Disks

Journaling

You can enable or disable journaling on individual disks.

To change a disks journaling state:

  1. Choose disk in the drop-down menu.
  2. Click the disable / enable button.
  3. Done!

What is file system journaling?

Journaling is a technique that helps protect the file system integrity. It both prevents the file system from getting into an inconsistent state and expedites file system repairs after a computer failure. Journaling was introduced in Mac OS X Server 10.2, and to the non-server OS with Mac OS X 10.3.

With journaling enabled a record of file system changes is maintained. If your computer halts because of a power failure or some other issue, the journal is upon restart used to restore file systems consistency. This eliminates the need to perform a consistency check on the entire file system during startup. With a journaled file system, restart takes just a few seconds, regardless the number of files, or the size of the volume. Although you may experience loss of user data that was buffered at the time of the failure, the file system is returned to a consistent state.

Keeping a journal of file system operations adds overhead to each transaction. Beside the actual file system operation such as write or copy the file system has to update the journal. Also, disk fragmentation becomes a problem much faster with journaling enabled than without.

Journaling is best suited for computers requiring high availability, computers containing volumes with many files, and computers containing data that is backed up at infrequent intervals. If your computer contains high-bandwidth usage data files, such as large video, graphics, or audio files, you may want to weigh the benefits of using journaling against the performance needed to access your data.

When deciding whether or not to journal a disk, think through the number of file changes (creations, additions, deletions) happening on that computer each day and determine how important those file transactions are. A computer which endures constant crashes or "forced reboots" might be better of with journaling enabled.

Online information