Data processing: database and file management or data structures – Database design – Data structure types
Reexamination Certificate
2000-10-13
2003-12-02
Rones, Charles (Department: 2175)
Data processing: database and file management or data structures
Database design
Data structure types
C707S793000
Reexamination Certificate
active
06658417
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention pertains to digital data processing and, more particularly, to the sharing of disk drives and other storage devices on a networked digital data processing system. The invention has application, for example, in the processing of video, graphics, database and other files by multiple users or processes on a networked computer system.
In early computer systems, long-term data storage was typically provided by dedicated storage devices, such as tape and disk drives, connected to a central computer. Requests to read and write data generated by applications programs were processed by special-purpose input/output routines resident in the computer operating system. With the advent of “time sharing” and other early multiprocessing techniques, multiple users could simultaneously store and access data—albeit only through the central storage devices.
With the rise of the personal computer and PC-based workstations in the 1980's, demand by business users led to development of interconnection mechanisms that permitted otherwise independent computers to access one another's storage devices. Though computer “networks” had been known prior to this, they typically permitted only communications, not storage sharing.
Increased power of personal computers and workstations is now opening ever more avenues for their use. Video editing applications, for example, have until recently demanded specialized video production systems. Now, however, such applications can be run on high-end personal computers. By coupling these into a network, multiple users can share and edit a single video work. Reservation systems and a host of other applications also commonly provide for simultaneous access to large files by multiple parties or processes. Still other tasks may require myriad small files to be accessed by multiple different parties or processes in relatively short or overlapping time frames.
Network infrastructures have not fully kept pace with the computers that they interconnect. Though small data files can be transferred and shared quite effectively over conventional network interconnects, such as Ethernet, these do not lend themselves, for example, to sharing of large files. Thus, although users are accustomed to seemingly instantaneous file access over a network, it can take over an hour to transfer a sixty second video file that is 1.2 GBytes in length.
Some interconnects permit high-speed transfers to storage devices. The so-called fiber channel, for example, affords transfers at rates of up to 100 MBytes/sec—more than two orders of magnitude faster than conventional network interconnects. Although a single storage device may support multiple fiber channel interfaces, the industry has only recently set to developing systems to permit those workstations to share such files on a storage device. Moreover, when a file is to be accessed by multiple users, the overhead of server intervention can result in loss of speed advantages and efficiencies otherwise gained from the high-speed interface. In this regard, techniques such as locking, maintaining ghost files, monitoring file changes and underking multi-step access, check-in or housekeeping operations may be unworkable when multi-user access to many small files must be provided quickly.
In many situations, and for many specific types of networks, the coherence and security of a centralized shared access system are desirable, but the nature of their storage transactions may be ill-suited to permitting shared access due for example, to the burden imposed by file management protocols for tracking files, versions, and file size changes, and so forth.
In view of the foregoing, an object of the invention is to provide improved digital data processing systems and, particularly, improved methods and apparatus of high-speed access to data in storage devices on a networked computer system.
A related aspect of the invention is to provide such systems that achieve fast operation with files of diverse sizes.
A related aspect of the invention is to provide such systems as can be implemented with minimum cost and maximum reliability.
Yet another object of the invention is to provide such systems as can be readily adapted to pre-existing data processing and data storage systems.
Yet still another object of the invention is to provide such systems as can be readily integrated with conventional operating system software and, particularly, conventional file systems and other input/output subsystems.
SUMMARY OF THE INVENTION
One or more of the foregoing and other desirable objects are attained by the invention, which provides novel term- or lease-based methods and apparatus for accessing shared storage on a networked digital data processing system.
A system according to one aspect of the invention includes a plurality of digital data processing nodes and a storage device, e.g., a disk drive, a “jukebox,” other mass storage device or other mapped device (collectively referred to herein after as “disk drive,” “storage device” or “peripheral device”). First and second ones of the nodes, which may be a client and a server node, respectively, are coupled for communication over a LAN, network or other communications pathway. Both the first and the second nodes are in communications with the storage device. This can be over the same or different respective logical or physical communications pathways.
By way of non-limiting example, the first node and the second node can be a client and a server, respectively, networked by Ethernet or other communications media, e.g., in a wide area network, local area network, the Internet interconnect, or other network arrangement. The server and/or client can be connected to the storage device via a SCSI channel, other conventional peripheral device channel, such as a fibre channel, “firewire” (i.e., IEEE 1394 bus), serial storage architecture (SSA) bus, high-speed Ethernet bus, high performance parallel interface (HPPI) bus or other high-speed peripheral device bus.
A file system or other functionality in the second (server) node receives and responds to at least selected requests—e.g., file OPEN requests—from the first (client) node for access to a file on the storage device, by generating a “lease”. The lease includes a block map or other administrative data (referred to elsewhere herein as “meta data”) for the requested file, as well as an expiry time indicating how long the administrative data is valid.
Upon grant of the lease, the client node accesses the storage device using the block map or other administrative data supplied with the lease. The server node assures that this administrative data remains valid for the period of the lease, e.g., such that list and order of blocks comprising the file does not change—e.g., shrink, disappear or become reassigned to other files, during the client's use of the file. Correspondingly, the client node ceases utilization of the administrative data (and, presumably, ceases at least direct access of the file) after lease expiry.
Related aspects of the invention provide a system as described above in which lease expiry is keyed to the time of the initial client request. Hence, both the client and server nodes can accurately determine lease expiry time by reference to their own clocks; network time synchronization is therefore not necessary for effective operation of the system.
Further aspects of the system provide a system as described above in which the client issues a request for read-only or a read/write access to the file, and in which the server node grants a corresponding lease. For read/write leases, the server effects defragmentation, clean-up or other administration of the file once the lease has expired, e.g., via the server file system or via a file management system or controller on the storage device. The server node can also monitor activity by read/write “leaseholders,” e.g., for rapid notification of meta data changes upon expiry of the lease.
Typically, no such administration is required at termination of a read-only lease, since
Haselton William
Stakutis Christopher J.
International Business Machines - Corporation
Konrad Raynes Victor & Mann LLP.
Rones Charles
Victor David W.
Wu Yicun
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