有關 Journaling Filesystems 的書摘

[悲]

最近在圖書館借閱此書：Unix Unleashed, Fourth Edition
http://www.amazon.com/exec/obidos/tg/detail/-/067232251X/qid=1037180040/sr=1-1/ref=sr_1_1/103-1399461-9675046?v=glance&s=books

剛看到有關 Journaling Filesystems 的章節，踫上 10.2.2 的昇級；故抄錄之。
小弟才疏，未譯，見諒。


Journaling Filesystems

Journaling filesystems do away with fsck and its concomitant superblock structures. All filesystem state information is internally tracked and monitored, in much the same way that database systems set up checkpoints and self-verifications.

With journaling filesystems, you have a better chance of full date recovery in the event of a system crash. Even unsaved data in buffers can be recovered thanks to the internal log. This kind of fault tolerance makes journaling filesystems useful in high-availability environments.

The drawback, of course, is that when a filesystem like this gets corrupted somehow, it presents major difficulties for recovery. Most journaling filesystems provide their own salvaging programs for use in case of emergency. This underscores how critical backups are, no matter what kind of filesystem software you’ve invested in. See Chapter 16, “Backups” for more information.

One of the earliest journaling filesystems is still a commercial venture: VxFS by Veritas. Another pioneer has decided to release its software into the public domain under GPL licensing: JFS by IBM. SGI’s xfs journaling fielsystem has been freely available under GPL since about 1999, although it is only designed to work under IRIX and Linux.

Maintenance of filesystem state incurs an overhead when using journaling filesystems. As a result, these filesystems perform suboptimally for small filesystem sizes. Generally, journaling filesystems are appropriate for filesystem sizes of 500MB or more.

參看：
http://whatis.techtarget.com/definition/0,289893,sid9_gci284007,00.html
http://oss.software.ibm.com/developerworks/opensource/jfs/
http://oss.sgi.com/projects/xfs/

[bryanchang]

這兒有中文的解說：
http://www.slat.org/project/software-map/v1.01/node49.html