Ext4

ext4 (fourth extended file system) is an open source disk file system 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.

Kernel
Activate the following kernel options for ext4 support:

Support for optional ext4 features:

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

USE flags
The package contains the utilities to work with the filesystem. In Gentoo Linux is part of the system set and should be already installed on the system.

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

Creation
To create an ext4 filesystem on the partition:

Please replace 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 's  option:

External resources

 * http://ext4.wiki.kernel.org - The second, third, and fourth extended file system wiki.