DOCUMENT:Q148425  08-AUG-2001  [winnt]
TITLE   :Duplexed Mirror Generation Fails with Insufficient Space
PRODUCT :Microsoft Windows NT
PROD/VER:WinNT:4.0
OPER/SYS:
KEYWORDS:kbnetwork

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The information in this article applies to:

 - Microsoft Windows NT Server version 4.0 
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SYMPTOMS
========

When you use duplexed SCSI controllers and a software mirror of either the
operating system partition or a data partition, you may receive the message
"Insufficient space on drive X" where X is the target drive or partition. This
can happen when using identical controllers and drives.

CAUSE
=====

When two SCSI controllers are used, the drive geometry is calculated differently
for controllers that have BIOS enabled and the identical controller with BIOS
disabled.

With a controller that has BIOS enabled, the operating system can query the
controller BIOS for drive geometry. The BIOS returns a generic drive geometry
translation. This translation will have a cylinder count of less than 1,024 to
work with MS-DOS. The number of heads is normally increased to arrive at a
correct overall size.

Because the second controller does not have BIOS enabled, all it can provide the
operating system is the size of a block (sector size) and the total number of
blocks on the device. Windows NT then uses a default translation of 32 tracks
per cylinder, 64 heads and adjusts the number of cylinders to arrive at a
correct approximate size. Because of the different translations, cylinder
boundaries will be in different places on the drives. This often results in a
drive's free space being 1 or 2 MB different on the two identical drives.

Internally, Windows NT uses a LARGE_INTEGER (64-bit) number for the number of
cylinders and is not constrained by MS-DOS or partition table limitations.

RESOLUTION
==========

To work around this problem, perform one of the following:

 - If the SCSI controller supports it, set the translation mode on the primary
   controller to 32 sectors per track and 64 heads.

 - Disable the BIOS on the primary controller, and enable it on the secondary
   controller. Because creating a mirror does not mirror the master boot record,
   it may also be necessary to set the active partition byte on the new boot
   drive with MS-DOS Fdisk.exe or with a sector editor. An alternative is to
   boot the computer from a Windows NT boot floppy disk. Information on how to
   create this disk can be found in the Windows NT Resource Kit and the Concepts
   and Planning Guide.

STATUS
======

Microsoft has confirmed this to be a problem in Windows NT SUR version 4.0. We
are researching this problem and will post new information here in the Microsoft
Knowledge Base as it becomes available.

Additional query words: prodnt

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Keywords          : kbnetwork 
Technology        : kbWinNTsearch kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400
Version           : WinNT:4.0
Issue type        : kbbug

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