    AST RESEARCH, INC.        TECHNICAL BULLETIN # 1055                  1-20-95

    			   RAID CONSIDERATIONS WITH AST'S MYLEX DAC

    PROBLEM
    A physical disk drive can not be rebuilt (using hot-swap or hot-standby
    techniques) when using AST's Mylex DAC products.

    CAUSE
    When the logical system drive was created, the physical disk drive was not
    supported by the DAC configuration utility software.

    PREREQUISITES
    Due to the comprehensive nature of the DAC subsystem, AST recommends the
    System Administrator receive proper training prior to configuring this
    subsystem.  This Technical Bulletin assumes the System Administrator has
    already received training from AST and is familiar with the DAC subsystem.

    SYSTEMS AFFECTED
    AST PART NUMBER           DESCRIPTION

    501453-001     1-CHANNEL EISA SCSI DISK ARRAY CONTROLLER
    501133-001     3-CHANNEL EISA SCSI DISK ARRAY CONTROLLER
    501133-002     5-CHANNEL EISA SCSI DISK ARRAY CONTROLLER

    PARTS AFFECTED
    AST PART NUMBER         DESCRIPTION

    230624-001     CONTROLLER DAC 1-CHANNEL
    230414-003     CONTROLLER DAC 3-CHANNEL
    230355-XXX     CONTROLLER DAC 5-CHANNEL
    221134-001     FRU DAC5 HD CTRL

    SOLUTION
    Reconfigure the logical system drive with the release of DAC utility software
    that supports the physical disk drive.

    BACKGROUND
    In order for the hot-replacement and hot-standby features to function
    properly, all physical disk drives that are being configured as logical
    drives must be the exact same size.  In most instances, when the same
    manufacturer and model are used, this is not a concern because the drives are
    usually the same size.  It is usually a concern when different manufacturer
    and/or models are used.  AST has qualified 500 megabyte, one gigabyte and two
    gigabyte disk drives for use with the DAC.

    AST assigns a single part number for 500 megabyte (230134-500), one gigabyte
    (230135-132 and 230135-133) and two gigabyte (230135-232) SCSI disk drives.
    Several different manufacturers and/or models are sourced under each part
    number.  As a result, (using the one gigabyte disk drive as an example) when
    a one gigabyte disk drive is requested from AST, there is no way to predict
    who the manufacturer and/or model of that disk drive will be when it is
    shipped from AST.  This is a concern because the size of each manufacturer's
    one gigabyte disk drive is not always exactly 1000 megabytes.  In fact, most
    one gigabyte disk drives are slightly larger then 1000 megabytes.  The actual
    size of the disk drive as it is delivered from the manufacturer is called the
    "native" size.  For example, the native size of the Quantum 1080s disk drive
    is 1029 megabytes, and the native size of the HP C2247 disk drive is 1003
    megabytes.  They both need to be exactly 1000 megabytes in order for the
    hot-replacement and hot-standby features to function properly.

    INTRODUCING DRIVE SIZING
    The native size of each disk drive needs to be modified so that all of the
    disk drives are the same size when they are connected to the DAC.
    This process is called "drive sizing".  In order for the hot-replacement and
    hot-standby features to function properly, all physical disk drives that are
    being configured as logical drives must be the exact same size.  AST provides
    utility software with the DAC to make disk drives with different native sizes
    appear as if they are exactly the same size.  For example, after the Quantum
    1080s disk drive has been sized properly, it is seen by the DAC as 1000
    megabytes instead of 1029 megabytes.

    DRIVE SIZING PROCESS
    The following dialog reviews the drive sizing process:

    AST provides utility software with the DAC to enable system administrators to
    configure one or more independent physical disk drives as a single logical
    disk drive.  A "logical disk drive" is commonly referred to as a "system disk
    drive".  During the course of configuring the system disk drive, each physical
    disk drive provides a drive identification header to the DAC.
    The identification header informs the DAC who the disk drive's manufacturer
    is and the disk drive's model number .  The identification header is cross
    referenced to a file called "ID.DAT".  The ID.DAT file is cross-referenced to
    several files with a file extension called "SIZ".  The file "ID.DAT" also
    contains a listing of all the disk drives that are supported by the DAC.
    Each supported disk drive is listed on a separate line in the file which is
    exactly 16 characters in length, and corresponds to a file with the extension
    "SIZ".  The files with the "SIZ" extension contain the modified size of the
    drive.

    DRIVE SIZING EXAMPLE
    The following text resides in the example file /DACCFG/ID.DAT:

    	QUANTUM EMPIRE_1
    	QUANTUM EMPIRE_5
    	HP      C2233-30
    	HP      C2235
    	HP      C2244
    	HP      C2247
    	QUANTUM PD1050iS
    	QUANTUM LPS525S
    	SEAGATE ST12400N
    	SEAGATE ST31200N
    	DEC     DSP3210S
    	QUANTUM EMPIRE_2
    	HP      C3323A

    The first line contains the SCSI identification header for the Quantum 1080's
    one gigabyte disk drive.  Because the header is located on the first line,
    it corresponds to the file called "1.SIZ".  The text located in the file
    1.SIZ is "1000".   When the Quantum 1080's disk drive is sized, the DAC does
    not recognize the native size of the disk drive.  Instead, the disk drive is
    recognized as 1000 megabytes.

    The sixth line contains the SCSI identification header for Hewlett Packard's
    one gigabyte disk drive.  Because the header is located on the sixth line,
    it corresponds with the file called "6.SIZ".  The text located in the file
    1.SIZ is "1000". When the Hewlett Packard disk drive is sized, the DAC does
    not recognize the native size of the disk drive.  Instead, the disk drive is
    recognized as 1000 megabytes.

    After both disk drives have been sized, they are exactly 1000 megabytes and
    can be used in a RAID configuration without any problems.  In this example,
    because two disk drives are being discussed, they can be configured in a
    RAID 1 configuration and the hot-replacement and hot-standby features will
    function properly.

    DRIVE SIZING VERIFICATION
    It is important for a System Administrator to be able to verify that all of
    the physical disk drives connected to the DAC are properly drive sized.
    Following the procedure below enables the System Administrator to verify the
    disk drives are properly sized:

    1.  Boot the latest release of the DAC DOS utility diskette.

    2.  Load the mouse driver that accompanies the mouse that is connected to the
        computer system.

    3.  Change to the directory called "DACCFG" by entering the command
        "CD \DACCFG".

    4.  Execute the DAC Disk Array Configuration program by entering the command
        "DAC960CF".

    5.  Click on the "VIEW/UPDATE CONFIGURATION" button.

    6.  Click on the "FORMAT SCSI DRIVE" button.  The button is located on the
        lower right portion of the screen.

    7.  Click on the graphical representation of each disk drive.  A box
        containing several fields will be displayed in the upper left portion of
        the screen.  Each field reviews specifics about that particular disk
        drive.  One field needs to be reviewed to verify the disk drive is
        properly sized.  The first field reads "Capacity [MB] : nnnn", where
        "nnnn" is the modified size of the drive. For a 500 megabyte disk drive,
        "nnnn" must be equal to "500".
        For a one gigabyte disk drive, "nnnn" must be "1000".  For a two gigabyte
        disk drive, "nnnn" must be equal to "2000". The disk drive is not properly
        sized if "nnnn" contains any other numbers .

    8.  Click on the "EXIT" button that is located in the upper right portion
        of the screen, next to the clock.

    9.  Use the steps outlined above to verify each physical disk drive.

    10.  After all disk drives have been reviewed, click on the "QUIT" button
    	to exit the menu.

    DRIVE SIZING RESOLUTION
    The logical system drive needs to be recreated if one of the physical disk
    drives is not properly sized.  Since recreating a system drive requires
    reinitializing the system drive, all of the data must be backed up prior to
    creating the new system drive.  The data is restored after the system drive
    is initialized.

    Notes
    1.  It is important to perform a full system backup prior to initializing a
        system drive because initializing a system drive will destroy all data.

    2.  Please reference the Disk Array User's Manual for the procedure that
        explains how to use the DAC Configuration Utility to create new system
        drives.

    3.  The latest release of the DAC DOS utility diskette is located on AST's
        BBS in the Systems file area.  The name of the file is "SMP7.EXE".  AST's
        BBS can be reached by dialing (817) 230-6850.  AST's BBS supports modem
        speeds up to 28.8k bps.  This file will also be posted on:

    	- CompuServe
    	   Go ASTSUPPORT

    	- AST Worldwide Web Site
    	  http://www.ast.com