Ext4

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ext4 (fourth extended file system, quarto file system esteso) è un open source filesystem e la versione più recente della serie estesa di filesystem. È il file system principale in uso da molti sistemi Linux, rendendolo probabilmente il file system più stabile e ben testato supportato 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.

Installazione

Kernel

Attivare le seguenti opzioni del kernel per abilitare il supporto ext4:

KERNEL Abilitare il supporto a ext4
File systems  --->
   <*> The Extended 4 (ext4) filesystem

Supporto per funzionalità ext4 opzionali:

KERNEL Abilitare funzionalità opzionali di ext4
File systems  --->
   [*]   Ext4 POSIX Access Control Lists
   [*]   Ext4 Security Labels
   [ ]   EXT4 debugging support


Ext3

Nota
A normal ext4 system will not need to enable ext3 or ext2 options. These options are here solely for historical purposes.

Activate the following kernel options for ext3 support:

KERNEL Enabling ext3 support
File systems  --->
   <*> Ext3 journalling file system support

Support for optional ext3 features:

KERNEL Enabling ext3 features
File systems  --->
   [*]   Default to 'data=ordered' in ext3 
   [*]   Ext3 extended attributes
   [*]     Ext3 POSIX Access Control Lists
   [*]     Ext3 Security Labels

Ext2

Nota
Ext2 does not have journaling, support for this was added in Ext3

Activate the following kernel options for ext2 support:

KERNEL Enabling ext2 support
File systems  --->
   <*> Second extended fs support

Support for optional ext2 features:

KERNEL Enabling ext2
File systems  --->
   [*]   Ext2 extended attributes
   [*]     Ext2 POSIX Access Control Lists
   [*]     Ext2 Security Labels
Nota
The original ext3 filesystem code was removed from the Linux Kernel with version 4.3, instead the ext4 filesystem code can now handle ext2, ext3 and ext4 filesystems. It will maintain compatibility if the filesystem is mounted as ext2 or ext3, and will provide upgradability when mounted as ext4. Additionally tune2fs can be used to add ext3- and ext4-specific features to an existing ext2 or ext3 filesystem, though certain hard limits will remain.
The original ext2 filesystem code remains available.
Nota
Both ext2 and ext3 file timestamps are affected by the year 2038 problem, while ext4 is Y2k38-safe since 2016, Kernel 4.3.6 and e2fsprogs 1.43.

Supporto per unità di grandi dimensioni

KERNEL Abilitazione di unità di grandi dimensioni per i kernel x86
-*- Enable the block layer  --->
    [*]   Support for large (2TB+) block devices and files

USE flags

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

+tools Build extfs tools (mke2fs, e2fsck, tune2fs, etc.)
archive Add support for mke2fs to read a tarball as input. This allows not needing privileges. Needs app-arch/libarchive.
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)

Emerge

The sys-fs/e2fsprogs package and should be available as part of the default system set.

root #emerge --ask sys-fs/e2fsprogs

Utilizzo

Creazione

Attenzione
Il comando mkfs.ext4 distrugge irreversibilmente ogni contenuto della partizione che sarà per essere formattata. Assicurati di selezionare la partizione giusta!

Per creare un filesystem ext4 nella partizione /dev/sda1:

root #mkfs.ext4 /dev/sda1

Mounting

See filesystem.

Utilities

Utilities included in the package consist of:

Utility Description Man page
badblocks A small program for stress testing block devices. badblocks(8)
debugfs An ext2/ext3/ext4 file system debugger. debugfs(8)
dumpe2fs A tool to dump ext2/ext3/ext4 filesystem information. dumpe2fs(8)
e2fsck A tool for checking ext2/ext3/ext4 filesystems. e2fsck(8)
e2image A tool for saving critical ext2/ext3/ext4 filesystem metadata to a file. e2image(8)
e2label A tool to change the label on an ext2/ext3/ext4 filesystem (symlinks to tune2fs).
e2undo A tool to replay an undo log for an ext2/ext3/ext4 filesystem. e2undo(8)
fsck.ext2 Checks, specifically, an ext2 filesystem (symlinks to e2fsck).
fsck.ext3 Checks, specifically, an ext3 filesystem (symlinks to e2fsck).
fsck.ext4 Checks, specifically, an ext4 filesystem (symlinks to e2fsck).
fsck.ext4dev Checks, specifically, an ext4dev filesystem (symlinks to e2fsck).
logsave A tool to save the output of a command in a logfile. logsave(8)
mke2fs The base program for creating ext2/ext3/ext4 filesystems. Creation commands symlink here. mke2fs(8)
mkfs.ext2 Creates, specifically, an ext2 filesystem (symlinks to mke2fs).
mkfs.ext3 Creates, specifically, an ext3 filesystem (symlinks to mke2fs).
mkfs.ext4 Creates, specifically, an ext4 filesystem (symlinks to mke2fs).
mkfs.ext4dev Creates, specifically, an ext24dev filesystem (symlinks to mke2fs).
resize2fs An ext2/ext3/ext4 filesystem resizer. resize2fs(8)
tune2fs Adjust tunable filesystem parameters on ext2/ext3/ext4 filesystems. tune2fs(8)
chattr Change file attributes on a Linux filesystem. chattr(1)
lsattr List file attributes on a Linux second extended filesystem. lsattr(1)
e2freefrag Report free space fragmentation information. e2freefrag(8)
e4defrag An online defragmenter for ext4 filesystem. e4defrag(8)
filefrag Report on file fragmentation. filefrag(8)
mklost+found Create a lost+found directory on a mounted Linux second extended filesystem. mklost+found(8)

Vedere anche

  • Ext4 encryption — provides instructions on encrypting files in a home partition using the ext4 filesystem's built-in file based encryption.
  • JFS — un filesystem journaling a 64 bit creato da IBM
  • Btrfs — un filesystem CoW (copy-on-write, copia-in-scrittura) adatto a Linux che mira ad implementare funzionalità avanzate, concentrandosi sulla tolleranza agli errori, la riparazione e la facilità di amministrazione.
  • XFS — un filesystem journaling ad alte prestazioni
  • F2FS — un filesystem progettato per dispositivi basati su flash NAND.

Risorse esterne

References