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AST RESEARCH, INC.        TECHNICAL BULLETIN # 1185                5-15-95

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  INCOMPATIBILITY WITH AST'S MYLEX DAC AND THE SEAGATE ST31200N DISK DRIVE


PROBLEM

When a Seagate ST31200N disk drive is configured as a fault tolerant drive 
with AST's Mylex DAC960 controller, it can not be reliably rebuilt when it 
fails under the SCO UNIX or ODT operating systems.

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 ubsystem.

CAUSE

The drive can not be low-level formatted reliably when firmware release 1.24 
is used in the DAC960 controller.  If it is low-level formatted, the disk 
drive will usually be formatted to an incorrect capacity.  Each time the drive 
is low-level formatted, the capacity changes.  During a test analysis, AST 
formatted the drive several times, and each time the drive size capacity was 
reported as being between negative 200MB and positive 9GB.  Sometimes, 
although rarely, the drive size was reported as being the proper size after a 
low-level format.  This symptom occurs when the drive is low-level formatted 
using the DAC960CF DOS utility under DOS or the "rbld" command under UNIX.


SYSTEMS AFFECTED
AST PART NUMBER AND DESCRIPTION

501133-002     5-CHANNEL EISA SCSI DISK ARRAY CONTROLLER


PARTS AFFECTED
AST PART NUMBER AND DESCRIPTION

230355-XXX      CONTROLLER DAC 5-CHANNEL
221134-001      FRU DAC5 HD CTRL
230135-132      SEAGATE ST31200N DISK DRIVE
230135-122      SEAGATE ST31200N DISK DRIVE


SOLUTIONS

1.  Avoid using either of the two methods available to low-level format the 
Seagate disk drive.  The first method uses DOS; the second method uses 
UNIX.

To avoid low-level formatting the disk drive with the DAC960CF utility 
under DOS, do not use the low-level format option that is provided.  To avoid 
low-level formatting the drive under UNIX, use the "-n" option of the "rbld" 
command.  The "-n" option inhibits the drive from being low-level formatted 
before it is rebuilt.

2.  AST will replace Seagate ST31200N disk drives purchased from AST, 
with an alternative manufacturer's drive if requested.  To request this drive, 
call AST Technical Support at (800) 727-1278, or contact the nearest AST 
Authorized Service Center.

NOTES

1.  AST was stocking the Seagate ST31200N disk drive under two part numbers.  Originally it was stocked under the part number 230135-132.  
This is the universal part number for 1GB SCSI disk drives, with several 
different manufacturers and/or models sourced under this part number.

Ordering drives using this part number makes it impossible to predict which 
manufacturer and/or model of that drive size will be shipped.  This raises a 
concern if a customer elects not to use the ST31200N disk drive with the 
DAC controller after reading this Technical Bulletin.

Because of this concern, AST has removed the ST31200N from the universal 
part number and has assigned the ST31200N its own unique part number, 
230135-122.

2.  AST has also tested and qualified a replacement 1GB Seagate disk drive.  
The model is ST31230N, carrying the AST part number 230135-120.  
This drive can be successfully low-level formatted.