File System Types

The Default File System for RH 7.3 is ext3 (Extended-3 File System)

journalled file system
keeps a transaction table

Other Unix/Linux journalled filesystems

JFS (used by IBM enterprise servers, available on Linux)
XFS (used by SGI, available for Linux)
ReiserFS (developed by NameSys for Linux)

Common File systems supported by Linux

FAT (File Allocation Table)

original FS used by DOS and Win 3.x
no security features
its weakness is that it wastes disk space
large cluster size when used with large partition size

a cluster is the smallest amount of space allocatable on a disk partition

FAT16 (VFAT)

used by Win 95
supports long filenames
a FAT16 volume greater than 2,048MB gives you a cluster size of 64K

means you will have an average of 32K of unused disk space per file.

FAT32

file system used by OSR2 version of Win95
support file systems up to 2 Terabytes (2,0498 GB)
DOS, earlier versions of Win 95 and Win NT can't read FAT32
Default cluster size of 4K

more storage efficiency than FAT and FAT16

NTFS

used by Win NT and Win 2000 (NTFS v 5)
upgrading to Win 2000 upgrades NTFS to v 5
Journalled file system

keeps transaction table for easy recovery

UFS

used by Sun's Solaris OS

ext2 (Extended-2 File System)

Most popular Linux file system
similar to most versions of UNIX
must use fsck to recover damaged file system

Structures that make up a UNIX file system

Each filesystem type has is own way of storing data on the disk
Contain special structures which allow the OS to access the data

Inodes

Contain all the information about a file except its name and its data
location on the disk, size, permissions, owner, etc
directories contain the names of the files

Data blocks

a chunk of data stored on the disk, typically a 1024-byte block
the data block contains file data or directory entries

Superblock

Contains the information about a file system

size of file system, number of inodes, number of free inodes, etc

allows OS to mount the file system and access data
at mount time the information from the superblock is stored in memory

# dumpe2fs /dev/hda2

Buffers

special areas in memory that hold data temporarily
minimizes seek time by reading ahead and storing in buffers
flushed at certain intervals (every 30 seconds)

Maximum file size and file system size

2.2 kernel

i386 file size 2GB
Sparc or Alpha: 2**63
partition size 2.2 kernel 38GB

2.4 kernel on Intel arch

partition 2 TB
file size ext2 & ext3 2 TB

The Alpha architecture supports 8KB blocks thus larger file and partition size

Some operating systems may not know how to read file systems other than those native to them. Linux is a versatile operating system and understands the file systems used by Windows 95, Windows 98, Windows NT and Windows 2000

Diagram and text from http://home.att.net/~ejuke/papers/tlos1.0/filesys.htm

The Linux Virtual File System (VFS) allows Linux to support many, often very different, file systems. Each of these filesystems are presented to the VFS through a common software interface. The details of the individual file systems are translated by software making the file systems appear identical to the rest of the Linux kernel and to all of the other processes in the system. Through this VFS layer, Linux allows you to transparently mount the many different file systems at the same time. Diagram of File System Layers: