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Annotation of 43BSDReno/share/doc/smm/14.fastfs/1.t, revision 1.1

1.1     ! root        1: .\" Copyright (c) 1986 The Regents of the University of California.
        !             2: .\" All rights reserved.
        !             3: .\"
        !             4: .\" Redistribution and use in source and binary forms are permitted
        !             5: .\" provided that the above copyright notice and this paragraph are
        !             6: .\" duplicated in all such forms and that any documentation,
        !             7: .\" advertising materials, and other materials related to such
        !             8: .\" distribution and use acknowledge that the software was developed
        !             9: .\" by the University of California, Berkeley.  The name of the
        !            10: .\" University may not be used to endorse or promote products derived
        !            11: .\" from this software without specific prior written permission.
        !            12: .\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
        !            13: .\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
        !            14: .\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            15: .\"
        !            16: .\"    @(#)1.t 6.2 (Berkeley) 3/7/89
        !            17: .\"
        !            18: .ds RH Introduction
        !            19: .NH
        !            20: Introduction
        !            21: .PP
        !            22: This paper describes the changes from the original 512 byte UNIX file
        !            23: system to the new one released with the 4.2 Berkeley Software Distribution.
        !            24: It presents the motivations for the changes,
        !            25: the methods used to effect these changes,
        !            26: the rationale behind the design decisions,
        !            27: and a description of the new implementation.
        !            28: This discussion is followed by a summary of
        !            29: the results that have been obtained,
        !            30: directions for future work,
        !            31: and the additions and changes
        !            32: that have been made to the facilities that are
        !            33: available to programmers.
        !            34: .PP
        !            35: The original UNIX system that runs on the PDP-11\(dg
        !            36: .FS
        !            37: \(dg DEC, PDP, VAX, MASSBUS, and UNIBUS are
        !            38: trademarks of Digital Equipment Corporation.
        !            39: .FE
        !            40: has simple and elegant file system facilities.  File system input/output
        !            41: is buffered by the kernel;
        !            42: there are no alignment constraints on
        !            43: data transfers and all operations are made to appear synchronous.
        !            44: All transfers to the disk are in 512 byte blocks, which can be placed
        !            45: arbitrarily within the data area of the file system.  Virtually
        !            46: no constraints other than available disk space are placed on file growth
        !            47: [Ritchie74], [Thompson78].*
        !            48: .FS
        !            49: * In practice, a file's size is constrained to be less than about
        !            50: one gigabyte.
        !            51: .FE
        !            52: .PP
        !            53: When used on the VAX-11 together with other UNIX enhancements,
        !            54: the original 512 byte UNIX file
        !            55: system is incapable of providing the data throughput rates
        !            56: that many applications require.
        !            57: For example, 
        !            58: applications
        !            59: such as VLSI design and image processing
        !            60: do a small amount of processing
        !            61: on a large quantities of data and
        !            62: need to have a high throughput from the file system.
        !            63: High throughput rates are also needed by programs
        !            64: that map files from the file system into large virtual
        !            65: address spaces.
        !            66: Paging data in and out of the file system is likely
        !            67: to occur frequently [Ferrin82b].
        !            68: This requires a file system providing
        !            69: higher bandwidth than the original 512 byte UNIX
        !            70: one that provides only about
        !            71: two percent of the maximum disk bandwidth or about
        !            72: 20 kilobytes per second per arm [White80], [Smith81b].
        !            73: .PP
        !            74: Modifications have been made to the UNIX file system to improve
        !            75: its performance.
        !            76: Since the UNIX file system interface
        !            77: is well understood and not inherently slow,
        !            78: this development retained the abstraction and simply changed
        !            79: the underlying implementation to increase its throughput.
        !            80: Consequently, users of the system have not been faced with
        !            81: massive software conversion.
        !            82: .PP
        !            83: Problems with file system performance have been dealt with
        !            84: extensively in the literature; see [Smith81a] for a survey.
        !            85: Previous work to improve the UNIX file system performance has been
        !            86: done by [Ferrin82a].
        !            87: The UNIX operating system drew many of its ideas from Multics,
        !            88: a large, high performance operating system [Feiertag71].
        !            89: Other work includes Hydra [Almes78],
        !            90: Spice [Thompson80],
        !            91: and a file system for a LISP environment [Symbolics81].
        !            92: A good introduction to the physical latencies of disks is
        !            93: described in [Pechura83].
        !            94: .ds RH Old file system
        !            95: .sp 2
        !            96: .ne 1i

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