The Ext4 file system: A real improvement in Linux file storage?

The Ext4 file system is backward compatible to the Ext3 file system, which is backward compatible to the Ext2 file system, which was invented in the early 1990s. Remember how big a big hard drive was in those days? Exactly, about 40 MB (yes, megabytes, not gigabytes) was considered huge at those days. Hence, the Ext2 file system was never developed with the multi-terabyte volumes that people tend to create now. That also means that the default maximum file and volume sizes in Ext2 and also in Ext3 are limited. If the default block size of 4 KB is used, a file with a maximal size of 2 TB can be created, and the maximal size for a volume or partition is 8 TB. Given the storage needs that companies have nowadays, this imposes a serious limitation.

When starting the development of Ext4, initially there were two directions in the project team. The first was to develop Ext4 as a fork of Ext3, making it completely compatible with this file system. The other option was to develop a completely new file system with support for new features, such as b-tree indexing and an undelete feature. At the end, the compatibility option has prevailed, making Ext4 completely compatible with Ext3. Therefore, an upgrade option exists from Ext3 to Ext4, without any need to recreate the volume and copy all files over to the new Ext4 volume. You can mount an existing Ext3 volume as an Ext4 file system, allowing you to benefit from the more efficient engine that the Ext4 driver offers.

New features in Ext4
The most important limitation in Ext3, was the maximum size of files that could be used. Ext4 addresses this limitation by using extents. An extent...

Digg This!     StumbleUpon     Del.icio.us

RELATED CONTENT Linux backup and storage Access and repair an ext3 file system with the superblock After delay, Fedora 10 finally available Comparing blades with rack servers on price, performance Whirlwind Tech Tour: Linux questions and expert responses SteelEye combines Linux server failover and remote data replication Centralized access with iSCSI wraps it up: Open source SANs, part 4 Setting up DRBD in an open source SAN: Open source SANs, part 2 Adding Heartbeat to your open source SAN: Open source SANs, part 3 Installing the MySQL database server securely Ubuntu remote backup Linux administration and management Recovering a lost administration password on Ubuntu Server How to fix master boot record partition table problems Fixing Linux boot problems with GRUB Learning the craft of Linux administration with "Pro Linux System Administration" Troubleshooting Linux boot problems A look at real-world exploits of Linux security vulnerabilities Using virtualization to reinvent high-performance computing on Linux Five common Linux security vulnerabilities you may be overlooking Building a Linux infrastructure with maximum automation Linux regular expression tutorial High-performance Linux computing: clusters, grids, mainframes Case Study: Financial firm switches from Unix, Windows to Linux on the mainframe NYSE/Euronext powers ahead with Unix-to-Linux migration Migrating infrastructure from Unix to Linux One million Linux kernels booted by Sandia researchers using virtualization and HPC Linux clusters made easy Virtualization for high-performance computing on Linux: Critiques and challenges Using virtualization to reinvent high-performance computing on Linux Is OpenSolaris on IBM z yet? Euronext nears debut of Red Hat-based global trading platform After delay, Fedora 10 finally available

RELATED GLOSSARY TERMS Terms from Whatis.com − the technology online dictionary DRBD (Distributed Replicated Block Device)  (SearchEnterpriseLinux.com) gzip  (SearchEnterpriseLinux.com)

RELATED RESOURCES 2020software.com, trial software downloads for accounting software, ERP software, CRM software and business software systems Search Bitpipe.com for the latest white papers and business webcasts Whatis.com, the online computer dictionary

is a contiguous group of blocks, and in Ext4, files can allocate extents instead of individual blocks. This makes allocation storage much more efficient, decreases fragmentation, and most important, allows for much larger files and volumes. The maximal file size in Ext4 is 16 TB, whereas the maximum volume size is even set to 1 EB (that is 1024 x 1024 x 1 TB). The use of extents is not the only method that Ext4 uses to decrease chances of fragmentation, another feature added to accomplish this goal is preallocation. This means that blocks can be reserved, even if they are not used immediately. Related to that, is the delayed allocation feature, which means that the actual writing of files is delayed until the last possible moment, which simultaneously increases performance and decreases fragmentation.

Migrating from Ext3 to Ext4
Migration from Ext3 to Ext4 is rather easy; just mount the Ext3 file system as an Ext4 file system, using . This will automatically start using Ext4 features on the old Ext3 file system. There is a caveat though: if you do this, there is no way back. Once a file system uses specific Ext4 features, you cannot use it as an Ext3 file system anymore. Hence, you shouldn't forget to modify your to make sure that in the future your old Ext3 file system is mounted as Ext4 automatically after a system reboot.

Ext4 is the long awaited successor of the Ext3 file system. Since December 25, 2008, support is official in the Linux kernel. As migration is easy, and performance benefits are important, it's a good idea to start testing your migration from Ext3 to Ext4.

ABOUT THE AUTHOR: Sander van Vugt is an author and independent technical trainer, specializing in Linux since 1994. Vugt is also a technical consultant for high-availability (HA) clustering and performance optimization, as well as an expert on SLED 10 administration.

Rate this Tip To rate tips, you must be a member of SearchEnterpriseLinux.com. Register now to start rating these tips. Log in if you are already a member. DISCLAIMER: Our Tips Exchange is a forum for you to share technical advice and expertise with your peers and to learn from other enterprise IT professionals. TechTarget provides the infrastructure to facilitate this sharing of information. However, we cannot guarantee the accuracy or validity of the material submitted. You agree that your use of the Ask The Expert services and your reliance on any questions, answers, information or other materials received through this Web site is at your own risk.