Mac OS X Server version 10.2.2 provides a robust new journaling feature for the Mac OS Extended (HFS+) file system that enhances server availability and fault resilience. Journaling protects the integrity of the file system on Xserve and other Mac OS X Server-based systems in the event of an unplanned shutdown or power failure. It also helps to maximize the uptime of servers and server-attached storage devices by dramatically expediting repairs to the affected volumes when the system restarts.
Essentially, journaling tracks all modifications and operations on the file system and keeps a log of these actions in a journal file. In the event of a failure, your Mac can use this file to restore the system to a working state. This eliminates the need for a file system check during startup. Instead, the system will replay the recent entries in the journal to correct any problems that may exist. As a result, downtime is greatly reduced and the effective stability of the system is increased. This is essential for many server environments, where downtime can result in serious losses.
While Apple indicates that journaling is only available in Mac OS X Server 10.2.2, it is also present in the client release of the OS. To enable journaling on Mac OS X Server, simply open up the Disk Utility application, select a volume, and click "Make journaled" on the Information pane. In desktop version of Mac OS X 10.2.2, however, you must use the command line (CLI).
WARNING! IF YOU DONiT KNOW WHAT YOU ARE DOING WITH THE MAC OS X COMMAND LINE, WE DO NOT RECOMMEND THAT YOU TURN ON JOURNALING USING THIS METHOD!!!
If you would like to learn more about journaling and the command line, visit our Hardcore X! forum, and ask questions of the command line fiends that hang out there. You can also find out more about the CLI in Mac OS X Command Line: 101, our series by Richard Burton.
If, despite the warning above, you wish to turn on journaling, open a Terminal window and type "sudo diskutil enableJournal /" (without the quotes). Enter the admin password at the prompt. This enables the journaling feature. To disable the journal, type "sudo diskutil disableJournal /" (also without the quotes). Thatis it.
It should also be noted that journaling can exact a toll in the form of CPU usage.
More information on journaling in Mac OS X can be found in an Apple technology PDF. The Mac OS X 10.2.2 update is available via the Software Update pane in the System Preferences. For discussion of Mac OS X, journaling, or other related topics, visit the TMO forums.