Steps to Recover a Failed Mirrored System/Boot Partition

by Wayne Maples [Published on 20 April 2004 / Last Updated on 20 April 2004]

The fault tolerance (FT) driver cannot initialize after a failure of a mirrored boot partition (containing Windows NT system files) and system partition (containing NTLDR and boot loader files). This kbarticle provides a step-by-step system recovery procedure for such a failure : Q120227

A gotcha! when a mirror fails, the system boots when using a boot disk but not by itself even when the boot.ini from the boot disk is copied to the system partition.

The shadow disk, the surviving member of the mirror, the member that was not the active partition, is missing the Master Boot Record (MBR). See Master Boot Record Not Written to Mirrored Shadow Partition for background. NT mirroring does not duplicate the MBR. For the shadow to be able to boot, it must have an active partition's MBR. If you create a partition on the drive to be mirror and make it an active partion, the correct MBR will be created. You can then delete the partition and setup the mirror and it will be able to boot.

You could try to rewrite it with "fdisk /mbr" from a bootable DOS floppy that includes fdisk.exe, but there are potential problems. See Using FDISK /MBR for Troubleshooting Windows NT Boot Problems

A final possibility would be to use the low level disk editor, dskprobe.exe, from the Resource Kit to copy a working MBR.

Another gotcha! occurs when you try to delete a partition that was part of a broken mirror set, you receive this error message The drive cannot be locked for exclusive use. Please check to see if some applications are currently accessing the drive. If so, close them and try again. This is not exclusively a mirror issue.

Check to see if any of the conditions listed below apply as the standard reason(s) for not being able to lock a volume:

  • A paging file is on the volume.
  • A program that was started from the volume is still running.
  • A program that's running has loaded a .dll file from the volume.
  • A program has a file open on the volume.
  • A program's current folder is on the volume.
  • A service has a lock on the volume.
Except for the paging file issue, these can be eliminated by a reboot. If none of these apply, you can use Disk Administrator to select the partition you wish to delete. Use Tools | Assign Drive Letter To and then choose Do Not Assign A Drive Letter and click OK. You should now be able to successfully delete the partition.

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