Electrical computers and digital data processing systems: input/ – Input/output data processing – Input/output access regulation
Reexamination Certificate
1998-10-22
2001-01-30
Lee, Thomas C. (Department: 2782)
Electrical computers and digital data processing systems: input/
Input/output data processing
Input/output access regulation
C710S120000, C710S120000
Reexamination Certificate
active
06182167
ABSTRACT:
TECHNICAL FIELD
This invention relates to Small Computer Systems Interfaces (SCSI), and specifically to the SCSI interconnection of multiple hosts to a multiport SCSI device.
BACKGROUND OF THE INVENTION
The Small Computer Systems Interface (SCSI), e.g., SCSI-2, is a standardized relationship of commands and responses for communicating across a bus, widely used to couple peripheral devices, such as input and output devices and data storage devices (e.g., disks and tapes), to small and medium-size host computers, including to workstations and personal computers (PCs).
It may be advantageous for more than one host computer to non-concurrently utilize the same data storage device so that the host computers may share the same stored data. Several approaches have been advanced for allowing sharing of the same data storage device.
U.S. Pat. No. 4,975,838, Mizuno et al., describes a duplex, concurrent system with bus connecting units for selectively interconnecting two system busses, each having a memory unit. The specialized bus connecting units are operated under a specialized, non-standard arrangement to switch the connections to allow either system to operate separately, or to be interconnected to each other so that the memory units have the same addresses and are operated simultaneously. Non-concurrent use of the same data cannot be conducted using standard SCSI protocol, and requires coordination of the interconnection process.
U.S. Pat. No. 4,821,170, Bernick et al., provides a multiple-channel direct memory access device I/O controller for arbitrating data bus usage between two host processors by operating latches associated with each of two ports to “grant ownership” of the device controller to one of the ports. Again, the specialized logical interconnection process prevents non-concurrent use of the same data using standard SCSI protocol.
U.S. Pat. No. 5,471,634, Giorgio et al., interfaces a plurality of hosts with a controller which operates a SCSI initiator to interface with a plurality of peripheral target devices. The controller stores the status of each device for all host processors and, when a host requests status, the controller clears its memory for the host for the target. However, the hosts are on the same bus and a specialized host adapter is required to independently and logically connect through the SCSI initiator to a target device.
U.S. Pat. No. 5,596,727, Literati et al., provides gates which enable only one host and only one bank of devices at a time over a SCSI bus. The gates are specifically enabled and disabled, preventing non-concurrent use of the same data using standard SCSI protocol.
Another approach is to simply employ separate SCSI device ports for each of the hosts, allowing the hosts to non-concurrently share the device without requiring the changing of SCSI cables. Typically, under SCSI-2, while both device ports are online, the hosts are treated for the most part as if they were on the same SCSI bus.
This results in the problem that, when the storage device is recovering from a reset condition on one SCSI bus at one port, a host from another SCSI bus at another port may “steal” the storage device. Depending on the status of the device, for example, if a tape cartridge is loaded and ready on the device, the second host may reposition the tape and operate with the tape cartridge to the detriment of the original host.
SUMMARY OF THE INVENTION
It is an object of the present invention to allow multiple hosts to non-concurrently utilize the same multiport device, complying with SCSI standard protocol and using existing host software, while providing protection against other hosts on other ports.
Disclosed are a method, a multiport device, an article of manufacture comprising a computer readable medium having computer readable program code embodied therein, and a computer program product for coupling multiple host ports to a multiport device in a Small Computer Systems Interface (SCSI) system, each host port coupled at an associated device port of the multiport device. The SCSI system has OFFLINE or status signaling which indicates that a device is unavailable or offline, and has standard SCSI protocol device Reservation, device Release, and Device Reset capabilities.
The method comprises initially allowing any host port to reserve the multiport device at an associated one of the device ports of the multiport device. In response to a Reservation command for the multiport device from one of the host ports at the associated one device port, the method reserves the multiport device at the one device port in accordance with standard SCSI protocol, and implements at all the device ports other than the one device port the OFFLINE or status signaling which indicates that the multiport device is unavailable or offline. In one embodiment, the multiport device controller sets all the device ports other than the one device port offline. In response to a Device Reset from the one host port for the associated one device port, the method operates the multiport device in accordance with standard SCSI protocol, including resetting the reservation of the multiport device at the one device port in accordance with standard SCSI protocol, and additionally maintains the implemented OFFLINE signaling. In another embodiment, status signaling is employed to prevent other hosts from gaining the attention of the multiport device.
Then, in response to a Release command from the one host port for the associated one device port, the method releases the reservation of the multiport device in accordance with standard SCSI protocol, and additionally terminates the OFFLINE or status signaling.
Other standard SCSI protocol events than a Release command may be utilized to cause the device to be released. One example may comprise an operator selected Manual Online event.
For a fuller understanding of the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4821170 (1989-04-01), Bernick et al.
patent: 4975838 (1990-12-01), Mizuno et al.
patent: 5274773 (1993-12-01), Squires et al.
patent: 5471634 (1995-11-01), Giorgio et al.
patent: 5566345 (1996-10-01), Ostrowski
patent: 5596727 (1997-01-01), Literati et al.
patent: 5805821 (1998-09-01), Saxena et al.
patent: 5925120 (1999-07-01), Arp et al.
Basham Robert Beverley
Jesionowski Leonard George
Holcombe John H.
International Business Machines - Corporation
Kim Harold
Lee Thomas C.
Sullivan Robert M.
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