Repair Corrupted External Hard Drive on Mac

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Start With These 5 Basic Troubleshooting Steps

If your external drive shows any of these issues, try some basic troubleshooting before moving on to advanced fixes. Often, these simple steps can resolve the problem quickly. Begin with these five checks:

1. Check the Connections

First, inspect the connections. Many times, what seems like a corrupted drive is actually a loose or faulty cable. Try the following:

• Ensure the USB or Thunderbolt cable connecting your external hard drive to your Mac is secure. Simply reseating the cable can sometimes fix the issue.

• Try a different port on your Mac. A faulty port can make the drive appear malfunctioning.

• Test with another cable, as cables can wear out over time.

• Connect the drive to another Mac to rule out system-specific problems and determine if the issue is with the drive or your Mac.

Note. It’s best to connect external drives directly to your Mac or MacBook, without using hubs, as hubs can cause connection issues or limit power to the drive.

2. Check the Drive in Disk Utility

Next, check your external drive in Disk Utility, macOS’s built-in tool for managing and diagnosing storage devices. Disk Utility can verify whether your external drive is recognized by your Mac and shows the correct size—an important first step in assessing the drive’s health.

Here’s how to use Disk Utility to check your external hard drive:

• Open Disk Utility by navigating to the Utilities folder within Applications, or use Spotlight search to quickly find and launch it.

  

• In Disk Utility, go to the “View” menu and select “Show All Devices.” This provides that both drives and their corresponding partitions are visible in the sidebar.

  

• Select the external hard drive you wish to check from the sidebar in Disk Utility. This step confirms whether your Mac recognizes the drive.

• With the drive selected, examine the information displayed at the bottom of Disk Utility or click on the “Info” button for more detailed data. Check that the capacity and used space are accurately reported, which can confirm the drive’s proper functionality. You can also use specialized programs to check the drive’s health.

  

• If the drive’s information appears correct and the drive is recognized, it’s a positive sign of its operational status. However, if the drive does not appear or shows incorrect data, it may indicate physical issues with the drive or connection.

If Disk Utility doesn’t show your external drive at all, it could point to more serious problems, likely physical damage, that no DIY method can fix. In such cases, you may need to consider professional data recovery services.

3. Mount Partition in Disk Utility

If your external hard drive is recognized by Disk Utility but isn’t mounting automatically, you can try to mount it manually. This action can help restore access to your data if the drive itself doesn’t have severe physical or file system damage. Here’s how to manually mount a partition using Disk Utility:

1. In Disk Utility, find your external hard drive listed under the external section in the sidebar. Click on it to select it.

2. When the drive is selected, the partitions appear beneath the drive name. Select the partition you want to mount.

3. Click the “Mount” button at the top of the Disk Utility window or right-click on the partition and select “Mount”. If the mount button is greyed out, this could indicate that the system cannot mount the partition due to underlying issues.

   

4. After clicking mount, watch the partition appear on your Desktop or in the Finder sidebar. This indicates that the partition is now accessible.

If the partition doesn’t mount or Disk Utility shows errors during the process, you might need to take extra steps to repair the external hard drive on your Mac and fix any file system issues.

4. Show Drive in Finder

Sometimes, even if your external hard drive is working properly and mounted in Disk Utility, it may not show up in Finder or on your Desktop due to display settings. Here’s how to configure Finder to show your external hard drive:

1. Click on the Finder icon in your Dock to open a new Finder window.

2. In the Finder menu at the top of the screen, select ‘Settings’ or use the shortcut Command + “,“.

   

3. Click on the ‘Sidebar’ tab within the Finder Preferences window. Here, you can customize which items appear in the sidebar.

4. Under the ‘Locations’ section, use the checkbox ‘External disks’ to make all connected external hard drives visible in the Finder sidebar.

   

5. Navigate to the ‘General’ tab in the Finder Preferences. Make sure the ‘External disks’ option is checked under the ‘Show these items on the desktop’ section. This means that external hard drives appear on your Desktop as well.

   

6. Close the Preferences window to save your settings. Your external hard drive should now appear both in the Finder sidebar and on the Desktop.

Tip. If your external drive still doesn’t appear after adjusting Finder preferences, restart your Mac. A quick reboot often refreshes the system and helps the drive show up as expected.

5. Try Accessing the Hard Drive in Safe Mode

In some rare cases, software conflicts or third-party drivers might prevent your external hard drive from working properly. To rule this out, you can try accessing the drive in Safe Mode. Safe Mode limits the Mac to its basic functions, which prevents third-party software from interfering with the operating system and connected devices. Here’s how to access your hard drive in Safe Mode:

1. Turn on your Mac and immediately press and hold the Shift key. Release the Shift key when you see the login window. Note that startup is likely to take longer than usual.

2. Once your Mac starts in Safe Mode, connect your external hard drive. Check if the drive is recognized and whether you can access the files In Finder.

3. If the drive is accessible in Safe Mode, you can use this opportunity to back up your data or transfer important files from the external drive to your Mac.

4. After that, restart your Mac without holding any keys to exit Safe Mode and return to normal operation.

Note. Single User Mode for deeper diagnostics only works on Intel-based Macs.

If your hard drive is accessible in Safe Mode, it’s likely that non-essential software or drivers are causing the problem. After restarting macOS, review any recently installed apps or drivers and try uninstalling them one by one to identify the culprit.

However, if issues persist even in Safe Mode, this could point to more serious hardware problems or file system corruption that needs further investigation.

No Results Yet? Time for More Advanced Methods

If basic fixes haven’t resolved the issue, it’s time to move on to more advanced solutions. These methods address deeper problems with your external hard drive, whether from severe file system corruption or hardware issues on your Mac.

Method 1. Reset SMC and NVRAM

Resetting the System Management Controller (SMC) and Non-Volatile Random-Access Memory (NVRAM) can resolve various hardware-related issues. These resets can help fix problems with external drives caused by power management, battery behavior, and related system functions.

Here’s how to reset the SMC (for MacBooks with non-removable batteries and other Macs):

1. Shut down your Mac.

2. For MacBooks, hold down Shift + Control + Option on the left side of the built-in keyboard and press the power button at the same time. Hold these keys and the power button for 10 seconds.

3. For desktop Macs, unplug the power cord, wait 15 seconds, plug it back in, and wait another 5 seconds before turning it back on.

4. Release all keys and the power button at the same time.

5. Turn on your Mac.

Reset the NVRAM (only for Intel-based Macs)

1. Turn off your Mac.

2. Turn on your Mac and immediately press and hold Option + Command + P + R.

3. Hold these keys for about 20 seconds. On some Macs, the startup sound might play a second time, or the Apple logo might appear and disappear twice.

4. Release the keys after the second startup sound or the second appearance of the Apple logo.

Note. For Macs with Apple silicon, SMC functions are built into the M chip. There’s no separate SMC reset, so the closest equivalent is to simply restart your computer or turn it off and back on again, similar to NVRAM.

After performing these resets, reconnect your external hard drive and check if the issues have been resolved. These steps can sometimes rectify seemingly stubborn hardware-related problems and are particularly useful if your Mac fails to recognize an external hard drive or if you encounter persistent issues after trying previous fixes.

Method 2. Use First Aid for External Hard Drive

We’ve already talked about using Disk Utility to check your external hard drive, but now it’s time to take it a step further with First Aid. Disk Utility’s First Aid checks for various types of file system errors and attempts to correct them, which can resolve many common problems with corrupted hard drives. Here’s how to use First Aid to repair an external hard drive on a Mac:

1. Open Disk Utility.

2. In the Disk Utility sidebar, locate and select your external hard drive.

3. With the drive selected, click on the “First Aid” button located at the top of the Disk Utility window. Confirm that you want to run First Aid by clicking “Run” in the prompt that appears.

   

4. Disk Utility will begin checking the drive for errors and attempt to repair them. Keep an eye on the progress bar and any messages that appear during this process.

5. Once First Aid is complete, review the final report. Disk Utility will provide a summary of any repairs made or notify you if the drive cannot be repaired.

   

6. If First Aid reports that repairs were successful, it’s advisable to restart your Mac and recheck the drive’s functionality. If the drive still shows signs of issues or if First Aid cannot repair it, further troubleshooting may be required.

First Aid in Disk Utility can often fix minor file system errors and restore your external hard drive’s functionality. However, if this doesn’t resolve the issue, it may indicate more serious problems that require advanced recovery techniques or professional help.

How to Repair an External Hard Drive Using Mac Terminal

If standard methods fail, Terminal offers a more advanced way to repair your external hard drive. Some powerful built-in and third-party tools, like fsck and TestDisk, can only be run through Terminal. While less commonly used, these tools aren’t as complicated as they might seem. Here’s a detailed guide to get you started.

Method 1. Use the fsck Command to Repair the File System

The File System Check (fsck) command is a robust macOS Terminal tool for diagnosing and repairing file system issues on an external hard drive. Follow these steps to use fsck on your Mac:

1. Open Terminal from your Applications folder or Utilities subfolder, or use Spotlight to search and launch it directly.

2. Enter the appropriate fsck command sudo fsck_hfs -fy (for HFS formatted drives) or sudo fsck_apfs -y (for APFS formatted drives).

3. Monitor the output in Terminal as fsck processes the file system. It will report any corrections it makes or notify you if no issues are found.

   

4. Once the fsck process completes, restart your Mac, applying any changes made during the repair process.

Tip. It can be a good idea to run fsck command a few times, especially if it fixes something the first time around. Running it again makes sure everything is fully resolved and the file system is in good shape.

Method 2. Use TestDisk to Restore Partition

TestDisk is an advanced, open-source software tool designed to recover lost partitions and make non-booting disks bootable again. This tool can be incredibly useful when dealing with severe corruption or accidental deletion of partitions on your external hard drive. Here’s how to use TestDisk to attempt restoration of your drive’s partitions:

1. If you don’t already have Homebrew installed, open Terminal and enter the following command: /bin/bash -c “$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)”

2. After installing Homebrew, install TestDisk by typing brew install testdisk in Terminal and pressing Enter.

3. Once the installation is complete, type sudo testdisk in Terminal and press Enter to run the program with administrative privileges. You may need to enter your administrator password.

4. Follow the on-screen instructions to select your external hard drive from the list of available drives.

   

5. Choose the ‘Analyse’ option to search for lost partitions. TestDisk will scan your drive and attempt to find any deleted or damaged partitions.

   

6. If TestDisk finds partitions that can be recovered, it will display them. Select the partitions you wish to recover and follow the prompts to write the recovered partition structure back to the disk. Exercise caution during this step to avoid further data loss.

   

7. After completing the recovery process, exit TestDisk and reboot your Mac to make sure all changes take effect.

Note. Be careful when selecting the drive in TestDisk. Compare the disk size with what is shown in Disk Utility. Choosing the wrong drive could accidentally overwrite or delete important data, so double-check before proceeding.

If Nothing Worked, Recover Your Data and Start Fresh with a Format

If your external hard drive is still having issues at this point, it’s likely time to recover your data and reformat the drive. Reformatting usually resolves all non-physical problems, such as corrupted file systems, partition errors, and allocation issues. This process essentially resets the drive, making it like new. It clears all existing data structures, which is why it’s so effective for software-related problems.

Keep in mind that reformatting erases everything on the drive. To preserve your data, handle this in two steps: first, recover your files, then reformat the drive.

Step 1. Recover Data from a Corrupted External Hard Drive on a Mac

macOS doesn’t include built-in data recovery tools, so you’ll need third-party software to retrieve files from a corrupted external drive. After reviewing and testing many options, one of the best solutions is Disk Drill, a tool with over a decade of experience in data recovery. Here’s why we recommend it:

• Disk Drill works great with a variety of storage devices, including internal drives, memory cards, and of course, external hard drives.

• Disk Drill can recover data from drives that don’t show up in Finder but are visible in Disk Utility, even if the drive doesn’t mount properly.

• Can recover data from a wide range of file systems commonly found on external hard drives, including HFS+, APFS, FAT32, exFAT, and even NTFS, which isn’t natively supported by macOS.

• Can recover data from drives with severely damaged file systems or none at all thanks to its Signature Scan (It identifies file types based on their unique binary patterns, or “signatures,” rather than relying on the file system itself.)

• Can recover deleted/lost data from hard drives.

• Disk Drill also offers extra features like disk health monitoring and data protection tools.

Here’s a step-by-step guide on how to use Disk Drill to recover data from a corrupted external hard drive on a Mac:

Note. If your disk shows signs of severe damage, use Disk Drill’s “Byte-to-Byte Backup” feature to create an exact copy of the drive. This way, you can scan and recover files from the backup instead of the external drive itself, which protects the original drive from further stress. To make a backup, find Byte-to-Byte Backup in the main menu, select your drive, and click on the “Create Backup” button. Just make sure you have a target disk with free space that exceeds the total size of the problematic disk.

1. Visit the CleverFiles website to download the latest version of Disk Drill for macOS. Install it by dragging the application icon to your Applications folder.

   

2. Open Disk Drill from your Applications folder. You may need to allow the application permissions to access your disk drives in your system’s security settings.

3. Connect your external hard drive to your Mac. If the drive is detectable, Disk Drill should list it under the available drives.

4. Find your external hard drive and select it. If you previously created a Byte-to-byte Backup of the drive, you can click on “Attach disk image” instead and select the backup. Once selected, click “Search for lost data” to begin the recovery process.

   

5. Even before the scan is complete, you can click “Recover all” to immediately recover all files found so far, or click “Review found items” to browse through the files already detected. In the list of recoverable files, you’ll notice they are grouped into categories such as:

   • Existing files: These are files that are still present on the drive but might not be accessible through normal means.

   • Deleted or lost: These are files that were deleted/lost due to corruption or other issues.

   • Reconstructed: These are files that Disk Drill was able to piece back together from fragments using its recovery algorithms, often from severely damaged drives.

   You can browse these groups to locate the files you need to recover.

   

6. Mark the files or folders you want to recover and click the “Recover” button. To avoid potential data overwriting, it’s advisable to recover the files to a different drive than the one recovered from.

   

7. Click the “Next” button to save the files to your chosen location.

Step 2. Format External Hard Drive

Once you’ve successfully recovered your data, it’s time to reformat the external hard drive to fix any file system corruption or errors. To reformat the drive, we will once again use Disk Utility. Here’s how to format your external hard drive on a Mac:

1. Open Disk Utility.

2. Locate and select your external hard drive from the list of available drives.

3. Click the “Erase” button at the top of the Disk Utility window. You will be prompted to choose a file system format and a drive name.

4. Select a file system format suitable for your needs. Depending on your macOS version, choose APFS or Mac OS Extended (Journaled) for Mac compatibility, or choose exFAT for maximum compatibility with other OS.

5. Choose a name for your drive, and click “Erase” to begin formatting. Monitor the progress in Disk Utility.

   

6. Once the formatting is complete, Disk Utility will display a success message. Close Disk Utility and eject the drive properly before disconnecting it.

7. Reconnect your drive to verify that it appears correctly in Finder and is ready for use.

Formatting your external hard drive effectively resets it, giving you a clean slate for new data. Once formatted, the drive will be ready for use, and you can transfer your recovered files back onto it.

Note. When formatting, you’ll see an option for Scheme. If you’re unsure whether to use GUID Partition Map or Master Boot Record (MBR), choose GUID for better compatibility with macOS, especially on newer Macs. MBR is generally used for older Windows systems or drives that will only work with Windows. For dual compatibility between macOS and Windows, GUID Partition Map is recommended.

When to Contact Data Recovery Services

If you’ve tried all troubleshooting steps and recovery tools but your external hard drive remains inaccessible or malfunctioning, it may be time to consider professional data recovery services.

Professional services are ideal for severely corrupted drives that DIY methods cannot fix. They can handle complex cases, including drives with serious physical damage (from water, impact, or mechanical failures such as head crashes or motor issues).

These firms use advanced tools in controlled cleanroom environments to repair physically damaged drives without causing further harm. While professional recovery can be costly, the expense is often justified by the high success rates and the ability to recover data that might otherwise be lost permanently.

Note. Many services operate on a “no data, no fee” policy, meaning you only pay if your data is successfully recovered.

In Conclusion

In most cases, the DIY methods covered here are sufficient to fix a corrupted external hard drive on a Mac. Most problems arise from logical issues that can be resolved using macOS utilities or third-party tools like TestDisk or Disk Drill.

To prevent future issues, handle your external drive carefully: always use the safely eject option before unplugging, and consider a protective carrying case to guard against physical damage during transport.

Tip. Modern hard drives include S.M.A.R.T. (Self-Monitoring, Analysis, and Reporting Technology), which monitors your drive’s health by tracking temperature, read/write errors, and overall performance.

You can enable S.M.A.R.T. monitoring in Disk Drill, which will notify you if any issues are detected on your drives. Once turned on, a new icon will show the drive’s temperature and health status, making it easy to keep track of your drive’s condition.