Method and system for switching SCSI devices utilizing an analog multiplexor

• US 6,330,246 B1
• Filed: 08/21/1998
• Issued: 12/11/2001
• Est. Priority Date: 08/21/1998
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Klein, Craig Anthony, Denning, Donald Eugene, Emberty, Robert George
• Primary Examiner(s): VINCENT, DAVID ROBERT
• Application Number:
  US09/137,883
• Time in Patent Office: 1,208 Days
• Field of Search: 370/362, 370/364, 370/438, 370/439, 370/533, 370/535, 370/537, 710/101, 710/107, 710/126, 710/129
• US Class Current: 370/438
• CPC Class Codes: G06F 13/4022 using switching circuits, e.g. switching matrix, connection or expansion network G06F13/4009 takes precedence

Abstract

An analog SCSI switch comprising initiator device ports, target device ports and a controller utilizing at least one analog multiplexor circuit is connected between a SCSI interface and multiple SCSI devices. The controller monitors the SCSI bus and controls all interfaces and ports. By monitoring the SCSI bus, the controller is constantly informed of the arbitration, selection and re-selection acts of the initiator device or target devices. An analog multiplexor circuit selectively connects the initiator device and target device directly, allowing direct communication between the initiator device and a particular target device for duration of the connection. Logic for the controller, contained in the switch onboard memory, utilizes a secondary logical unit number of a target device to map a target device port. Utilizing the analog multiplexor circuit, the switch connects the initiator device port to a selected, mapped target device port. Error recovery is accomplished between the target device and initiator device, thus eliminating the need for buffers. Addressability of the SCSI interface is expanded to cover the number of target device ports multiplied by the number of target devices.

Claims

1. A switching apparatus, in a data processing system having an interface, an initiator device, a plurality of target devices and a SCSI bus interconnecting said interface and said initiator device with said plurality of target devices, comprising:

a switch, interposed between said SCSI bus and said plurality of target devices, having an analog multiplexor circuit for connecting said initiator device to a selected one of said plurality of target devices; and

controller means for selectively connecting and reconnecting said initiator device to said selected one of said plurality of target devices.

2. The switching apparatus in claim 1, wherein switch interposed between said SCSI bus and said plurality of target devices, having an analog multiplexor circuit for connecting said initiator device to a selected one of said plurality of target devices, further comprises:

an initiator device port;

a plurality of target device ports; and

a programmable controller having

a memory, said memory having logic for controlling said interface, monitoring a SCSI bus, and for connecting said initiator device port to a selected one of said plurality of target device ports utilizing said analog multiplexor circuit.

3. The switching apparatus in claim 2, further comprises a monitoring circuit for monitoring said SCSI bus which interconnects said initiator device with an initiator device port on said switch.

4. The switching apparatus in claim 1, wherein said interface is a SCSI interface.

5. The switch in claim 2, wherein said programmable controller having a memory, said memory having logic for controlling said interface, monitoring a SCSI bus, and for connecting said initiator device port to a selected one of said plurality of target device ports utilizing said analog multiplexor circuit, further comprises:

controller means for utilizing a secondary logical unit number as an address of said selected one of said plurality of target devices to map to said selected one of said plurality of target device ports;

modification means for changing a field in said secondary logical unit number to zero; and

regulation means for continuing connection of said initiator device and said selected one of said plurality of target device ports for the life of the communication.

6. A method for switching SCSI devices, in a data processing system having an initiator device, an interface, a SCSI bus, a plurality of target devices, and a switch having at least one initiator device port, a plurality of target device ports, a programmable memory and an analog multiplexor circuit, comprising:

interposing said switch between said SCSI bus and said plurality of target devices;

interconnecting said switch, said initiator device and said plurality of target devices, wherein said initiator device is connected to said initiator device port and said plurality of target devices are connected to said plurality of target device ports;

switching between said initiator device port and said plurality of target device ports;

transmitting I/O communications between said initiator device and a selected one of said plurality of target devices;

allowing said selected one of said plurality of target devices to interrupt said connection from said initiator device;

re-establishing said connection between said one of said plurality of target devices to said initiator device; and

continuing said I/O communication to completion.

7. The method in claim 6, wherein interposing said switch between said SCSI bus and said plurality of target devices, further comprises:

utilizing said switch for

controlling said interface,

monitoring said SCSI bus and

connecting said initiator device port to a selected one of said plurality of target device ports utilizing said analog multiplexor circuit.

8. The method in claim 7, further comprising:

utilizing a secondary logical unit number of a selected target device address to map said selected target device address to said selected one of said plurality of target device ports;

changing a field in said secondary logical unit number to zero;

maintaining connection of said initiator device and said selected one of said plurality of target device ports; and

continuing said I/O communication to completion of said I/O communication.