Journaling a Mac Volume is the process of recording each and every updates done to the file system in a special type of file, so that it can be in some dreadful situations. It protects the file system against system crash, power outages, unintentional system shut down, virus infection and many such unavoidable situations. It was first made available in Mac OS X Server 10.2.2.
Whenever changes are made to the files or to a file system, the entry describing the change will be updated in a special file called journal (usually it is a circular log which is present in a dedicated area of the file system). Journal, records all the changes that are made to the files. Simultaneously, these changes will get updated in these journals even before committing them to the main file system. In the event of system crash or power failure, these journals will come in handy in recovering your lost files, even when the server is down. Also, it reduces the risk of corrupting the files.
Enable and Disable Journals:
To Enable or Disable the journaling feature, use Disk Utility tool and follow as explained below:
Note: In Mac OS X 10.4 and later, you need to press Option to make Disable Journaling visible in the File menu.
What is the need for enabling Journals?
When the Journaling option is enabled on your Mac Volume, then all the changes made to the files and directories will be recorded and updated on a continuous basis. When power goes or your system crashes, the logged data from the journal can be utilized to restore your files and hence, it preserves the consistency of the system even when the system is restarted. That is, when journaling is turned on, and the server fails at midst of any operation, the file system can rewind and replay all the information that are stored on its journal and then completes the task when the server restarts; all these will just take few minutes.
But in case if the option is disabled, then when you the system is restarted after the system crash or power off the recovery may delay. This is because, the hard drive should scan all of its data structures to perform consistency check and reconnect each file to bring the file system to a known good-state. This might take hours together based on the amount of data stored. Sometimes it may even fail to achieve the consistency of the file system leading to loss of your data. Thus, journals help in