5.2. Mounting an Ext4 File System

An ext4 file system can be mounted with no extra options. For example:
# mount /dev/device /mount/point
The ext4 file system also supports several mount options to influence behavior. For example, the acl parameter enables access control lists, while the user_xattr parameter enables user extended attributes. To enable both options, use their respective parameters with -o, as in:
# mount -o acl,user_xattr /dev/device /mount/point
As with ext3, the option data_err=abort can be used to abort the journal if an error occures in file data.
# mount -o data_err=abort /dev/device /mount/point
The tune2fs utility also allows administrators to set default mount options in the file system superblock. For more information on this, refer to man tune2fs.

Write Barriers

By default, ext4 uses write barriers to ensure file system integrity even when power is lost to a device with write caches enabled. For devices without write caches, or with battery-backed write caches, disable barriers using the nobarrier option, as in:
# mount -o nobarrier /dev/device /mount/point
For more information about write barriers, refer to Chapter 21, Write Barriers.

Direct Access Technology Preview

Starting with Red Hat Enterprise Linux 7.3, Direct Access (DAX) provides, as a Technology Preview on the ext4 and XFS file systems, a means for an application to directly map persistent memory into its address space. To use DAX, a system must have some form of persistent memory available, usually in the form of one or more Non-Volatile Dual In-line Memory Modules (NVDIMMs), and a file system that supports DAX must be created on the NVDIMM(s). Also, the file system must be mounted with the dax mount option. Then, an mmap of a file on the dax-mounted file system results in a direct mapping of storage into the application's address space.