Abstract:
A cluster of computing systems is provided with guaranteed real-time access to data storage in a storage area network. Processes issue request for bandwidth reservation which are initially handled by a daemon on the same node as the requesting processes. The local daemon determines whether bandwidth is available and, if so, reserves the bandwidth in common hardware on the local node, then forwards requests for shared resources to a master daemon for the cluster. The master daemon makes similar determinations and reservations for resources shared by the cluster, including data storage elements in the storage area network and grants admission to the requests that don&#39;t exceed total available bandwidth.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation and claims the priority benefit of U.S. patent application Ser. No. 12/907,867 filed Oct. 19, 2010, now U.S. Pat. No. 8,589,499, that issued on Nov. 19, 2013, which is a continuation and claims the priority benefit of U.S. patent application Ser. No. 10/434,340 filed May 9, 2003, now U.S. Pat. No. 7,818,424, that issued on Oct. 19, 2010, which claims the priority benefit of U.S. provisional application No. 60/378,941 filed May 10, 2002, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to real-time computer processing and, more particularly, to accessing a storage area network by real-time computer systems. 
     2. Description of the Related Art 
     Real-time access to storage is needed by many applications, such as broadcast, multicast and editing of digital media files, and sensor data collection and processing. Many ways of providing real-time data access have been proposed and implemented including Guaranteed Rate I/O (GRIO) disk bandwidth scheduler, available from Silicon Graphics, Inc. (SGI) of Mountain View, Calif. In conjunction with the XLV disk volume manager, also available from SGI, guaranteed disk bandwidth reservations are provided by GRID at the local client level. Bandwidth reservations can be attached to individual files or entire file systems and can be shared between processes. The local storage has to be configured appropriately to support GRIO. If the amount of data required by an application is greater than can be provided by a single disk, the disk must be in a volume with the data striped across several disks or staggered to multiple disks so that different processes can access different disks independently. 
     GRIO is an integral part of the I/O system in IRIXO (SGI&#39;s version of UNIX) to ensure that real-time access can be guaranteed. GRIO uses a frame-based disk block scheduler without reordering requests and maintains a database of the different pieces of hardware in the system and their bandwidth characteristics. When a bandwidth reservation is received from a process executing on the local client node, determinations of available bandwidth are made for components along the entire physical I/O path, starting with the I/O adapter accessed by multiple processors and ending with the local data storage. The total reservations for all processes at each component along the path is kept below the total available bandwidth for that component. If this level would be exceeded, the GRID daemon denies admission to the request. Excess capacity may be used for overband consumption by a process provided the remaining reservations will not be adversely affected during the period of the overband request. 
     Although GRIO is available for individual client nodes, no known client software solutions provide guaranteed real-time access to data storage shared by a cluster of nodes via a storage area network (SAN). The closest known solution is to copy files stored on a SAN to local storage and use GRID to control synchronization of accesses to the files in local storage. This technique is adequate for some uses, such as non-linear editing; but is less than desirable for large-scale on-demand multicasting of video files, for example, due to the large amount of extra local storage that would be required and would not be needed if real-time access to the resources of the SAN could be guaranteed. 
     There are several benefits of SANs that are not obtained by the solution described above. Fault tolerance for accesses to the data is one of the primary benefits of a SAN. In addition, load balancing and enabling heterogeneous client access to the same physical storage are also benefits that can be obtained by a clustered file system using a SAN. 
     Other ways of obtaining some of these benefits include modifying disk controller firmware to schedule and reorder data requests and using intelligent disk networks as proposed by Nagle in “Active Storage Nets”, DARPA/ITO Active Nets Meeting July 1998. Nagle proposed a network of intelligent disk drives that can rearrange their striping configuration as needed to meet quality of service guarantees. This requires adding intelligence to the disk drives and providing an actively reconfigurable network linking the intelligent disk drives. A simpler solution requiring fewer modifications to a cluster file system that provides access to a SAN is preferable from a cost-benefit perspective. 
     SUMMARY OF THE PRESENTLY CLAIMED INVENTION 
     It is an aspect of the present invention to provide guaranteed data access rates to shared cluster storage. 
     It is another aspect of the present invention to provide guaranteed data access rates to shared cluster storage without requiring hardware modifications to storage devices or the interconnect. 
     It is a further aspect of the present invention to provide real-time access to files for broadcasting or multicasting while simultaneously permitting editing of files that are not currently being broadcasted or multicasted. 
     It is yet another aspect of the present invention to enable a process on one of the nodes in a cluster to determine whether a request for access to shared resources can be granted without requiring communication with other nodes in the cluster. 
     The above aspects can be attained by a method of accessing a storage area network by real-time applications, including requesting, from a master daemon by the real-time applications executing on nodes in the storage area network, reservation of bandwidth to access resources in the storage area network; and scheduling, by the master daemon, access to the resources in the storage area network by each real-time application. The scheduling may be performed by determining available bandwidth along a path required by each request; and granting admission to the resources of the storage area network only if total bandwidth reservations of all granted requests will be less than total available bandwidth. 
     Available bandwidth is preferably determined by determining a path from an input/output interface at the nodes in the storage area network issuing the request to each at least one storage element in the storage area network; and determining available bandwidth for at least one component along the path. These determinations are made using a master database of the reserved bandwidth and the total available bandwidth of components capable of being shared by the nodes in the storage area network and local databases of the reserved bandwidth for locally issued requests and the total available bandwidth for local node components shared by processes executed at each node that issues requests for bandwidth reservations. 
     Preferably, the method also includes distributing to each requesting node at least one schedule determined during scheduling by the master daemon; and limiting accesses to the resources in the storage area network by each real-time application on each requesting node according to a corresponding schedule included in the at least one schedule. 
     Optionally, the method may include reserving, by the nodes in the storage area network, an additional amount of bandwidth not requested by one of the real-time applications. In this case, the method preferably includes allocating, by a local daemon on one of the nodes in the storage area network, the additional amount of bandwidth for access to the storage area network, to applications executing on the one of the nodes and for which no bandwidth request was issued to the master daemon. Further, the allocating of the additional amount of bandwidth preferably includes allocating bandwidth to at least one of the real-time applications for which a bandwidth request was granted by the local daemon without requiring that the local daemon request additional bandwidth from the master daemon for the one of the nodes. Optionally, the additional bandwidth may also be used by applications that have not issued a bandwidth reservation request. 
     These together with other aspects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of embodiments of the invention will be apparent from the detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a block diagram of a cluster of computing systems connected to a SAN1. 
         FIG. 2  is a block diagram of components in two nodes and shared components in a SAN to illustrate the process of determining whether to grant a bandwidth reservation request. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention my be implemented in a SAN accessed by a cluster of computing systems each running UNIX or IRIX and a clustered file system, such as CXFS and volume manager XVM, both from SGI. Additional details of such an operating environment are provided in U.S. patent applications entitled CLUSTERED FILE SYSTEM having Ser. No. 10/162,258 by Costello et al., filed Jun. 5, 2002, and MESSAGING BETWEEN HETEROGENEOUS CLIENTS OF A STORAGE AREA NETWORK by Cruciani et al. and MULTI-CLASS HETEROGENEOUS CLIENTS IN A CLUSTERED FILE SYSTEM by Moore et al., both filed Apr. 16, 2003, all of which are incorporated herein by reference. 
     An example of such a cluster is illustrated in  FIG. 1 . In the example illustrated in  FIG. 1 , nodes  22  run the IRIX operating system from SGI while nodes  24  run the SolariS™ operating system from Sun Microsystems, Inc. of Santa Clara, Calif. and node  26  runs the Windows NT operating system from Microsoft Corporation of Redmond Wash. Each of these nodes is a conventional computer system including at least one, and in many cases several processors, local or primary memory, some of which is used as a disk cache, input/output (I/O) interfaces, and I/O devices, such as one or more displays or printers. According to the present invention, the cluster includes a storage area network in which mass or secondary storage, such as disk drives  28  are connected to nodes  22 ,  24 ,  26  via Fibre Channel switch  30  and Fibre Channel connections  32 . The nodes  22 ,  24 ,  26  are also connected via a local area network (LAN)  34 , such as an Ethernet, using TCP/IP to provide messaging and heartbeat signals. A serial port multiplexer  36  may also connected to the LAN and to a serial port of each node to enable hardware reset of the node. In the example illustrated in  FIG. 1 , only IRIX nodes  22  are connected to serial port multiplexer  36 . 
     Other kinds of storage devices besides disk drives  28  may be connected to the Fibre Channel switch  30  via Fibre Channel connections  32 . Tape drives  38  are illustrated in  FIG. 1 , but other conventional storage devices may also be connected. Alternatively, disk drives  28  or tape drives  38  (or other storage devices) may be connected to one or more of nodes  22 ,  24 ,  26 , e.g., via SCSI connections (not shown). 
     One use for a cluster like that illustrated in  FIG. 1  is a video broadcast studio in which video clips are stored in files on disk drives  28  (or tape drives  38 ). Non-linear video editors running on heterogeneous nodes  22 ,  24 ,  26  modify the video files while the files are accessible for broadcasting on television. A cluster aware real-time scheduler according to the present invention ensures that the timing needs and total bandwidth of the playback servers are met. 
     CXFS allows direct access to the SAN  28 ,  30 ,  32  from all the connected clients  22 ,  24 ,  26  and maintains coherency by leasing out tokens for various actions. For instance, read/write tokens exist for access to individual files and tokens exist for allocating new disk block extents. One of the nodes  22  serves as a metadata server for each file system and controls granting and replication of tokens. Relocation recovery of metadata servers is supported in CXFS. 
     To be able to efficiently resolve bandwidth utilization conflicts between different clients, in the preferred embodiment each client node  22 ,  24  or  26  runs a daemon named ggd which responds to requests for guaranteed access to any data. Each bandwidth reservation request preferably includes at least one storage element, a required periodic bandwidth, e.g., 1 MB per second, a start time and a duration of the reservation for access to the at least one storage element. 
     As illustrated in  FIG. 2 , one of the nodes serves as master node  40 . The remaining nodes are represented by client node  42 . The functions performed by ggd  44   m  in master node  40  are essentially the same as those in ggd  44   c  in client node  42 . In fact, ggd  44   m  receives requests from processes executing on master node  40 , as well as those received from other nodes  42  for managing bandwidth request to shared resources. When referring to operations performed by both ggd  44   c  and ggd  44   m , reference will be made to ggd  44 . 
     On each node  42 ,  44 , ggd  44  maintains a database of hardware with the total available or maximum bandwidth and total requested bandwidth. In addition, the hardware path to memory component is stored in the database, so that the available bandwidth of components along the path can be determined. The total requested bandwidth is the bandwidth set aside for processes that issued bandwidth reservation requests. The total available bandwidth may be less than the capacity of the specific hardware, if other processes use the shared hardware without making a bandwidth reservation request. However, it is preferred that all accessing applications and nodes in SAN  28 ,  30 ,  32  issue requests to local daemon ggd  44   c  (and through ggd  44   c  to ggd  44   m  if a shared resource is requested). Preferably, the total requested bandwidth is determined from information from each request that is maintained in the database. When the reserved time determined by the start time and duration has passed, the reservation request is removed from the database and the total requested bandwidth is reduced by the amount of bandwidth in that request. 
     Bandwidth reservations are made as nested transactions for hardware components shared by multiple processes. In a cache coherent multiprocessor systems like those manufactured by SGI, ggd  44  starts with the common point where all processors in the node  40  or  42  meet the I/O hardware at a memory interface  46 . On receipt of a request, ggd  44  queries the kernel for the hardware path to the requested storage element. With this information, ggd  44  loops down the path determining whether each part has enough unreserved bandwidth to admit the request. This is illustrated in the case of the client node by the directed-lines between memory interface  46 , PCI Bus  48  and Fibre Channel Adapter  50 . When ggd  44   c  in client node  42  determines that all hardware in its node has sufficient unreserved bandwidth, a request is issued to the master daemon in node  40  to check the available bandwidth of hardware shared throughout the cluster. 
     In the embodiment illustrated in  FIG. 2 , only shared disks  28  are shown as being queried for unreserved bandwidth by ggd  44   m  in response to a request from client node  42 , as indicated by the dashed lines. This might be the case where the at least one component in the request includes a portion of disk storage in the storage area network and the other components in the storage area network have sufficient capacity that the only bottleneck could occur in the shared disk. Preferably, the database maintained by ggd  44   m  includes any hardware in SAN  28 ,  30 ,  32  where a bottleneck could occur, such as Fibre Channel Adapters, Fibre Channel switches, disk controllers, etc. If each of the at least one component, i.e., storage element(s) on shared disk  28 , in the request for bandwidth reservation is determined by ggd  44   m  to have available bandwidth exceeding the required periodic bandwidth in the request, ggd  44   m  sends a message to ggd  44   c  granting admission to the request and increases the total requested bandwidth in the database maintained on the shared cluster components. Similarly, ggd  44   c  updates its database for the components in node  42  shared by multiple processes. 
     As an alternative to the master daemon maintaining a master database of requests to shared resources of the SAN  28 ,  30 ,  32 , a percentage of the total bandwidth of the shared resources of the SAN  28 ,  30 ,  32  may be allocated to each node  42 , either by a master daemon, or by messages transmitted between the local ggd  44   c  in each node  42 . In this alternative, the local ggd  44   c  in each node  42  would maintain information about the shared resources of the SAN  28 ,  30 ,  32  allocated thereto in addition to the shared resources within the node  42  itself. 
     Unlike the GRIO product from SGI, ggd  44   c  may not permit overband utilization of shared resources. This would ordinarily require additional communication between nodes during execution of a process. Given the time required to grant such access and the additional complexity to provide for the required communication, it is preferable in a system of generally under-utilized bandwidth to make bandwidth reservations that are high enough to avoid overband situations. Alternatively, client node  42  may issue to ggd  44   m  an additional bandwidth reservation request for processes executing on client node  42  without a specific request from one of those processes. If granted by ggd  44   m , the additional bandwidth reservation may be allocated by ggd  44   c  to processes on client node  42  that have not issued any bandwidth reservation requests, or to provide additional bandwidth to processes that issued a request, but need to exceed the bandwidth granted by ggd  44   m.    
     The present invention has been described with respect to an embodiment using SGI hardware and software However, the invention is not limited to SGI hardware and software, or for use with video editing and broadcasting. 
     The many features and advantages of the invention are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the invention that fall within the true spirit and scope of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.