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.