All about Mac OS X's file system journaling | Why is it needed | When to use it and more

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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.

What Is The Need Of Journaling ?

Power outages and system failures disrupt the write and read processes and they cause divergences between the file structure and its location. In a non-journaled file system, when a disk drive fails, it does not have a record of its activity just before the shutdown. To resume the activities, the system has to run a check and it requires scanning through the whole file system. This process takes many hours on a large volume, which results in undesirable downtime for server. A Journaled file system also allows a server to restart in some seconds, no matter how large the volume is or how many files are stored on it.

Journaling quickens the recovery process, which significantly improves the availability of a server. When the journaling feature is turned on, the server starts tracking file operations while maintaining a record of these activities in a file, named “journal.”

When Use Journaling?

If a computer contains large videos, audio files or graphics, it is the right situation when you should take the benefit of journaling; this would significantly increase the file access performance. In many cases, the affect of journaling is unnoticeable to users; it is because the data access calls outnumber the benefits of journaling. Journaling is also suitable for servers that require high availability and those servers that contain volumes with a large number of files.

Turning Journaling On And Off

To enable or disable journaling, follow these steps:

1. Open up Disk Utility from the Applications -> Utilities.

2. Choose the volume that you want to turn on or off journaling on.

3. To turn journaling on, click the button that says Enable Journaling. To turn it off, open the File menu and select Disable Journaling.

Note: The Disable Journaling option is not visible in Mac OS X 10.4 and later, you need to press Options to make it visible in the File menu.