ATTO Technology 1500D/E, 1550D/E operation manual Cabling, Cable types, Examples

Cabling

Cables and devices must be chosen to maximize performance and minimize the electrical noise from the high-speed data transfers available with the SCSI protocol. Cabling and termination methods become important considerations for proper performance. SCSI cables and devices are subject to specific length and number limitations to deal with electrical problems that arise at increased operating speeds.

Cable types

Use high-quality cables rated for the type of SCSI transfers required: well-insulated SCSI cables ensure error free communications. Try to keep cable lengths as short as possible to ensure higher signal quality and performance.

Examples

The SCSI specification limits total bus cable length for single-ended SCSI in a non-UltraSCSI environment to 3 meters (combined length of both internal and external cable lengths).

In an UltraSCSI workgroup environment with a 7- drive tower, you are limited to 1.5 meters between the host and the tower, including the cabling for the tower. If the 7-drive tower requires 1 meter of cabling to connect all of its drives, the distance from the tower to the host must be .5 meters.

Note

UltraSCSI is very sensitive to SCSI bus noise, cable distances and the number of devices connected on the SCSI bus. Carefully connect your devices when working with UltraSCSI.

Exhibit 1.5-1 Various types of SCSI operate at different speeds and require different bus lengths to support a certain number of devices.

	Bus speed	Bus width	Max. bus lengths in meters			Max. device
STA terms	MB/sec. max.	bits				support
			Single-ended	Differential	LVD
Fast SCSI	10	8	3	25	n/a	8
Fast/WIDE SCSI	20	16	3	25	n/a	16
UltraSCSI	20	8	1.5	25	n/a	8
Ultra/WIDE SCSI	40	16	n/a	25	n/a	16
Ultra/WIDE SCSI	40	16	1.5	n/a	n/a	8
Ultra/WIDE SCSI	40	16	3	n/a	n/a	4
Ultra2 SCSI	80	16	n/a	n/a	12	8
Ultra2/WIDE SCSI	80	16	n/a	n/a	12	16
Ultra3/WIDE SCSI	160	16	n/a	n/a	12	16

12 Installation: SCSI connections