Abstract:
At least one network device that moves storage blocks based upon a session layer or higher protocol set is employed to facilitate communication between at least one host and at least one target storage device. The at least one network device may include a server and a switch. Transactions related to data storage access are expressed in a non-network protocol and transmitted via a network protocol data unit across at least a portion of the network by employing encapsulation. An adapter card associated with the data storage unit is employed to extract the non-network protocol transaction. Multiple, mirrored data storage units that are separated by relatively large physical distance may be employed to reduce the likelihood of catastrophic data loss due to an event such as a fire. Further, READ transactions may be facilitated by preloading data storage units with READ metadata for subsequent transmission to a client device to enable expedited access to data stored on the data storage units.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     A claim of priority is made to U.S. Provisional Patent Application Ser. No. 60/208,472, entitled Data Access in a Network Environment, filed on Jun. 2, 2000. 
    
    
     FIELD OF THE INVENTION 
     The present invention is generally related to network communications, and more particularly to applications for networked storage systems. 
     BACKGROUND OF THE INVENTION 
     Techniques that enable multiple computers to access multiple data storage devices in a network are known. For example, personal computers may access a Redundant Array of Independent Disks (RAID) through a server. The personal computers may communicate with the server via a Local Area Network (LAN) employing Ethernet, Token Ring or FDDI, while the server communicates with the storage devices associated with the RAID in accordance with a non-network protocol such as Small Computer System Interface (SCSI). However, such known configurations have limitations. For example, the number of data storage devices that can be addressed via each SCSI interface is limited to only 4, 8 or 16, depending on the version of SCSI that is implemented. Further, the physical characteristics of the SCSI cabling that connects the data storage devices to the server impose limitations on the geographic placement of the data storage devices. In particular, the server and the data storage devices must be located in relatively close physical proximity because the maximum practical length of the SCSI cabling is relatively short. Such proximity results in vulnerability to catastrophic data loss due to events such as fire. While techniques for communicating SCSI transmissions over larger distances via Internet Protocol (IP) and Fiber Channel (FC) have been proposed, some of the problems remain. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, at least one network device that moves storage blocks based upon a session layer (Open Systems Interconnection (“OSI”) Layer 5) or higher protocol set is employed to facilitate communication associated with storage between at least one host and at least one target storage device. The network device may be a switch. Further, the switch may be situated within the network, rather than at the network edge. Transactions related to data storage access may be expressed in a non-network protocol and transmitted via a network protocol data unit across at least a portion of the network by employing techniques such as encapsulation. 
     The present invention enables network data storage implementations with enhanced performance and reduced likelihood of catastrophic data loss. Performance is enhanced because a relatively large number of data storage devices may be addressed, thereby enabling N-way striping and mirroring. The likelihood of catastrophic data loss is reduced because the physical distance between individual data storage devices can be increased. For example, data stored in a first data storage device may be mirrored by a second data storage device that is located at a sufficiently great physical distance from the first data storage device to mitigate the possibility of contemporaneous destruction of both data storage devices by an event such as a fire. Flexibility in the choice of physical location for data storage devices combined with N-way mirroring enables load balancing and storage of selected data on a faster communication path relative to selected network devices, such as devices that most frequently access the data, without precluding data access by other network devices. Further, network scalability is facilitated by simplifying network connections. Hence, many devices may share a file store and data storage devices may be easily added to the network. 
     In another embodiment of the present invention, a READ operation is facilitated by transmitting READ metadata to the filesystem associated with the client. The READ metadata describes a procedure for accessing data stored on at least one networked storage device, and may be maintained by a filesystem associated with a content owner device. When a client transmits a READ transaction to the networked storage device, READ metadata is transmitted from the networked storage device to the client device. The transmitted READ metadata is selected to be sufficient to enable the client device to obtain the data associated with the READ operation from the networked storage device without communication with the content owner device. The client employs the metadata with a “read only” read utility to obtain the data. Since a “local copy” of the metadata is employed and the content owner device is not included in the read transaction, performance is improved. The content owner device may issue an update by providing new metadata to the networked storage device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention will be more fully understood from the following Detailed Description and Drawing, of which: 
         FIG. 1  is a block diagram of a portion of a network that illustrates use of a storage services protocol set to facilitate network storage; and 
         FIG. 2  is a block diagram of a portion of a network that illustrates a READ operation in a network where the data is owned by a content owner device. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a block diagram of a portion of a network. Client devices  8 ,  9 ,  10 ,  11 ,  12 ,  13 ,  14  are connected with a plurality of data storage units  16 ,  18 ,  20 ,  22 ,  24 ,  26  via hosts  33 ,  34 ,  35  and a switch  50  capable of moving storage blocks based upon a session layer or higher (“storage services”) protocol set. Each device in the network is associated with a network address, such as an Internet Protocol (IP) address. Each data storage unit includes an interface adapter  38  and at least one physical storage device  40  such as a disk. 
     The storage services protocol set is employed to facilitate transmission of data units associated with storage operations between the clients and the data storage units. Transactions between the clients and the hosts may be represented in network protocol data units  42 , such as packets, frames or cells. In the illustrated embodiment, communication of transactions between the clients and the hosts is in accordance with Transport Control Protocol (TCP) or Unacknowledged Datagram Protocol (UDP) over IP over Ethernet. Corresponding communications between the hosts, switch  50  and data storage units  16 – 26  employ modified representations of the network protocol data units wherein SCSI, IDE or similar command sets are employed by the storage services protocol set. In particular, corresponding non-network protocol transactions are generated and encapsulated in network protocol data units  44  to provide, for example, SCSI or IDE over TCP or UDP over IP over Ethernet. Those skilled in the art will recognize that other protocols may be utilized. 
     The hosts employ metadata to generate the encapsulating data units. For example, in a READ operation initiated by the client  10 , a representation of at least one block or file to be retrieved is transmitted from the client to the host  34  via data unit  42 . Following receipt of the data unit  42 , the host  34  determines where data that corresponds to the READ operation is located at the storage devices by employing metadata that is maintained on a filesystem  46  associated with the host  34 . The metadata describes the directory hierarchy, file attributes, permissions, and file layout in terms of a block address chain. The host may first employ the metadata to determine whether to allow the client access to the data. Techniques for determining whether to allow access are well known in the art. If access to the data is to be allowed, the host employs the metadata to generate a corresponding non-network protocol READ transaction that is encapsulated in at least one network protocol data unit  44 . For example, a SCSI transaction and a header portion may be generated and combined to form the new protocol data unit  44 , where the SCSI transaction is placed in the payload portion of the data unit. The new network protocol data unit  44  is then transmitted to the switch  50 , which directs the data unit  44  to the appropriate data storage unit  26  based on predetermined criteria, such as IP destination address and storage services protocol set information. 
     The data storage units operate upon the encapsulated transactions following receipt thereof. For example, the READ transaction is executed by retrieving the data that is specified by the encapsulated SCSI transaction and returning that data to the host  34 . Following receipt of the network protocol data unit  44  by the designated data storage unit  26 , the encapsulated transaction is extracted from the data unit. In particular, the interface adapter  38  associated with the data storage unit  26  is employed to strip the header portion of the data unit from the payload portion. The IP source address and other information from the header portion may be retained to facilitate transmission of data from the data storage unit to the host. The remaining non-network protocol transaction is employed to retrieve data in accordance with techniques known in the art. The interface adapter  38  is employed to encapsulate the retrieved data in at least one network protocol data unit  46  that designates the IP address of the host in the destination field. The network protocol data unit  44  is transmitted to the host  34  via the switch  50  based on predetermined criteria, such as IP destination address and storage services protocol set information. Following receipt of the data unit  44  that contains the data, the host generates at least one corresponding network protocol data unit  48  that indicates the IP address of the client in the destination address field. The client  10  extracts the data from the data unit  48 . 
     The predetermined criteria for directing the data units may include employing the storage services protocol set at the switch or elsewhere to facilitate implementation of the data storage units as a Redundant Array of Independent Disks (RAID). If data is mirrored, striped or otherwise located on a plurality of the data storage units, the data units associated with the transactions are replicated at the switch based on storage services protocol set information. Reliable unicast or reliable multicast may be employed by the switch to transmit the data units between the hosts to the data storage units. 
     The storage services protocol set may also be employed to enhance performance by balancing the data access load and testing for data integrity. In the case of a READ operation where mirroring is implemented, load data may be employed by the switch to determine the data access load on each data storage unit, and to balance the load on the data storage units by transmitting the data unit associated with the transaction only to a selected data storage unit with relatively less load. Alternatively, the data unit may be transmitted to each mirrored data storage unit in order to obtain data from the fastest responding mirrored data storage unit. Alternatively, data returned from a plurality of mirrored data storage units may be compared by the switch to provide greater assurance of data integrity. 
     In order to provide protection against catastrophic data loss, the mirrored data storage units may be separated by relatively large physical distances. In mirroring, multiple identical copies of data are maintained on multiple disks, typically one copy per disk where each data storage unit includes at least one disk. The disks associated with mirrored pairs are separated by a sufficiently large distance to protect against contemporaneous destruction by a catastrophic event such as fire. Further, performance may be enhanced by implementing an N-way mirrored RAID, where N is limited only by the number of available IP addresses. Individual mirrored disks associated with the N-way mirrored RAID are disposed along a respective fast communication path relative to areas of greater network activity. For example, a mirrored disk may be located near each one of a group of urban areas. 
     Referring now to  FIG. 2 , data access may also be enhanced by providing metadata to the clients. In the illustrated network portion, hosts are not employed and data ownership is asserted by a content owner device  56 . The content owner  56  retains control of READ and WRITE privileges for at least some of the data stored in the data storage units  16 – 26 . However, metadata from filesystem  62  is provided to the data storage units by the content owner device via at least one data unit  60 . To obtain owned data, the client  10  initially transmits a READ transaction to at least one of the data storage units. The READ transaction employs at least one network protocol data unit  58  that designates at least one file or block of data that is to be transmitted to the client. The data unit  58  is transmitted from the client to the Layer 3 router  36 , and from the Layer 3 router to the designated data storage units. The receiving data storage units process the READ transaction to determine whether to grant the client access to the data. Techniques for determining whether to allow access are well known in the art. If access to the data is to be allowed, the data storage unit selects READ metadata that describes the location of the data associated with the READ transaction in terms of a block address chain. The selected READ metadata is transmitted from the data storage unit to the client via the Layer 3 router in at least one network protocol data unit  70 . 
     The transmitted READ metadata is employed by the filesystem  64  of the client  10  to directly access the associated data from the data storage units. A new READ transaction is generated by the client and transmitted to the data storage units via at least one network protocol data unit  72 . In particular, a non-network protocol READ transaction is placed in a payload portion of at least one protocol data unit, and a header portion is generated for the protocol data unit. The header portion of the protocol data unit  72  includes a source address field that contains the IP source address that is associated with the client  10 , and a destination address field that contains the IP destination address that is associated with the appropriate data storage unit  22 . The data unit is then transmitted to the Layer 3 router, which routes the data unit to the data storage unit designated by the IP destination address. Following receipt of the network protocol data unit by the data storage unit, the encapsulated non-network protocol READ transaction is extracted from the data unit  72 . In particular, the interface adapter  38  associated with the data storage unit  22  is employed to strip the header portion of the data unit from the payload. The IP source address and other information from the header portion may be retained to facilitate transmission of data from the data storage unit to the client. The READ transaction is executed by retrieving the data that is specified by the READ transaction and returning that data to the client. As described above, the interface adapter is employed to place the retrieved data in at least one network protocol data unit that designates the IP address of the client in the destination field. The network protocol data units are then transmitted to the client via the Layer 3 router. A host could alternatively be employed to mitigate the client&#39;s computational overhead associated with encapsulating non-network protocol transactions. The content owner device transmits updated metadata to the data storage units when the storage content changes. 
     The described technique is compatible with RAID implementations and mirrored sites in an Internet environment. In the case of a READ operation where mirroring is implemented, the READ metadata that is transmitted from the content owner device to the data storage units and from the data storage units to the client may each be selected to achieve one or more performance objectives. For example, load data may be employed to determine the data access load on each data storage unit, and balance the load on the data storage units by transmitting READ metadata that corresponds to a selected data storage unit with relatively less load. Alternatively, READ metadata corresponding to a data storage unit that is located along a relatively faster communication path to the client relative to other data storage units may be transmitted to the client. The READ metadata may alternatively correspond to a plurality of data storage units in order to obtain data from the fastest responding data storage unit. 
     Variations, modifications and different applications of the invention taught in the Detailed Description and Drawing will be apparent to those skilled in the art. For example, it will be understood by those skilled in the art that the described storage services protocol set based processing functions may be performed by a device other than the illustrated switch. Accordingly, it should be understood that other embodiments of the invention might be practiced without departing from the spirit and scope of the invention as defined by the appended claims.