APPENDIX C: SCSI DEVICE & CABLING LIMITATIONS
Due to the electrical noise incurred with high-speed data transfer rates, SCSI has cabling and device limitations. Table C-1 explains the maximum number of devices you may use relative to your cable distance. For example, take the single-ended distance in an UltraSCSI environment (Cells 3 & 4 in the single-ended bus length column). Look at the corresponding cells in the maximum devices column to determine the maximum number of devices you may connect at the specific distance. In an UltraSCSI environment, using a single-ended bus length of 3 meters, you can only connect 4 devices. Using a single-ended bus length of 1.5 meters, you can connect up to 8 devices.
SCSI Type | Single-Ended | Differential | LVD | Maximum |
| Bus Length | | | Devices |
| | | | |
Fast SCSI | 3 Meters | 25 Meters | 12 Meters | 8 |
| | | | |
Fast/WIDE SCSI | 3 Meters | 25 Meters | 12 Meters | 16 |
| | | | |
UltraSCSI | 1.5 Meters | 25 Meters | 12 Meters | 8 |
| | | | |
UltraSCSI | 3 Meters | N/A | N/A | 4 |
| | | | |
Ultra/WIDE SCSI | N/A | 25 Meters | 12 Meters | 16 |
| | | | |
Ultra/WIDE SCSI | 1.5 Meters | N/A | N/A | 8 |
| | | | |
Ultra/WIDE SCSI | 3 Meters | N/A | N/A | 4 |
| | | | |
Ultra2 SCSI | N/A | N/A | 12 Meters | 8 |
| | | | |
Ultra2/WIDE | N/A | N/A | 12 Meters | 16 |
SCSI | | | | |
| | | | |
Table C-1: UltraSCSI Cabling and Device Limitations
Table C-1 lists the maximum number of devices you may connect at specific cable distances using differential and single-ended SCSI in various SCSI environments. In an UltraSCSI workgroup environment with a 7-drive tower, you are limited to 1.5 meters between the host and tower (this distance includes the cabling in the tower). For example, if the 7-drive tower requires 1 meter of cabling to connect all of its drives, the distance from the tower to the host would be .5 meters. Adding an ATTO SCSI Sidekick to this configuration would increase the distance between the host and tower to 2 meters.
Ultra2 SCSI is less sensitive to SCSI bus noise and offers you the ability to connect a full load of devices up to 12 meters. Use table C-1 to assist you when attempting to configure your workgroup. If you have any questions or issues occur with your configuration, please call an ATTO technical support representative.
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