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The top example in Figure 2 shows an internal hard disc at one end of the SCSI bus with the SCSI controller at the other end (both are terminated). The bottom example shows two additional SCSI devices connected externally—this means the SCSI controller is no longer on the end of the SCSI chain and should not be terminated. Note. Some controllers prefer to remain terminated even if they are in the middle of the chain. Also, some controllers treat the internal and external chains as separate logical buses. This means you may need to terminate both the first and last devices on both logical buses to achieve proper termination. If necessary, refer to your system or controller documentation to see how this is handled in your particular system. Barracuda 4LP Installation Guide, Rev. B For information about how to terminate your drive, refer to the appropriate drive-specific section. Internal SCSI cable Internal SCSI device Internal SCSI device Controller Internal SCSI device Internal SCSI device Controller External SCSI device External SCSI device External SCSI cable Internal SCSI cable Terminate Terminate Figure 2. SCSI bus termination Terminator power You usually will not need to change this option and can normally leave the drive configured as it was shipped from the factory. For information about how to change the terminator power option on your drive, refer to the appropriate drive-specific section. I/O circuits and data path widths • “WD” and “DC” models use differential I/O circuits. You cannot mix these models with single-ended models (“N,” “W,” “WC”) on the same SCSI bus. The circuits are incompatible with each other. • “W,” “WD,” and “WC” models have a “wide” (16-bit) SCSI data bus rather than the standard (non-wide) 8-bit SCSI data bus; however, you can use these wide drives on a standard (nonwide) 8-bit data bus. Barracuda 4LP Installation Guide, Rev. B Figures 3a, 3b, 3c, and 3d show typical drive connections. The following table lists the maximum cable lengths and number of devices with single-ended I/O circuits allowed on a daisy-chain cable for <10 and <20 M transfers/sec I/O data transfer rates. Table 4. Cable characteristics for single-ended circuits I/O transfer rate Maximum number of devices on line Maximum cable length allowed <10 M transfers/s 8 (reg. SCSI bus) 6 meters (19.7 ft.) <10 M transfers/s 16 (wide SCSI bus) 6 meters (19.7 ft.) <20 M transfers/s 4 (reg./wide SCSI bus) 3 meters (9.8 ft.) <20 M transfers/s 8 (reg./wide SCSI bus) 1.5 meters (4.9 ft.) For devices having differential I/O circuits, a maximum cable length of 25 meters (82 feet) is allowed. A maximum of 8 devices can be connected on an 8-bit wide data bus, and a maximum of 16 devices can be connected on a 16-bit wide data bus. Barracuda 4LP Installation Guide, Rev. B Pin 1 HDA Figure 3a. Fifty pin I/O connection to drive Pin 1 HDA Figure 3b. Sixty-eight pin connection to drive Barracuda 4LP Installation Guide, Rev. B Host Adapter PCB Pin 1 (check your adapter for Pin 1 location) SCSI ID X (or last drive) [1] SCSI ID 1 SCSI ID 0 SCSI ID 7 Additional SCSI devices “N” Model Drive [1] “X” means up to 6 or the maximum allowable number of devices on the SCSI bus. See Table 4 and system documentation. Figure 3c. Multiple drive connection to host adapter 24 Barracuda 4LP Installation Guide, Rev. B [1] Do not mix “W” and “WD” model drives on the daisy chain. [2] “X” means up to 15 or the maximum allowable number of devices on the SCSI bus. See Table 4 and system documentation. [3] External terminator. Figure 3d. Multiple-drive connection to host adapter Host Adapter PCB Pin 1 (check your adapter for Pin 1 location) “W” Model Drive [1] “WD” Model Drive [1] SCSI ID 1 SCSI ID 0 SCSI ID 7 SCSI ID X (or last drive) [2] Additional SCSI devices [3] Barracuda 4LP Installation Guide, Rev. B Note. This drive model plugs directly into a backplane connector and therefore uses no cables. Figure 3e. Drive model “WC” or “DC” with single 80-pin I/O and power connector Barracuda 4LP Installation Guide, Rev. B Providing adequate cooling The enclosure design must ensure adequate cooling for the drive. The maximum ambient temperature is 50°C. The drive’s product manual (77767491) describes how to evaluate the air-flow design. The evaluation consists of ensuring that the case temperature of certain critical components remains within acceptable limits during drive operation. We recommend orienting the drive or directing the air flow in a way that creates the least amount of air-flow resistance while providing air flow above the circuit boards and around the head and disc assembly (HDA). Also, choose the shortest possible path between the air inlet and exit. This minimizes the distance traveled by air that is heated by the drive and by other nearby heat sources. Figure 4 shows two design approaches with one or more fans used to generate air flow. The air-flow patterns can be created by the fans either pushing or drawing air. The overall flow pattern can b...

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