Erik Eckel shares some tips for diagnosing and recovering a failing Mac hard disk.
Potentially the greatest technology stress and heartbreak results from failed hard drives, a risk from which Mac users certainly aren't immune. The more business data or even personal information a user maintains on a Mac, the more important a Time Machine and even automated offsite backup (such as a Carbonite or Mozy) becomes. When hard disk trouble is suspected, it's critical that troubleshooting begin quickly.
If the Mac will boot
When the Mac still starts up properly, the best first step to take is to make a complete backup of the system's data. Once a full backup is confirmed, troubleshooting can begin.
Obviously, if audible clicks can be heard, that's a sign the hard disk's head may be striking the platters. In such cases it's likely best to simply replace the drive. At a minimum diagnostic tests should be run on the disk. The Mac's native Disk Utility application can help determine whether a system's hard drive is encountering trouble. While Disk Utility doesn't fix physically failing disks, it can help speed diagnosis.
- Using Mac OS X Lion, open Disk Utility (found in Applications\Utilities).
- Select the Mac's system disk and click the Verify Disk or Repair Disk button found on the First Aid tab.
The utility will check the hard disk. Typically the utility should respond that the volume checked "appears" to be OK. If you receive an error message instead, or warnings indicating damage, the disk should likely be replaced (additional tests could be run on the disk using a utility such as DiskWarrior or TechTool Pro, which can further diagnose bad blocks and report detailed SMART status disk health information).
I believe that, once bad blocks appear, businesses are best served replacing the failing drive. Some, however, choose to continue using the disk, hoping that the damage is limited to specific blocks or sectors.
If a connected disk doesn't appear within Drive Utility or the Mac's System Information report (reached by clicking the Apple icon from the menu bar and selecting About This Mac | More Info | System Report), that's a probable sign the disk is experiencing difficulty.
If the Mac won't start up
When faced with a Mac disk issue that prevents proper startup, I often first check to determine the system's warranty coverage with Apple. If the system is covered by Apple's initial warranty or an extended AppleCare Protection Plan, I ask the client or user whether they wish to let Apple perform the diagnosis and repair to help lower the repair cost. But if the system's disk is out of warranty I usually remove the drive from the failing system and connect it to a test system to determine whether I can run diagnostic tests on the slaved drive.
Another option available to Mac users whose systems possess a Lion recovery partition (such as is found on many new models) is to attempt booting using Recovery Mode. Enter Recovery Mode on recovery partition-equipped systems by holding the Command and R keys during startup. The Mac OS X Utilities window should appear, from which you can run the Disk Utility to determine if the application can verify or repair disk issues.
Another option is to boot from the Mac Install DVD. To do so, install the DVD, start the Mac while depressing the C key and select Disk Utility from the resulting Mac OS X Utilities window.