Abstract:
Systems and methods for providing an efficient partitioned resource server. In one embodiment, the partitioned resource server comprises a plurality of individual servers, and the individual servers appear to be equivalent to a client. Each of the individual servers may include a routing table that includes a reference for each resource that is maintained on the partitioned resource server. Requests from a client are processed as a function of the routing table to route the request to the individual server that maintains or has control over the resource of interest.

Description:
RELATED APPLICATION(S) 
       [0001]    This application is a continuation of U.S. application Ser. No. 10/217,118, filed Aug. 12, 2002. The entire teachings of the above application(s) are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to file access over a network and in particular to transparent routing of client requests for files and/or other resources that reside on a plurality of servers. 
         [0003]    Larger corporations and other organizations may want to store records, files and other resources across several servers servicing their needs. It becomes desirable in such situations to group several servers together so that they appear to a client as a single, logical unit. Ideally, such a single logical unit would have no duplication of data objects contained therein. Furthermore, the single logical unit should have as little overhead as possible in servicing any given resource request that arrives at a server belonging to the distributed logical unit. In many situations, the requested resource object may not reside at the same server that originally receives the resource request, so that some form of forwarding, routing, or acquisition of the desired resource must occur in order to service that original resource request. 
         [0004]    Multi-server environments are known wherein a client wishing to access specific information or a specific file is redirected to a server that has the piece of the requested information or file. The client then establishes a new connection to the other server upon redirect and severs the connection to the originally contacted server. However, this approach defeats the benefit of maintaining a long-lived connection between the client and the initial server. 
         [0005]    Another approach is “storage virtualization” where an intermediary device is placed between the client and the servers, with the intermediary device providing the request routing. None of the servers is hereby aware that it is providing only a portion of the entire partitioned service. Adding the intermediary device adds complexity to the system. 
         [0006]    It would therefore be desirable to provide a method and system that allows a client to contact any server in a multi-server environment and to access resources, such as files, distributed across the multi-server environment while maintaining a connection only to the contacted server. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention is directed to a system and a method that allow a resource request made to a server group to be laterally routed to the server having the desired resource object without making expensive query-response transactions with each and every server in the group. The connection with the server having the desired resource object should be long-lived, with that server returning said resource object to the requesting client. 
         [0008]    It is another object of the present invention to share group membership information between the group members so that such group membership information may be deterministically processed, along with a requested resource object, to indicate a particular server assigned to have the desired resource object and do so from any server. 
         [0009]    In accordance with the invention as embodied and broadly described herein, the invention provides, inter alia, methods, computer program products, and systems for allowing a plurality of servers to provide coherent support for incoming requests for services. To this end, the systems and methods described herein distribute, organize and maintain resources across a plurality of services. The servers are truly equivalent in that they each can respond to an incoming request in the same manner. Thus, the server appear equivalent to those clients that are requesting access to resources maintained on the system. In one embodiment, this appearance of equivalence is achieved, at least in part, by providing each server within the distributed server system, a table that lists a reference for each resource maintained by the distributed server system. The reference is preferably a direct reference in that it directly points to or otherwise references the server that is actually responsible for or has control over the resource associated with that reference. Thus, a server group according to the invention provides a system for distributed resource allocation that reduces network traffic associated with other forms of distributed resource allocation, by providing for a fixed ceiling of one level of redirection for each request for access to a resource. 
         [0010]    Each server has access to the entire group membership information stored in the routing table. This routing table may be updated with each access and reflects changes in group membership due to additions, removals, or temporary unavailability of the various servers that make up the group. When changes have propagated through the server group, all relevant routing tables at each server will contain identical information. 
         [0011]    When a server receives a resource request, it uses the relevant routing table to identify which group member should actually hold the resource object or a part of the resource object. The request may then be serviced by laterally accessing the desired data object from the correct server without making expensive query-response transactions over the network. 
         [0012]    More particularly, the invention, in one aspect, includes methods for accessing a resource distributed over a plurality of servers in a network. The methods establish a connection to a server via the network, request the resource from the server, determine a distribution of the resource among the plurality of servers, and return the resource distributed over the plurality of servers via the server while maintaining a network connection to the server. Optionally, the distribution is determined from a routing table that resides on each of the plurality of servers and is synchronized between the plurality of servers. The routing table may contain a reference to the resource or to a portion of the resource residing on each of the plurality of servers. The reference may be a direct reference to the associated resource. 
         [0013]    In another aspect the invention provides a client-server system for accessing a distributed resource. The system may comprise a plurality of servers connected to a network, a resource distributed over the plurality of servers, with each server including a routing table which associates the resource or the portion of the resource with a corresponding one of the servers. 
         [0014]    Further features and advantages of the present invention will be apparent from the following description of preferred embodiments and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The following figures depict certain illustrative embodiments of the invention in which like reference numerals refer to like elements. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. 
           [0016]    The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention. 
           [0017]      FIG. 1  is a schematic diagram of a client-server architecture with servers organized in server groups; 
           [0018]      FIG. 2  is a schematic diagram of the server groups as seen by a client; 
           [0019]      FIG. 3  shows details of the information flow between the client and the servers of a group; and 
           [0020]      FIG. 4  is a process flow diagram for retrieving resources in a partitioned resource environment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    A description of example embodiments of the invention follows. 
         [0022]    The teachings of all patents, published applications and references cited herein are incorporated by reference in their entirety. 
         [0023]    While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. 
         [0024]    The systems and methods described herein include systems for organizing and managing resources that have been distributed over a plurality of servers on a data network. The invention, in part, is directed to transparent request routing for retrieving distributed resources in a partitioned resource environment. Although the systems and methods described herein will be largely directed to storage devices and applications, it will be understood by those of skill in the art that the invention may be applied to other applications, including distributed file systems, systems for supporting application service providers and other applications. Moreover, it will be understood by those of ordinary skill in the art that the systems and methods described herein are merely exemplary of the kinds of systems and methods that may be achieved through the invention and that these exemplary embodiments may be modified, supplemented and amended as appropriate for the application at hand. 
         [0025]    Referring first to  FIG. 1  one embodiment of a system according to the invention is depicted. As show in  FIG. 1 , one or several clients  12  are connected, for example via a network  14 , such as the Internet, an intranet, a WAN or LAN, or by direct connection, to servers  161 ,  162 ,  163  that are part of a server group  16 . 
         [0026]    The client  12  can be any suitable computer system such as a PC workstation, a handheld computing device, a wireless communication device, or any other such device, equipped with a network client capable of accessing and interacting with the server  16  to exchange information with the server  16 . The network client may be a web client, such as a web browser that can include the Netscape web browser, the Microsoft Internet explorer web browser, the Lynx web browser, or a proprietary web browser, or web client that allows the user to exchange data with a web server, and ftp server, a gopher server, or same other type of network server. Optionally, the client  12  and the server  16  rely on an unsecured communication path, such as the Internet  14 , for accessing services at the remote server  16 . To add security to such a communication path, the client and the server can employ a security system, such as any of the conventional security systems that have been developed to provide to the remote user a secured channel for transmitting data aver the Internet. One such system is the Netscape secured socket layer (SSL) security mechanism that provides to a remote user a trusted path between a conventional web browser program and a web server. 
         [0027]    The server  16  may be supported by a commercially available server platform, such as a Sun Sparc.™. system running a version of the Unix operating system and running a server capable of connecting with, or transferring data between, any of the client systems. In the embodiment of  FIG. 1 , the server  16  can include a web server, such as the Apache web server or any suitable web server. The operation of the web server component at the server can be understood more fully from Laurie et al., Apache The Definitive Guide, O&#39;Reilly Press (1997). 
         [0028]    The server  16  may also include other components that extend its operation to accomplish the transactions described herein, and the architecture of the server  16  may vary according to the application. For example, the web server may have built in extensions, typically referred to as modules, to allow the server to perform the operations hereinafter, or the web server may have access to a directory of executable files, each of which files may be employed for performing the operations, or parts of the operations. 
         [0029]    In such an arrangement, the client  12  will contact one of the servers, for example server  161 , in the group  16  to access a resource, such as a file, database, application, or other resource, that is available over the network  14 . The contacted server  161  itself may not hold or have control over the resource. Typically, the client  12  connects to one server within the group  16 . The server group  16  is configured to make the partitioned resources available to the clients  12 . For illustration, the diagram shows two resources, one resource  18  that is partitioned over all three servers, servers  161 ,  162 ,  163 , and another resource  17  that is partitioned over two a of the three servers. There is no specific limit on the number of servers in a server group  16 . Similarly, there is no specific limit on the number of resources. In other words, each resource may be contained entirely on a single server, or it may be partitioned over several servers—all of the servers in the server group, or a subset of the server group. In practice, there may of course be limits due to implementation considerations, for example the amount of memory available in the servers or the computational limitations of the servers. Moreover, the grouping itself, i.e., deciding which servers will comprise a group, may in one practice comprise an administrative decision. In a typical scenario, a group might at first contain only a few servers, perhaps only one. The system administrator would add servers to a group as needed to obtain the level of service required. Increasing servers creates more space (memory, disk storage) for resources that are stored, more CPU processing capacity to act on the client requests, and more network capacity (network interfaces) to carry the requests and responses from and to the clients. It will be appreciated by those of skill in the art that the systems described herein are readily scaled to address increased client demands by adding additional servers into the group  16 . 
         [0030]    An exemplary resource in the context of the present invention can be one or more volumes of data stored in form of blocks, wherein different blocks can be stored on different servers. This so-called “block storage service” can be viewed as essentially representing a network-accessible disk drive. In a conventional storage server, such a volume is contained within a single server. A conventional server may provide more than one volume, but always stores volumes in their entirety. 
         [0031]    Referring now to  FIG. 2 , a client  12  connecting to a server  161  ( FIG. 1 ) will see the server group  16  as if the group were a single server. The client  12  is not aware that the server group  16  is constructed out of a potentially large number of servers  161 ,  162 ,  163 , nor is it aware of the partitioning of the resources  17 ,  18  over the several servers  161 ,  162 ,  163 . As a result, the number of servers and the manner in which resources are partitioned among the servers may be changed without affecting the network environment seen by the client  12 . 
         [0032]    Referring now to  FIG. 3 , in the partitioned server group  16 , any volume may be spread over any number of servers within the group  16 . As seen in  FIGS. 1 and 2 , one volume  17  (Resource  1 ) may be spread over servers  162 ,  163 , whereas another volume  18  (Resource  2 ) may be spread over servers  161 ,  162 ,  163 . Advantageously, the respective volumes are arranged in fixed-size groups of blocks, also referred to as “pages”, wherein an exemplary page contains 8192 blocks. Other suitable page sizes may be employed. In an exemplary embodiment, each server in the group  16  contains a routing table  165  for each volume, with the routing table  165  identifying the server on which a specific page of a specific volume can be found. For example, when the server  161  receives a request from a client  12  for volume  3 , block  93847 , the server  161  calculates the page number (page  11  in this example for the page size of 8192) and looks up in the routing table  165  the location or number of the server that contains page  11 . If server  163  contains page  11 , the request is forwarded to server  163 , which reads the data and returns the data to the server  161 . Server  161  then send the requested data to the client  12 . In other words, the response is always returned to the client  12  via the same server  161  that received the request from the client  12 . 
         [0033]    It is transparent to the client  12  to which server  161 ,  162 ,  163  he is connected. Instead, the client only sees the servers in the server group  16  and requests the resources of the server group  16 . It should be noted here that the routing of client requests is done separately for each request. This allows portions of the resource to exist at different servers. It also allows resources, or portions thereof, to be moved while the client is connected to the server group  16 —if that is done, the routing tables  165  are updated as necessary and subsequent client requests will be forwarded to the server now responsible for handling that request. At least within a resource  17  or  18 , the routing tables  165  are identical. The described invention is different from a “redirect” mechanism, wherein a server determines that it is unable to handle requests from a client, and redirects the client to the server that can do so. The client then establishes a new connection to another server. Since establishing a connection is relatively inefficient, the redirect mechanism is ill suited for handling frequent requests. 
         [0034]      FIG. 4  depicts an exemplary process flow  40  for handling client requests in a partitioned server environment. The process  40  begins  41  by receiving a request for a resource, such as a file or blocks of a file, step  42 . The process checks in step  43  if the requested resource is present at the initial server that received the request from the client. If the requested resource is present at the initial server, the initial server returns the requested resource to the client, step  48 , and the process  40  terminates, step  49 . Conversely, if the requested resource is not present at the initial server, the server will consult a routing table, step  44 , to determine which server actually holds the specific piece of data requested by the client, step  45 . The request is then forwarded to the server that holds the requested resource, step  46 , which returns the requested resource to the initial server, step  48 . The process then goes to step  48  as before, to have the initial server forward the requested resource to the client, step  48 , and the process  40  terminates, step  49 . 
         [0035]    The resources spread over the several servers can be directories, individual files within a directory, or even blocks within a file. Other partitioned services could be contemplated. For example, it may be possible to partition a database in an analogous fashion or to provide a distributed file system, or a distributed or partitioned server that supports applications being delivered over the Internet. In general, the approach can be applied to any service where a client request can be interpreted as a request for a piece of the total resource, and operations on the pieces do not require global coordination among all the pieces. 
         [0036]    Although  FIG. 1  depicts the system as an assembly of functional block elements including a group of server systems, it will be apparent to one of ordinary skill in the art that the systems of the invention may be realized as computer programs or portions of computer programs that are capable of running on the servers to thereby configure the servers as systems according to the invention. Moreover, although  FIG. 1  depicts the group  16  as a local collection of servers, it will be apparent to those or ordinary skill in the art that this is only one embodiment, and that the invention may comprise a collection or group of servers that includes server that are physically remote from each other. 
         [0037]    As discussed above, in certain embodiments, the systems of the invention may be realized as software components operating on a conventional data processing system such as a Unix workstation. In such embodiments, the system can be implemented as a C language computer program, or a computer program written in any high level language including C++, Fortran, Java or basic. General techniques for such high level programming are known, and set forth in, for example, Stephen G. Kochan, Programming in C, Hayden Publishing (1983). 
         [0038]    While the invention has been disclosed in connection with the preferred embodiments shown and described in detail, various modifications and improvements thereon will become readily apparent to those skilled in the art. Accordingly, the spirit and scope of the present invention is to be limited only by the following claims.