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How to terminate A SCSI hard drive?

August 23rd, 2009

SCSI Hard Drive With today’s high speed hard drives combined with long cable runs, only use high quality ‘twisted pair’ cable and external active (cable end) terminators. Active termination boosts data integrity and reliability. With active termination, a 110-ohm resistor on each signal line connects to a voltage regulator. The regulator ensures signal quality over the entire length of the SCSI bus. This reduces under and overshoot signals typically found on passive resistor termination schemes.

Passive termination draws its electrical power from the SCSI host adapter. A 220/330-ohm resistor is used to provide the necessary impedance to prevent the data signal from ‘reflecting’ back. Fluctuations in termination power (or failing cables) can show up as error symptoms in the drive, yet do not originate there. In general we recommend you enable SCSI Termination Power if available.

  • Maxtor (and Quantum) SCSI disk drives have either onboard active termination (jumpers). Older drives (circa 1994) enable active termination by two removable (10-pin) termination resistors. Some use passive termination with three removable (8-pin) terminating resistor packs. Seagate does not supply terminating resistor packs for older drives.
  • SCSI Single Ended Hard drives using active onboard termination have a jumper setting labeled ‘TE’ to control the termination setting.
  • All Quantum Single-Ended SCSI drives ship defaulted to provide SCSI Termination Enable.
  • SCSI LVD(low voltage differential) drives do not supply SCSI Termination Enable. Refer to the drive configuration guides for proper setting of this feature.Notes:
    1. Some Quantum SCSI disk drives are available in both Single-Ended and LVD versions. Specifically, the Atlas III and Viking II drives offer both types of termination. Atlas III Narrow (50 pin) drives are Single-Ended, while the Wide (68 pin) and SCA (80 pin) versions are LVD models. Viking II Wide drives are available in both SE and LVD models. The part number for an SE drive will contain “W”, and the LVD will contain a “L” (e.g. PX09L011 would be LVD). All Viking II SCA drives are LVD models. All fifty pin Quantum SCSI drives are all SCSI Single-Ended.
    2. LVD cables and SCSI bus terminators can be purchased from TMC (The Mate Co.) or a local retailer.
    3. Use due diligence when installing or adding SCSI devices. Unlike most electronic devices, SCSI may operate if improperly terminated, but performance and reliability will be seriously at risk.
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