Installation guide

Chapter 6.
39
The Ext3 File System
The ext3 file system is essentially an enhanced version of the ext2 file system. These improvements
provide the following advantages:
Availability
After an unexpected power failure or system crash (also called an unclean system shutdown),
each mounted ext2 file system on the machine must be checked for consistency by the e2fsck
program. This is a time-consuming process that can delay system boot time significantly,
especially with large volumes containing a large number of files. During this time, any data on the
volumes is unreachable.
The journaling provided by the ext3 file system means that this sort of file system check is no
longer necessary after an unclean system shutdown. The only time a consistency check occurs
using ext3 is in certain rare hardware failure cases, such as hard drive failures. The time to
recover an ext3 file system after an unclean system shutdown does not depend on the size of the
file system or the number of files; rather, it depends on the size of the journal used to maintain
consistency. The default journal size takes about a second to recover, depending on the speed of
the hardware.
Note
The only supported journaling mode in ext3 is data=ordered (default).
Data Integrity
The ext3 file system prevents loss of data integrity in the event that an unclean system shutdown
occurs. The ext3 file system allows you to choose the type and level of protection that your data
receives. By default, the ext3 volumes are configured to keep a high level of data consistency with
regard to the state of the file system.
Speed
Despite writing some data more than once, ext3 has a higher throughput in most cases than ext2
because ext3's journaling optimizes hard drive head motion. You can choose from three journaling
modes to optimize speed, but doing so means trade-offs in regards to data integrity if the system
was to fail.
Easy Transition
It is easy to migrate from ext2 to ext3 and gain the benefits of a robust journaling file system
without reformatting. Refer to Section 6.2, “Converting to an Ext3 File System” for more on how to
perform this task.
The Red Hat Enterprise Linux 6 version of ext3 features the following updates:
Default Inode Sizes Changed
The default size of the on-disk inode has increased for more efficient storage of extended attributes,
for example ACLs or SELinux attributes. Along with this change, the default number of inodes created
on a file system of a given size has been decreased. The inode size may be selected with the mke2fs
-I option, or specified in /etc/mke2fs.conf to set system-wide defaults for mke2fs.