Two commercial Unix file systems have been ported (rewritten) to allow them to be used in Linux. IBM has provided its Journaled File System (JFS) that is used with its commercial Unix named AIX. Silicon Graphics, Inc. (SGI) has provided its XFS file system used by its commercial Unix named IRIX. Because these file systems are generally suited for enterprise systems rather than home or small office systems, it seems likely that they are offered in Fedora to ease the transition of IRIX and AIX users to Linux by eliminating the need for these users to reformat their very large file systems.
Beginning with kernel 2.6, XFS is fully supported in the kernel.
DOS File Systems
The extent of DOS file system support in Linux is often surprising to newcomers, but the DOS file system proved to be a viable option in the early years of Linux. Because Microsoft has been the dominant operating system on Intel computers, Linux has always worked toward coexistence with DOS.
Microsoft DOS and the consumer-oriented Windows operating systems use a file system known as FAT (File Allocation Table). FAT32 is the typical system used today. The number following the FAT name indicates the size of the space for naming address pointers; the more space, the larger a section of contiguous space can be identified and accessed. FAT32 is the most recent version of FAT, and it is backward compatible with other versions of FAT. Older versions are not forward compatible.
The Fedora kernel can access all versions of FAT-formatted partitions (including floppy disks), using the vfat kernel module.
CD-ROM File Systems
If you use CD-ROM or DVD-ROM media, you need to understand a little bit about the file system and how it works with Linux. To the average user, the file system of a CD-ROM looks just like a native Linux file system. It is not the native file system, but the features of the Virtual File System make it possible for it to appear that way. The CD-ROM file system standards continue to evolve to accommodate new technology.
The file system typically used on a CD-ROM is known as iso9660, the name of the standard that defines the format. Each operating system translates the iso9660 file system into the native file system of the operating system (with some restrictions). Several extensions have been created to address certain special needs. The Rock Ridge extension allows long filenames and Unix-like symbolic links. The Joliet extension allows Unicode characters and long filenames, useful when dealing with non-English languages. El Torito CDs contain a bootable image and, with a suitable BIOS, can boot an operating system from the CD.
The Universal Disk Format (UDF) is the file system used on DVD discs. UDF has a number of built-in features such as allowing larger files, having improved file descriptors, and packet writing that the iso9660 file system cannot easily accommodate. The UDF format is the next step in compact disc technology.
Creating a File System
To create a file system on a disk that has never had a partition table on it or to change the partition table (called repartitioning the disk), you must first create the new partition table. In this section, you begin by learning about the basic structure and workings of the disk as a storage device. This information is fundamental to your understanding of the file system creation process. You then learn to create a partition table by using the fdisk and GNUparted commands. As with all similar Linux commands, each has its own strengths and weaknesses and none is a perfect choice for all situations. In the end, the partition table you create will be the same no matter which command you use. You then learn to create the file system, using commands appropriate for the type of file system you want to create.
The Microsoft version of fdisk creates both a partition table and the bootloader. In Linux, fdisk creates only the partition table. The bootloader is created later by LILO, GRUB, or another bootloader; no bootloader is necessary to create a file system and store data on a disk, just a partition table.
In fact, IDE disks physically installed as something other than /dev/hda (such as /dev/hdc, the secondary master drive) do not have a bootloader written to them; the space where the bootloader code normally resides is likely to be blank. For SCSI disks, the drive designated in the BIOS as the bootable drive has the bootloader written to it.
The Disk as a Storage Device
Because data storage devices are central to the file system, it is important to understand the workings of the most common data storage device: the hard disk drive. Although they work with a different medium, the basic storage functions of floppy disks and removable disk drives are similar to those of the hard disk.
Mechanically, the hard drive is a metal box that encloses disks, also known as platters, which have a magnetic coating on each side. Multiple disks are typically connected to the same spindle and rotated by a motor. The read and write heads for each side of the disk are moved by a second motor to position them over the area of the disk where the data you are looking for is stored. Each platter is organized into cylinders (the default size is 512 bytes) and sectors, and each platter has a head. Each drive has some electronics on a controller card that, along with the disk controller card on the motherboard of the computer, are capable of placing the heads at the correct space to retrieve the data.
The three components, cylinders, heads, and sectors (CHS), are referred to as the
The first sector of the disk is called the MBR, or Master Boot Record. It is the most important sector on the disk because it contains the bootloader code and the partition table (the table containing pointers to beginning and end of the logical partitions on the disk). The BIOS gets the system's hardware ready, and then executes the bootloader code. The bootloader code and the bootloader program load the kernel and turn over control of the system to the kernel. Then, Linux is on its way to providing us with one of the best operating system experiences in the world.
The MBR sector is 512 bytes long; the first 446 bytes contain the bootloader code. The next 64 bytes contain the partition table, and the final 2 bytes contain a special code (the hexadecimal values of 55 and AA, respectively) that identifies that sector as the MBR. More details about the MBR can be found Chapter 13, 'Backing Up.'
