File Systems: Difference between revisions

FilesystemsFile systems are the machineoperating system's waymethod of ordering your data on readablepersistent and/orstorage writabledevices medialike disks. They provide aan logicalabstracted wayinterface to access thedata stuffon thatthese youdevices havein downsuch ona disk soway that youit can be read or modifymodified itefficiently. Which file system youis useconvenient depends uponon whatthe youtarget wantapplication toof dothe withoperating itsystem. For example, Windows uses the Fat32FAT32 or NTFS filesystemfile system. If youra disk ishas reallya large hugecapacity, thenFAT32 there'sis no point using Fat32inconvenient, because the FAT system was designed inconsidering the days when nobody hadsmaller disks asavailable bigat asthat we do nowtime. At the same time, there'san noNTFS pointfile usingsystem ais NTFSnot filesystemconvenient on a tiny disk, because it was designed to work with large volumes of data - the overheadthere would be pointlessexcessive for,overhead say,when readingusing devices such as a 1.44m44 MB floppy disk.

A filesystem provides a generalized structure over persistent storage, allowing the low-level structure of the devices (e.g., disk, tape, flash memory storage) to be abstracted away. Generally speaking, the goal of a filesystem is allowallowing logical groups of data to be organized into ''files'', which can be manipulated as a unit. In order to do this, the filesystem must provide some sort of index of the locations of files in the actual secondary storage. The fundamental operations of any filesystem are:

==== Inodesinodes ====

Inodesinodes (information nodes) are a crucial design element in most Unix filesystemsfile systems: Each file is made of data blocks (the sectors that contains your raw data bits), index blocks (containing pointers to data blocks so that you know which sector is the nth in the sequence), and one inode block.

The inode is the root of the index blocks, and can also be the sole index block if the file is small enough. Moreover, as unixUnix filesystemsfile systems support hard links (the same file may appear several times in the directory tree), inodes are a natural place to store metadataMetadata such as file size, owner, creation/access/modification times, locks, etc.

All these file systems are a way to create a large, distributed storage system from a collection of "back end" systems. That means you cannot (for instance) format a disk in 'NFS' but you instead mount a 'virtual' NFS partition that will reflect what's on another machine. Note that a new generation of Filefile Systemssystems is under heavy research, basing on latest P2P, cryptography and error correction techniques (such as the Ocean Store Project or Archival Intermemory.)

There are only fourfive filesystems that are both relatively easy to implement and worth to consider. There is no general recommendation as the choice depends largely on style and OS design. Instead you can read the comparison and make your own educated decision.

* <code>-</code> No support for large (>4GB4 GB) files

* <code>-</code> No support for unixUnix permissions

* <code>+</code> Supports unixUnix permissions

* <code>+</code> Can be read and written from linuxLinux

* <code>-</code> Can not natively be read and written from windowsWindows (but [http://www.fs-driver.org/ drivers] are available)

* <code>-</code> Of these fourbeginner filesystems, this is the most complex filesystem

'''[[SFSBMFS]]'''

* <code>+</code> ByImplementation farAvailable theas easieststatic to implementlibrary

* <code>+</code> CanComes bewith pututility program for creating disk images on floppiesLinux and harddisksWindows

* <code>+</code> MinimalComes overheadwith FUSE bindings, allowing it to be mounted on Linux systems

* <code>-</code> NoDoes not support for unix permissionsfragmentation

There are many different kinds of filesystems around, from the well-known to the more obscure ones. The most unfortunate thing about filesystems is that every hobbyist OS programmer thinks that the filesystem they design is the ultimate technology, when in reality it's usually just a copy of FAT with a change here and there, perhaps because it is one of the easiest to implement. The world doesn't need another FAT-like filesystem. Investigate all the possibilitespossibilities before you decide youto roll your own.