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Q145600: Creating Mirror Fails with Insufficient Disk Space

Article: Q145600
Product(s): Microsoft Windows NT
Version(s): beta99
Operating System(s): 
Keyword(s): kbnetwork
Last Modified: 08-AUG-2001

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The information in this article applies to:

- Microsoft Windows NT Server versions 3.5, 3.51, 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, an "Insufficient space on drive
X" appears where X is the target drive or partition.

CAUSE
=====

This problem may occur even when you use identical SCSI controllers and drives
but whose BIOS is disabled on the second SCSI controller. When two identical
SCSI controllers are used, the drive geometry is calculated differently for the
controller with the BIOS enabled and the controller with the BIOS disabled.

For 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 1024 to
work with MS-DOS. The number of heads is normally increased to arrive at a
correct overall size.

When the second SCSI controller does not have its BIOS enabled, it provides the
operating system with the size of a block (sector size) and the total number of
blocks on the device. Windows NT uses a default translation of 32 tracks per
cylinder, 64 heads and adjusts the number of cylinders for a correct approximate
size. Due to the different translations, cylinder boundaries are located in
different places on the drives. This often results in free space being one or
two megabytes (MB) different on the two identical drives or whatever 1 cylinders
worth of data is. 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, do one of the following:

- Set the translation mode on the primary controller to 32 sectors per track
  and 64 heads (if the SCSI controller supports this translation mode).

  -or-

- Disable the BIOS on the primary SCSI controller and enable it on the
  secondary controller. When you create a mirror, the master boot record is not
  part of the mirror. Therefore, set the active partition byte on the new boot
  drive with MS-DOS FDISK.EXE or a disk sector editor. Another method is to
  boot the computer from a Windows NT boot floppy disk. For more information on
  how to create this boot floppy disk, refer to the Windows NT Resource Guide
  or the Windows NT Concepts and Planning Guide.

STATUS
======

Microsoft has confirmed this to be a problem in Windows NT 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 kbWinNT351search kbWinNT350search kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbWinNTS351 kbWinNTS350 kbWinNTS351search kbWinNTS350search
Version           : beta99

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