Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Scaricare il pdf (Pagina 87)

Chapter 5.

The ext3 File System

With the release of Red Hat Linux 7.2, Red Hat changed the default ﬁle system from the venerable

ext2 format to the journaling ext3 ﬁle system.

5.1. Features of ext3

The ext3 ﬁle system is essentially an enhanced version of ext2 ﬁle system. These improvements pro-

vide 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, espe-

cially 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 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.

Data Integrity

The ext3 ﬁle system provides stronger 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, Red Hat Linux 7.3 conﬁgures ext3 volumes 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.

Easy Transition

It is easy to change from ext2 to ext3 and gain the beneﬁts of a robust journaling ﬁle system

without reformatting. See Section 5.3 for more on how to perform this task.

If you perform a fresh installation of Red Hat Linux 7.3, the default ﬁle system assigned to the system’s

Linux partitions is ext3. If you upgrade from a version of Red Hat Linux that uses ext2 partitions, the

installation program allows you to convert these partitions to ext3 partitions without losing data. See

the appendix titled Upgrading Your Current System in the Ofﬁcial Red Hat Linux Installation Guide

for details.

The following sections will walk you through the steps for creating and tuning ext3 partitions. If you

have ext2 partitions and are running Red Hat Linux 7.3, you can skip the partitioning and formating

sections below and go directly to Section 5.3.

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Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Pagina 87