the file system files -------- long-term storage ram --------- short-term storage programs, data,...
DESCRIPTION
Disk Architecture Sector Track Platter Arm Block: 4kb Read/write headTRANSCRIPT
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THE FILE SYSTEM
Files -------- long-term storageRAM --------- short-term storage
Programs, data, and text are all stored in files, which is stored on hard disk and other media, such as tape and floppy disk.
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THE FILE SYSTEMUNIX files are organized by a hierarchy of labels ---- directory structure
Three kinds:+ Regular files, containing a sequence of bytes that generally corresponds to code or data. Referenced via the standard I/O system calls.+ Directory files, a special format and forming the backbone of the file system. Referenced only via directory-specific system calls.+ Special files, correspond to peripherals such as printers and disks, and interprocess communication mechanisms, such as pipes and sockets. Referenced via the standard I/O system calls.
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Disk ArchitectureSector
Track
Platter
Arm
Block: 4kb
Read/write head
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Interleaving1:1 interleave
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2
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45
6
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89
10
11
1213
14
15
16
Delay, interleave factor, between each block due to the overhead of the communication between the disk controller and the device driver
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Interleaving1:3 interleave
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2
3 4
5
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78
9
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11 12
13
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1516
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Storing a File
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3
45
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89
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121314
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16
First 4K
Second 4K
Last 1K
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Inodes—Index nodeTo store information about each file+ the type of the file: regular, directory, block special, character special, etc.+ file permissions+ the owner and group IDs+ a hard link count+ the last modification time and last access time+ the location of the blocks if the file is a regular or directory file+ the major and minor device numbers if the file is a special file+ the value of the symbolic link if the file is a symbolic link
In other words, it contains all of the information when you perform an “ls -l”, except for the filename
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Inodes—Index node
Every inode in a particular file system is allocated a unique inode number.
Every file has exactly one inode.
All the inodes associated with the files on a disk are stored in a special area at the start of the disk called the inode list
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Every file has an inode
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45
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89
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121314
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Block mapInode
0123
72
14
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The Block MapInode only stores the first 10 blocks of a file. (most UNIX files are less than 40K)
An indirect access scheme is used for addressing larger files.
Direct block pointers
Indirect pointer
Disk blocks
Inode
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Direct block pointers
Indirect pointer
Disk blocks
Inode
Double indirect pointer
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File System Layout
boot block: first logical block of a disk, containing some executable code that is used when UNIX is first activated.
super block: second logical block of a disk, containing information concerning the disk itself.
inode list: following fixed-size set of blocks, holding all of the inodes associated with the files on the disk.
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File System Layout
Boot block
Super block
Inode 1…40
Inode 41..80
User block
User block
User block
Logical disk layout
Physical disk layout
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The SuperblockIt contains information pertaining to the entire file system.
+ the total number of blocks in the file system+ the number of inodes in the inode free list+ the size of a block in bytes+ the number of free blocks+ the number of used blocks
Free
Used
Free
Free
Used
Free
Disk blocks
1 0 1 1 0 1
Bitmap
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DirectoriesInode number 2 contains the location of the block possessing the root directory. (inode number 1 for bad blocks)
/2
bin3
ls5 cp7
usr4
Test.c6
. 2
.. 2
bin 3
usr 4
label Inode #
Hard Link
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Mounting File SystemsThe mount utility allows a superuser to splice the root directory of a file system into the existing directory hierarchy.
/
bin usrmnt
/
tmp1 tmp2
/
bin usrmnt
tmp1 tmp2
$ mount /dev/flp /mnt
$ unmount /dev/flp or $unmount /mnt