDE adapters, or the like. The aforementioned adapters  214  are typically significantly less expensive than the RAID controllers  120 .  
         [0047]    In one embodiment, the control module  212  disables or quiesces the primary RAID controller  120   a  in response to failure of the primary RAID controller  120   a.  The control module  212  may also include a driver configured to translate operating system calls into storage commands. These operations may include augmented or enhanced services such as recovery operations, diagnostic operations, firmware update operations, and the like.  
         [0048]    In the depicted alternate control storage system  200   b,  the primary RAID controller  120   a  resides on the host  110  and receives storage commands via the internal bus  216 . In one embodiment, the primary RAID controller  120   a  is a peripheral card such as a PCI card, that is inserted into a slot to electrically connect to the internal bus  216 . In another embodiment, the primary RAID controller  120   a  is integrated onto a motherboard residing on the host  110  and directly connected to the internal bus  216 . In either arrangement, placing the primary RAID controller  120   a  within the host  110  may eliminate interface hardware associated with the external primary RAID controller  120   a,  increase system performance, and reduce the cost of providing redundancy within a storage system.  
         [0049]    [0049]FIG. 4 is a schematic block diagram illustrating one embodiment of a storage  13  control apparatus  400  of the present invention. As depicted, the storage control apparatus  400  includes a control module  212 , a primary RAID controller  120   a,  a storage adapter  214   b,  a path selection module  410 , a RAID controller emulation module  412 , a failure detection module  414 , and an augmented services module  416 . The control module  212  facilitates redundant control of a storage array using a single RAID controller  120   a.    
         [0050]    The path selection module  410  directs storage commands to either the primary RAID controller  120   a  or the storage adapter  214   b.  In one embodiment, the path selection module  410  is essentially a multipath software layer within the system code of the host. During normal operation, the path selection module  410  directs standard storage commands received from the host  110  to the primary RAID controller  120   a.    
         [0051]    In one embodiment, the failure detection module  414  informs the path selection module  410  when the primary RAID controller  120   a  is not functioning properly. In response to the failure, the path selection module  410  directs commands received from the host  110  to the RAID controller emulation module  412 . When activated, the emulation module  412  may translate high-level storage commands including RAID commands into corresponding low-level storage commands supported by the storage devices  134 .  
         [0052]    During normal operation, the path selection module  410  may also direct requests for augmented or enhanced services to the augmented services module. The augmented services module  416  performs services on the storage devices  134  that are not available on the RAID controller  120   a.    
         [0053]    In one embodiment, the primary RAID controller  120   a  and the storage adapter  214   b  may both communicate with the storage devices  134  simultaneously through managed synchronization. While the primary RAID controller  120   a  is executing operations on the storage devices  134 , the storage adapter  214   b  may also perform augmented services on the storage devices  134 . In other embodiments, the RAID controller  120   a  is put on standby or is disabled during service operations conducted by the storage adapter  214   b.    
         [0054]    [0054]FIG. 5 a  is a flow chart illustrating one embodiment of a failure response method  500  of the present invention. The storage control method  500  may be conducted in conjunction with the storage control apparatus  400 , the storage system  200   a,    200   b,  or the like. As depicted, the failure response method  500  includes a failure detected test  510 , a retrieve configuration step  520 , an initialize emulator step  530 , and a shutdown RAID controller step  540 . The failure response method  500  facilitates fault tolerant handling of RAID control failures.  
         [0055]    While depicted in a certain sequential order, the depicted functionality of the failure response method  500  may be conducted in various sequences according to the needs and capabilities of the particular embodiment. For example, in one embodiment the depicted functionality is invoked by system events such that the order of execution is event dependent.  
         [0056]    The failure detected test  510  ascertains whether a failure has occurred to a RAID controller. In one embodiment, status query messages are sent to the RAID controller and a timeout event is set in case the RAID controller does not respond. In another embodiment, status registers on the RAID controller are accessed to assess the status of the controller. In yet another embodiment, a test sequence such as sending a write command to the RAID controller and accessing striping information on individual storage devices is conducted in order to ascertain if the RAID controller is functioning properly.  
         [0057]    The retrieve configuration step  520  retrieves RAID configuration information such as RAID level and striping information from local configuration files, system configuration files, registers within one or more RAID controllers, or similar sources. The RAID configuration information may facilitate providing augmented services or alternate control of a RAID array. For example, the RAID configuration information may facilitate monitoring a RAID controller, detecting RAID controller failures and emulating a RAID controller.  
         [0058]    The initialize emulator step  530  initializes a controller emulator such as a RAID controller emulator. In one embodiment, the initialize emulator step  530  uses the configuration information retrieved at step  510  to initialize the controller emulation module depicted in FIG. 4.  
         [0059]    The shutdown controller step  540  attempts to shutdown a faulty RAID controller, or the like. In one embodiment, the controller is quiesced to clear the processing queues within the controller. Subsequently data caches on the controller may be flushed to clear any write data within data caches, and followed by invocation of a disable command to prevent further processing by the controller. In response to completion of the shutdown controller step  540  the depicted failure response method  500  ends  545 .  
         [0060]    [0060]FIG. 5 b  is a flow chart illustrating one embodiment of a storage control method  550  of the present invention. The storage control method  550  may be conducted in conjunction with the storage control apparatus  400 , the storage system  200   a,    200   b,  or the like. The depicted embodiment of the storage control method  550  includes a receive command step  555 , an augmented service test  560 , a perform augmented service step  565 , a controller functional test  570 , a perform standard service step  575 , and a transmit command step  580 .  
         [0061]    The method begins with the receive command step  555 . In one embodiment, a storage command or the like is received from a storage manager or the like executing on the host  110 . Upon reception of the storage command, the method proceeds to the augmented service test  560 . At the augmented service test  560 , the method  500  determines whether the command corresponds to an augmented or enhanced service.  
         [0062]    If the received command corresponds to an augmented or enhanced service, the method proceeds to the perform augmented service step  565 . In one embodiment, the augmented services include disabling or quiescing the RAID controller, conducting diagnostic operations, recovery operations, firmware updates, or the like. Upon completion of the perform augmented service step  565 , the storage control method  550  loops to the receive command step  555 .  
         [0063]    If an augmented or enhanced service was not requested, the method continues with the controller functional test  570 . At the controller functional test,  570  the method determines whether a dedicated controller (such as a RAID controller) is functional. If the dedicated controller is not functional, the method proceeds to the perform standard service step  575 . In one embodiment, standard services are performed by an emulation module and include conducting RAID operations on a storage array. Upon completion of the perform augmented service step  565 , the storage control method  550  loops to the receive command step  555 .  
         [0064]    If the controller is functional, the storage control method  500  proceeds to the transmit command step  580  in order to invoke the supported service within the RAID controller or the like. Thereafter, the method  550  returns to the receive storage command step  555 . The depicted storage control method  550  facilitates providing alternate control of a storage array in the event of a failure of a dedicated controller while also providing host-based augmented storage services not available on the dedicated controller.  
         [0065]    [0065]FIG. 6 is a flow chart illustrating one embodiment of a storage system service method  600  of the present invention. The depicted storage system service method  600  includes an install service module step  610 , a connect storage adapter step  620 , a transfer control step  630 , a service controller step  640 , a recover data step  650 , and a service storage devices step  660 .  
         [0066]    The depicted storage system service method  600  may be performed by a service technician or the like in order to install or service the alternate control system  200  or the like. While depicted in a certain sequential order, the depicted steps may be performed in a manner or order appropriate to the particular system being serviced. For example, the service controller step  640  and the recover data step  650  may be omitted in systems wherein the steps are not needed.  
         [0067]    The install service module step  610  installs a service module, or the like, on the host  110 . In one embodiment, the service module  610  is essentially the control module  212  with additional functionality appropriate to installing or servicing the alternate control storage system  200 , or the like.  
         [0068]    The installed service module may perform or direct completion of the storage system service method  600 . At the connect storage adapter step  620 , a storage adapter such as the storage adapter  214   b  is connected to a storage array such as the storage devices  134  via an interconnection network such as the interconnection network  132 . In one embodiment, the service module (not shown) executing on the host computer indicates which storage devices  134  are accessible via the storage adapter  21   4   b.  The storage adapter  21   4   b  may be an adapter newly installed in conjunction with step  620  or an adapter previously available on the host  110 .  
         [0069]    In conjunction with the install service module step  610  and the connect storage adapter step  620 , RAID configuration information such as RAID level and striping information may be retrieved from system configuration files, registers within one or more RAID controllers, or similar sources. The RAID configuration information may facilitate providing augmented services or alternate control of a RAID array. For example, the RAID configuration information may facilitate monitoring a RAID controller, detecting RAID controller failures and emulating a RAID controller.  
         [0070]    The transfer control step  630  transfers control of the storage devices to the service module (not shown), the control module  212 , or the like. In one embodiment, transferring control includes quiescing or disabling a dedicated controller such as the RAID controller  120   a.  Transferring control may facilitate continued operation while performing diagnostic or maintenance services on the storage system.  
         [0071]    The service controller step  640  services a dedicated controller such as the RAID controller  120   a.  In one embodiment, servicing the dedicated controller includes updating firmware on the controller. In another embodiment, servicing the dedicated controller includes replacing the controller with a different controller.  
         [0072]    The recover data step  650  performs data recovery operations. In one embodiment, the data recovery operations restore images on the storage devices  134  to a desired state. In another embodiment, the data recovery operations transfer data within obsolete storage devices to newly installed storage devices.  
         [0073]    The service storage devices step  660  services the storage devices  134  or the like. In one embodiment, servicing the storage devices  134  includes updating firmware associated with the storage devices  134 . In another embodiment, servicing the storage devices  134  includes conducting diagnostic operations.  
         [0074]    [0074]FIG. 7 is a schematic block diagram illustrating selected embodiments of the interconnection network  132  in accordance with the present invention. The depicted embodiments of the interconnection network  132  are intended to illustrate without limitation various interconnection technologies and topologies that may be used with the present invention. The interconnection network  132  may include a variety of elements appropriate to interconnecting storage devices such as point-to-point connections  710 , storage device connections  720 , controller connections  730 , redundant controller connections  740 , parallel buses  750 , hubs  760 , and hub interconnections  770 .  
         [0075]    The controller connection  730  provides operable connectivity such as electrical, optical, or wireless connectivity from and to a dedicated controller, such as the RAID controller  120   a.  The redundant connection  740  provides operable connectivity such as electrical, optical, or wireless connectivity from and to a host-based storage adapter such as the storage adapter  214   b.  The storage device connections  720  provide operable connectivity such as electrical, optical, or wireless connectivity from and to storage devices such as the storage devices  134  depicted in various Figures.  
         [0076]    The selected embodiments shown in FIG. 7 include a point-to-point interconnection network  132   a,  a bused interconnection network  132   b,  and a storage area network  132   c.  The depicted point-to-point interconnection network  132   a  includes a set of point-to-point connections  710 , such as fiberchannel connections or the like, that operably connect the controller connection  730 , the redundant controller connection  740 , and the storage device connections  720 . In one embodiment, the point-to-point connections  710  form a loop of bi-directional connections such that the interconnection network  1   32   a  remains functional in the event of a device or connection failure.  
         [0077]    The depicted bused interconnection network  132   b  includes a parallel bus  750 . The parallel bus  750  operably connects the controller connection  730 , the redundant controller connection  740 , and the storage device connections  720 . The parallel bus  750  enables operative commands to be sent to each storage device in parallel. Through the controller connection  730 , the dedicated controller, such as a controller, sends operative commands. The operative commands travel through the parallel bus  750  to the storage device connections  720 . Storage devices such as the storage devices  134  receive the operative commands from the storage device connections  720 .  
         [0078]    The depicted storage area network  132   c  includes one or more hubs  760  connected by one or more hub interconnects  770 . In the depicted embodiment, two hubs  760  are shown connected by one hub interconnect  770 . The hub  760   a  is operably connected to the controller connection  730  and the storage device connections  720 . The hub  760   b  is operably connected to the redundant controller connection  740  and additional storage device connections  720 . The hub  760   a  receives operative commands from the dedicated controller, such as a RAID controller, from the controller connection  730 . The operative commands pass to the storage device connections  720  via hub  760   a  and the hub  760   b.    
         [0079]    The present invention provides secondary or augmented control of a storage array in a cost-effective manner. 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.