Windows NT will not Boot from a Shadow Mirror Drive

 Last reviewed: December 31, 1997
Article ID: Q167045
The information in this article applies to:
  • Microsoft Windows NT operating system version 3.1
  • Microsoft Windows NT Advanced Server version 3.1
  • Microsoft Windows NT Server versions 3.5, 3.51, and 4.0

SUMMARY

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 it will boot in the case of a primary disk failure.

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 booting and is partition specific.

For more information, please see the following article in the Microsoft Knowledge Base: 

   ARTICLE-ID: Q119467
   TITLE     : Creating a Boot Disk for an NTFS or FAT Partition
In many cases, booting from the shadow drive will work, 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 NTDETECT.COM.

  5. The primary drive must be inaccessible or disconnected while booting back into Windows NT using the shadow drive or a STOP 0x1E will occur.

  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

A. The primary and shadow drives are not identical. Geometry or 

   firmware revision differences cause the drive to be translated
   differently.

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

   WARNING: Using Registry Editor incorrectly can cause serious, system-
   wide problems that may require you to reinstall Windows NT to correct
   them. Microsoft cannot guarantee that nay problems resulting from the
   use of Registry Editor can be solved. Use this tool at your own risk.

   1. Run Registry Editor (Regedt32.exe) and go to the following subkey:

      HKEY_LOCAL_MACHINE\Hardware\Devicemap\Scsi\ScsiPortx\ScsiBusx\
      TargetIdx\LogicalUnitIdx

      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

      SEAGATE ST32430N   0510

      then 0510 is the firmware revision value.
B. The controller that contains the shadow drive had it's BIOS disabled 
   and the translation being performed is now different from the original
   Primary drive.

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

   Solution: Prior to mirroring 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.

   For more information, see the following article in the Microsoft
   Knowledge base:

      ARTICLE-ID: Q165181
      TITLE     : EISA Configuration Boot Code Is Replaced on Mirror Drives
D. The Primary partition on the shadow drive is not marked active. 

   Solution:

      1. Run MS-DOS FDISK utility and make sure you have an active
         partition.

      -OR-

      2. Use Disk Administrator to mark the partition active.
E. When you boot from the shadow - you get a STOP 0X0000001E 

   Solution:  The primary drive is still accessible - this causes a stop
   0x0000001E while entering kernel mode. Disable the primary drive by
   either unplugging the power or SCSI connector.

   For more information, please see the following article in the Microsoft
   Knowledge Base:

      ARTICLE-ID: Q141242
      TITLE     : STOP Msg: 0x0000001E Testing New Fault Tolerance Boot
                  Disk
F. 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.

   Solution: The shadow drive was mirrored to as a raw drive so 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 Will ensure the Intel
   boot code was placed on sector 0.

   For more information, please see the following article in the Microsoft
   Knowledge Base:

      ARTICLE-ID: Q117131
      TITLE     : Master Boot Record Not Written to Mirrored Shadow
                  Partition.

How To Guarantee Booting from the Shadowed Drive

In case of 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, please see the following article in the Microsoft Knowledge Base: 

   ARTICLE-ID: Q138364
   TITLE     : 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.

Additional query words: boot mirror shadow
Keywords : ntboot NTSrvWkst kbsetup
Version : WinNT:3.1,3.5,3.51,4.0
Platform : winnt

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Last reviewed: December 31, 1997
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