?
Solved

Help understanding SCSI connections, channels, Buses  and Termination

Posted on 2010-09-02
6
Medium Priority
?
631 Views
Last Modified: 2013-11-14
We have a server which has an onboard SCSI controller and an Adaptec 2100S PCI SCSI card installed. From the SCSI card is a cable with 6 connections. The second connection on the cable is connected to a disk RAID Array which contains 5 disks via a SAF-TE hot swap backplain.

Can you confirm that the system sees the onboard SCSI controller completely seperately from the SCSI PCI card? That is they can both have their own sequence of SCSI IDs. Would they be on seperate BUSES and can each BUS have is own sequence.

My understanding is that everydevice (including cards) would have their own SCSI ID. Is the following correct/possible?

Bus A SCSI ID 1 - Onboard SCSI Controller
Bus A SCSI ID 2 - Tape Drive

Bus B (PCI Card) SCSI ID 1 - PCI SCSI Card
Bus B SCSI ID 2   - RAID Hotswap BackPlain
Bus B SCSI ID 3 - SCSI Drive 1 in RAID
Bus B SCSI ID 4 - SCSI Drive 2 in RAID
Bus B SCSI ID 5 - SCSI Drive 3 in RAID
Bus B SCSI ID 6 - SCSI Drive 4 in RAID
Bus B SCSI ID 7 - SCSI Drive 5 in RAID


My final question is about termination. If the first cable connector is connected to the PCI Card (with auto termination) and the Second cable connector connected to the RAID backplain, should the terminator be at the third cable connctor possition or is it ok to have the connector at the very end of the ribbon with entry connectors? At the moment is is at the very end of the cable and clips on so that it can not be easily removed.

Thanks for your help
 
0
Comment
Question by:EICT
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 4
6 Comments
 
LVL 5

Accepted Solution

by:
helpnet earned 420 total points
ID: 33585903
The SCSI configuration you have listed is possible (but can't say it is correct without seeing the computer).  

The onboard SCSI controller acts like another scsi card and its bus is totally separate to that of the SCSI card

Each bus is it's own scsi chain, and should be terminated.

Termination must be present at two and only two positions on the SCSI bus, at the beginning of the bus, and at the end, and must occur within 4 inches of the physical ends of the SCSI bus. Often, the host will be installed at one end of the bus, and will provide one of the two terminations required.
0
 
LVL 5

Assisted Solution

by:helpnet
helpnet earned 420 total points
ID: 33585947
So technically if the end of the scsi cable is more than 4 inches from the raid backplane, it should be moved.

(and yes scsi cards/controllers do have their own SCSI ID)

For performance reasons it is usually recommended for a Raid array, that the Raid array is the only thing on that SCSI bus.  If for example a TAPE drive is added to the same SCSI bus as the RAID array, it could dramatically decrease the access speed for the RAID array.  This is why most servers have more than one scsi controller.

More infor on SCIS termination
http://www.scsita.org/aboutscsi/SCSI_Termination_Tutorial.html
0
 
LVL 47

Assisted Solution

by:David
David earned 80 total points
ID: 33585951
Yes, above is possible, and even better ... reasonable.  You want to put the Tape on a separate channel, which you did.   SCSI ID #2 is for the SAF-TE target device to be accurate, not for the backplane.  Helpnet's answer regarding termination is accurate.

0
Turn your laptop into a mobile console!

The CV211 Laptop USB Console Adapter provides a direct Laptop-to-Computer connection for fast and easy remote desktop access with no software to install.

 

Author Comment

by:EICT
ID: 33585956
Hi Helpnet, when you say end to you mean end of the chain (i.e in the 3rd connector) or end of the cable in the 6th connector.

Thanks for the clarification.

Mattt
0
 
LVL 5

Assisted Solution

by:helpnet
helpnet earned 420 total points
ID: 33585995
The end of the chain is the last device with a SCSI ID.. the Raid array is at the end of the chain, so I would put the terminator on the 3rd connector.
0
 
LVL 5

Expert Comment

by:helpnet
ID: 33586020
You will probably find the tape drive has a jumper setting you can use to terminate the first SCSI chain. (Bus A)
0

Featured Post

Supports up to 4K resolution!

The VS192 2-Port 4K DisplayPort Splitter is perfect for anyone who needs to send one source of DisplayPort high definition video to two or four DisplayPort displays. The VS192 can split and also expand DisplayPort audio/video signal on two or four DisplayPort monitors.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Concerto Cloud Services, a provider of fully managed private, public and hybrid cloud solutions, announced today it was named to the 20 Coolest Cloud Infrastructure Vendors Of The 2017 Cloud  (http://www.concertocloud.com/about/in-the-news/2017/02/0…
Backups and Disaster RecoveryIn this post, we’ll look at strategies for backups and disaster recovery.
This Micro Tutorial will teach you how to reformat your flash drive. Sometimes your flash drive may have issues carrying files so this will completely restore it to manufacturing settings. Make sure to backup all files before reformatting. This w…
In this video, Percona Solutions Engineer Barrett Chambers discusses some of the basic syntax differences between MySQL and MongoDB. To learn more check out our webinar on MongoDB administration for MySQL DBA: https://www.percona.com/resources/we…

801 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question