Ext4

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ext4 (fourth extended file system) is an open source disk filesystem and most recent version of the extended series of filesystems. It is the primary file system in use by many Linux systems rendering it to be arguably the most stable and well tested file system supported in Linux.

Initially created as a fork of ext3, ext4 brings new features, performance improvements, and removal of size limits with moderate changes to the on-disk format. It can span volumes up to 1 EB and with maximum file size of 16TB. Instead of the classic ext2/3 bitmap block allocation, ext4 uses extents, which improve large file performance and reduce fragmentation. Ext4 also provides more sophisticated block allocation algorithms (delayed allocation and multiblock allocation) giving the filesystem driver more ways to optimize the layout of data on the disk.

Installation

Kernel

Activate the following kernel options for ext4 support:

KERNEL Enabling ext4 support

File systems  --->
   <*> The Extended 4 (ext4) filesystem

Support for optional ext4 features:

KERNEL Enabling optional features for ext4

File systems  --->
   [*]   Ext4 POSIX Access Control Lists
   [*]   Ext4 Security Labels
   [ ]   EXT4 debugging support

Optional ext4 support definitions
Option	Description
Ext4 POSIX Access Control Lists	Enable ACL permissions.
Ext4 Security Labels	Enable POSIX capabilities support.
EXT4 debugging support	(Not recommend) Use when debugging ext4 (advanced users only).

Large drive support

When the system has large disks (2 TB or greater) and a 32-bit (x86) kernel is being used, the following option must be enabled:

KERNEL Enabling large drives for x86 kernels

-*- Enable the block layer  --->
    [*]   Support for large (2TB+) block devices and files

USE flags

The sys-fs/e2fsprogs package contains the utilities to work with the filesystem. In Gentoo Linux sys-fs/e2fsprogs is part of the system set and should be already installed on the system.

USE flags for sys-fs/e2fsprogs Standard EXT2/EXT3/EXT4 filesystem utilities

`cron`	Install e2scrub_all cron script
`fuse`	Build fuse2fs, a FUSE file system client for ext2/ext3/ext4 file systems
`nls`	Add Native Language Support (using gettext - GNU locale utilities)
`static-libs`	Build static versions of dynamic libraries as well
`test`	Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently)
`tools`	Build extfs tools (mke2fs, e2fsck, tune2fs, etc.)

Data provided by the Gentoo Package Database · Last update: 2024-03-03 04:00 More information about USE flags

Emerge

After setting the USE flag update the system so the changes take effect:

root #emerge --ask --changed-use --deep @world

Usage

Creation

Warning
The mkfs.ext4 command irreversibly destroys any content of the partition it is told to format. Be sure to select the right partition!

To create an ext4 filesystem on the /dev/sda1 partition:

root #mkfs.ext4 /dev/sda1

Please replace /dev/sda1 with the actual partition to format.

By default, 5% of available disk space is reserved for the root user. This is usually a good thing for the partition where the / directory is mounted, but it may be not desirable on other partitions. To lose reserve disk space for the root user use mkfs.ext4's -m 0 option:

root #mkfs.ext4 -m 0 /dev/sda1

External resources

The second, third, and fourth extended file system wiki