Книга: Fedora™ Unleashed, 2008 edition

Network and Disk File Systems

Network and Disk File Systems

File systems can be separated into two broad categories: those that can be used over a network and local disk file systems. You are provided with all the applications necessary to work with both categories of file systems when using Fedora.

Network file systems are physically stored somewhere other than your local computer but appear as if they are mounted on your local computer.

Some common network file system types are:

? NFS — The Network File System was developed by Sun and is in common use. It has no built-in security because it was originally designed to run over friendly networks. Although considered problematic by some, it is easy to implement. It is typically used between Unix peers. Fedora supports client and server installations of this file system.

? Coda — Similar to NFS, Coda offers support for disconnected operation and security caching (keeping a local copy of files in case the network connection is lost). Fedora provides only kernel compatibility with Coda; the actual client and server code is available fromhttp://www.coda.cs.cmu.edu/.

? InterMezzo — Similar in features to Coda, InterMezzo is a GPL project. The server daemon can be obtained fromhttp://www.inter-mezzo.org/.

? SMB —The network-focused Server Message Block protocol was developed by Microsoft. The Linux implementation is known as Samba and is one of the most advanced open-source projects available. It is typically used between Linux and Microsoft Windows peers. Netatalk is the Macintosh equivalent protocol.

Disk file systems are found on a physical device; they are the hard drive in your desktop or laptop computer. Some common disk file system types are:

? FAT is a disk-oriented, table-based (a linked list) file system used by Microsoft. It has been regularly extended to add functionality. Microsoft's Enterprise-level file system is known as NTFS. (You learn more about this system in "DOS File Systems," later in this chapter.)

? ext2, ext3, and reiserfs are inode-based. (You learn about reiserfs in "The Reiser File System (reiserfs)," later in this chapter.)

The JFS (Journaled File System from IBM) and XFS (from Silicon Graphics) file systems are available for use with Fedora, but primarily serve as migration aids for those migrating existing file systems to Linux.

A journaling file system adds a journal, or hidden file, to the data on the drive. Because of the way data is written to a disk, the kernel might be holding some of the data while it is deciding where to place it. If your computer were to suffer a failure, that cached data would be lost. A journaling file system keeps that data in a special place until the kernel decides to formally write it to the disk. If a system failure occurs, a special application (fsck) knows that the data was never formally written and makes certain that it is written in the correct place. This ensures that no data is lost. Journaling file systems are actually much more complex than this, but the mechanics of them are beyond the scope of this chapter. Journaling file systems such as ext3, reiserfs, JFS, and XFS are major improvements over older, nonjournaling file systems.

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