When you use the Disk Management snap-in to convert a hard disk to a dynamic disk, after the process completes, you are prompted to restart your server. You must restart as you are unable to cancel this dialog.
This behavior will occur if any disk that you are trying to convert is mounted by Windows 2000, or mounted by a program.
NOTE: The Disk Management snap-in notifies you if disks are mounted before you start the conversion.
To workaround this behavior, make sure that none of the disks that you want to convert are mounted before you start the conversion.
NOTE: See Disk Concepts and Troubleshooting.