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+.\" Copyright (c) 1983 The Regents of the University of California.
+.\" All rights reserved.
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+.\"    may be used to endorse or promote products derived from this software
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+.\"
+.\"	@(#)motivation.ms	6.2 (Berkeley) 4/16/91
+.\"
+.ds RH Motivation
+.NH
+Motivation
+.PP
+These benchmarks were performed for several reasons.
+Foremost was our desire to obtain guideline to aid
+in choosing one the most expensive components of any
+VAX UNIX configuration, the disk storage system.
+The range of choices in this area has increased dramatically
+in the last year.
+DEC has become, with the introduction of the UDA50/RA81 system,
+cost competitive
+in the area of disk storage for the first time.
+Emulex's entry into the VAX 11/780 SBI controller
+field, the SC780, represented a important choice for us to examine, given
+our previous success with their VAX 11/750 SC750 controller and
+their UNIBUS controllers.
+The Fujitsu 2351A
+Winchester disk drive represents the lowest cost-per-byte disk storage
+known to us.
+In addition, Fujitsu's reputation for reliability was appealing.
+The many attractive aspects of these components justified a more
+careful examination of their performance aspects under UNIX.
+.PP
+In addition to the direct motivation of developing an effective
+choice of storage systems, we hoped to gain more insight into
+VAX UNIX file system and I/O performance in general.
+What generic characteristics of I/O subsystems are most
+important?
+How important is the location of the controller on the SBI/CMI versus
+the UNIBUS?
+Is extensive buffering in the controller essential or even important?
+How much can be gained by putting more of the storage system
+management and optimization function in the controller as
+DEC does with the UDA50?
+.PP
+We also wanted to resolve particular speculation about the value of
+storage system optimization by a controller in a UNIX
+environment.
+Is the access optimization as effective as that already provided
+by the existing 4.2BSD UNIX device handlers for traditional disks?
+VMS disk handlers do no seek optimization.
+This gives the UDA50 controller an advantage over other controllers
+under VMS which is not likely to be as important to UNIX.
+Are there penalties associated with greater intelligence in the controller?
+.PP
+A third and last reason for evaluating this equipment is comparable
+to the proverbial mountain climbers answer when asked why he climbs
+a particular mountain,
+``It was there.''
+In our case the equipment
+was there.
+We were lucky enough to assemble all the desired disks and controllers
+and get them installed on a temporarily idle VAX 11/780.
+This got us started collecting data.
+Although many of the tests were later rerun on a variety of other systems,
+this initial test bed was essential for working out the testing bugs
+and getting our feet wet.
+.ds RH Equipment
+.bp