From: Dennis Wang (
Date: Thu Dec 17 1992 - 09:56:08 CST

Here is what I got back as answers to my query re SCSI-2
(Interesting that two of the responses to a nationwide broadcast come from my own domain :)

----Begin Include ----

>From Tue Dec 15 16:40:58 1992
Return-Path: <>
Date: Tue, 15 Dec 92 16:41:05 -0500
From: (Larry Schuette)
Subject: Re: SCSI-2 on Sun SPARC 10
Newsgroups: nrl.misc,comp.sys.sun.hardware
Organization: Naval Research Lab, Physical Acoustics, Washington, DC
Content-Length: 569
Status: RO
X-Lines: 16

you cannot mix fast and slow scsi. the drives will work, but only
at slow scsi speeds. This is true for the Western Digital
Version WD33C93B, revision C controllers.
(which are used on newer SGI machines)


	"The quality of the kite matters little.  Success depends upon
		the man who sits in it."		BMv. Richthofen

Lawrence C. Schuette Code 7133 (202)767-2739 Naval Research Laboratory (202)767-5561 (fax) Washington D.C. 20375-5320

>From Wed Dec 16 10:37:32 1992 Return-Path: <> Date: Wed, 16 Dec 92 10:37:39 EST From: Loren Buchanan <> To: Subject: Re: SCSI-2 on Sun SPARC 10 Newsgroups: nrl.misc,comp.sys.sun.hardware Organization: Naval Research Lab, Washington, DC Content-Length: 2381 Status: RO X-Lines: 46

In article <> you write: >Does anyone know of any problems using the SCSI-2 on a SPARC 10 ? I am getting some >conflicting stories. > >1. "No problem mixing fast SCSI-2 and slow SCSI" - Sun rep

He is probably right, no problem unless you want the speed from your fast SCSI-2 devices. If you mix them you will get the speed of the slowest device on the bus.

>2. "Big problem mixing fast SCSI and slow SCSI, you should put all your >slow SCSI devices on the SPARC 10 embedded controller and all the fast SCSI on >a separate differential SCSI controller board (you will have to buy diff SCSI >drives also - about $200 more per drive). Sun really messed up with the active >termination on the embedded controller. " - 3rd party drive supplier

This is the correct solution. We are ordering two HP 735s, each with one slow SCSI and one fast wide SCSI. There are several advantages to this solution, the big and obvious one is fast drives on the fast bus will go fast. The differential bus will have significantly less errors and you will not have to pay as much attention to your total bus length. By putting your CD-ROM drive and tape drive(s) on the slow bus and your hard disks on the fast bus you will speed up software installation and backups (although the gain may be small depending on other factors). Another thing to be aware of is if you ever have a flakey device on one of the busses, by moving devices from one bus to another you will be able to isolate the problem

>3. "No problem mixing fast SCSI and slow SCSI" - another 3rd party drive supplier

We recently bought 3 fast SCSI drives and have them all on slow SCSI busses. They are all working well. Another thing to be aware of is that the raw data rate of reading from or writing to a drive is limited to the bits that pass under a single head. Most advertising will not mention this number. The current crop of 2G drives probably are 5Mbytes/second give or take 750KBytes/second depending on inner or outer tracks. You will need two or more drives to take advantage of the fast bus.

B Cing U


-- Loren Buchanan ( | #include <standard.disclaimer> NRL Code 5842, 4555 Overlook Ave. | #include <> Washington, DC 20375 (202) 767-3884 | #include <> Phone tag, America's fastest growing business sport.

>From Wed Dec 16 14:06:07 1992 Return-Path: <> Date: Wed, 16 Dec 92 11:06:16 PST From: (Ron Nash) To: Subject: Re: SCSI-2 on Sun SPARC 10 Newsgroups: nrl.misc,comp.sys.sun.hardware Organization: SDSU Computing Services Cc: Content-Length: 879 X-Lines: 17 Status: RO

As I understand it, yes you can mix SCSI and SCSI-2 devices. The SCSI-2 bus negotiates with each device the speed it runs - but (you knew there was a but didn't you?!) active SCSI devices will drop the thruput of your SCSI-2 devices to roughly the SCSI (5MB/s) rate.

It is important to keep the SCSI-2 devices close the the machine. Total bus length should be under 4 feet for SCSI-2 devices unless you modify you SCSI-2 driver and terminator to use IBM's FPT technology. I have not used FPT, but other posts have indicated it costs about $40 per end from Aeronics and improves SCSI-2 thruput over SUN's active termination.

,--, | Ron Nash San Diego State University _ ___/ /\| | ,;`( )__, ) ~ | // // '--; | Gin-N-Tonic Learning to be an endurance horse ' \ | | Luv on Fire trusty trail horse ^ ^

--- Dennis Wang Solar Physics Branch - Code 7660 U.S. Naval Research Laboratory. 4555 Overlook Ave SW Washington DC 20375-5000

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