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+.\" Copyright (c) 1986, 1993
+.\"	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.
+.\"
+.\"	@(#)2.t	8.1 (Berkeley) 6/8/93
+.\"
+.ds RH Old file system
+.NH
+Old File System
+.PP
+In the file system developed at Bell Laboratories
+(the ``traditional'' file system),
+each disk drive is divided into one or more
+partitions.  Each of these disk partitions may contain
+one file system.  A file system never spans multiple
+partitions.\(dg
+.FS
+\(dg By ``partition'' here we refer to the subdivision of
+physical space on a disk drive.  In the traditional file
+system, as in the new file system, file systems are really
+located in logical disk partitions that may overlap.  This
+overlapping is made available, for example,
+to allow programs to copy entire disk drives containing multiple
+file systems.
+.FE
+A file system is described by its super-block,
+which contains the basic parameters of the file system.
+These include the number of data blocks in the file system,
+a count of the maximum number of files,
+and a pointer to the \fIfree list\fP, a linked
+list of all the free blocks in the file system.
+.PP
+Within the file system are files.
+Certain files are distinguished as directories and contain
+pointers to files that may themselves be directories.
+Every file has a descriptor associated with it called an
+.I "inode".
+An inode contains information describing ownership of the file,
+time stamps marking last modification and access times for the file,
+and an array of indices that point to the data blocks for the file.
+For the purposes of this section, we assume that the first 8 blocks
+of the file are directly referenced by values stored
+in an inode itself*.
+.FS
+* The actual number may vary from system to system, but is usually in
+the range 5-13.
+.FE
+An inode may also contain references to indirect blocks
+containing further data block indices.
+In a file system with a 512 byte block size, a singly indirect
+block contains 128 further block addresses,
+a doubly indirect block contains 128 addresses of further singly indirect
+blocks,
+and a triply indirect block contains 128 addresses of further doubly indirect
+blocks.
+.PP
+A 150 megabyte traditional UNIX file system consists
+of 4 megabytes of inodes followed by 146 megabytes of data.
+This organization segregates the inode information from the data;
+thus accessing a file normally incurs a long seek from the
+file's inode to its data.
+Files in a single directory are not typically allocated
+consecutive slots in the 4 megabytes of inodes,
+causing many non-consecutive blocks of inodes
+to be accessed when executing
+operations on the inodes of several files in a directory.
+.PP
+The allocation of data blocks to files is also suboptimum.
+The traditional
+file system never transfers more than 512 bytes per disk transaction
+and often finds that the next sequential data block is not on the same
+cylinder, forcing seeks between 512 byte transfers.
+The combination of the small block size,
+limited read-ahead in the system,
+and many seeks severely limits file system throughput.
+.PP
+The first work at Berkeley on the UNIX file system attempted to improve both
+reliability and throughput.
+The reliability was improved by staging modifications
+to critical file system information so that they could
+either be completed or repaired cleanly by a program
+after a crash [Kowalski78].
+The file system performance was improved by a factor of more than two by
+changing the basic block size from 512 to 1024 bytes.
+The increase was because of two factors:
+each disk transfer accessed twice as much data, 
+and most files could be described without need to access
+indirect blocks since the direct blocks contained twice as much data.
+The file system with these changes will henceforth be referred to as the
+.I "old file system."
+.PP
+This performance improvement gave a strong indication that
+increasing the block size was a good method for improving
+throughput.
+Although the throughput had doubled, 
+the old file system was still using only about
+four percent of the disk bandwidth.
+The main problem was that although the free list was initially
+ordered for optimal access,
+it quickly became scrambled as files were created and removed.
+Eventually the free list became entirely random,
+causing files to have their blocks allocated randomly over the disk.
+This forced a seek before every block access.
+Although old file systems provided transfer rates of up
+to 175 kilobytes per second when they were first created,
+this rate deteriorated to 30 kilobytes per second after a
+few weeks of moderate use because of this
+randomization of data block placement.
+There was no way of restoring the performance of an old file system
+except to dump, rebuild, and restore the file system.
+Another possibility, as suggested by [Maruyama76],
+would be to have a process that periodically
+reorganized the data on the disk to restore locality.
+.ds RH New file system
+.sp 2
+.ne 1i