IBM 865741Y Handbook - Page 93

If you install wide (16-bit) SCSI devices, you can set the IDs to any whole number between 0 and 6, or between 8 and 15. If you install narrow (8-bit) SCSI devices, you can set the IDs to any whole number between 0 and 6. SCSI Logical Unit Number Each physical device has a physical unit number (PUN) and a logical unit number (LUN). If a physical device supports no logical devices, its LUN is 0. Most SCSI devices support only LUN 0. Certain types of physical SCSI devices (bridge controllers) can support more than one logical device. For example, a printer controller might support up to eight printers. The printer controller is a physical device, and each printer is a logical device. If the printer controller is assigned to ID 2, the ID of the first printer appears in the SCSI device configuration as PUN 2, LUN 0. The IDs of the other printers are PUN 2, LUN 1; PUN 2, LUN 2; on up to PUN 2, LUN 7. Termination Requirements All Netfinity 3500 servers come with an UltraSCSI controller on the system board. This UltraSCSI controller provides termination for one end of the SCSI bus (cable) in your server. However, the SCSI bus must be terminated at both ends only. Any SCSI devices that are installed must have their termination set to Disabled. When you install devices in bays 2, 3, 5, and 6, you must disable the termination for the devices before you install them. If you connected external SCSI devices to your server, set the termination for the last device on the external cable to Enabled. See the device documentation for instructions. Refer to the instructions that come with the SCSI device for more information about termination. Chapter 4. Installing Options 75