1998-01-09 09:40:53 +03:00
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.\" $NetBSD: motivation.ms,v 1.2 1998/01/09 06:41:01 perry Exp $
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.\"
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1994-06-19 04:07:16 +04:00
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.\" Copyright (c) 1983 The Regents of the University of California.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)motivation.ms 6.2 (Berkeley) 4/16/91
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.\"
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.ds RH Motivation
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.NH
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Motivation
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.PP
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These benchmarks were performed for several reasons.
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Foremost was our desire to obtain guideline to aid
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in choosing one the most expensive components of any
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VAX UNIX configuration, the disk storage system.
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The range of choices in this area has increased dramatically
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in the last year.
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DEC has become, with the introduction of the UDA50/RA81 system,
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cost competitive
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in the area of disk storage for the first time.
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Emulex's entry into the VAX 11/780 SBI controller
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field, the SC780, represented a important choice for us to examine, given
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our previous success with their VAX 11/750 SC750 controller and
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their UNIBUS controllers.
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The Fujitsu 2351A
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Winchester disk drive represents the lowest cost-per-byte disk storage
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known to us.
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In addition, Fujitsu's reputation for reliability was appealing.
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The many attractive aspects of these components justified a more
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careful examination of their performance aspects under UNIX.
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.PP
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In addition to the direct motivation of developing an effective
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choice of storage systems, we hoped to gain more insight into
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VAX UNIX file system and I/O performance in general.
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What generic characteristics of I/O subsystems are most
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important?
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How important is the location of the controller on the SBI/CMI versus
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the UNIBUS?
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Is extensive buffering in the controller essential or even important?
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How much can be gained by putting more of the storage system
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management and optimization function in the controller as
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DEC does with the UDA50?
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.PP
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We also wanted to resolve particular speculation about the value of
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storage system optimization by a controller in a UNIX
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environment.
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Is the access optimization as effective as that already provided
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by the existing 4.2BSD UNIX device handlers for traditional disks?
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VMS disk handlers do no seek optimization.
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This gives the UDA50 controller an advantage over other controllers
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under VMS which is not likely to be as important to UNIX.
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Are there penalties associated with greater intelligence in the controller?
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.PP
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A third and last reason for evaluating this equipment is comparable
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to the proverbial mountain climbers answer when asked why he climbs
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a particular mountain,
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``It was there.''
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In our case the equipment
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was there.
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We were lucky enough to assemble all the desired disks and controllers
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and get them installed on a temporarily idle VAX 11/780.
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This got us started collecting data.
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Although many of the tests were later rerun on a variety of other systems,
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this initial test bed was essential for working out the testing bugs
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and getting our feet wet.
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.ds RH Equipment
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.bp
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