10 Essential Tasks to Keep Leopard Purring

2. Make Sure Your Hard Drive Is Healthy

There was a time (before the release of Mac OS X) when Mac users religiously ran Disk Utility or an alternate hard drive utility at least once a month to verify the integrity of their hard drive directory structures.

A hard drive's directory structures are created when a disk is formatted or partitioned; they're essentially a map of the drive's magnetic platters. They translate the physical sectors that store bits of data on a drive to usable space for files, applications and Mac OS X system components. If they become damaged or corrupted, the Mac can have a tough time locating pieces of files as needed to accomplish tasks like opening files, launching applications and even booting up.

The good news is that technology has come a long way since the days when Disk Utility was a frequent necessity. The default file system for Leopard is Mac OS Extended Journaled, or HFS+J. Journaled file systems keep a transaction log of changes to data on the hard drive. (Microsoft Corp.'s NTFS is another example.) Should the hard drive experience a problem like an unexpected reboot or removal without being ejected properly -- the two most common causes of damage to directory structures -- the file system can rely on the transaction log to repair the damage.

Even so, hard drives can develop some directory corruption over time, particularly if a hard drive is repeatedly unplugged or removed without being properly ejected or if the drive is formatted using an older nonjournaled file system such as the Mac OS or Mac OS Extended file systems, also known as HFS and HFS+, respectively.

So it's still a good idea to use a disk utility occasionally, especially whenever you experience unexplained problems, crashes or failures to open items. If you have drives that aren't journaled, you should still do this on a regular (close to monthly) basis. Journaled drives, however, can be checked less frequently. You can try Disk Utility's Verify Disk and Repair Disk features or a third-party utility such as Micromat's TechTool Pro, Prosoft's Drive Genius, or Alsoft's DiskWarrior, all of which cost around US$100.

These tools essentially work by comparing a drive's directory with its actual contents , also called verifying or examining the disk. If problems are found, the utilities can attempt to repair the directory.

The extent to which they are successful depends on the format of the disk, the extent of the damage and the utility being used. In general, third-party utilities tend to be somewhat more successful than Disk Utility in recovering severely damaged directories, though your mileage may vary.

Generally, Disk Utility (found in /Applications/Utilities) is the first stop for checking for hard drive issues because it is freely available and relatively easy to use for identifying and resolving most problems. To verify or repair a drive's directory structures, select the drive from Disk Utility's list box, click the First Aid tab, and click the Verify Disk or Repair Disk button.

When you repair a disk, Disk Utility will first verify the disk and then attempt to repair the directory information if it finds problems.

Note: If you are comfortable working from the command line, you can also boot a Mac into single-user mode and use the Unix fsck command, though this is more commonly used as a troubleshooting option if a Mac's hard drive is so corrupted that it can't boot successfully.

The same functionality is available in Disk Utility, which is generally easier and safer for many users, as fsck 's options and single-user mode provide unrestricted access to a Mac's file system.

Then there are the physical components to any hard drive. These include the spinning magnetic disks (known as platters) that hold data, the read/write heads that scan and access those platters, the drive motors, the cache RAM chips that speed up data access, and the chips that tell the drive how to function and interact with the other components of a computer. A failure in any of these physical components can lead to problems much more serious than disk directory problems.

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.

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