File Systems in Red Hat

Red Hat offers a variety of file systems from which to choose:

• ext4

  The fourth extended file system (ext4) is a journaling file system for Linux, developed as the successor to ext3. This file system is the fourth edition of ext or extfs for Linux and is supported since Linux kernel 2.6.28. As an optimized version of ext3, ext4 modifies some major data structures in ext3. The maximum size of the ext4 file system is 1 EB and the maximum file size is 16 TB.

• ext3

  The third extended file system (ext3) is a journaling file system developed by the open-source community. This file system supports multiple log types and is highly available. As an extension of ext2, ext3 is compatible with ext2. The maximum size of the ext3 file system is 16 TB and the maximum file size is 2 TB.

• ext2

  The second extended file system (ext2) is a standard file system for Linux. ext2 is an extension of the Minix file system. ext2 has outstanding file access capability, particularly in processing small and medium-sized files. This file system is gradually replaced by ext3.

• tmpfs

  tmpfs is a memory-based file system similar to a virtual disk. It can use RAM and swap space for storage. Different from virtual disks, tmpfs is available immediately after being installed. tmpfs is the best RAM-based file system.

Virtual disks are block devices available only after being formatted by mkfs.

• cramfs

  The compressed ROM file system (cramfs) does not compress all contents in it to the memory at a time. During data access, this file system first locates the requested data and then decompresses the data to the memory in real time. The data is accessed in the memory instead of in the file system.

You can run the following command to view the types of the mounted file systems:

[root@localhost ~]# df -Th  

Filesystem    Type    Size  Used Avail Use% Mounted on  

/dev/sda1     ext4    272G 34G  224G  13% /  

tmpfs        tmpfs    7.8G 96K  7.8G 1% /dev/shm  

/dev/sdd      ext3     20G  173M 19G 1% /mnt/file_sdd  

/dev/sdf      ext3     20G  173M 19G 1% /mnt/file_sdf  

[root@localhost ~]#

The preceding output shows that the mounted file systems are ext4, ext3, and tmpfs.