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

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Windisk is the utility that manages disk partitioning in Windows NT Server. When it establishes a mirrored partition on a previously unused disk, it does not check for the existence of valid boot code in the Master Boot Record. At startup, the system BIOS of an Intel 80x86-based computer expects the Master Boot Record to contain executable code which is responsible for locating and passing control to the boot sector on the active partition. When this code is not present, the processor attempts to execute random memory and the computer hangs.

NOTE: If the disk used to hold the shadow of the mirrored system partition was previously partitioned, either by Windows NT Server, MS-DOS, or any other operating system which uses the same partitioning scheme, the Master Boot Record will already contain valid boot code and the system will boot successfully when started from the former shadow partition. Only when the secondary disk was not previously partitioned will this result in your computer hanging.

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Through the use of a Windows NT "boot floppy", the operating system can still be initialized. For information on how to create such a floppy, see pages 161 and 162 of the "Windows NT Advanced Server Concepts and Planning Guide," or see the following article in the Microsoft Knowledge Base:



It is possible to initialize the boot code in the Master Boot Record by using WINDISK.EXE to modify the disk partition structure. When you manually make and format a primary partition Windisk.exe will initialize the master Boot Records boot code.

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Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.

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