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+.\" Copyright (c) 1983 The Regents of the University of California.
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"	This product includes software developed by the University of
+.\"	California, Berkeley and its contributors.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"	@(#)conclusions.ms	6.2 (Berkeley) 4/16/91
+.\"
+.ds RH Conclusions
+.NH
+Conclusions
+.PP
+Peak available throughput is only one criterion
+in most storage system purchasing decisions.
+Most of the VAX UNIX systems we are familiar with
+are not I/O bandwidth constrained.
+Nevertheless, an adequate disk bandwidth is necessary for
+good performance and especially to preserve snappy
+response time.
+All of the disk systems we tested provide more than
+adequate bandwidth for typical VAX UNIX system application.
+Perhaps in some I/O-intensive applications such as
+image processing, more consideration should be given
+to the peak throughput available.
+In most situations, we feel that other factors are more
+important in making a storage choice between the systems we
+tested.
+Cost, reliability, availability, and support are some of these
+factors.
+The maturity of the technology purchased must also be weighed
+against the future value and expandability of newer technologies.
+.PP
+Two important conclusions about storage systems in general
+can be drawn from these tests.
+The first is that buffering can be effective in smoothing
+the the effects of lower bus speeds and bus contention.
+Even though the UDA50 is located on the relatively slow
+UNIBUS, its performance is similar to controllers located on
+the faster processor busses.
+However, the SC780 with only one sector of buffering shows that
+little buffering is needed if the underlying bus is fast enough.
+.PP
+Placing more intelligence in the controller seems to hinder UNIX system
+performance more than it helps.
+Our profiling tests have indicated that UNIX spends about
+the same percentage of time in the SC780 driver and the UDA50 driver
+(about 10-14%).
+Normally UNIX uses a disk sort algorithm that separates reads and
+writes into two seek order queues.
+The read queue has priority over the write queue,
+since reads cause processes to block,
+while writes can be done asynchronously.
+This is particularly useful when generating large files,
+as it allows the disk allocator to read
+new disk maps and begin doing new allocations
+while the blocks allocated out of the previous map are written to disk.
+Because the UDA50 handles all block ordering,
+and because it keeps all requests in a single queue,
+there is no way to force the longer seek needed to get the next disk map.
+This disfunction causes all the writes to be done before the disk map read,
+which idles the disk until a new set of blocks can be allocated.
+.PP
+The additional functionality of the UDA50 controller that allows it
+to transfer simultaneously from two drives at once tends to make
+the two drive transfer tests run much more effectively.
+Tuning for the single drive case works more effectively in the two
+drive case than when controllers that cannot handle simultaneous
+transfers are used.
+.ds RH Acknowledgements
+.nr H2 1
+.sp 1
+.SH
+\s+2Acknowledgements\s0
+.PP
+We thank Paul Massigilia and Bill Grace
+of Digital Equipment Corp for helping us run our
+disk tests on their UDA50/RA81.
+We also thank Rich Notari and Paul Ritkowski
+of Emulex for making their machines available
+to us to run our tests of the SC780/Eagles.
+Dan McKinster, then of Systems Industries,
+arranged to make their equipment available for the tests.
+We appreciate the time provided by Bob Gross, Joe Wolf, and
+Sam Leffler on their machines to refine our benchmarks.
+Finally we thank our sponsors,
+the National Science Foundation under grant MCS80-05144,
+and the Defense Advance Research Projects Agency (DoD) under
+Arpa Order No. 4031 monitored by Naval Electronic System Command under
+Contract No. N00039-82-C-0235.
+.ds RH References
+.nr H2 1
+.sp 1
+.SH
+\s+2References\s0
+.LP
+.IP [McKusick83] 20
+M. McKusick, W. Joy, S. Leffler, R. Fabry,
+``A Fast File System for UNIX'',
+\fIACM Transactions on Computer Systems 2\fP, 3.
+pp 181-197, August 1984.
+.ds RH Appendix A
+.bp