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    AST RESEARCH, INC.         TECHNICAL BULLETIN # 1158                4-26-95

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    			 MANHATTAN SMP HOT REPLACEMENT AND HOT SWAP

    This is an informational bulletin.

    The information contained in this bulletin is intended to assist trained
    technicians in performing Hot Swap and Hot Replacements of hard disks
    with the Empire DAC 960 disk array subsystem, on the Manhattan SMP.

    Knowledge of the Manhattan SMP and the operation of the DAC 960 and
    associated utilities is required.

    Do not attempt a Hot Replacement of a hard disk, unless all hardware and
    software configuration for the Manhattan SMP, the Empire DAC 960, the
    operating system, and the replacement drive are set correctly.  Attempting a
    Hot Replacement with hardware or software incorrectly configured may
    result in loss or corruption of data.

    For more information regarding the Manhattan SMP, see the Manhattan SMP
    Installation and Maintenance Manual, AST Part Numbers 001169-001 or
    001725-001.

    For more information on the Empire DAC 960, see the AST Disk Array
    Users Manual, AST Part Number 001724-001.

    This document is divided into two sections.  Section one lists problems that
    may have led a Hot Replacement drive to fail.  Section two lists problems
    that may have led a Hot Stand-by to fail.

    HOT REPLACEMENT FAILURES

    If a Hot Replacement drive fails, verify that the following guidelines have
    been met, and/or check for the following error or configuration conditions.

    1. The replacement drive must be the same capacity or larger than the failed
       drive.

    2. The replacement drive must be installed into the failed drive's drive bay.

    3. Ensure that the replacement drive is the drive intended to be replaced, and
       that its hardware configuration (i.e. SCSI ID) is as intended.

    4. The replacement drive must have been low level formatted.

    5. Ensure that the replacement drive does not have a SCSI ID conflict.  A
       SCSI ID conflict may stop all the drives on the same channel, and crash the
       system.

    6. Ensure that the SCSI ID cables are connected correctly.  Pin 1 of the SCSI
       ID cable, must be connected to SCSI ID jumper pin 1.  If the cable is
       reversed, the SCSI ID will not be set correctly.

    7. Ensure that the termination is set correctly on the replacement drive.
       A termination conflict may cause the sub-system to fail.  The termination
       is set on the backplane of the Manhattan SMP, and therefore hard drives
       should have termination disabled.

    8. Ensure that the drive is set to spin when initialized by the DAC 960.

    9. If the replacement drive can not be set to Stand-by, wait 10 seconds, and
       then try the command again (the drive may be in the process of spinning
       up).  Check to make sure that the drive status is Dead.  If it is not Dead,
       then use the Kill option in the DAC960TK utility to change the drive's
       status to Dead.

    Note: Use care with the Kill option.  If the wrong drive has its status set to
    Dead by the Kill command, the system will crash.

    HOT STAND-BY FAILURES

    If a Hot Stand-by drive fails, investigate the following areas, and take the
    appropriate steps to bring the system back to its expected configuration.
    Determine why the hot Stand-by failed and take any required action to ensure
    that the configuration will function with a Hot Stand-by drive.

    1. The Hot Stand-by Drive may be the wrong capacity.  The Hot Stand-by
       needs to be the same capacity as the failed drive.  (See also Technical
       Bulletin number 1055, RAID Considerations with AST's Mylex DAC.)
       Perform a Hot Replacement of the failed drive and not the Stand-by drive.

    2. The Hot Stand-by drive may have been used previously as a data drive.
       If the Hot Stand-by has been used as a data drive, use the Hot Replacement
       method to replace the failing drive, then low level-format the Hot Stand-by
       drive and set its status to 'Standby.'

    3. A Hot Stand-by drive may have been installed, when a hot replacement
       was required.  Perform a Hot Replacement of the failed drive using its
       drive bay location.

    4. A drive may have been killed using the DAC960TK 'kill' command.  A Hot
       Replacement must be performed on the drive that was killed.  The 'kill'
       option will not start a rebuild on a Hot Stand-by.

    5. The RAID configuration may be either RAID level 0 or RAID level 7.
       These RAID environments are not redundant, and can not be rebuilt.
       The drive must be replaced, reconfigured, and data restored from a backup.
       If no backup is available and there may be corrupt data on the RAID drive,
       the user can attempt to set the dead drive's status to 'on-line' to recover.

    6. The Hot Stand-by drive may have failed while rebuilding data.  Perform a
       Hot Replacement on the Hot Standby-by drive.  A new drive should be
       placed in the original failed drive's location, low level formatted, and
       set to 'Stand-by.'

    7. The Hot Stand-by may have been installed into the wrong drive bay.
       Perform a Hot Replacement of the failed drive.  When the failed drive is
       removed from the system and the new hot standby is installed, the new hot
       standby drive must be installed into the failed drive's drive bay.  The new
       Hot Stand-by drive must be low level formatted, the drive must spin up, and
       the drive must be set to 'Stand-by.'

    8. A new Hot Stand-by drive may have failed.  Perform a Hot Replacement
       on either the failed drive, or the Hot Stand-by.  Use the DAC960TK utility's
       remap command, to determine which drive needs replacement.  The new Hot
       Stand-by drive must be low level formatted, the drive must spin up, and the
       drive must be set to 'Stand-by.'

    9. Eight Hot Stand-bys may have been performed.  Perform a Hot Replacement of
       the failed drive.  Check the number of Stand-by Rebuilds using the remap
       option of the DAC960TK utility.  Reset using the DAC960CF.BAT utility
       (view/edit - save).