Abstract:
Providing shared access to data storage resources in a cluster computing environment, including detecting when a computer node requests access to a data storage device in a manner that excludes a computing device from accessing the data storage device, where the computer node is configured to communicate with the data storage device along a first communications channel, and where the computing device is configured to communicate with the data storage device along a second communications channel that is exclusive of the first communications channel, and responsive to the detecting, causing the data storage device to allow the computer node and the computing device to share access to the data storage device.

Description:
FIELD OF THE INVENTION 
     The present invention relates to computer networks in general, and more particularly to providing shared access to data storage resources. 
     BACKGROUND OF THE INVENTION 
     In a cluster computing environment multiple computer nodes typically share data storage devices. In order to prevent conflicts that may arise when multiple nodes in a cluster attempt to access the same data storage device at the same time, techniques have been developed to provide access to data storage devices in a controlled manner, such as where a node is given exclusive ownership over part or all of a data storage device for a period of time. For example, in a SCSI-based Storage Area Network (SAN), a node may issue a “SCSI reserve” command to obtain exclusive ownership of a SCSI device. Once a SCSI device is reserved in this manner, it refuses all commands from all other nodes until exclusive ownership of the SCSI device is revoked, such as after an “SCSI reset” command is received by the SCSI device. 
     Back-up copies of data stored on data storage devices, such as for disaster-recovery purposes, are often made without taking the data storage devices off-line, thus ensuring that primary data providers/consumers, such as computer users and other processes and applications, have continuous access to data. Such back-ups are often made by dedicated back-up servers that access data storage devices by making data requests of the nodes in a cluster that are connected to the data storage devices. Unfortunately, this results in additional processing overhead for such participating nodes. Alternatively, dedicated back-up servers access data storage devices via data communications channels that are separate from those that are normally used to provide data to primary data providers/consumers. This is done to minimize the impact that the data back-up service has on the performance and responsiveness of the overall system. Unfortunately, in a cluster computing environment where the nodes themselves control access to data storage devices, a dedicated back-up server may be denied access to a data storage device, thus hindering the data back-up service. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention a method and computer program product provide shared access to data storage resources in a cluster computing environment, including detecting when a computer node requests access to a data storage device in a manner that excludes a computing device from accessing the data storage device, where the computer node is configured to communicate with the data storage device along a first communications channel, and where the computing device is configured to communicate with the data storage device along a second communications channel that is exclusive of the first communications channel, and responsive to the detecting, causing the data storage device to allow the computer node and the computing device to share access to the data storage device. 
     In another aspect of the invention a system provide shared access to data storage resources in a cluster computing environment, the system including a data storage device, a plurality of computer nodes operating in a cluster computing environment and being configured to communicate with the data storage device along a first communications channel, and a computing device configured to communicate with the data storage device along a second communications channel that is exclusive of the first communications channel, where at least one of the computer nodes is configured with a filter device driver that is configured to receive from the computing device a request to access the data storage device, detect when the computer node that is configured with the filter device driver requests access to the data storage device in a manner that excludes the computing device from accessing the data storage device, and cause the data storage device to allow the computing device to share access to the data storage device with the computer node that is configured with the filter device driver. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the appended drawings in which: 
         FIG. 1  is a simplified conceptual illustration of a system for providing shared access to data storage resources in a cluster computing environment, constructed and operative in accordance with an embodiment of the invention; 
         FIG. 2  is a simplified sequence diagram of an exemplary method of operation of the system of  FIG. 1 , operative in accordance with an embodiment of the invention; and 
         FIG. 3  is a simplified block diagram illustration of an exemplary hardware implementation of a computing system, constructed and operative in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is now described within the context of one or more embodiments, although the description is intended to be illustrative of the invention as a whole, and is not to be construed as limiting the invention to the embodiments shown. It is appreciated that various modifications may occur to those skilled in the art that, while not specifically shown herein, are nevertheless within the true spirit and scope of the invention. 
     As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. 
     Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical data storage device, a magnetic data storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. 
     A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. 
     Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing. 
     Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user&#39;s computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). 
     Aspects of the present invention are described below with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks. 
     The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     Reference is now made to  FIG. 1 , which is a simplified conceptual illustration of a system for providing shared access to data storage resources in a cluster computing environment, constructed and operative in accordance with an embodiment of the invention. In the system of  FIG. 1 , a cluster, generally designated  100 , of computer nodes is shown, including at least a node  102  and a node  104 . The nodes in cluster  100  share a data storage device  106 , such as in a SCSI-based Storage Area Network (SAN) environment where the nodes in cluster  100  access data storage device  106 , on which production data is stored, via SAN data communications channels  108  in accordance with conventional techniques. An end-user computer  110  is shown, such as may communicate with any of the nodes in cluster  100  via a network  112 . 
     The system of  FIG. 1  also includes a computing device, such as a back-up server  114  having a back-up repository  116  onto which back-up server  114  stores back-up copies of data. Back-up server  114  is preferably a dedicated back-up server that is capable of accessing data storage device  106  via a SAN data communications channel  118  that is separate from SAN data communications channels  108 . 
     In the system of  FIG. 1 , each of the nodes in cluster  100  are configured with a filter device driver  120  that monitors communications sent to and from the node that relate to controlling access to data storage device  106 . 
     Reference is now made to  FIG. 2 , which is a simplified sequence diagram of an exemplary method for providing shared access to data storage resources in a cluster computing environment, operative in accordance with an embodiment of the invention. The method of  FIG. 2  may be used to operate the system of  FIG. 1 , where the back-up server, cluster node, filter device driver, and data storage device referred to in  FIG. 2  represent back-up server  114 , cluster node  102  or  104 , filter device driver  120 , and data storage device  106  of  FIG. 1  respectively. In the method of  FIG. 2 , a filter device driver initially operates in a pass-through mode, where communications that are to be sent by a given node in a cluster and that relate to controlling access to a data storage device are allowed by the filter device driver at that node to be sent by the node without modification. Thus, for example, where a node wishes to send an exclusive access command, such as a “SCSI reserve” command, to a data storage device in order to obtain exclusive access to the data storage device, if the filter device driver at that node is operating in pass-through mode, the filter device driver at that node allows the “SCSI reserve” command to be sent to the data storage device. When a back-up server wishes to back-up data stored on the data storage device, the back-up server sends messages to each of the filter device drivers at each of the nodes in the cluster, where the messages identify the back-up server, such as by using a World Wide Name (WWN), and indicate that the back-up server wishes to perform a backup of data on the data storage device. After receiving the message from the back-up server, each filter device driver enters a “hook” mode of operation and preferably sends an acknowledgement to the back-up server acknowledging receipt of the message. While in hook mode each filter device driver ensures that its node takes no action that would prevent the back-up server from backing-up data stored on the data storage device. For example, if the filter device driver at a node is in hook mode, and the node attempts to send an exclusive access command, such as a “SCSI reserve” command, to the data storage device in order to obtain exclusive access to the data storage device, before the command is sent the filter device driver at that node changes the command to a shared access command, such as a “SCSI persistent reserve” command. The “SCSI persistent reserve” command is then sent to the data storage device together with an identification of at least the node, as the requesting node, and the back-up server. The “SCSI persistent reserve” command thus provides both the requesting node and the back-up server with shared access to the data storage device, although the back-up server is preferably limited to read-only access of the data storage device. The node may then access the data storage device as needed, while at the same time the back-up server may back-up the data storage device, preferably only after receiving messages from each of the filter device drivers in the cluster acknowledging receipt of the back-up server&#39;s message. While in hook mode the filter device driver preferably allows other node commands to be sent without modification where the command would not prevent back-up server from backing-up data. 
     If the filter device driver at a node enters hook mode after the node has issued an exclusive access command, such as a “SCSI reserve” command, to the data storage device in order to obtain exclusive access to the data storage device, the filter device driver at that node preferably cancels the exclusive access command and sends a shared access command, such as a “SCSI persistent reserve” command, to the data storage device as described above, providing the back-up server with shared access to the data storage device. Similarly, if the filter device driver at a node enters hook mode after the node has issued a shared access command, such as a “SCSI persistent reserve” command, to the data storage device in order to obtain shared access to the data storage device, but which does not provide the back-up server with shared access to the data storage device, the filter device driver at that node preferably causes the data storage device to provide the back-up server with shared access to the data storage device, such as by cancelling the shared access command and resending the shared access command to the data storage device together with an identification of at least the node, as the requesting node, and the back-up server as described above. 
     Although the invention has been described by way of example with respect to a data backup server, it will be appreciated that the invention is not limited to use with a data backup server or data backup applications. Rather, the invention may be used to provide any computing device with access to a shared data storage device in a cluster computing environment for any purpose that requires access to the shared data storage device. 
     Referring now to  FIG. 3 , block diagram  300  illustrates an exemplary hardware implementation of a computing system in accordance with which one or more components/methodologies of the invention (e.g., components/methodologies described in the context of the drawing figures shown and described herein) may be implemented, according to an embodiment of the invention. 
     As shown, the techniques for controlling access to at least one resource may be implemented in accordance with a processor  310 , a memory  312 , I/O devices  314 , and a network interface  316 , coupled via a computer bus  318  or alternate connection arrangement. 
     It is to be appreciated that the term “processor” as used herein is intended to include any processing device, such as, for example, one that includes a CPU (central processing unit) and/or other processing circuitry. It is also to be understood that the term “processor” may refer to more than one processing device and that various elements associated with a processing device may be shared by other processing devices. 
     The term “memory” as used herein is intended to include memory associated with a processor or CPU, such as, for example, RAM, ROM, a fixed memory device (e.g., hard drive), a removable memory device (e.g., diskette), flash memory, etc. Such memory may be considered a computer readable storage medium. 
     In addition, the phrase “input/output devices” or “I/O devices” as used herein is intended to include, for example, one or more input devices (e.g., keyboard, mouse, scanner, etc.) for entering data to the processing unit, and/or one or more output devices (e.g., speaker, display, printer, etc.) for presenting results associated with the processing unit. 
     The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. 
     While the methods and apparatus herein may or may not have been described with reference to specific computer hardware or software, it is appreciated that the methods and apparatus described herein may be readily implemented in computer hardware or software using conventional techniques. 
     While the invention has been described with reference to one or more specific embodiments, the description is intended to be illustrative of the invention as a whole and is not to be construed as limiting the invention to the embodiments shown. It is appreciated that various modifications may occur to those skilled in the art that, while not specifically shown herein, are nevertheless within the true spirit and scope of the invention.