File systems

A file system is a hierarchical structure (file tree) of files and directories.

This type of structure resembles an inverted tree with the roots at the top and branches at the bottom. This file tree uses directories to organize data and programs into groups, allowing the management of several directories and files at one time.

A file system resides on a single logical volume. Every file and directory belongs to a file system within a logical volume. Because of its structure, some tasks are performed more efficiently on a file system than on each directory within the file system. For example, you can back up, move, or secure an entire file system. You can make an point-in-time image of a JFS file system or a JFS2 file system, called a snapshot.

Note: The maximum number of logical partitions per logical volume is 32,512. For more information on file system logical volume characteristics, see the chlv command.

The mkfs (make file system) command or the System Management Interface Tool (smit command) creates a file system on a logical volume.

To be accessible, a file system must be mounted onto a directory mount point. When multiple file systems are mounted, a directory structure is created that presents the image of a single file system. It is a hierarchical structure with a single root. This structure includes the base file systems and any file systems you create. You can access both local and remote file systems using the mount command. This makes the file system available for read and write access from your system. Mounting or unmounting a file system usually requires system group membership. File systems can be mounted automatically, if they are defined in the /etc/filesystems file. You can unmount a local or remote file system with the umount command, unless a user or process is accessing that file system. For more information on mounting a file system, see Mounting.

The basic type of file system used by AIX® is called the journaled file system (JFS). This file system uses database journaling techniques to maintain its structural consistency. This prevents damage to the file system when the system is halted abnormally.

The AIX operating system supports multiple file system types including the journaled file system (JFS) and the enhanced journaled file system (JFS2). For more information on file system types and the characteristics of each type, see File system types.

Some of the most important system management tasks have to do with file systems, specifically:

  • Allocating space for file systems on logical volumes
  • Creating file systems
  • Making file system space available to system users
  • Monitoring file system space usage
  • Backing up file systems to guard against data loss if the system fails
  • Maintaining file systems in a consistent state

These tasks should be performed by your system administrator.