113 lines
4.8 KiB
Perl
113 lines
4.8 KiB
Perl
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.\" Copyright (c) 1986, 1993
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.\" The Regents of the University of California. 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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.\" @(#)1.t 8.1 (Berkeley) 6/8/93
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.\"
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.ds RH Introduction
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.NH
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Introduction
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.PP
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This paper describes the changes from the original 512 byte UNIX file
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system to the new one released with the 4.2 Berkeley Software Distribution.
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It presents the motivations for the changes,
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the methods used to effect these changes,
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the rationale behind the design decisions,
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and a description of the new implementation.
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This discussion is followed by a summary of
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the results that have been obtained,
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directions for future work,
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and the additions and changes
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that have been made to the facilities that are
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available to programmers.
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.PP
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The original UNIX system that runs on the PDP-11\(dg
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.FS
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\(dg DEC, PDP, VAX, MASSBUS, and UNIBUS are
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trademarks of Digital Equipment Corporation.
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.FE
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has simple and elegant file system facilities. File system input/output
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is buffered by the kernel;
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there are no alignment constraints on
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data transfers and all operations are made to appear synchronous.
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All transfers to the disk are in 512 byte blocks, which can be placed
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arbitrarily within the data area of the file system. Virtually
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no constraints other than available disk space are placed on file growth
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[Ritchie74], [Thompson78].*
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.FS
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* In practice, a file's size is constrained to be less than about
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one gigabyte.
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.FE
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.PP
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When used on the VAX-11 together with other UNIX enhancements,
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the original 512 byte UNIX file
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system is incapable of providing the data throughput rates
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that many applications require.
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For example,
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applications
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such as VLSI design and image processing
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do a small amount of processing
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on a large quantities of data and
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need to have a high throughput from the file system.
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High throughput rates are also needed by programs
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that map files from the file system into large virtual
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address spaces.
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Paging data in and out of the file system is likely
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to occur frequently [Ferrin82b].
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This requires a file system providing
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higher bandwidth than the original 512 byte UNIX
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one that provides only about
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two percent of the maximum disk bandwidth or about
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20 kilobytes per second per arm [White80], [Smith81b].
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.PP
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Modifications have been made to the UNIX file system to improve
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its performance.
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Since the UNIX file system interface
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is well understood and not inherently slow,
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this development retained the abstraction and simply changed
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the underlying implementation to increase its throughput.
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Consequently, users of the system have not been faced with
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massive software conversion.
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.PP
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Problems with file system performance have been dealt with
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extensively in the literature; see [Smith81a] for a survey.
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Previous work to improve the UNIX file system performance has been
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done by [Ferrin82a].
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The UNIX operating system drew many of its ideas from Multics,
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a large, high performance operating system [Feiertag71].
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Other work includes Hydra [Almes78],
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Spice [Thompson80],
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and a file system for a LISP environment [Symbolics81].
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A good introduction to the physical latencies of disks is
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described in [Pechura83].
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.ds RH Old file system
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.sp 2
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.ne 1i
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