"Journaling" is a feature that helps protect the file system against power outages or hardware component failures, reducing the need for repairs. Journaling was first introduced in Mac OS X Server 10.2.2, then to the non-server OS in Mac OS X 10.3 Panther. This document explains some of the benefits of using this feature and how it works.
Journaling for the Mac OS Extended (HFS Plus) file system enhances computer availability and fault resilience, which is especially noteworthy for servers. Journaling protects the integrity of the file system on Xserve and other computers using Mac OS X Server in the event of an unplanned shutdown or power failure. It also helps to maximize the uptime of servers and connected storage devices by expediting repairs to the affected volumes when the system restarts.
