Mac OS X's Journaling Feature
Journaling is Mac OS X’s new feature, which helps defend the files against hardware failures, power outages and reduces the necessity for repairs. The journaling feature is available in Mac OS X 10.3 and later versions. It is also offered in Mac OS X Server 10.2.2 and newer versions.
Journaling is a “must-have" feature for servers because it watches over the file system’s integrity. It also assists in increasing servers’ uptime. This feature is of significant importance for servers. When journaling is enabled, a continuous trace of modifications to the files is kept in the journal and if a computer shuts down due to a power outage or other problem; the journal will be used in order to restore the affected disk to a previous healthy state, as soon as the server reboots.
When an operation is running on a server, the system logs all the activities as they happen. If the operation stops in the middle, the information in the log can be replayed to finish the operation, when the server reboots. Note that the user data can still be lost if it was in the buffer when the operation failed. Therefore, it is always wise to backup the data as often as necessary.
The journaled file system also offers backward compatibility with Mac OS Extended file system. It allows users to use journaled volumes on computers, which don’t have a journaling feature.