Information AboutExt2 |
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The ext2 or '''second extended file system''' is a File System for the Linux Kernel . It was initially designed by Rémy Card as a replacement for the Extended File System (ext). It is fast enough that it is used as the Benchmarking standard. Although ext2 is not a Journaling File System , its successor, Ext3 , provides journaling and is almost completely compatible with ext2. The canonical implementation of ext2 is the ext2fs filesystem driver in the Linux kernel. Other implementations (of varying quality and completeness) exist in GNU Hurd , Mac OS X (third-party), Darwin (same third-party as Mac OS X but untested), some BSD kernels and as third-party Microsoft Windows drivers. ext2 was the default filesystem in several Linux Distribution s, including Debian and Red Hat Linux , until supplanted more recently by Ext3 . HISTORY The early development of the Linux kernel was made as a cross-development under the Minix operating system. Naturally, it was obvious that the Minix File System would be used as Linux's first file system. The Minix file system was mostly free of Bugs , but used 16-bit offsets internally and thus only had a maximum size limit of 64 Megabyte s. There was also a filename length limit of 14 characters. Because of these limitations, work began on a replacement native file system for Linux. To ease the addition of new file systems and provide a generic file modification and data modification Timestamp s. As a solution for these problems, two new filesystems were developed in January 1993: Xiafs and the second extended file system ('''ext2'''), which was an overhaul of the extended file system incorporating many ideas from the Berkeley Fast File System . ext2 was also designed with extensibility in mind, with space left in many of its on-disk data structures for use by future versions. Since then, ext2 has been a testbed for many of the new extensions to the VFS API. Features such as POSIX ACLs and Extended Attribute s were generally implemented first on ext2 because it was relatively simple to extend and its internals were well-understood. On Linux kernels prior to 2.6, restrictions in the block driver mean that ext2 filesystems have a maximum file size of 2047 gigabytes (2 terabytes). Later Linux kernels allow for larger file sizes, however 32-bit systems are still restricted to 2 TiB file sizes. EXT2 DATA STRUCTURES The space in ext2 is split up in Block s, and organized into block groups, analogous to Cylinder Group s in the Unix File System. This is done to reduce Internal Fragmentation and minimize the number of Disk Seek s when reading a large amount of consecutive data. Each block group contains a superblock, the group block bitmap, inode bitmap, followed by the actual data blocks. The Superblock contains important information that is crucial to the booting of the Operating System , thus backup copies are made in every block group of each block in the file system. However, only the first copy of it, which is found at the first block of the file system, is used in the booting. The group descriptor stores the value of the block bitmap, inode bitmap and the start of the inode table for every block group and these, in turn is stored in a group descriptor table. Example of ext2 inode structure: FILE SYSTEM LIMITS The reason for certain limits of the ext2-file system can be the file format of the data medium on one hand and the operating system's kernel on the other hand. Mostly these factors will be determined once when the file system is built. They basically depend on the block size and the ratio of the number of blocks and inodes. Block sizes of 8 KB are only possible on alpha-architectures by default. There are also many userspace-programs with a lack of being able to handle files with a size above 2 GB. The limit of sublevel-directories is about 32768. If the number of files in a directory exceeds 10000 to 15000 files, the user will normally be warned that operations can last for a long time. The actual limit of the number of files in a directory is very theoretical, because before reaching the limit of 1.3 × 1020 files it will become hard to find new well-defined file names. SEE ALSO
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