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Reasons why Windows NT does not boot from a shadow mirror drive

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Microsoft Windows NT supports Disk Mirroring and Disk Duplexing of the operating system partition. This article is intended to help clarify why the shadow drive does not always boot and how to ensure that it will boot in the case of a primary disk failure. The most common symptom when trying to boot from the shadow drive is that the system will hang after POST with a blinking cursor and no boot menu options are displayed.

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More information

Microsoft does NOT guarantee the ability to start from a mirrored drive without the use of a Windows NT Fault tolerant boot disk. This is because Windows NT mirrors partitions and information contained in the Bios parameter block in the master boot sector of the partition on the primary drive may not be valid for the partition we are mirroring to on the shadow drive. The bios parameter block contains vital information required for starting and is partition specific.

In many cases, booting from the shadow drive works, but this is dependent on the following requirements:
  1. Both the primary drive and shadow drive MUST be identical in make, model, and in many cases firmware revision. This is to ensure that the drive geometry is identical and is being translated identically.
  2. Both the primary and shadow drive must be attached to identical controllers with the same BIOS and Firmware revisions. Both controllers must have translation options set identically - either both enabled or both disabled.
  3. Both the primary and shadow drive must be identically partitioned for the location of the operating system partition and partitions before the operating system partition must also be identical. If an EISA partition exists on the primary drive, an identical partition must exist on the shadow drive.
  4. The shadow drive must contain a primary partition that is marked active and contains a valid Boot.ini file along with NTLDR and
  5. The primary drive must be inaccessible or disconnected while you start Windows NT again using the shadow drive or a STOP 0x1E occurs.
  6. The shadow drive must contain valid boot code in the Master Boot Record (MBR).
Failing to meet ANY of the above requirements may prevent booting into Windows NT from the shadow drive.

Possible problems and solutions


The primary and shadow drives are not identical. Geometry or firmware revision differences cause the drive to be translated differently.


Ensure drives are identical. To check firmware revision of the same manufacturer and model disk drive, perform the following steps:

Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.
  1. Run Registry Editor (Regedt32.exe) and go to the following subkey:
    where x varies according to device number.
  2. Look at the REG_SZ identifier value to see the model number and firmware revision values. For example, if you see the following REG_SZ identifier value
    SEAGATE ST32430N 0510
    0510 is the firmware revision value.


The controller that contains the shadow drive had its BIOS disabled and the translation being performed is now different from the original Primary drive.


Many SCSI Bioses disable translation mode if the bios is disabled. This prevents the drives attached to the SCSI controller from being translated and effects the boot process. Ensure BOTH SCSI controllers have their BIOS and translation options set the same.


The primary drive had an EISA partition in front of the system partition and you mirrored to a drive that did not contain an EISA partition.


Before you mirror to the shadow drive, make an identically-sized EISA partition. It may be possible to move the shadow drive to another Windows NT computer to modify the MBS Hidden Sector value by using the Windows NT 4.0 resource kit utility Dskprobe.exe to make it bootable.
165181 EISA configuration boot code is replaced on mirror drives


The Primary partition on the shadow drive is not marked active.


Use one of the following methods to mark the a partition active.
  • Run the MS-DOS FDISK utility and make sure you have an active partition.
  • Use Disk Administrator/Management to mark the partition active.


When you boot from the shadow, you receive a STOP 0X0000001E error message.


This behavior occurs because primary drive is still accessible. This causes a stop 0x0000001E error message while entering kernel mode. To resolve this behavior, disable the primary drive by either unplugging the power or the SCSI connector.

For more information, click the following article number to view the article in the Microsoft Knowledge Base:
141242 STOP Msg: 0x0000001E testing new fault tolerance boot disk


After you make the previously shadowed partition of a mirrored system partition into the primary partition; when you restart your computer, it stops responding. Only the initial system and peripheral BIOS startup text is displayed on the monitor.


The shadow drive was mirrored to as a raw drive so the Intel boot code was never initialized on sector 0. Prior to mirroring, Use Disk Administrator to make and format a primary partition. Then delete the new partition to make free space. This procedure ensures the Intel boot code is placed on sector 0.

How to guarantee booting from the shadowed drive

If you have a primary drive failure, using the fault tolerant boot floppy disk always enables you to boot to the shadow drive because you are relying on the floppy disk drive to act as the boot device. This works because the computer is not relying on the shadow drive's boot partitions BIOS parameter block in the master boot sector to locate and load the NTLDR and Boot.ini files. If you then maintained a small bootable FAT partition at the beginning of the shadow drive to act as the boot partition, it would, in effect, take the place of the fault tolerant boot floppy (by loading the NTLDR and boot.ini files and displaying the boot menu). This small FAT partition can be made prior to establishing the mirror on the shadow drive and take the place of the EISA partition if one is located on the primary drive.

Because the shadow drive must contain enough free space to contain the operating system partition you are mirroring, you need to plan this scenario ahead of time and, if necessary, make the same size small FAT bootable partition on the primary drive prior to installing Windows NT. This will ensure you can always boot from the primary or shadow drive. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
138364 Windows NT partitioning rules during setup
It may be necessary to pre-partition the drive prior to installing Windows NT in order to get 2 primary partitions created. This can be accomplished by moving the drive to another computer running Windows NT and use Disk Administrator to create 2 primary partitions. This is because MS-DOS FDISK will not allow you to create a second primary partition.

If the primary partition fails to boot, you can run MS-DOS FDISK and mark the small FAT partition as the active partition so you have 100 percent boot backup without the need of a Windows NT boot floppy disk.
|---------------------- EXAMPLE NUMBER 1 ----------------------|

 DISK-0     | FAT  PRIMARY | * NT OS on 2nd PRIMARY Partition  |
 PRIMARY    | (backup boot)|   SET ACTIVE                      |

 DISK-1     |* FAT PRIMARY |     SHADOW DRIVE                  |
 SHADOW     |  SET ACTIVE  |       of NT OS                    |

|---------------------- EXAMPLE NUMBER 2 ----------------------|

 DISK-0     |     EISA     | * NT OS on PRIMARY Partition      |
 PRIMARY    |  PARTITION   |       SET ACTIVE                  |

 DISK-1     |* FAT PRIMARY |     SHADOW DRIVE                  |
 SHADOW     |  SET ACTIVE  |       of NT OS                    |
Note: Make sure the ARC path is set correctly in the Boot.ini files located on the FAT partitions.

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Keywords: KB167045, kbsetup, kbinfo

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Article Info
Article ID : 167045
Revision : 8
Created on : 12/29/2006
Published on : 12/29/2006
Exists online : False
Views : 533