Summary

Although some people believe that journaling file systems provide only fast restart times, this chapter has shown that not to be the case. Journaling file systems are scalable, reliable, and fast. Whether you are running an enterprise server, a cluster supercomputer, or a small web site, Ext3, XFS, JFS, and ReiserFS add credibility and performance improvements to Linux.

One of the great things about open source is that choice is looked on favorably. Linux is the only operating system with four journaling file systems in production. All four file system types have the GPL license, and source code is available at http://www.kernel.org or on each project's home page. Each of the journaling file system teams follows a community model and welcomes users and contributors. In fact, the teams share their best ideas, and competitive benchmarking encourages constant improvement of all the systems.

Table 11-1 summarizes the features and limits of the four Linux journaling file systems. The first section provides some history of when the journaling file systems were accepted into the kernel.org source trees. The next section lists some of the features of the file systems.

Table 11-1. A Comparison of Journaling File Systems

Kernel Support	Ext3	ReiserFS	XFS	JFS
In kernel.org source tree 2.4.x	2.4.15	2.4.1	2.4.25	2.4.20
In kernel.org source tree 2.6.x	2.5.0	2.5.0	2.5.36	2.5.6
License	GPL	GPL	GPL	GPL
Features
Largest block size supported on IA32	4KB	4KB	4KB	4KB
File system size maximum	16384GB	17592GB	18,000Pb	4Pb
File size maximum	2048Gb	1Eb*	9,000Pb	4Pb
Growing the file system size	Patch	Yes	Yes	Yes
Online snapshot	Yes	Yes	Yes	Yes
Access control lists	Yes	Yes	Yes	Yes
Extended attributes	Yes	Yes	Yes	Yes
Dynamic disk inode allocation	No	Yes	Yes	Yes
Data logging	Yes	Patch	No	No
Place log on an external device	Yes	Yes	Yes	Yes

For complete feature lists of each journaling file system, see the respective project web pages.

Because the 2.4 kernel has a limit of 2 terabytes for a single block device, no file system larger than that can be created at this time. This restriction has been increased in the 2.6 kernel, and the limit has been raised to 16 terabytes.