Almost all modern hard drives include a technology known as Self Monitoring and Reporting Technology, or SMART. SMART allows hard drives to continuously check, diagnose and report the state of their physical components. While SMART status information won't prevent a hard drive from failing, primarily because such a failure is a physical problem with the hardware rather than corruption of directory data, it can alert you to problems before they become so severe that you can no longer access the hard drive.
Most hard drive utilities allow you to view a drive's SMART status. In Disk Utility, the SMART status is listed along with general information about a disk at the bottom right of the window. (Note: To view the SMART status of a drive, you need to select the drive itself rather than a volume that exists on the drive.) ISlayer.com's free iStat Pro and iStat Menus show you SMART status and other system information from the Dashboard or the Mac's menu bar.
If a drive's SMART status says Verified, the drive is healthy. If the status is About to Fail or Failed, you should immediately back up all data and replace the drive.
3. Don't overfill your hard drive
Today's Macs serve as a hub for all kinds of digital media content, whether you've produced it yourself, purchased it from the iTunes Store, or ripped it from your CD and DVD collection. All of those videos, photos and songs can fill a Mac's hard drive pretty quickly. Which brings us to another way to keep Leopard running smoothly -- don't overfill a Mac's hard drive.
Like other operating systems, Leopard uses the hard drive to store not only your data, but also various temporary and cache files needed to support the data and run applications properly. It also relies on the hard drive for virtual memory, in which data not in active use gets swapped out of RAM to the hard drive to accommodate active applications. Leopard invisibly performs these functions without any intervention from the user.
However, in order for this to happen, there has to be free space on the hard drive for Leopard to use. If the hard drive is too full, Leopard has to rely on the start-up drive for these purposes, which means the Mac's performance will seriously degrade. In some cases, you may even notice some erratic behavior and application crashes if the hard drive is almost completely full.
That's why being aware of the free space on your hard drive is important in keeping your Mac functioning at its best. A good rule of thumb is to make sure that you have at least 10% of your drive free at any given time. You can see a drive's free space at the bottom of any Finder window for a folder that resides on the drive (or for the drive itself).