ALERT

[FREE DEMO] Deploy Your Enterprise Cloud in Minutes

SCSI Termination

Definition - What does SCSI Termination mean?

SCSI termination is the process of preventing the reflection of electrical signals from the ends of SCSI buses in order to ensure reliable operation. This termination is done passively via the use of various resistors connected to the signal lines at the connector end or actively through the application of a small amount of electricity. If termination is not done, the data signals themselves can reflect back from the ends of the bus and cause various anomalies in the data because of the pulse distortion or it results in outright data loss.

SCSI termination is also known as SCSI bus termination.

Techopedia explains SCSI Termination

SCSI termination is similar to grounding, a necessary step so that the signal is not reflected back from the end of the bus. The SCSI bus is likened to a taut string in that, when one end is vibrated, it causes the vibration to travel through the string until it reaches the other end, and then because it has nowhere to go, the vibration is reflected back to the direction it came from, bouncing from end to end until all the energy is dissipated. This is the same thing that happens with the electrical pulses that go through the SCSI bus; they are reflected back from where they came if proper termination has not been observed. As would be expected, this prevents any actual data from being recognized because of the noise and interference generated.

The electrical wave has to be terminated at the physical ends of the bus, i.e., at the connectors where it meets open air. This is done by installing a terminator at the ends of the bus after all of the actual devices on the chain.

Types of termination:

  • Single-ended (SE) — The SCSI controller pushes out signals to all devices using a single data line and each device at the end acts as a ground. Because the signal degrades quickly, SE SCSI is limited to a maximum of 3 m. This is the most common signaling used in PCs.
  • High-voltage differential (HVD) — Each device connected to the SCSI bus has a signal transceiver and uses this as a signal booster so that signals can reach further (25 m). This is usually used on servers.
  • Low-voltage differential (LVD) — A variation of HVD, but instead of the transceiver being built into the device, it is smaller and built into the SCSI adapter on each device so the voltage required for communication is also lower. Cheaper to implement compared to HVD but only has half the range at about 12 m.

Techopedia Deals

Connect with us

Techopedia on Linkedin
Techopedia on Linkedin
Tweat cdn.techopedia.com
"Techopedia" on Twitter


'@Techopedia'
Sign up for Techopedia's Free Newsletter!

Email Newsletter

Join thousands of others with our weekly newsletter

Resources
The 4th Era of IT Infrastructure: Superconverged Systems
The 4th Era of IT Infrastructure: Superconverged Systems:
Learn the benefits and limitations of the 3 generations of IT infrastructure – siloed, converged and hyperconverged – and discover how the 4th...
Approaches and Benefits of Network Virtualization
Approaches and Benefits of Network Virtualization:
Businesses today aspire to achieve a software-defined datacenter (SDDC) to enhance business agility and reduce operational complexity. However, the...
Free E-Book: Public Cloud Guide
Free E-Book: Public Cloud Guide:
This white paper is for leaders of Operations, Engineering, or Infrastructure teams who are creating or executing an IT roadmap.
Free Tool: Virtual Health Monitor
Free Tool: Virtual Health Monitor:
Virtual Health Monitor is a free virtualization monitoring and reporting tool for VMware, Hyper-V, RHEV, and XenServer environments.
Free 30 Day Trial – Turbonomic
Free 30 Day Trial – Turbonomic:
Turbonomic delivers an autonomic platform where virtual and cloud environments self-manage in real-time to assure application performance.