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    AST RESEARCH, INC.          TECHNICAL BULLETIN # 1142               4-14-95

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    				    ENSURING PROPER SCSI TERMINATION

    This is an informational bulletin.

    Manhattan servers use a SCSI disk sub-system, which must be correctly
    terminated at each of its ends. Termination must only be installed at each end
    of the SCSI bus.  All devices in the middle of the SCSI bus must have their
    termination disabled/removed .

    The following provides an overview of the termination required for various
    AST Manhattan Servers. The configurations are assumed to be using internal
    SCSI subsystems only.

    NOTE:  For all configurations, any device attached in the middle of the SCSI
    bus (between the terminator on the SCSI backplane and the terminator on the
    system board) must have its termination removed/disabled.

    1) In an AST Manhattan P system, the termination is built into both the system
    board and the SCSI backplane.

    2) In an AST Manhattan V system, the termination is built into the system
    board.  The termination on the last device on the SCSI bus must be enabled.

    3) In an AST Manhattan SMP system, the termination is built into the Empire-5
    DAC and a terminator  (167300-003) must be installed on the SCSI backplane.

    4) In an AST Manhattan G system, the termination is built into the NCR PCI
    SCSI II controller. The termination on the last device must be enabled.

    For other configurations please refer to the system documentation.

    When a SCSI disk sub-system is incorrectly terminated, the sub-system may
    fail.  Failures can include: drives intermittently dropping off-line;
    data-corruption on the hard drives; and duplicated or shadowed drives.
    These problems can be caused by either a lack of termination, incorrectly
    placed termination, or over termination of the sub-system.

    An example of an incorrectly terminated SCSI sub-system would be one in which
    all hard drives have termination enabled.  In this case, the drives may been
    seen by the controller, and be configurable, but they may drop off-line
    intermittently.

    Due to the complexity of SCSI disk sub-systems, a termination tester is
    available from the vendor listed below.  The tester is plugged into an
    external SCSI port (or cable attached to the system board or SCSI backplane),
    and will indicate whether the SCSI bus is properly terminated, unterminated,
    or over-terminated.  This testing should be performed on any system that
    exhibits problems, such as those described in this bulletin.

    WARNING: Before performing any tests to the system, ensure that all data has
    been backed up and all configuration settings have been recorded.  Changes
    made to the SCSI bus or termination could result in the loss of data,
    configuration information, or RAID settings on the hard drives.  The tester
    does not operate as a terminator and does not determine the location of the
    terminators found.  The system should not be operated while the tester is
    installed.

    In addition to the Termination Tester, a cable is required on some systems to
    attach the tester to the system. To use the tester with a Manhattan Server,
    you should follow these guidelines:

    A) For Manhattan P/V using embedded NCR controller:

    Use cable Part Number 501623-001 - External cable connection kit.  This kit
    contains a cable (AST P/N 221344-001), which attaches to the external SCSI
    controller connector on the system board (location J56B or J57B).  The Tester
    is then attached to the external cable connection (at the end of the newly
    added cable).  To test the system, termination must be disabled in System
    Setup before testing, and if required re-enabled after testing.

    B) For Manhattan P/V using DPT PCI Disk Array Controller:

    No cable is necessary to use the tester.  The tester is attached to the
    external SCSI II port on the DPT PCI controller.  To test the system,
    termination must be disabled in the DAC configuration utility (accessed
    using  during a boot) before testing, and if required re-enabled
    after testing.

    NOTE: This method will only test the first SCSI Channel.  To test the second
    channel, follow warnings above, and move drives from the second to the first
    channel, and then perform the termination testing.

    C) For Manhattan SMP using Mylex DAC 960 Controller:

    Use cable kit Part Number 501622-001 - External cable connection kit.  The kit
    contains a 50 pin SCSI cable (AST P/N 221383-001) which can be attached to the
    SCSI backplane.  Follow warnings above before testing.  The backplane
    terminator (167300-003) should be removed, and the external cable attached to
    the backplane in its place.  The Termination Tester can then be attached to
    the end of the cable for testing.

    D) For Manhattan G using the NCR PCI SCSI II controller:

    No cable is necessary to use the tester. T he tester is attached to the
    external SCSI II port on the NCR PCI SCSI II controller.  To test the system,
    termination must be disabled on the NCR PCI SCSI II controller before testing,
    and if required re-enabled after testing.

    E) For Manhattan XP
    No cable is necessary to use the tester.  Remove the external SCSI cable
    attached to the SCSI II port on the back of the Manhattan XP and attach the
    Tester to the Manhattan XP external SCSI II port.

    SCSI TERMINATION TESTER

    VENDOR: METHODE ELECTRONICS - DATAMATE
    VENDOR PART NUMBER: DMTT - 50HD
    VENDOR DESCRIPTION: SCSI SINGLE-ENDED 50 POSITION TERMINATION TESTER

    CONTACT INFORMATION:
    Call 1-800-323-6858 or 708-867-9600
    Corporate Headquarters:
    7444 West Wilson Avenue
    Chicago, IL 60656

    Methode-Electronics - Datamate has international subsidiaries in many
    countries. Refer to your local directory assistance, or call the number above
    for a referral to your nearest international distributor.