All SCSI devices on the SCSI bus must have unique IDs assigned to the. If two devices have the same ID, neither device will work properly because they will try to act on commands destined for that ID. This also applies to SCSI controllers participating on the bus. It is recommended that the controller cards be assigned IDs 6 and 7 in a two-node cluster.

The ID number for controller cards can be set using the controller’s setup program. See the documentation that came with the controllers for instructions on how to enter the setup utility.

Setting ID numbers on SCSI disks is usually accomplished using DIP switches. Again, because each device is unique in configuration, see the documentation that came with the hardware for instructions on how to change the ID.

As mentioned in Part I of this article, each controller has a limit as to the length of the SCSI bus, if this bus length is exceeded, signals could be lost. As a result, the cluster will fail over repeatedly or not work at all.

The maximum length for most SCSI controllers is 12 meters for Ultra2 buses. To find out the maximum cable length of the bus the cluster uses, refer to the documentation that came with the controller.

[tags]microsoft,diana huggins,cluster node,scsi,cluster fault tolerance,fibre channel[/tags]