>I tried to mirror my bootable NT System partion, after that I break the mirror. although I saw the same files and directory in both disks, but the second disk could boot, how do i do that.
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Modify BOOT.INI to provide an entry that references the second physical drive's partition (copy the basic NT boot entry and change the ARC address to point at the second physical drive rather than the first. Without knowing how your system is configuraed, I can't tell you what the ARC address of the second drive is, however, just about any technical reference book (the 'For Dummies' study guides for the MCSE exams are cheap and have what you'd need in them) will have details on figuring out your ARC address for various partitions.