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5. Filesystems and Storage

Fourth Extended Filesystem (ext4) Support

The fourth extended filesystem (ext4) is now a fully supported feature in Red Hat Enterprise Linux 5.6. ext4 is based on the third extended filesystem (ext3) and features a number of improvements, including: support for larger file sizes and offsets, faster and more efficient allocation of disk space, no limit on the number of subdirectories within a directory, faster file system checking, and more robust journaling.

To complement the addition of ext4 as a fully supported filesystem in Red Hat Enterprise Linux 5.6, the e4fsprogs package has been updated to the latest upstream version. e4fsprogs contains utilities to create, modify, verify, and correct the ext4 filesystem.


In previous Red Hat Enterprise Linux 5 releases, the ext4 filesystem was a Technology Preview feature and might have been known by the release name, ext4dev.

5.1. Logical Volume Manager (LVM)

Volume management creates a layer of abstraction over physical storage by creating logical storage volumes. This provides greater flexibility over just using physical storage directly. Red Hat Enterprise Linux 5.6 manages logical volumes using the Logical Volume Manager (LVM).


The Logical Volume Manager Administration document describes the LVM logical volume manager, including information on running LVM in a clustered environment.
Mirroring Mirror Logs

LVM maintains a small log (on a separate device) which it uses to keep track of which regions are in sync with the mirror or mirrors. Red Hat Enterprise Linux 5.6 introduces the ability to mirror this log device.

Splitting a Redundant Image of a Mirror

Red Hat Enterprise Linux 5.6 introduces the use of the --splitmirrors argument of the lvconvert command to split off a redundant image of a mirrored logical volume to form a new logical volume.


LVM in Red Hat Enterprise Linux 5.6 also provides additional configuration options for default data alignment and volume group metadata.