LINUX EXTENDED FILE SYSTEM

Historical development of the Extended File System

MLinux the first version based on the Minix file system. After Linux has an advanced, Extended File System (Ext FS) was introduced. There are Some significant changes but still less than satisfactory performance. In 1994 the Second Extended Filesystem (Ext2) is introduced. Trust In Addition there are new features, Ext2 highly efficient, reliable and flexible so That the file system is the most widely Used Linux.

Linux Second Extended File System (Ext2FS)

For most users, and the common system administration tasks, files and directories Easier to Be Accepted as a tree structure. However computers Can not see it as a tree structure.
Each partition has its own file. By imagining the Same file system, We Can form an idea about the tree structure of all systems, but not that simple. In a system file, the file represented by inode, a kind of a unique serial number Which contains information on the actual data That make up a file: the file belongs to Whom, and Nowhere The files are located on the hard disk.
Each partition has its own set of inodes, That on systems have many partitions, there Could be the Same Trust files with inode numbers.
Each inode describes a data structure on disk, save the properties of files, including the physical location of data files. When the hard drive be prepared to accept data storage, usually During the initial system installation process or Pls adding extra disks to the existing system, a number of inodes per partition must be created. This amount will of some of the maximum number of files, of Various types (including directories, special files, links, etc. ..) Which Can Appear At The Same Time on a partition. In general 'there is one inode per 2 to 8 KB.
Mechanism of the Second Extended File System (Ext2FS)

Ext2fs using a mechanism similar to the BSD Fast File System (ffs) in allocating blocks of data from files, Which distinguishes are:
• In ffs, files are allocated to the disk in blocks of 8kB, and the blocks Were divided into fragments 1KB for storing small files or blocks are partially filled at the end of the file.
• ext2fs does not use fragment, the allocation in units Smaller. The default block size is 1KB in ext2fs, although Also it supports the allocation of 2KB and 4KB.
• allocation on ext2fs is Designed to place the blocks in a logical point of view of the file to physical blocks on the disk, Thus the I / O requests for blocks on the disk Trust secagai single operation.

Second Extended File System Reliability Ext2FS

• The system administrator cans choose the optimal block size (from 1024 up to 4096 bytes), depending on the length of the average file, Pls help creating the file system.
• Administrators Can choose a lot of inodes in Each partition Pls help creating the file system.
• Strategies to minimize the security update from system crashes.
• Supports automatic consistency checking Pls booting.
• Support for immutable files (Files That Can not be modified) and append-only (a file contents Whose Can only be added at the end of the file).


Stored information in the inode
• Device Nowhere is the inode
• Fashion File
• Locking information
• The owner and group owner of the file.
• File type (regular, directory, etc.).
• The permissions on the file.
• Time-making, reading, and recent changes.
• Time change information in the inode.
• Number of links pointing to this file.
• The size of the file.
• The address indicates the actual location of data files.
One - That Is the only information not stored in the inode is the file name and directory.This information is stored in a special directory files. By Comparing the file name and inode number, the system builds a tree structure cans That Can be understood by users.Users cans see the inode numbers using the-i option on the ls command. Each inode has a separate memory space on the disk.

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