How to Run First Aid on an External Drive in Disk Utility on a Mac

Quick Answer

To run First Aid on an external drive:

1. Connect the drive to your Mac and close files or apps using it.
2. Open Disk Utility from Applications > Utilities.
3. Choose View > Show All Devices.
4. Select the external drive, volume, or container in the sidebar.
5. Click First Aid, then click Run.
6. Wait for the process to finish and review the result.

First Aid checks and repairs certain file-system and directory problems. It does not recover deleted files, repair every hardware failure, or guarantee that a damaged drive is safe to use. If the drive contains important data, back it up before attempting repairs whenever possible.

Before Running First Aid

First Aid can modify file-system information while it checks the drive. It normally does not erase personal files, but a severely damaged drive can become less accessible during or after a repair attempt. Follow these precautions first:

• Save open documents.
• Quit apps that are reading from or writing to the external drive.
• Do not disconnect the drive while First Aid is running.
• If the drive is still accessible, copy important files to another location before repairing it.
• Connect a portable drive directly to your Mac instead of through an unreliable hub or adapter when possible.
• Make sure the Mac has enough power, especially if you are using a Mac notebook.

If the drive is making clicking, grinding, or repeated spin-up sounds, stop using it as soon as possible. Those symptoms can indicate physical failure. Repeated repair attempts may put additional stress on a failing drive.

Open Disk Utility and Show the External Drive

Disk Utility can display only mounted volumes by default. To see the physical drive and its containers, change the sidebar view.

1. Connect the external drive to your Mac.
2. Open Finder.
3. Select Applications in the sidebar.
4. Open the Utilities folder.
5. Double-click Disk Utility.
6. In the menu bar, choose View > Show All Devices.

With this view enabled, Disk Utility may show several levels:

• Physical device: The actual external SSD, hard drive, or USB flash drive.
• Container: A storage area used by some file systems, including APFS.
• Volume: The named storage area that usually appears in Finder.
• Partition: A section of a physical drive, commonly used with formats such as ExFAT or older Mac file systems.

Selecting the correct level matters. If you need help understanding the sidebar, see How to Use Show All Devices in Disk Utility on Mac.

Run First Aid on an External Drive

1. Select the external drive or volume

In the Disk Utility sidebar, identify the external drive by its name, capacity, or connection type. Do not select your Mac’s internal startup drive by mistake.

If you are checking a particular volume, select the volume first. If the external drive contains multiple volumes, you can check each accessible volume separately.

2. Click First Aid

Click First Aid in the Disk Utility toolbar. You can also choose Edit > First Aid from the menu bar if the toolbar button is not visible.

A confirmation message explains that First Aid will check the volume for errors. Click Run to begin.

3. Wait for the check to finish

First Aid may take a few moments or much longer, depending on the drive’s size, connection speed, file system, and condition. Do not:

• Unplug the drive.
• Put the Mac to sleep intentionally.
• Force quit Disk Utility.
• Open or modify files on the drive.
• Restart the Mac unless Disk Utility becomes completely unresponsive.

Disk Utility displays status messages as it checks the drive. Some repairs require the volume to be unmounted temporarily. If macOS asks to unmount the volume, confirm only after closing apps and saving work that uses the drive.

4. Review the result

When the process finishes, Disk Utility reports whether First Aid found problems and whether it repaired them.

A successful result may state that the volume appears to be OK or that repairs were completed. If Disk Utility reports that it cannot repair the drive, copy any accessible files immediately and avoid treating the drive as reliable.

Click Done when finished.

Run First Aid at Each Level

For a more complete check, run First Aid on the relevant items from the lowest level upward. The exact items shown depend on the drive’s format.

A typical order is:

1. The external drive’s volume.
2. The volume’s container, if one is shown.
3. The physical external device.

Select one item at a time and click First Aid. Wait for each operation to complete before moving to the next level.

Checking the volume first is usually the most useful starting point because it contains the file and directory information macOS uses. Checking the container and physical device can reveal broader structural problems.

Do not repeatedly run First Aid on a drive that is producing unusual mechanical noises or disconnecting. If the drive is failing physically, software repair is unlikely to solve the underlying problem.

What First Aid Can and Cannot Fix

First Aid is designed to check and repair certain logical problems. A logical problem affects the way information is organized, rather than the physical components of the drive. Examples can include damaged directory records, volume structures, or file-system metadata.

First Aid cannot reliably:

• Recover files that were deliberately deleted.
• Restore files permanently overwritten by other data.
• Repair a broken USB cable, port, enclosure, or power supply.
• Restore a drive with widespread physical damage.
• Guarantee that a drive will remain healthy after a successful repair.
• Remove malware.
• Replace a backup.

If the drive mounts after First Aid, copy important files to a different disk. A repair that succeeds once does not prove that the hardware is healthy.

What to Do If First Aid Finds Errors

The next step depends on the message Disk Utility displays.

If repairs were completed successfully

Open the drive in Finder and test a few files. If everything appears normal, make a current backup before continuing to use the drive.

If the same errors return, the drive may be developing a hardware problem or the connection may be unstable. Try a different cable, port, or enclosure, but do not use troubleshooting changes as a substitute for backing up the data.

If Disk Utility says the volume cannot be repaired

First, stop writing new data to the drive. Copy files that are still accessible to another disk. Do not erase the original until you have confirmed that the copies open correctly.

After securing the data, you may need to erase and reformat the drive. Erasing removes the existing files and file-system structure, so it is not an appropriate first step when you still need the data. Review How to Erase a Mac Drive Securely in Disk Utility before taking that action.

If the drive does not appear in Disk Utility

Check the physical connection first:

1. Disconnect and reconnect the drive.
2. Try another USB, Thunderbolt, or other compatible port.
3. Try a different cable.
4. Connect the drive directly to the Mac instead of through a hub.
5. If the drive has its own power adapter, verify that it is connected and switched on.
6. Restart the Mac and open Disk Utility again.
7. Choose View > Show All Devices.

If the drive appears dimmed, select it and click Mount in the toolbar. Mounting makes the volume available to macOS and Finder. For related steps, see How to Mount and Unmount a Disk in Disk Utility on Mac.

If the physical device never appears, the problem may involve the cable, enclosure, port, power supply, or drive hardware rather than the file system.

If First Aid is unavailable or dimmed

First Aid may be unavailable when:

• No disk or volume is selected.
• The selected item is not recognized.
• The drive is locked or inaccessible.
• Another operation is already using the disk.
• The drive has disconnected.

Select the external volume or device in the sidebar, close apps using it, and try again. If the drive repeatedly disappears, focus on preserving data rather than running more repairs.

If First Aid stops or reports an input/output error

An input/output error means macOS had trouble reading from or writing to the drive. It can result from a failing drive, damaged cable, inadequate power, or a faulty enclosure.

Stop unnecessary activity on the drive and copy the most important accessible files first. Try a different cable or direct connection once, then reassess. If errors continue, consider professional data-recovery help, especially when the files exist nowhere else.

If the drive is encrypted

An encrypted volume may need to be unlocked before macOS can access its contents. Enter the password when macOS requests it, then select the unlocked volume in Disk Utility and run First Aid.

Keep the password or recovery information available. Without the required credentials, repairing or accessing the data may not be possible.

Run First Aid from macOS Recovery

If the external drive is being used by an app, cannot be repaired while macOS is running, or behaves differently during normal startup, you can try Disk Utility from macOS Recovery.

Warning: Starting macOS Recovery restarts the Mac and closes open apps. Save all work before continuing.

1. Save your work and shut down or restart the Mac.
2. Start macOS Recovery using the startup procedure appropriate for your Mac.
3. When the Recovery screen appears, choose Disk Utility.
4. Click Continue.
5. Choose View > Show All Devices.
6. Select the external drive or volume.
7. Click First Aid, then click Run.
8. When finished, quit Disk Utility.
9. Choose Restart from the Apple menu or Recovery options.

Recovery can provide a less active environment for checking disks, but it cannot repair physical hardware. If the drive is not detected even in Recovery, investigate the connection or hardware.

Should You Use Terminal Instead?

For most people, Disk Utility is the safer and clearer way to run First Aid. Terminal provides command-line tools that can be useful for advanced troubleshooting, but selecting the wrong disk can cause serious data loss.

Avoid using Terminal commands unless you can identify the correct device and understand the results. Do not copy commands from an unverified source, and do not use erase commands while attempting to repair a drive.

For ordinary external-drive repairs, Disk Utility provides the necessary controls without requiring you to work with device identifiers.

Frequently Asked Questions

Does First Aid delete files from an external drive?

First Aid is intended to check and repair file-system information, not erase the drive. However, any repair operation on a damaged disk carries risk. Back up important files first whenever possible.

How long does First Aid take?

The time varies with the drive’s capacity, connection, file system, and condition. A healthy small volume may finish quickly, while a large or damaged drive can take much longer. Do not disconnect the drive because the process appears slow.

Can First Aid repair a corrupted external hard drive?

It can repair some logical file-system problems, but it cannot repair physical damage. If the drive is failing, disconnecting, or producing unusual sounds, prioritize data recovery and replacement.

Should I run First Aid on the volume or the whole drive?

Start with the volume containing your files. For a broader check, run First Aid on the volume, its container if present, and then the physical device, waiting for each check to finish.

What happens if First Aid says the disk is OK but files are still missing?

A successful First Aid result does not recover deleted files or guarantee that every file is intact. Check your backups and avoid writing new data if you suspect files were deleted or overwritten.

Can I use the external drive while First Aid is running?

No. Close apps using the drive and avoid opening, saving, moving, or deleting files until First Aid finishes.

Final Thoughts

Running First Aid in Disk Utility is a practical first step when an external drive behaves unexpectedly. Show all devices, select the correct external drive or volume, let the check finish without disconnecting the disk, and back up accessible files afterward. If repairs fail or the drive shows signs of physical failure, stop relying on it and focus on data recovery or replacement.