Items to consider when mirroring a dynamic boot volume or system volume

Article:TECH9456  |  Created: 2001-01-08  |  Updated: 2004-01-07  |  Article URL
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Technical Solution



Items to consider when mirroring a dynamic boot volume or system volume


The following are considerations when mirroring a dynamic system or boot volume:

1. It is recommended that a boot floppy of the system partition be made. This will allow booting the system if something goes wrong with the original system and boot volume or its mirror. Test the boot floppy while the system is in a known good state.

2. To boot to the mirror of a system or boot volume, make necessary changes to the boot.ini file. Note that in order to boot from a mirrored system volume, its offset from the beginning of the disk must be in the same location as that of the original system volume's offset. Attempting to add a mirror to a system volume where there are no dynamic disks that can have the offset in the same location, a message will display to that effect and you will be prompted whether to continue or not. Choosing to continue will create a mirror at a different offset. Data will be correctly mirrored, but you cannot boot from the mirror.

3. Volume Manager software does not allow adding a mirror to the current system or boot partition when Windows 2000 Professional is installed. This is due to limitations within Windows 2000 Professional (support for mirrored system volumes is not provided.)

4. When adding a mirror to a system or boot volume, the operation will fail with the error message "Insufficient disk space" if the available dynamic disks do not have enough space for the mirror.

5. Volume Manager does not allow removing the mirror of the volume that Windows 2000 is using to boot from. A mirror of the boot volume can be broken off but the resulting new volume - the broken off mirror -  will not be usable as a boot volume.  

Note: Additional references on booting from mirrored drives can be found on the Microsoft support Web site.
Q167045 - "Reasons Why Windows NT Does Not Boot From a Shadow Mirror Drive" offers additional information on mirroring the system partition and is a good beginning reference.

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