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Diffstat (limited to 'sbin/fsck_ffs/SMM.doc/2.t')
| -rw-r--r-- | sbin/fsck_ffs/SMM.doc/2.t | 76 |
1 files changed, 38 insertions, 38 deletions
diff --git a/sbin/fsck_ffs/SMM.doc/2.t b/sbin/fsck_ffs/SMM.doc/2.t index c6a8e4b..0f0bef7 100644 --- a/sbin/fsck_ffs/SMM.doc/2.t +++ b/sbin/fsck_ffs/SMM.doc/2.t @@ -32,22 +32,22 @@ .\" $FreeBSD$ .\" @(#)2.t 8.1 (Berkeley) 6/5/93 .\" -.ds RH Overview of the file system +.ds RH Overview of the filesystem .NH -Overview of the file system +Overview of the filesystem .PP -The file system is discussed in detail in [Mckusick84]; +The filesystem is discussed in detail in [Mckusick84]; this section gives a brief overview. .NH 2 Superblock .PP -A file system is described by its +A filesystem is described by its .I "super-block" . -The super-block is built when the file system is created (\c +The super-block is built when the filesystem is created (\c .I newfs (8)) and never changes. The super-block -contains the basic parameters of the file system, +contains the basic parameters of the filesystem, such as the number of data blocks it contains and a count of the maximum number of files. Because the super-block contains critical data, @@ -56,7 +56,7 @@ replicates it to protect against catastrophic loss. The .I "default super block" always resides at a fixed offset from the beginning -of the file system's disk partition. +of the filesystem's disk partition. The .I "redundant super blocks" are not referenced unless a head crash @@ -64,7 +64,7 @@ or other hard disk error causes the default super-block to be unusable. The redundant blocks are sprinkled throughout the disk partition. .PP -Within the file system are files. +Within the filesystem are files. Certain files are distinguished as directories and contain collections of pointers to files that may themselves be directories. Every file has a descriptor associated with it called an @@ -82,7 +82,7 @@ the range 5-13. .FE The inode structure may also contain references to indirect blocks containing further data block indices. -In a file system with a 4096 byte block size, a singly indirect +In a filesystem with a 4096 byte block size, a singly indirect block contains 1024 further block addresses, a doubly indirect block contains 1024 addresses of further single indirect blocks, @@ -92,30 +92,30 @@ blocks (the triple indirect block is never needed in practice). In order to create files with up to 2\(ua32 bytes, using only two levels of indirection, -the minimum size of a file system block is 4096 bytes. -The size of file system blocks can be any power of two +the minimum size of a filesystem block is 4096 bytes. +The size of filesystem blocks can be any power of two greater than or equal to 4096. -The block size of the file system is maintained in the super-block, -so it is possible for file systems of different block sizes +The block size of the filesystem is maintained in the super-block, +so it is possible for filesystems of different block sizes to be accessible simultaneously on the same system. The block size must be decided when .I newfs -creates the file system; +creates the filesystem; the block size cannot be subsequently -changed without rebuilding the file system. +changed without rebuilding the filesystem. .NH 2 Summary information .PP Associated with the super block is non replicated .I "summary information" . The summary information changes -as the file system is modified. +as the filesystem is modified. The summary information contains -the number of blocks, fragments, inodes and directories in the file system. +the number of blocks, fragments, inodes and directories in the filesystem. .NH 2 Cylinder groups .PP -The file system partitions the disk into one or more areas called +The filesystem partitions the disk into one or more areas called .I "cylinder groups". A cylinder group is comprised of one or more consecutive cylinders on a disk. @@ -125,7 +125,7 @@ describing available blocks in the cylinder group, and summary information describing the usage of data blocks within the cylinder group. A fixed number of inodes is allocated for each cylinder group -when the file system is created. +when the filesystem is created. The current policy is to allocate one inode for each 2048 bytes of disk space; this is expected to be far more inodes than will ever be needed. @@ -158,12 +158,12 @@ and the beginning of the cylinder group information stores data. Fragments .PP To avoid waste in storing small files, -the file system space allocator divides a single -file system block into one or more +the filesystem space allocator divides a single +filesystem block into one or more .I "fragments". -The fragmentation of the file system is specified -when the file system is created; -each file system block can be optionally broken into +The fragmentation of the filesystem is specified +when the filesystem is created; +each filesystem block can be optionally broken into 2, 4, or 8 addressable fragments. The lower bound on the size of these fragments is constrained by the disk sector size; @@ -173,17 +173,17 @@ records the space availability at the fragment level. Aligned fragments are examined to determine block availability. .PP -On a file system with a block size of 4096 bytes +On a filesystem with a block size of 4096 bytes and a fragment size of 1024 bytes, a file is represented by zero or more 4096 byte blocks of data, and possibly a single fragmented block. -If a file system block must be fragmented to obtain +If a filesystem block must be fragmented to obtain space for a small amount of data, the remainder of the block is made available for allocation to other files. For example, consider an 11000 byte file stored on -a 4096/1024 byte file system. +a 4096/1024 byte filesystem. This file uses two full size blocks and a 3072 byte fragment. If no fragments with at least 3072 bytes are available when the file is created, @@ -191,26 +191,26 @@ a full size block is split yielding the necessary 3072 byte fragment and an unused 1024 byte fragment. This remaining fragment can be allocated to another file, as needed. .NH 2 -Updates to the file system +Updates to the filesystem .PP Every working day hundreds of files are created, modified, and removed. Every time a file is modified, the operating system performs a -series of file system updates. -These updates, when written on disk, yield a consistent file system. -The file system stages +series of filesystem updates. +These updates, when written on disk, yield a consistent filesystem. +The filesystem stages all modifications of critical information; modification can either be completed or cleanly backed out after a crash. -Knowing the information that is first written to the file system, +Knowing the information that is first written to the filesystem, deterministic procedures can be developed to -repair a corrupted file system. +repair a corrupted filesystem. To understand this process, the order that the update requests were being honored must first be understood. .PP -When a user program does an operation to change the file system, +When a user program does an operation to change the filesystem, such as a .I write , the data to be written is copied into an internal @@ -225,9 +225,9 @@ is eventually written out to disk. The real disk write may not happen until long after the .I write system call has returned. -Thus at any given time, the file system, +Thus at any given time, the filesystem, as it resides on the disk, -lags the state of the file system represented by the in-core information. +lags the state of the filesystem represented by the in-core information. .PP The disk information is updated to reflect the in-core information when the buffer is required for another use, @@ -239,7 +239,7 @@ or by manual operator intervention with the .I sync (8) command. If the system is halted without writing out the in-core information, -the file system on the disk will be in an inconsistent state. +the filesystem on the disk will be in an inconsistent state. .PP If all updates are done asynchronously, several serious inconsistencies can arise. @@ -263,4 +263,4 @@ really written to disk) when they are being deallocated. Similarly inodes are kept consistent by synchronously deleting, adding, or changing directory entries. -.ds RH Fixing corrupted file systems +.ds RH Fixing corrupted filesystems |
