Mylex DAC960 RAID Controller Causes "Missing Operating System"

When you try to install Windows NT on a system that is using the Mylex DAC960 RAID controller or an OEM version of this controller, NT will under some circumstances complete the first phase of setup but fail when rebooting into GUI mode, displaying the following error message:

When formatting the partition, prior to the initial file copy operation, Windows NT might also have warned you that the partition you were creating contained more than 1024 cylinders.

This error occurs because the RAID controller misrepresents the geometry of the logical drives it presents to Windows NT. (When there is only one logical drive of less than 2 gigabytes (GB), or if a formatted partition already exists, Windows NT is able to correctly determine the geometry.)

There are two ways to avoid this problem:

• Prior to installing Windows NT, create and format a partition on the boot logical drive using Microsoft MS-DOS or another operating system -or-
• Create only one logical drive of a size smaller than 2 GB on the RAID array, using the configuration software that was supplied with the controller. After NT is installed, you may create additional logical drives.

Microsoft has confirmed this to be a problem in Windows NT versions 3.5 and 3.51. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

This problem has been reproduced on the Mylex DAC960 RAID controller and the IBM RAID controller.