Abstract:
A system and method to allow scalability of file storage in terms of capacity and performance through a symmetric multicomputer architecture with shared storage, in which storage and protocol processing resources can be added to (or removed from) the system without any need of recognizing and/or explicitly migrating the data stored in the system. The invention permits accessing files stored (i.e., written) in any of multiple external protocol processing nodes to be retrieved from any other external protocol processing node.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application is related to commonly owned, co-pending U.S. patent application entitled “Scalable Storage System” by David Raccah et al., filed Nov. 10, 2000. (Atty. Dkt. ZAM-0001), U.S. Appln. Ser. No. 09/659,107, entitled “Storage System Having Partitioned Migratable Metadata,” filed Sep. 11, 2000 (Atty. Dkt. ZAM-0003) and U.S. Appln. Ser. No. 09/659,107, entitled “File Storage System Having Separation of Components,” filed Sep. 19, 2000 (Atty. Dkt. ZAM-0004), commonly owned by the present assignee, the contents of each being incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention is generally directed to a multi-computer storage architecture and more particularly, to methods and systems that support high scalability in performance and capacity in shared file storage.  
         BACKGROUND OF THE INVENTION  
         [0003]    Conventionally, files stored in a given file server must be retrieved from the same file server. In a massively scalable system with a very large number of file servers, whenever a given file server runs out of space or runs out of processing resources, a portion of the file data and metadata must be explicitly migrated to another file server and the remote nodes must be explicitly reconfigured to observe this change.  
           [0004]    Looking first at FIG. 1, a conventional implementation of Network Attached Storage (NAS)  100  is illustrated. In NAS  100 , network protocols such as, without limitation, a Network File System (NFS) client  102 , a Common Internet File System (CIFS) client  104 , a Hypertext Transfer Protocol (HTTP) client  106 , and a File Transfer Protocol (FTP) client  108  are connected through an access network  110  to a plurality of file servers  112   a ,  112   b , and  112   c.  Each file server  112  is connected to a dedicated storage array  114 , and each storage array  114  services a dedicated disk  116 . That is, file server  112   a  is connected to a storage array  114   a , which in turn is connected to a disk  116   a . In an alternate embodiment, a network administrator may reconfigure the network such that file server  112   a  is connected to storage array  114   b , file server  112   b  is connected to storage array  114   c , and file server  112   c  is connected to storage array  114   a . The characteristic of this architecture is that the reconfiguration of the network requires the intervention of that network administrator.  
           [0005]    Looking now at FIG. 2, a conventional Storage-Area Network (SAN)  200  is illustrated. In SAN  200 , network protocols such as, without limitation, a Network File System (NFS) client  202 , a Common Internet File System (CIFS) client  204 , a Hypertext Transfer Protocol (HTTP) client  206 , and a File Transfer Protocol (FTP) client  208  are connected through an access network  210  to a plurality of file servers  212   a ,  212   b , and  212   c.  Each file server  212  communicates with a storage array using a block level protocol, and each file server  212  is assigned to one or more disk volumes  216 . For example and without limitation, file server  212   a  can be assigned to a disk volume  216   a   1 , file server  212   b  can be assigned to disk volumes  216   a   2  and  216   c   1 , file server  212   c  can be assigned to all of  216   b,  and disk volume  216   c   2  can be an unassigned, spare disk volume available for later assignment. Although the file servers of a SAN can be fully connected to all the disk volumes, that is a file server could access any disk volume on the storage-area network, the file server can use a disk volume assigned to this file server and must not directly use disk volumes assigned to other file servers. The characteristic of this architecture is that the disk resources are assigned logically to a file server rather than physically. However, once resources are assigned, another file server cannot use those resources until a formal reassignment occurs. No effort has been made to extend the conventional approach to file servers, dedicated “filers” and hierarchical mass storage systems in a manner that is distinctively different from existing cluster-based file storage solution exploiting Storage Area Networks (SAN).  
           [0006]    In these traditional approaches to a file storage system built of multiple file servers, each file server “owns” a part of a global file system (i.e., a part of the file system  namespace  and  metadata  of all the files belonging to this part of the namespace). Thus, a file stored on a given file server can be accessed later only through this particular file server. Although in the case of hierarchical storage systems, the file servers may share physical file data repository (e.g. tape or optical disk jukebox), a file can be accessed (in a read-write mode) only through a file server that keeps the file&#39;s entry in the file system namespace and metadata (file attributes).  
           [0007]    SAN-based cluster file systems on the other hand, may enable sharing of block-oriented devices between cluster nodes. However, this functionality depends on specific support built into the storage devices, such as SCSI locks, etc. Thus, a SAN-based cluster file system solution is limited because of its dependency on the additional functionality being built into the storage device.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention is a symmetric shared storage architecture wherein a file stored by one of the external protocol processing nodes on a storage server and associated storage device can be retrieved through any other node. Thus, it is sufficient just to add a new external protocol processing node to scale performance of the system or an empty storage node to scale capacity of the system in a way that is transparent to external client applications.  
           [0009]    This approach also enables transparent “vertical” scalability of the storage architecture. One can use a limited number of expensive, high-performance file servers that hold a “working set” of data, and also have a large amount of inexpensive storage (such as low-performance, inexpensive file servers, tape robots, jukeboxes with optical disks, etc.) to provide storage capacity for the “aging” data. The migration of data is entirely transparent and automatic (on-demand upon a request to read or write to a file, or asynchronously whenever a file is being migrated to tertiary storage). Also file data stored initially on any given BSS node can be migrated later to any other node.  
           [0010]    A symmetric shared storage architecture according to the invention enables configuration of redundant sets of nodes within the system such as gateway or storage servers rather than disks within a traditional storage array (set of disks). In a traditional storage array (RAID), data stays available when a disk crashes but becomes unavailable when a file server attached to the storage array goes down. In a symmetric shared storage architecture, a crash of any component (in particular any protocol processing node or storage node) does not affect availability of the data.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    These and other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures, wherein:  
         [0012]    [0012]FIG. 1 illustrates a conventional file storage system using network attached storage;  
         [0013]    [0013]FIG. 2 illustrates a conventional file storage system using storage-area network technology;  
         [0014]    [0014]FIG. 3 illustrates an example of a file storage system according to the present invention;  
         [0015]    [0015]FIG. 4 is a block diagram of a scalable file storage system according to an embodiment of to the present invention;  
         [0016]    [0016]FIG. 5 is a diagram showing metadata and data storage including hierarchical storage management according to one example of the present invention;  
         [0017]    [0017]FIGS. 6A to  6 D show data structures used in various examples of the present invention;  
         [0018]    [0018]FIG. 7 is a block diagram of storage devices with varying cost and performance characteristics according to an embodiment of the present invention; and  
         [0019]    [0019]FIG. 8 is a simplified routine showing data migration according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    The present invention will now be described in detail with reference to the drawings, which are provided as illustrative examples of the invention so as to enable those skilled in the art to practice the invention. Notably, the implementation of certain elements of the present invention may be accomplished using software, hardware or any combination thereof, as would be apparent to those of ordinary skill in the art, and the figures and examples below are not meant to limit the scope of the present invention. Moreover, where certain elements of the present invention can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present invention will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the invention. Further, the present invention encompasses present and future known equivalents to the known components referred to herein by way of illustration.  
         [0021]    An example of a symmetric shared storage system  300  according to an embodiment of the present invention is illustrated in FIG. 3. As shown in FIG. 3, clients of symmetric shared storage system  300  access the data network of the filer through a variety of application programs *such as an NFS client  302 , a CIFS client  304 , an HTTP client  306  or an FTP client  308 . These types of applications are provided for purposes of illustration only, and are not limiting. The client applications connect to the data network through a load-balancing node  310 . A load-balancing node can be one or more load balancing nodes that make up a private load-balancing network  311  to provide increasing levels of availability, redundancy, and scalability in performance. For example, two load-balancing nodes can provide greater availability, redundancy, and scalability of performance than one load-balancing node. Three load balancing nodes can provide more than two, etc. A single load-balancing node is shown in FIG. 3 for purposes of illustration only and is not limiting.  
         [0022]    Load balancing node  310  then connects to one or more gateway service nodes  312 . Gateway service nodes  312  are connected to an internal network  314 . In one implementation, internal network  314  is a switched Internet Protocol (IP) based network, but the invention is not limited to that. Internal network  314  consists of one or more network services that provides connectivity to a distributed Bitfile Storage Service (BSS)  324  made up of one or more Bitfile Storage Servers  324   a - d.  Internal network  314  is also connected to a distributed Metadata Service (MDS)  315  made up of one or more metadata servers  316 , a Bitfile Storage Service Manager (BSS Manager)  320 , a System Management Service (SMS)  328 , and Life Support Service (LSS)  330  made up of a primary  331  and backup server  332 , and a Configuration to Database Service (CDB)  329  made up of one or more CDB servers  325   a - b.  Although filer  300  is illustrated as comprising a distributed BSS made up of four Bitfile Storage Servers  324   a - d,  a distributed MDS  316  made up of two metadata servers  316   a  and  316   b,  an LSS  330  made up of a primary server  33  land backup server  332 , a CDB Service  329  made up of two CDB servers  325   a - b,  one instance of BSS Manager server  320  and one instance of SMS  328 , those skilled in the relevant art(s) will understand, based on the teachings contained herein, that additional bitfile storage servers  324 , metadata servers  316 , BSS Manager servers  320 , SMS instances  328 , and LSS instances may be added to the network and still be within the spirit and scope of the invention. Most services provide redundancy, that is, they have a pair of servers. However, some services such as BSS Manager and SMS are stateless and will be automatically restarted. With this pair scheme and stateless feature, the system is completely redundant and does not have a single point of failure.  
         [0023]    Gateway Service (GS) nodes  312   a  through  312   c  provide external access to the entire system and are the only service that can be accessed by a user. GS is connected to both the internal private network  314  and to an outbound load-balancing network  310 . However, those skilled in the relevant arts(s) would recognize that although the GS communicates with internal clients and external clients, internal private network  314  and outbound load-balancing network  310  are but examples, and the physical and virtual network layouts are not limited to these or any particular layout. In this way, each of the GS nodes  312  provides access to all the files stored in the system for applications that are executed on the GS node, as well as remote outbound nodes that communicate through the network using standard file access protocols such as NFS, CIFS, HTTP, IMAP, POP, etc. Files stored in the system can be accessed in an identical way from an application executed on any of the GS nodes and GS nodes can enable network access to the file repository. Thus, the system  300  is “symmetrical” in that the each gateway node has uniform access to metadata stored in MDS  315  and file data stored in BSS  324  so that client requests for file access can be serviced by any gateway node without any performance penalty. Further, the particular gateway node that is directed by load balancer  310  to service the client request for file access is transparent to the client.  
         [0024]    A GS node does not hold either file data or metadata persistently, but rather mediates communication between an application or a remote network node and the services that hold persistent file data (BSS) and metadata (MDS). Thus, the GS need not keep any persistent (nonvolatile) state, but it can keep volatile state; for example, it can cache both file data and metadata to provide better performance.  
         [0025]    A GS node  312  communicates directly with a BSS node  324  to perform an I/O operation on file data. However, in order to determine what BSS node  324  to communicate with, it uses the file data location provided by the MDS  315 . The MDS  315  gets all the file system namespace and attribute operations (for example, look-up files by name, read directory entries, get and set file attributes) from its communication with the GS nodes who implement the file access applications such as NFS, CIFS, HTTP, IMAP, POP, etc. The Metadata Service (MDS)  315  holds the file system namespace and the file metadata (attributes). Holding the file system namespace and file attributes in the MDS eliminates any need for the GS nodes to keep persistent state about file system namespace and file metadata (attributes). However, the GS nodes may cache this information for better performance.  
         [0026]    The Bitfile Storage Service (BSS)  324  provides persistent storage for the file data stored in the system. Each of the nodes  324   a - d  offers shared network access to storage devices  326   a - d  it can control directly.  
         [0027]    The BSS Manager  320  manages crash recovery in the BSS, as well as file data migration and replication between different nodes in a manner that will be described in more detail in connection with FIGS. 7 and 8. The BSS Manager makes this process transparent to the Gateway Service and to clients who access the system through it.  
         [0028]    The Life Support Service (LSS)  330  monitors resource shortages and failures and routes around planned and unplanned resource outages to minimize human interaction to manage the system. This is a logical service that does not require dedicated physical resources, but rather uses physical resources of the GS, MDS, and BSS.  
         [0029]    The System Management Service (SMS)  328  configures, monitors, and controls physical and logical resources associated with the symmetric shared storage system. Most of this service is a logical service that does not require dedicated physical resources, but rather uses physical resources of GS, MDS, and BSS. However, the SMS accesses the CDB  329  for stored information. CDB  329  must be hosted separately and may require its own physical resources.  
         [0030]    In general, each GS node  312  need not be aware of the other GS nodes and need not keep any state about other nodes, and each BSS node  324  need not be aware of the other BSS nodes and need not keep any state about other nodes. However, each of the GS nodes can communicate with any other node (for example, to guarantee cache consistency) and all BSS to nodes can communicate between each other (for example to migrate file data between nodes). One advantage of not keeping any state about other nodes is that nodes can be transparently added to or removed from the GS and the BSS. As will be explained in more detail in connection with FIG. 4, adding GS nodes improves performance of the system by increasing the Gateway Service processing resources, while adding BSS nodes increases capacity of the system without the requirement of any explicit migration of file data or metadata. Unlike the case of a traditional file server, the system performance and capacity are not limited by performance or capacity of any single server even if all the users attempt to access or store data in the same part of the file system.  
         [0031]    For example, in network  100  (FIG. 1), the combination of storage arrays  114  and disks  116  and in network  200  (FIG. 2), the combination of storage arrays  214  and disks  216  contain both stored data as well as the metadata associated with that data. In the present invention, however, bitfile storage servers  324  and their respective disk storage  326  contain stored bitfiles, while the metadata associated with the stored bitfiles from all of the bitfile storage servers  324  is stored in metadata server  316  and its associated disk storage  318 . The terms  bitfile  and  file data  are equivalent and can be, for example and without limitation, file content (data) of a file, file extents (variable size portion of a file), set of blocks of data (in a block oriented storage), etc. The terms  bitfile  and  file data  should not be construed as to limit the invention to any particular semantic.  
         [0032]    An example of filing and retrieving data in the present invention as compared to the prior art will now be provided. Referring back to FIG. 1, an application accesses NAS  100  by using an application program running on a client such as NFS client  102  and using a network protocol such as NFS. The command to store data from the application is routed via access network  110  to a selected file server  112  (e.g., file server  112   a ). The data is then stored by the respective storage array (e.g., storage array  114   a ) onto the corresponding disk  116  (e.g., disk  116   a ). The metadata associated with that data is created as part of this storage process and is also stored on the same disk (e.g., disk  116   a ). When a client desires to access the data to either read it or to modify it, the client must then access the data through the same file server (e.g., file server  112   a ) to the same storage array and disk (e.g., storage array  114   a  and disk  116   a ). If the client were to access file server  112   b , the client would not be able to gain access to the data.  
         [0033]    Referring back to FIG. 2, an example of storing and retrieving data is herein provided. An application accesses SAN  200  by using an application running on for example NFS client  202  and using a network protocol such as NFS. The command to store data from the application is routed via access network  210  to a selected file server  212  (e.g., file server  212   b ). The data is then stored by the assigned storage array (e.g., storage array  214   a ) onto the corresponding assigned disk volume  216  (e.g. disk volume  216   a   1 ). The assigned disk volume can be any on the network. The metadata associated with that data is created as part of this storage process and is also stored on the same disk volume (e.g., disk volume  216   a l). When a client desires to access the data to either read it or to modify it, the client must then access the data through the same file server (e.g., file server  212   b ) that is assigned to the same storage array, and disk volume (e.g. storage array  214   a  and disk volume  216   a   1 ). If the client were to access file server  212   a , the client would not be able to gain access to the data. However, the network administrator would be able to reassign storage array  214   a  and disk volume  216   a   1  to  212   a .  
         [0034]    In the present invention (FIG. 3), the application accesses data storage network  300  by using an application running on, for example and without limitation NFS client  302  and using a network protocol, such as, for example and without limitation, NFS. The command to store data is then routed through load balancing node  310 . Load balancing node  310  then routes the command to store the data to one of the gateway service nodes  312  (e.g. gateway service node  312   a ). The data is then routed through internal network  314  to a selected bitfile storage server  324  and corresponding disk  326  (e.g., bitfile storage server  324   a  and disk  326   a ) using a proprietary file/block oriented protocol according to a policy directed by bitfile storage service manager  320 . This policy may be, for example and without limitation, to store the data on the disk that has the most available storage capacity. When the data is stored on disk  326 , the metadata created corresponding to that stored data (e.g. by gateway service node  312   a  in communication with BSM  320 ) is then stored by MDS  315 , for example and without limitation, by one of the Metadata servers  316  (e.g. Metadata server  316   a ) on one of the disks  318  (e.g. on disk  318   a ). Thus, the file data (on Bitfile Storage Server  324  and disk  326 ) and the metadata (on Metadata Server  316  and disk  318 ) associated with the file data are stored in two separate locations. All metadata associated with data stored in data storage network  300  is stored by for example and without limitation MDS  315  on Metadata Server  316  and disk  218 .  
         [0035]    When the original client, or another client, attempts to access this stored data at a subsequent time, the command to access the data is routed from the client&#39;s application (e.g., NFS  302  or CIFS  304 ) through load balancing node  310  to a gateway service node  312 . This gateway service node does not have to be the same node as was used to store the data originally. The command to access the data is then routed from Gateway Service node  312  (e.g., Gateway Service node  312   b ) through internal network  314  to Metadata Server  316  (e.g.  316   a ). Metadata Server  316  obtains the metadata for the requested data from disk  318  (e.g.  318   a ) and directs the request for the data to the appropriate Bitfile Storage Server  324  and corresponding disk  326  (e.g., Bitfile Storage Server  324   a  and disk  326   a ). If the data is modified as a result of the access (e.g., more data is added), the metadata is correspondingly updated.  
         [0036]    Thus, according to the present invention, the client does not need to know where the data is stored when a request is made to access that data, and the request to access it can be routed through any of the gateway service nodes  312 .  
         [0037]    Example data structures used to enable this transparency and symmetry, and to maintain correspondence between file identifiers known by clients, and file locations that are transparent to clients are shown in FIGS. 6A to  6 D. These data structures are maintained in MDS  315  by servers  316  in disks  318 , and are thus used as a portion of the metadata in one example of the present invention. Those skilled in the relevant arts will understand, based on the teachings contained herein, that other data structures may be used and fall within the spirit and scope of the invention. For example, other data structures may be used to maintain file attributes and other information not including file locations in system  300 .  
         [0038]    As shown in FIG. 6A, bitfile storage locator (BSL)  602  is a metadata entry that corresponds a single file having a file identifier (e.g. a filename and/or directory path) specified in field  604  with a physical identifier (e.g. one of the storage servers  324   a - d  and storage device  326   a - d ) specified in field  606  that provides a location for the bitfile data of the file in storage service  324 . The correspondence between a file and its location in the BSS can be created in accordance with communications with BSM  320  and certain policies implemented by BSM  320  (e.g. store the file in the device having the most space), for example. Thus, a client requesting access to a file need only supply the identifier of the file to the gateway service. The receiving gateway service node  312  then communicates with MDS  315  to retrieve the location in BSS  324  of the file corresponding to the given filename.  
         [0039]    [0039]FIG. 6B illustrates another example of data structures that can be used to implement a portion of the metadata maintained by MDS  315 . In this example, the physical file locations can be represented as logical (symbolic) locations and mappings (translation tables) from the logical to physical locations (e.g. as established by BSM  320 ). Accordingly, BSL  612  includes a field  614  that corresponds a logical storage identifier (e.g. a volume identifier) with a file identifier known to a client specified in field  616 . The data structures further include a table  623  that corresponds logical storage identifiers with physical storage identifiers reflecting the physical locations of the corresponding logical storage in the BSS  324 . Thus, a client requesting access to a file still need only supply the identifier of the file to the gateway service. The receiving gateway service node  312  then communicates with MDS  315  to retrieve the location in BSS  324  of the file corresponding to the given filename, in the process the MDS  315  looking up the physical location from a logical identifier associated with the given filename.  
         [0040]    [0040]FIG. 6C illustrates another example of data structures used to implement a portion of the metadata maintained by MDS  315  wherein mirroring is used to provide redundancy (e.g. as established by BSM  320 ). As shown in FIG. 6C, table  632  includes entries that correspond a first logical identifier (e.g. “vol. 0”) with second logical identifiers (e.g., “vol. 1” and “vol. 2”) to identify where two copies of the same file are stored. In this example, if one of the servers or one of the storage devices becomes inaccessible, the data will continue to remain available using the mirrored data. The technique of mirroring data is used to increase data availability. The data structures further include a table  633  that corresponds logical storage identifiers with physical storage identifiers reflecting the physical locations of the corresponding logical storage in the BSS  324 . Thus, a client requesting access to a file still need only supply the identifier of the file to the gateway service. The receiving gateway service node  312  then communicates with MDS  315  to retrieve the location in BSS  324  of the file corresponding to the given filename. In the process of providing the location information, the MDS  315  looks up the logical identifier corresponding to the given filename in table  632  to determine if any mirrors have been specified for the corresponding logical identifier. In either event, MDS  315  looks up in table  633  and provides the physical locations from the logical identifier(s) associated with the given filename back to the gateway service.  
         [0041]    [0041]FIG. 6D illustrates another example of data structures used to implement a portion of the metadata maintained by MDS  315  wherein a single file might be stored across one or more storage devices in a group of physical storage devices (e.g., a redundant array of independent disks (RAID), a cluster of disk drives, etc. as established by BSM  320 ). In this example, BSL  642  further includes an index field  646  used to identify in which storage device the start of data is stored. In an embodiment using “striping,” an array of disk drives  650  might be used. In the example shown in FIG. 6D, four storage devices  651 - 654  are shown. A file is stored across array of drives  650 . The storage device ( 651 - 654 ) where the start of the file is located is identified by the value in the index field  646 . Data in a file is then stored in blocks in a sequential fashion across the array of storage devices beginning at the start the storage device identified by the index field  646  value. The size of the blocks is usually limited to not exceed a certain predefined block size. For example, if a file size is 40 Kb and the index field  646  points to storage device  651 , the first 16 KB of the data in a file will be stored in storage device  651 , the second 16 kb of the data in the file will be stored in storage device  652 , and the remaining data (8 kb) will be stored in storage device  653 . Smaller files (less than the block size) may be stored in any one of the storage devices  651 - 654 . Larger files can wrap around in sequence across the array of storage devices  650 . The striping technique can be used to provide parallel access to multiple storage servers and storage devices in order to improve performance.  
         [0042]    The following descriptions provide examples of how the transparency and symmetry features of the present invention, as enabled by the storage system architecture illustrated in FIG. 3 and the data structures shown in FIG. 6, can be exploited by various file storage schemes for certain advantages.  
         [0043]    [0043]FIG. 4 is a block diagram of a scalable and redundant file storage system  400  according to an embodiment of the present invention. Scalable means that any system resource can be increased by adding more nodes. Redundant means that any system resource can remain available even if any of its components fail. Scalable and redundant file storage system  400  includes a scalable and redundant Gateway Service  410 , and a scalable and redundant Metadata Service  420  coupled to Gateway Service  410  through a network  480 . A scalable and redundant storage service  440  is coupled to Gateway Service  410  through network  480 . A System Management Service (SMS)  450 , a Life Support Service (LSS)  460  and a Storage Service Manager  470  are also coupled to network  480 . SMS  450 , LSS  460 , and Storage Service Manager  470  are scalable logical services that do not have dedicated servers, but instead run on other servers in the system, for example and without limitation Metadata Server  421 . SMS  450  and Storage Service Manager mediates access to configuration database (CDB)  429 , through network  480 . CDB  429  is a service hosted separate from the SMS and Storage Service Manager which may require its own physical resources. It should be apparent to those skilled in the art that, although GS  410 , MDS  420  and Storage Service  440  are all shown as being scalable, only certain one(s) of them may be scalable.  
         [0044]    CDB  435  provides information about the current state of resources in each of GS  410 , MDS  420  and BS  440 . The SMS uses this information to start and enable various servers. Once the servers are ready for operation, they register with LSS  460 . The LSS  460  is responsible for delivering service routing and connectivity information to the various nodes to enable them to communicate with one another as resources are added and removed. The registration with LSS and the subsequent delivery of service routing and connectivity information enables scalability and redundancy of the present embodiment. Scalable and redundant Gateway Service  410  includes a plurality of external protocol processing nodes  411 - 413 . Scalable and redundant storage service  440  includes a plurality of storage servers  441 - 443  and storage devices  491 - 493 . Metadata Service  420  in one embodiment is scalable and redundant, and includes metadata servers  421  and  422 , and MDS databases  431  and  432 .. SMS  450  in one embodiment is scalable. LSS  460  in one embodiment is scalable and includes primary server  461  and backup server  462 . CDB Service  429  is scalable and redundant in one embodiment and includes CDB servers  425   a - b  and CDBs database  427   a - b.  BSS Manager  470  in one embodiment is scalable.  
         [0045]    [0045]FIG. 5 is a diagram showing metadata and data storage implementing a hierarchical storage management (HSM) scheme in a scalable and redundant file storage system according to one example of the present invention. In this example, MDS  320  includes one or more metadata nodes. Metadata node  321  includes a Metadata server  421  coupled to a storage device  423 . Similarly, Metadata node  322  includes a metadata server  422  coupled to a storage device  424 . Storage devices  423  and  424  can be any type of storage device including, but not limited to, devices used in an HSM scheme such as, but not limited to, disk drives. Metadata Servers  421 ,  422  can be any type of control logic for managing and controlling access to respective storage devices  423 ,  424 . Such control logic can be provided as software, firmware, hardware, or any combination thereof in any type of processor unit. Storage devices  423 ,  424  can be any type of data storage device storing on any type of media, including but not limited to, disk drives (magnetic or optical), memory, etc. Configuration Database Service  429  includes a CDB server  425   a  coupled to a configuration database  427   a  and CDB server  425   b  coupled to a configuration database  427   b.  Configuration database  427   a  includes logical/physical mappings  440  and configuration database  427   b  includes logical/physical mappings  441 . Logical/physical mappings  440  and  441  are described further with respect to FIG. 6.  
         [0046]    BSS  350  includes one or more storage nodes. Storage node  351 includes a storage server  451  coupled to a storage device  452 . Storage node  352  includes a storage server  453  coupled to a storage device  454 . Storage node  353  includes a storage server  455  coupled to a storage device  456 . Similarly, storage node  354  includes a storage server  457  coupled to a storage device  458 . Storage devices  452 ,  454 ,  456 , and  458  can be any type of storage device including, but not limited to, devices used in an HSM scheme such as, but not limited to, disk drives and tape drive units. A variety of storage devices can be used to create a logical hierarchy of storage devices that allows frequently accessed data to be stored on disk and infrequently accessed data to be stored on tape. Data can also be migrated between storage nodes as needed.  
         [0047]    Storage devices  423  and  424  store metadata. A metadata entry holds for example and without limitation, a file system namespace, file metadata attributes, and identifies the logical or physical (one or more) locations of file data in scalable storage system  300 . Storage devices  452 ,  454 ,  456 , and  458  store data, such as files of any type of format and content (e.g., digital data representing text, audio, video, or any other type of multimedia content or other information). For example, as shown in FIG. 5 and explained in more detail in connection with FIG. 6, in scalable file storage system  300 , a metadata entry (“metadata 1”) can be stored in storage device  423 . “Metadata1” identifies the location of a file stored as “data 1” in storage device  452 . “Metadata 2” is stored in storage device  424 . “Metadata 2” identifies the location of a file stored as “data 2” in storage device  458 . “Metadata 3” is stored in storage device  423 . “Metadata 3” identifies the location of a file stored as “data 3” in storage device  456 . “Metadata1” can also identify a copy of “data 1” that has been migrated to tertiary storage (i.e., to storage device  454  or to any other storage node or device). Data migration will be described further with respect to FIGS. 7 and 8.  
         [0048]    Separation of the file metadata from the file data enables transparent migration of file data between nodes in the BSS layer. However, to achieve transparent data migration from one location in BSS to another also requires consistent updating of file data locations in the MDS and the invalidation of old locations cached in the external protocol processing nodes. The ability to migrate data transparently further enables usage of the symmetric shared file storage system according to the invention as a hierarchical storage management (HSM) system and provides all the benefits and functionality of traditional HSM systems. For example and without limitation, the BSS servers can control storage devices with different cost and performance characteristics. The BSS provides persistent storage for the file data stored in a file storage system, while the BSM manages file data migration between the different nodes.  
         [0049]    [0049]FIG. 7 is a diagram showing a flexible BSS  640  controlling storage devices with varying cost and performance characteristics in a file storage system according to one example of the present invention. Those skilled in the relevant arts will understand, based on the teachings contained herein, that other storage devices and combinations may be used and fall within the spirit and scope of the invention.  
         [0050]    Each storage server offers shared network access to some storage it can control directly. In this example, BSS  640  includes disk storage devices, tape storage device, and shared storage devices. Storage node  641  is coupled to a disk storage device  651 . Storage node  642  is coupled to tape storage device  652 . Storage node  643  is coupled to disk storage device  653  and tape storage device  654 . Storage nodes  644  and  645  are coupled to disk storage device  655  and  656 , respectively, and shared tape library storage device  665  (e.g. tape drives  666   a  and  666   b ). An operational process of file data migration between different locations within the BSS layer is described at a high-level. The operational process is often represented by a flowchart. The flowchart is presented herein for illustrative purposes only, and is not limiting. In practice, those skilled in the relevant art(s) will appreciate, based on the teachings contained herein, that the invention can be achieved via a number of methods. Furthermore, the flow of control represented by the flowchart is also provided for illustrative purposes only, and it will be appreciated by persons skilled in the relevant art(s) that other operational control flows are within the scope and spirit of the invention.  
         [0051]    [0051]FIG. 8 is a flowchart of a routine for data migration  600  according to an embodiment of the present invention (steps  810 - 840 ). In step  810 , a file is copied to a target destination. For example, data  1  can be copied from storage device  653  to tertiary storage  654 . This copy operation can be performed as part of hierarchical storage management where, for example, it may be desirable to move data accessed less frequently to less expensive storage media such as tape storage. This copy operation can be initiated manually or automatically through BSS Manager  670  for any reason.  
         [0052]    In step  820 , metadata entries corresponding to the migrated data are updated to reflect the new locations of the file data determined in step  810 . For example, the BSL entries in the data structures shown in FIG. 6 are updated to reflect the new locations for each filename corresponding to the files that have been moved.  
         [0053]    In step  830 , data at old locations can be optionally removed. Once data is copied to another location, the MDS can maintain entries that point to both the data at the old location and data at the new location by mirrors for example. However, the data from the old location can be deleted for any reason. Removal of old data is done transparently to the user.  
         [0054]    In step  840 , external protocol processing nodes access the updated metadata and have continuous access to file data regardless of its location. In addition, this data migration and access to the new locations is transparent to the external client. The symmetry between the gateway service processing nodes provides a further advantage of the present invention in that any of gateway service processing nodes  611 - 614  (and any future external protocol processing nodes added in scaling file system  700 ), by using the updated metadata, can access the migrated data.  
         [0055]    Although the present invention has been particularly described with reference to the preferred embodiments thereof, it should be readily apparent to those of ordinary skill in the art that changes and modifications in the form and details may be made without departing from the spirit and scope of the invention. It is intended that the appended claims include such changes and modifications. It should be further apparent to those skilled in the art that the various embodiments are not necessarily exclusive, but that features of some embodiments may be combined with features of other embodiments while remaining with the spirit and scope of the invention.