Server + - SCSI Cable Length?

Author

SCSI Cable Length?

muon

2002-03-28, 2:33 am

There are some inconsistencies in the SCSI cable length indicated in Exam Notes/Cramsession study guide and the Trevor Kay's Server+ Bible.

For example, in Trevor's book, on p.213, there is a table where various SCSI cable lengths are shown and classified according to signal types used (SE, HVD, LVD), but Exam Notes study guide made no mention of signal types used.

Furthermore, SCSI3 supposedly required only LVD signaling, and Trevor indicated the maximum length is 25m LVD, while Cramsession showed 12m --- which is correct?

For those who have taken the test, I hope the actual exam question actually tells you what signal type to use unlike the low-quality Boson test packs.

wbafrank

2002-03-28, 3:25 am

of this ....

http://www.cableco.com/scsi_doc.html

ace123

2002-03-28, 7:23 am

Good link. Thanks

Supertech

2002-03-28, 7:45 am

Short and Sweet.

http://www.startech.com/scsischool/...ferrer=mainscsi

muon

2002-03-28, 11:44 am

Thanks to those who replied --- I have managed to answer my own question. I am posting my findings here to share the knowledge.

I searched the T10 web site (the SCSI standards committee), but the information contained within were all overly technical.

Google has a helpful directory of SCSI-related information:

http://directory.google.com/Top/Com...are/Buses/SCSI/

I browsed a few, and managed to find the exact information I wanted at:

http://www.scsita.org/aboutscsi/SCS...n_Tutorial.html

Table 1 on the above web page summarizes the answer I was seeking. Based on my searches, the Ultra3 SCSI cable length indicated in the Server+ Bible (p.213) is probably INCORRECT --- the answer is 12 m.

For examination purposes, know that for HVD, the cable length is 25m; for LVD, it is 12m. For SE, the range is from 1.5m to 6m.

I would memorize this table as it summarizes the bus speed, cable length, the number of devices supported more succintly.

Fiber_Optix

2002-03-28, 12:35 pm

Good job on the research man, I am thinking of emailing comptia and seeing where they stand for the purposes of the test just so none of us miss a question due to studying the wrong information. I am sure they must conform to the the standards of the industry though. Good luck in studying, I am going through the same headache!

Doug_Black

2002-03-28, 9:38 pm

I think I am going to call the folks at Adaptec, seeing they are on the SCSI standards board and are also members of CompTIA exam board.

I also get different answers when I compare to Seagate, Adaptec and others sources I have. There are also appearantly many conditions that can change the answer including mixing of different SCSI device standards and multiple or single devices on the chain. I hope they don't ask about the minimum distances between devices on the SCSI chain or that is really tough!

I will add a couple other web-sites for refences too:

http://www.ramelectronics.net/html/scsi_connecters.html (read the Notes at bottom of their chart and have pictures of connectors - some are different for MAC or SUN or country - Japan)

http://www.seagate.com/support/kb/d...face_cable.html (read their chart and it shows 12 meter maximum)

http://ask.adaptec.com/cgi-bin/adap...nduser/home.php

"Each bus segment is electrically isolated and maintains the performance and configuration parameters of that segment, including termination and cabling requirements. In order to correctly calculate your cable lengths you need to add the cable length of each bus segment independently.

The Ultra2 / LVD bus segment supports the following cable lengths:

25 meters (82.02 ft) point-to-point cable length with one device only
12 meters (39.37 ft) with four devices or fewer

The Legacy / SE bus segment supports the following cable lengths:

SCSI-1 or 2 (5 MB/Sec) 6 meters (20 ft)
SCSI-2 Fast Narrow (10 MB/Sec) 3 meters (10 ft)
SCSI-2 Fast Wide (20 MB/Sec) 3 meters (10 ft)
SCSI-2 Ultra Narrow (20 MB/Sec) 1.5 meters (5 ft)
SCSI-2 Ultra Wide (40 MB/Sec) 1.5 meters (4.5 ft)"

http://www.t10.org/scsi-3.htm

Kind of strange that CompTIA brings together all these great computer vendors and manufacturers to create an exam, but they can't endorse a book for studying to pass their exams!

dagger

2002-03-29, 6:37 am

quote:
Originally posted by Doug_Black

Kind of strange that CompTIA brings together all these great computer vendors and manufacturers to create an exam, but they can't endorse a book for studying to pass their exams!

I've asked CompTIA about that
and they said they don't endorse any text books because they want to stay vendor neutral.

Doug_Black

2002-03-29, 1:26 pm

Vendor neutral is fine, but with some of the vast differences in technical specifications how does CompTIA decide what the answers are for their exams and more importantly, how are we the test takers suppose to know what is correct. I truely understand what is Real World versus what is Vendor acceptable and that cost me several points on the Microsoft Network Essentials exam years ago.

That is why I posted Adaptec's Web-Site seeing they are the leader in SCSI controllers & chip-sets, Seagate who is the leader in SCSI Hard Drives, a generic SCSI cable & connector company and then the ANSI standards folks Web-Sites. Hopefully when I get the answers I am willing to accept I will post them for all to read and learn for the exam seeing I know somebody who helped write the exam!

King Rat

2002-04-16, 4:06 am

Cable length questions were not asked on my exam. I had one on buses though and a SCSI speed question.

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