How to determine if your Mac’s hard drive is failing

HardDriveIconXYour hard drive failing can mean loss or corruption to important data, or perhaps to applications and system software that can destabilize the system. If your Mac is regularly showing hangs, is running exceptionally sluggishly, crashes, or you get odd permissions denied errors about the inability to access certain files for which you previously had access, then your drive may be about to fail.

Before any detail of hard drive health is considered, be sure you have a full backup of your drive. Therefore, even if your drive is not experiencing problems, set your system up with Time Machine or a system cloning tool, and get a regular backup going that can be used to restore your system to a fully-working state.

The first option for testing your drive is to check its S.M.A.R.T. status, which is a series of built-in tests that the drive regularly checks on itself. If any of these are out of place, then the drive will notify the system when a S.M.A.R.T. verification is performed. This can be done at any time by opening Disk Utility (in the Applications > Utilities folder), selecting your drive device, and reading the S.M.A.R.T. status at the bottom of the window. If this status says anything but “Verified,” then you need to replace your drive.

S.M.A.R.T. status check in Disk Utility

Select the drive device (above any volume names) and then check the S.M.A.R.T. status at the bottom of the window (click image for larger view).

Disk Utility is not the only option for checking the S.M.A.R.T. status, as there are numerous third-party programs like S.M.A.R.T. Utility (some of which are free), that may be an even more thorough S.M.A.R.T. verifier than Disk Utility.

If the S.M.A.R.T. status shows no problems, then check the disk’s formatting with Disk Utility, and do this regularly. With use, the formatting on your drive can become damaged, but if your drive is experiencing problems then format damage may occur at a higher rate. If your first check shows any formatting errors, then boot to the Recovery HD partition by holding Command-R at startup, and use Disk Utility there to fix the drive. Follow this by checking the drive formatting regularly (every other day, or more), to ensure no more errors crop up. If they do, then this indicates the drive may be failing.

Finally, use a third-party utility like Drive Genius or Disk Tools Pro to check the drive’s media integrity with a surface scan. This will check for bad blocks, and replace them with spare ones, if necessary. If you do find bad blocks with a scan, then again repeat this scan the following day after using your system for a while, and continue to do so for a few more days. If bad blocks regularly appear, then this suggests the drive will likely need to be replaced.

For external drives, unfortunately S.M.A.R.T. status checking is not supported; however, you can still check their formatting and perform surface scans. In addition, you can troubleshoot any daisy-chain setups you have to ensure proper connectivity and power for drives. Improper daisy-chaining can lead to loss in power or data connection that can corrupt drive contents, causing it to either not mount, or suddenly eject.

Lastly, for any mechanical drive, be it internal or external, if you cannot mount it, then hold your ear to the drive and see if you can detect any regular clicking, whirring, or grinding sounds at regular intervals. Most drive noise should be random or continuous, and regular intermittent clicking indicates the drive is attempting to perform some action, failing, and then repeatedly trying again.

If this is the case, then you can try the following:

  1. Check power connections for the drive and troubleshoot daisy-chaining of it and other peripherals.
  2. Dissect the device and place the raw drive in a new enclosure, since a failing USB or FireWire bridge controller in the enclosure, or fault in power handling, may result in the drive failing.
  3. Attempt a fix for deep formatting problems with the drive.
  4. Replace the drive.

6 thoughts on “How to determine if your Mac’s hard drive is failing

  1. Ken Kelly

    Your current advice regarding the SMART status of a hard drive (“If this status says anything but “Verified,” then you need to replace your drive.”) differs from a previous article of yours from Macfixit in which you mentioned that the this status was not 100% reliable and you had first hand knowledge of drives functioning correctly for years even though disk utility showed a faulty SMART status.
    I remember this clearly because I came across the article while researching information for my own drive which was showing a SMART problem and wanted to find out what to do. I heeded your advice and never changed the hard drive. Over 2 years later the SMART status still shows that the drive is about to fail but the computer works as well as when I first purchased it. Why then has your advice changed?

    1. Topher Kessler Post author

      Apologies for any confusion. In general, when a metric like SMART suggests a drive is failing, then it is best to look into replacing the drive. This has always been my stance, but while it is true that a drive showing a SMART error can last for a while (perhaps years), and even be unaffected by a SMART warning, if your data and workflow is important then I would not rely on the drive. It is very possible the drive could last forever, but any error that the system shows with the drive means it is potentially unstable, and for the sake of data security its best to replace the drive.

      If you would like, since Disk Utility is not necessarily the most thorough SMART status reader, you can use a dedicated third-party SMART status program to see if you get the same errors.

      1. Ken

        Thank you for your reply to my comment and I should add there is certainly no need to apologise. In the original article “What to do about SMART errors in OS X” (May 22nd 2012) you wrote the following:

        “If you plan on relying on the drive as a main boot device or for one that will store important information, then you might wish to play it safe and replace the drive, but if not then you can investigate the SMART status a bit more to see if you can discern the exact problem.”

        So, in fact, your advice was much the same, replace the drive, with the caveat that if the drive did not contain important information, to perhaps investigate the problem a little further before taking a decision. The computer in question DOES NOT contain important information and so I decided to take a chance and not replace the drive. I di not, however, follow up and investigate why the drive was showing the SMART error. I should also add that I incorrectly stated it had been running fine for over two years when it has not quite been two years since the error showed. My apologies then for getting my “facts” wrong.
        I have always enjoyed your Macfixit columns, and learned a great deal from them. I wish you all the best in your new endeavour! Keep up the good work.

  2. David

    All of the above addresses the platters, mechanism and data integrity. Unfortunately a significant number of drives die because their electronics fail. The most common cause of electronic failures is excessive heating and cooling cycles. Treat your Mac the same way you’d treat a baby:
    1. Protect it against extreme cold.
    2. Protect it against extreme heat.
    3. Protect it against sudden temperature changes
    4. Don’t put it in direct sunlight
    5. Don’t leave it in a car on a hot day.
    6. Don’t trust the baby to keep itself cool.

    Don’t trust Apple to adjust the speed of the cooling fans. Their goals are to keep your computer as quiet and energy efficient as possible and that means they’ve programmed the cooling fans to spin up only when absolutely necessary to avoid overheating. That means internal components are allowed to get hot and allowed to do so quickly. There are several apps out there that can adjust fan speed based on the temperature of the components they are blowing on. That reduces the rate of temperature change and limits the maximum temperature in all but the most extreme conditions.

  3. Art

    “For external drives, unfortunately S.M.A.R.T. status checking is not supported…”

    Actually, it is, via a third-party kext:

  4. Jay

    Firmware can also be an issue. I saw a SMART status fail on a western digital external and a brand new Crucial M500, firmware updates resolved both SMART status issues.

    Also, just found this new site, looks good :)


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