Tascam MMR-8, MMP-16 manual Scsi Cables, Cable Quality, Cable Length and Device Support

SCSI Tips for MMR/MMP Users

We have found that the quality of materials and attention to detail in setting up external SCSI devices for use with the MMR/MMP system can have a profound effect on the reliability and performance of the system. This document provides details on some of the issues that have been found to impact a successful and trouble-free installation.

SCSI Cables

There is a considerable difference in quality and performance of cables used to connect SCSI devices. It is imperative that users pay close attention to this issue.

Cable Quality

High quality SCSI cables are essential for proper MMR/MMP system performance. Low quality cables, which are often thin, may cause data transmission errors, file corruption, and system malfunctions. This is often due to improper and insufficient grounding, incorrect pin wiring, and unwired pins. The following SCSI cable manufacturers are highly recommended as a source for MMR/MMP SCSI cables:

Paralan Corporation -	Black Box Corporation -
www.paralan.com	www.blackbox.com
4655 Ruffner St., San Diego, CA 92111	1000 Park Drive Lawrence, PA 15055-1018
Tel. (619) 560-7266 Fax 619-560-8929	Tel: 724-746-5500 Fax: 724-746-0746
email: scsi@paralan.com	email info@blackbox.com

Cable Length and Device Support

The MMR/MMP SCSI host card supports from one to eight SCSI devices. However when one to four SCSI devices are connected, total cable length should not exceed three meters. When five to eight SCSI devices are connected, total cable length should not exceed 1.5 meters. Note that total cable length includes the internal cabling in carriers or drive bays. Thus if a 4-bay drive enclosure contains ribbon cable internally that measures one meter in length, the external cable must not exceed 2 meters. Improper cable length often causes an MMR system to freeze while mounting volumes. (Note: Paralan can provide custom-length SCSI cables).

Cabling Wide and Narrow Devices in a System

NARROW SCSI uses 8-bit data transfers. It generally uses a 50-pin connector.

WIDE SCSI uses 16-bit data transfers. It generally uses a 68-pin connector. Wide SCSI may also refer to 32-bit SCSI data transfers but 32-bit wide SCSI is not as common.

Narrow drives should always be placed at the end of a SCSI chain. This is due to the fact that when a Wide to Narrow connection is made, 8 bits are not passed through, so the Wide drive (and all subsequent SCSI devices in the chain) receives only 8 bits of data instead of 16. If a Narrow drive is connected after a Wide drive, the Wide drive still receives all 16 bits of data.

SCSI Tips for MMR/MMP Users 3 rev 1.0 1/26/99