When using duplexed mirror sets, load balance the controllers. Include the same number of disks on each controller, if possible. This step helps with performance. Here is a typical Boot.ini file for starting a computer with a mirrored boot partition, and each disk of the mirror set is on a different SCSI controller. Both the original and shadow disks are assigned SCSI ID 0 on their respective controllers.
Many SCSI controllers have more than one channel on the adapter card.
Even though there is a single card, it appears to the computer as if there are two separate controllers. There is quite a bit of variation in the way different manufacturers handle multiple channels. Be sure to test starting up from each of the channels and disks. If a valid ARC path cannot be found to start the computer from the shadow boot partition, you need to make changes in the system configuration. It might be necessary to consult with the controller vendor to determine the correct configuration to be able to start Windows NT Server from the shadow partition if the original disk or SCSI channel fails.