System, apparatus, and method for automatic node isolating scsi

Abstract

System, apparatus, arid method for automatically detecting power-down, disconnection, or other failure of a SCSI bus connected device and isolating the SCSI node from the rest of the computer environment. Sensing a problem at the device node and substituting a buss termination circuit for the termination that had been provided by the device. Sensing the reconnection or power-up of a device at a SCSI bus mode and simultaneously reconnects the device's own terminator and removes the termination provided at disconnection. Particularly useful in clustered computer environments, such as for example, for data base server systems in which a plurality of server computers share a common data base comprised of one or more disk drives on a SCSI bus. Permits any of the servers to be disconnected from the clusters system or network and be repaired or replaced without powering-down or otherwise disabling the entire system or other devices on the system. One embodiment provides a switching circuit including 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,. a voltage comparator circuit for comparing an externally provided first voltage with the reference voltage and for generating a switch control signal, and a switch for coupling the first port terminals to the terminator circuit and decoupling the first port terminals from the second port terminals to isolate the first port terminals from the second port terminals in response to receipt of a state of the switch control signal and for coupling the first port terminals to the second port terminals in response receipt of another state of the switch control signal.