System, apparatus, and method for automatic node isolating SCSI terminator switch

A clustered computer system comprising:

• a first computer;
• a second computer;
• a plurality of disk drives storing data;
• a Small Computer System Interface (SCSI) bus coupling a plurality of port terminals at each of said first computer, said second computer, and said plurality of disk drives;
• and
• a bus switching circuit interposed on said SCSI bus between said first computer and said plurality of disk drives for automatically terminating said SCSI bus and decoupling and isolating at least some of said port terminals of said first computer from said second computer when said first computer is disconnected from said SCSI bus or powered-down, said switching circuit receiving a termination power voltage from said bus and selectively providing electrical termination of said SCSI bus.

A clustered computer system comprising:

• a first server computer at a first node;
• a second server computer at a second node;
• a plurality of hard disk drives for storing data;
• a Small Computer System Interface (SCSI) bus coupling said first server said second server, and said plurality of disk drives;
• and
• a bus switching circuit interposed on said SCSI bus between said first computer and said plurality of disk drives for automatically terminating said SCSI bus and isolating said first server computer from said second computer when said first computer is disconnected from said SCSI bus or powered-down, said bus switching circuit receiving a termination power voltage from said bus and selectively providing electrical termination of said SCSI bus;
• said bus switching circuit further comprising:
• a first input/output port having a plurality of first port terminals;
• a second input/output port having a plurality of second port terminals;
• a terminator circuit having predetermined electrical characteristics,
• a reference voltage generator for generating a reference voltage;
• a voltage comparator circuit for comparing a termination power (TERM PWR) voltage received over said SCSI bus from a first side of said SCSI bus with said reference voltage and for generating a switch control signal having a first state when said first voltage has a predetermined magnitude relationship relative to said reference voltage;
• and
• a multi-pole switch for coupling said first port terminals to said terminator circuit in response to receipt of said first state of said switch control signal and for coupling said first port terminals to said second port terminals in response to receipt of another state of said switch control signal.

A Small Computer System Interface (SCSI) bus switching circuit comprising:

• a first multi-line SCSI input/output port having a plurality of first port terminals;
• a second multi-line SCSI input/output port having a plurality of second port terminals;
• a bus termination circuit coupled to and receiving a termination power voltage from a first side of said bus and selectively providing electrical termination of said SCSI bus;
• a reference voltage generator for generating a reference voltage;
• a voltage comparator circuit for comparing a termination power (TERM PWR) voltage received over said SCSI bus from a first side of said SCSI buss with said reference voltage and for generating switch control signals having a first state when said first voltage has a predetermined magnitude relationship relative to said reference voltage;
• a plurality of individual field-effect transistors (FETs), each responsive to said switch control signals to couple one of said first port terminal lines of said multi-line SCSI bus to either said second port terminals or said terminator circuit, said coupling to said terminator circuit including decoupling said first port terminals from said second port terminals to automatically isolate said multiline SCSI bus within a isolation time of between substantially 1 nanosecond and substantially 50 nanoseconds, said FETs coupling said first port terminals to said bus termination circuit in response to receipt of said first state of said switch control signals and for coupling said first port terminals to said second port terminals in response to receipt of another state of said switch control signal;
• and
• said bus termination circuit provides automatic termination on said SCSI bus when a SCSI device connected to said second input/output port loses power, is powered-down, or becomes disconnected from the SCSI bus.

In a Small Computer System Interface (SCSI) bus based computer system, a method for bus switching comprising steps of:

• coupling a terminator circuit to and receiving a termination power voltage from a first side of said bus and selectively providing electrical termination of said SCSI bus;
• generating a reference voltage;
• comparing a said termination power voltage received over said SCSI bus from a first side of said SCSI bus with said generated reference voltage;
• generating switch control signals having a first state when said first voltage has a predetermined magnitude relationship relative to said reference voltage;
• and
• receiving said control signals by a plurality of transistor switches and selectively coupling said first port terminals to said terminator circuit and decoupling said first port terminals from said second port terminals to isolate said first port terminals from said second port terminals in response to receipt of said first state of said switch control signal and coupling said first port terminals to said second port terminals in response to receipt of second state of said switch control signals.

A Small Computer System Interface (SCSI) bus switching circuit comprising:

• a first SCSI input/output port having a plurality of first port terminals;
• a second SCSI input/output port having a plurality of second port terminals;
• a terminator circuit coupled to and receiving a termination power (TERM PWR) voltage from a first side of said buss and selectively providing electrical termination of said SCSI bus;
• a reference voltage generator for generating a reference voltage;
• a voltage comparator circuit for comparing a termination power (TERM PWR) voltage received over said SCSI bus from a first side of said SCSI bus with said reference voltage and for generating a switch control signal having a first state when said first voltage has a predetermined magnitude relationship relative to said reference voltage;
• a first multi-pole switch for coupling said first port terminals to said terminator circuit and decoupling said first port terminals from said second port terminals to isolate said first port terminals from said second port terminals in response to receipt of said first state of said switch control signal;
• and
• a second multi-pole switch for coupling said first port terminals to said second port terminals in response to receipt of another state of said switch control signal.