SUMMARY: set scsi_options=0x3f8 in /etc/system

From: Anchi Zhang (
Date: Wed Nov 16 1994 - 00:22:39 CST

My original posting:

 Would anybody know what "set scsi_options=0x3f8" in /etc/system
 on a Sparc Solaris 2.3 machine was for?

Many thanks to

 gravatt@batman (Larry Gravatt) (Cindy Yoho) (GREGOR E FELLERS ) (Rick Pluta)
 Casper Dik <>
 rauthenberg@HHI.DE (Stefan Rauthenberg) (Peter Samuel) (Daniel F. Kamm)
 Timothy G Smith - Special Projects <tgsmith@Sun.COM> (Johnny Hui) (Bern Fox) (Dave Johnson)
 Andre Saile <>
 Nate Itkin <>

most of whom stated that "set scsi_options=0x3f8," the default
setting, would turn on all the scsi_options defined in
/usr/include/sys/scsi/autoconf.h. The most descriptive reply
from Larry Gravatt (gravatt@batman) is appended.


>From gravatt@batman Fri Nov 11 08:36:49 1994
Subject: Re: set scsi_options=0x3f8 in /etc/system

        "set scsi_options=0x3f8" in /etc/system
        is used to slow all SCSI ports to asynchronous operation.
        For all other fast SCSI hosts attaching devices that do not
         conform with the fast SCSI requirements, the operating system
         should be modified to run all SCSI ports in asynchronous mode.
         This slower mode fully interlocks all the SCSI data transfer
         signals and provides for reliable operation of the Extended
         Storage Module at the end of a SCSI bus. It allows Sun
         configurations containing both fast SCSI drives and
         nonconforming devices to operate reliably on fast SCSI ports.

         If the system configuration meets the standard SCSI
         requirements, reliable operation can usually be provided
         with third-party components and peripherals as well. The
         slower data rate applies to all SCSI ports on the system. Some
         applications may show a decrease in performance because of the
         slower data rate.

                To change to the slower asynchronous data rate,
                add the following line to /etc/system file:
                         set scsi_options = 0x58
                then reboot the system.
                 To turn synchronous transfer back on at the
                 highest possible speed without using tagged
                 queueing, change the scsi_options line to:
                         set scsi_options = 0X178

                To turn synchronous transfer back on at the
                 highest possible speed allowing tagged queueing
                 (if available in the operating system),
                 change the scsi_options line to:
                         set scsi_options = 0X1f8


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