How to Fix Corrupted External Hard Drive on a Mac

A corrupted external hard drive poses a serious problem for Mac users, often leading to error messages, blocked file access, or sluggish performance. We’ll walk you through different ways to fix a corrupted external hard drive on your Mac, using tools and features already built into macOS, as well as third-party apps. These steps should help you recover your data and get your external hard drive back to normal.

How macOS and the Drive Itself Indicate That External Drive Is Corrupted

When an external drive becomes corrupted, both macOS and the drive will often give you clear signs that something is wrong, such as:

• 🚫 Error messages. Frequent alerts such as “Disk not readable” or “Error writing to disk” may appear when you attempt to access or write data to the drive.
• 🐌 Slow performance. A clear drop in data transfer speeds or long delays, when you try to open files, can signal deeper hard drive problems.
• ❓ Missing files. Files that suddenly disappear or become inaccessible, even though they were not manually deleted, can signal corruption within the drive.
• 🔉 Strange noises. Unusual sounds like clicking or grinding from the drive often indicate physical damage, which can lead to data corruption.
• 🗃️ Inconsistent file listings. Changes in file or folder visibility without any user action suggest errors in the drive’s directory structures.
• 🔌 The drive disconnects/fails to mount. A corrupted external drive may randomly disconnect from your Mac without warning. You may also encounter situations where the drive doesn’t mount at all when you plug it in.

Start With These 5 Basic Troubleshooting Steps

If your external drive shows any of these signs, before jumping into advanced fixes, try some basic troubleshooting steps that can often resolve the issue quickly. Start with these five simple checks:

1. Check the Connections

First of all, you need to check the connections. Quite often, a bad connection between your external hard drive and your Mac might look like the drive is corrupted when in reality it’s just a loose or faulty cable. Here’s what you can try:

• Check that the USB or Thunderbolt cable connecting your external hard drive to your Mac is secure. Sometimes, simply reseating the cable can resolve connectivity issues.
• Switch the cable to a different port on your Mac. A faulty port can cause the drive to malfunction, so testing multiple ports can help isolate the issue.
• Cables can degrade or become faulty over time. Try a different cable to determine if the issue lies with the original one.
• Connect your external hard drive to another Mac to avoid system-specific issues. This step can help determine whether the problem is with the drive itself or your computer’s configuration.

2. Check Drive in Disk Utility

The next step is to check your external drive in Disk Utility. This built-in macOS tool is designed to manage and diagnose issues with storage devices. We can use it to verify whether your external hard drive is recognized by your Mac and displayed with the correct size. This can be an initial indicator of the drive’s health and a preliminary step in troubleshooting drive issues. Here’s how you can utilize Disk Utility to check your external hard drive:

1. You can Access Disk Utility by navigating to the Utilities folder within your Applications folder or simply using Spotlight search to find and open Disk Utility.
2. 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.
3. Select the external hard drive you wish to check from the sidebar in Disk Utility. This step confirms whether your Mac recognizes the drive.
4. 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.
5. 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.

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.

If you can access your hard drive in Safe Mode, it’s likely that non-essential software or drivers are to blame. After you restart macOS, check any apps or drivers you’ve recently installed. Try to uninstall them one by one to figure out which one might be causing the issue.

However, if problems persist even in Safe Mode, it may indicate more severe hardware issues or file system corruption that requires further investigation.

No Results Yet? Time for More Advanced Methods

If the basic fixes haven’t done the trick, it’s time to try more advanced solutions. These methods tackle deeper issues with your external hard drive, whether it’s severe file system corruption or hardware problems on your Mac.

Method 1. Reset SMC and NVRAM

Resetting the System Management Controller (SMC) and Non-Volatile Random-Access Memory (NVRAM) on your Mac can help resolve various hardware-related issues. These resets can fix corrupted hard drives on Mac caused by problems related to power management, battery behavior, etc. Here’s how to properly reset the SMC and NVRAM:

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.

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 resolve minor file system errors and restore the functionality of your external hard drive. However, if this method does not fix the problem, more severe issues may be involved, requiring advanced recovery techniques or professional assistance.

How to Repair External Hard Drive Using Mac Terminal

If the standard methods haven’t worked, you can use Terminal for a more advanced way to repair your external hard drive. There are some capable built-in and third-party tools, like fsck and TestDisk, that can only be run through Terminal. This makes them less popular with users, but they’re not as complicated as they may seem. We’ll walk you through the detailed process.

Method 1. Use fsck Command To Repair File System

The File System Check (fsck) command is a powerful tool available in macOS’s Terminal that can help diagnose and repair file system issues on your external hard drive. Here’s a step-by-step guide on how to use the fsck command to repair an external hard drive using a Mac terminal:

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.

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.

If Nothing Worked, Get Back Your Data and Clean the Slate with a Fresh Format

Now, if at this point your external hard drive is still giving you problems, it’s likely time to recover your data and reformat the drive. Reformatting usually fixes all non-physical issues, such as corrupted file systems, partition problems, and allocation errors. This process resets the drive as if it were brand new. It clears out all data structures, which is why it’s so effective at resolving software-related issues.

Just remember, this process erases everything on the drive. If you want to keep your data, you’ll need to handle it 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 come with any built-in data recovery tools, so you’ll need to rely on third-party software to recover data from a corrupted external hard drive. We’ve reviewed and tested many data recovery options, and one of the best for this task is Disk Drill, a tool that’s been around for more than a decade. 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, providing a clean slate for new data. After formatting, the drive will be ready for use, and you can transfer your recovered data back onto it.

When to Contact Data Recovery Services

If you’ve tried all the troubleshooting methods and data recovery tools available, but your external hard drive is still inaccessible or not functioning properly, it may be time to consider professional data recovery services.

Professional data recovery services are a good option when faced with a corrupted external hard drive that DIY methods cannot restore. These services are equipped to handle complex recovery scenarios beyond the reach of standard software solutions. This includes drives with severe physical damage, such as those affected by water or impact, and those suffering from serious mechanical failures like head crashes or motor issues.

Professional data recovery firms use advanced tools and technologies in controlled cleanroom environments to open and repair physically damaged drives without causing further harm. While they can be expensive, the cost is often justified by the high success rates and the ability to recover data that would otherwise be permanently lost.

In Conclusion

In most cases, the DIY methods we covered in this article are enough to fix a corrupted hard drive using a Mac. Usually, these issues come from logical problems that you can fix with macOS utilities or third-party apps like TestDisk or Disk Drill.

To avoid these issues again, it’s important to treat your external drive with care. Always use the safely eject option before you unplug your drive to prevent data corruption. Plus, consider a carrying case for your external hard drive to protect it from physical damage while you transport it.