A: Journaling is a process that is designed to protect a drive’s file system from damage in the event of a hardware or power failure. The idea is to protect the information on the drive by keeping a running log of actions on — and changes to — the files on the disk as they occur. In most cases, this is a good thing, as it provides a nice layer of protection for the files.
However, journaling can slow down access to data on a disk. For this reason, many manufacturers recommend disabling journaling on audio and video drives in Mac OS X systems. Note that it won’t hurt anything to disable journaling; it just shuts off the logging process for the disk. The data on the drive will not be affected. For the final word on whether or not journaling will affect your DAW’s performance, consult your DAW manufacturer.
PUBLIC SERVICE ANNOUNCEMENT: Journaling is not a substitute for backing up data! Regardless of whether you have journaling on or not, for the safety of your data and your own peace of mind, backup often! The latest version of Mac OS X (10.5 or Leopard) even has a built-in utility (Time Machine) that makes backing up a simple background process that you never have to think about.