Electrical computers and digital processing systems: multicomput – Master/slave computer controlling – Master accessing slave storage
Reexamination Certificate
1999-01-05
2001-03-27
Vu, Viet D. (Department: 2154)
Electrical computers and digital processing systems: multicomput
Master/slave computer controlling
Master accessing slave storage
C709S241000, C709S241000, C710S074000, C710S120000
Reexamination Certificate
active
06209023
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to storage support systems for storage area networks and more particularly to a system and method of virtualizing SCSI semantics from a host computer or server onto a non-SCSI transport medium of a storage area network.
2. Description of the Related Art
For the last couple of decades, the number of computer systems has grown exponentially and the capabilities of the average computer system to assimilate and process data has doubled every eighteen months. These two facts have created a spectacular rise in the demand for raw data storage capacity to support the growing capabilities of computers to assimilate and process data. The demand to add more data storage capability to computer networks, service more users, and provide data security in the form of data backup storage has been unrelenting. The trend in recent years has been to provide a separate data storage network, or storage area network (SAN), for storing data for a network of computers.
The primary advantage of a SAN is the ability of a group of computer users to pool their data without using a local area network (LAN) for tasks like transferring data files and providing backup of stored data files. For example, on a LAN when one station on the LAN generates a 500 MB video file, a second station can access the 500 MB video file if the first station simply transfers the read/write permissions for the video data file to the second station. A very large data file that might take hours to transfer on a LAN can be transferred to a SAN in minutes or seconds. The use of a SAN as opposed to a LAN frees valuable bandwidth on the LAN for client applications and provides scalability not found in the more traditional approaches to data storage such as connecting read/write servers directly to the LAN. Other advantages of a SAN configuration over a LAN configuration include computer clustering, topological flexibility, fault tolerance, high availability, and remote management. Because of the clear advantages of a SAN over a LAN, SAN approach to data storage has been implemented with success between a variety of high data access devices like file servers, backup servers, database servers, and shared storage arrays.
The primary storage interface for servers deployed in SAN systems is a parallel Small Computer System Interface (SCSI). While various forms of parallel SCSI's exist, the predominant form of parallel SCSI has been termed SCSI-2. SCSI-2 introduced enhanced SCSI device data transfer methodologies while maintaining the asynchronous transfer of data, instructions, and messages from earlier SCSI implementations.
Due to certain limitations inherent in a parallel SCSI, many designers of network systems are starting to turn from a traditional parallel SCSI to a non-SCSI transport medium such as a Fibre Channel interconnect medium. As computers and peripheral devices have continued to improve in performance capability, the limitations imposed by a parallel SCSI became apparent. Higher performance processors demanded higher throughput of the subsystem used to store data. A Fibre Channel interconnect medium has substantially addressed these concerns. A Fibre Channel interconnect medium has a serial interface which supports increased bandwidth, additional connectivity, longer distance operation, and greater flexibility.
Several topologies are defined for a Fibre Channel interconnect medium including Fabric, point-to-point, and the Arbitrated Loop. The Fabric topology is a switched connection that allows multiple pairs of devices to exchange messages simultaneously, creating a high aggregate bandwidth. The point-to-point topology is probably the simplest, consisting of a single connection between two devices. The most popular topology is the Arbitrated Loop (FC-AL) in which the out-bound cable of one device becomes the in-bound cable for the next, allowing for the connection of up to 126 devices at a time.
All of the topologies share a single coding scheme and framing protocol. A Fibre Channel interconnect medium currently sends information in frames containing a 24-byte header followed by up to 2118 bytes of data. At most, handshaking occurs after the transmission of every frame of data, unlike the synchronous transfer mode in a SCSI protocol in which a ‘sender’ is allowed to perform a fixed number of transfers before the ‘sender’ (target or initiator) stalls waiting for an acknowledgment. Like the traditional parallel bus SCSI protocol, every transaction has an initiator and a target and makes use of the SCSI command set semantics.
Current operating system environments are designed to be able to communicate with SCSI-2 devices attached via the traditional parallel SCSI bus. The SCSI-2 standard is currently in the process of being updated to produce a SCSI-3 standard. One of the key features of SCSI-3 is an attempt to separate the command protocol from dependencies on the physical interconnection medium, thus allowing for SCSI-3 command and data flow over a serial bus such as a Fibre Channel interconnect medium. Current operating system environments, however, have bene unable to handle many aspects of supporting a SCSI-3 device on a non-parallel bus because of the semantic differences between parallel and non-parallel busses. In addition, so far as is known, the notion of ‘bridging’ SCSI-2 servers across a serial bus environment or non-SCSI transport medium to SCSI-2 devices such as tape drives, storage medium changers, printers, scanners, optical memory devices, CD-ROM drives or hard disk drives is not provided for by an established or developing standard.
The first SCSI-3 devices available are likely to be SCSI-3 hard disk drives. Certain other devices which are available as SCSI-2 devices may not be offered as SCSI-3 devices for some time. Since Fibre Channel interconnect medium protocol (SCSI-FCP) is currently a SCSI-3 protocol, the use of Fibre Channel interconnect medium has precluded proper connectivity of SCSI-2 servers-command initiators to target SCSI-2 devices.
SUMMARY OF THE INVENTION
Briefly, the present invention provides a firmware system and method of virtualizing SCSI semantics SCSI server-command initiators onto a non-SCSI transport medium of a storage area network. A bridge having a non-SCSI front end and a SCSI back end provides firmware for virtualizing SCSI semantics onto a non-SCSI transport medium. Virtualization of the SCSI semantics permits the non-SCSI transport medium to support SCSI devices. A non-SCSI transport medium refers to a transport medium other than a traditional parallel interface. A non-SCSI front end refers to a front end of a bridge coupled to a non-SCSI transport medium.
In the disclosed embodiment, a storage area network having a Fibre Channel interconnect medium (a non-SCSI-2 transport medium) includes a plurality of hosts or initiators, a SCSI bus or plurality of SCSI busses coupled to a plurality of SCSI devices, and a bridge having a Fibre Channel front end coupled to the Fibre Channel interconnect medium and a SCSI-2 back end couples to the SCSI bus or plurality of SCSI busses. The bridge provides firmware for performing various techniques for virtualizing certain SCSI-2 semantics to ensure proper operation of a SAN using a SCSI-2 devices in a Fibre Channel interconnect medium. Examples of these SCSI-2 semantics include: (a) RESERVE/RELEASE support, (b) unit attention support, and (c) non-tagged command processing support for the initiators.
RESERVE/RELEASE support is virtualized by implementing virtual command responses to the RESERVE and RELEASE SCSI-2 commands. A World Wide Name data table stores the Fibre Channel word wide names (WWN) and the arbitrated loop addresses (ALPA) for the initiator nodes. When the bridge of the present invention receives the RESERVE command from an initiator, a reserve flag is set within a logical device record of a device table for the target unit or device to indicate that a reserve is in effect for the target. At login time, a check is made of the targets for rese
Dimitroff John E.
Freeman Eugene E.
Grant David L.
Gready Robert S.
Ritter Raymond A.
Akin Gump Strauss Hauer & Feld & LLP
Compaq Computer Corporation
Vu Viet D.
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