Chapter 18. Getting started with an ext4 file system

As a system administrator, you can create, mount, resize, backup, and restore an ext4 file system. The ext4 file system is a scalable extension of the ext3 file system. With Red Hat Enterprise Linux 8, it can support a maximum individual file size of 16 terabytes, and file system to a maximum of 50 terabytes.

18.1. Features of an ext4 file system

Following are the features of an ext4 file system:

  • Using extents: The ext4 file system uses extents, which improves performance when using large files and reduces metadata overhead for large files.
  • Ext4 labels unallocated block groups and inode table sections accordingly, which allows the block groups and table sections to be skipped during a file system check. It leads to a quick file system check, which becomes more beneficial as the file system grows in size.
  • Metadata checksum: By default, this feature is enabled in Red Hat Enterprise Linux 8.

  • Allocation features of an ext4 file system:

    • Persistent pre-allocation
    • Delayed allocation
    • Multi-block allocation
    • Stripe-aware allocation
  • Extended attributes (xattr): This allows the system to associate several additional name and value pairs per file.

  • Quota journaling: This avoids the need for lengthy quota consistency checks after a crash.

    Note

    The only supported journaling mode in ext4 is data=ordered (default). For more information, see Is the EXT journaling option "data=writeback" supported in RHEL? Knowledgebase article.

  • Subsecond timestamps — This gives timestamps to the subsecond.

Additional resources

  • The ext4 man page.

18.2. Creating an ext4 file system

As a system administrator, you can create an ext4 file system on a block device using mkfs.ext4 command.

Prerequisites

Procedure

  1. To create an ext4 file system:

    • For a regular-partition device, an LVM volume, an MD volume, or a similar device, use the following command: 

      # mkfs.ext4 /dev/block_device

      Replace /dev/block_device with the path to a block device.

      For example, /dev/sdb1, /dev/disk/by-uuid/05e99ec8-def1-4a5e-8a9d-5945339ceb2a, or /dev/my-volgroup/my-lv. In general, the default options are optimal for most usage scenarios.

    • For striped block devices (for example, RAID5 arrays), the stripe geometry can be specified at the time of file system creation. Using proper stripe geometry enhances the performance of an ext4 file system. For example, to create a file system with a 64k stride (that is, 16 x 4096) on a 4k-block file system, use the following command: 

      # mkfs.ext4 -E stride=16,stripe-width=64 /dev/block_device

      In the given example:

      • stride=value: Specifies the RAID chunk size
      • stripe-width=value: Specifies the number of data disks in a RAID device, or the number of stripe units in the stripe.
    Note

    • To specify a UUID when creating a file system: 

      # mkfs.ext4 -U UUID /dev/block_device

      Replace UUID with the UUID you want to set: for example, 7cd65de3-e0be-41d9-b66d-96d749c02da7.

      Replace /dev/block_device with the path to an ext4 file system to have the UUID added to it: for example, /dev/sda8.

    • To specify a label when creating a file system: 

      # mkfs.ext4 -L label-name /dev/block_device

  2. To view the created ext4 file system: 

    # blkid

Additional resources

  • The ext4 man page.
  • The mkfs.ext4 man page.

18.3. Mounting an ext4 file system

As a system administrator, you can mount an ext4 file system using the mount utility.

Prerequisites

Procedure

  1. To create a mount point to mount the file system: 

    # mkdir /mount/point

    Replace /mount/point with the directory name where mount point of the partition must be created.

  2. To mount an ext4 file system:

  3. To view the mounted file system: 

    # df -h

Additional resources

18.4. Resizing an ext4 file system

As a system administrator, you can resize an ext4 file system using the resize2fs utility. The resize2fs utility reads the size in units of file system block size, unless a suffix indicating a specific unit is used. The following suffixes indicate specific units:

  • s (sectors) - 512 byte sectors
  • K (kilobytes) - 1,024 bytes
  • M (megabytes) - 1,048,576 bytes
  • G (gigabytes) - 1,073,741,824 bytes
  • T (terabytes) - 1,099,511,627,776 bytes

Prerequisites

Procedure

  1. To resize an ext4 file system, take the following steps:

    • To shrink and grow the size of an unmounted ext4 file system: 

      # umount /dev/block_device
# e2fsck -f /dev/block_device
# resize2fs /dev/block_device size

      Replace /dev/block_device with the path to the block device, for example /dev/sdb1.

      Replace size with the required resize value using s, K, M, G, and T suffixes.

    • An ext4 file system may be grown while mounted using the resize2fs command: 

      # resize2fs /mount/device size
      Note

      The size parameter is optional (and often redundant) when expanding. The resize2fs automatically expands to fill the available space of the container, usually a logical volume or partition.

  2. To view the resized file system: 

    # df -h

Additional resources

  • The resize2fs man page.
  • The e2fsck man page.
  • The ext4 man page.

18.5. Creating and mounting ext4 file systems using RHEL System Roles

This section describes how to create an ext4 file system with a given label on a disk, and persistently mount the file system using the storage role.

Prerequisites

  • An Ansible playbook including the storage role exists.

For information on how to apply such a playbook, see Applying a role.

18.5.1. Example Ansible playbook to create and mount an ext4 file system

This section provides an example Ansible playbook. This playbook applies the storage role to create and mount an ext4 file system.

The playbook creates an ext4 file system with a given label defined in fs_label:, and persistently mounts the file system. 

---
- hosts: all
  vars:
    storage_volumes:
      - name: barefs
        type: disk
        disks:
          - sdb
        fs_type: ext4
        fs_label: label-name
        mount_point: /mnt/data
  roles:
    - rhel-system-roles.storage

Additional resources

18.6. Comparison of tools used with ext4 and XFS

This section compares which tools to use to accomplish common tasks on the ext4 and XFS file systems.

Taskext4XFS

Create a file system

mkfs.ext4

mkfs.xfs

File system check

e2fsck

xfs_repair

Resize a file system

resize2fs

xfs_growfs

Save an image of a file system

e2image

xfs_metadump and xfs_mdrestore

Label or tune a file system

tune2fs

xfs_admin

Back up a file system

dump and restore

xfsdump and xfsrestore

Quota management

quota

xfs_quota

File mapping

filefrag

xfs_bmap