Text

EXT3 AND EXT4Linux File Systems

What is EXT3?

EXT3 Definition

• ext3, or third extended

filesystem, is a

journaled file system

that is commonly used

by the Linux kernel.

More About EXT3

• It adds the following features to ext2 : a journal, online

file system growth, HTree indexing for larger directories.

• Without these features, any ext3 file is also a valid ext2

file.

• ext3 lacks "modern" filesystem features, such as

dynamic inode allocation and extents.

• The max number of blocks for ext3 is 232. The size of a

block can vary, affecting the max number of files and the

max size of the file system

Levels of journaling available in

the Linux implementation of

ext3

Journal( lowest risk )

• Both metadata and file contents

are written to the journal before

being committed to the main file

system.

• Because the journal is relatively

continuous on disk, this can

improve performance, if the journal

has enough space.

• In other cases, performance gets

worse, because the data must be

written twice—once to the journal,

and once to the main part of the

filesystem.

Ordered( medium risk )

• Only metadata is journaled; file

contents are not, but it's guaranteed

that file contents are written to disk

before associated metadata is

marked as committed in the journal.

• This is the default on many Linux

distributions.

• If there is a power outage or kernel

panic while a file is being written or

appended to, the journal will indicate

that the new file or appended data

has not been "committed", so it will

be purged by the cleanup process.

Writeback( highest risk )

• Only metadata is

journaled; file contents

are not.

• The contents might be

written before or after the

journal is updated.

• As a result, files modified

right before a crash can

become corrupted.

What is EXT4?

EXT4 Definition

• ext4 was born as a series

of backward compatible

extensions to ext3, many

of them originally

developed by Cluster File

Systems for the Lustre file

system between 2003 and

2006, meant to extend

storage limits and add

other performance

improvements.

More About EXT4

• The ext4 filesystem can support volumes with sizes up to 1

exbibyte (EiB) and files with sizes up to 16 tebibytes (TiB)

• ext4 is backward compatible with ext3 and ext2, making it

possible to mount ext3 and ext2 as ext4.

• ext4 can pre-allocate on-disk space for a file. To do this on

most file systems, zeros would be written to the file when

created.

• ext4 uses a performance technique called allocate-on-flush

also known as delayed allocation.

EXT3 VS EXT4

Ext3 stands for third extended

file system.

Ext4 stands for fourth extended

file system.

It was introduced in 2001.

Developed by Stephen Tweedie.It was introduced in 2008.

The main benefit of ext3 is that it

allows journaling.

Supports huge individual file size

and overall file system size

Starting from Linux Kernel 2.4.15

ext3 was available.

Starting from Linux Kernel 2.6.19

ext4 was available.