You can repair many common file-system problems on a Mac with Disk Utility’s First Aid feature. Open Disk Utility, select the volume you want to check, and choose First Aid. For the most thorough check, run First Aid on the volume, its container, and finally the physical disk. If the startup disk cannot be repaired while macOS is running, use macOS Recovery instead.
Quick Answer
- Back up important files before repairing a disk.
- Open Disk Utility from Applications > Utilities.
- Choose View > Show All Devices.
- Select the volume you want to check, such as Macintosh HD, and click First Aid.
- Run First Aid on the volume, its APFS container, and the physical disk when available.
- If Disk Utility reports that the disk cannot be repaired, start up from macOS Recovery and run First Aid there.
- If First Aid still cannot repair the disk, back up or recover your data and replace or erase the disk as appropriate.
First Aid checks and repairs certain directory and file-system problems. It does not recover every deleted file, repair all hardware failures, or fix damage caused by a failing drive.
What First Aid Does
A Mac disk is organized in layers:
- Volume: A usable storage area that appears in Finder, such as Macintosh HD or an external drive’s name.
- APFS container: A storage pool that can contain one or more APFS volumes.
- Physical disk: The actual internal or external storage device.
On newer Macs and many newer external drives, the file system is commonly APFS, Apple’s modern file system. Older drives may use Mac OS Extended, also called HFS+.
First Aid checks the selected item for problems such as damaged directory information, invalid file-system structures, or volume errors. Depending on what you select, it may check a single volume, the container that holds APFS volumes, or the entire physical disk.
First Aid is not a general-purpose data-recovery tool. It cannot guarantee that damaged files will be restored, and it cannot repair every hardware problem.
Back Up Before Running First Aid
Although First Aid is designed to check and repair disk structures, any disk repair operation carries some risk if the drive is already failing. Make a current backup before proceeding whenever the Mac and disk are still accessible.
Use Time Machine or another backup method to copy important documents, photos, videos, and other files to a different storage device or backup destination.
If the disk is showing serious symptoms—such as repeated disconnections, clicking sounds, very slow access, or frequent read and write errors—prioritize copying or recovering your data. Avoid repeatedly running repair tools on a drive that may be physically failing.
Warning: Before starting First Aid, save your work and close apps that use the disk. The process may require a volume to be unmounted, and closing apps prevents unsaved changes or file-access conflicts.
Repair a Mac Disk in Disk Utility
Use this method when macOS is running normally and you want to check an internal data volume or an external disk.
1. Open Disk Utility
- Open Finder.
- Select Applications in the sidebar.
- Open the Utilities folder.
- Double-click Disk Utility.
You can also press Command-Space, type Disk Utility, and press Return.
2. Show the complete disk structure
In Disk Utility, choose View > Show All Devices from the menu bar.
This view displays the storage hierarchy instead of showing only usable volumes. You may see a structure similar to this:
- Physical disk
- APFS container
- Macintosh HD
- Macintosh HD – Data
The exact names and layout vary by Mac and disk format.
3. Run First Aid on the volume
- Select the volume you want to check in the sidebar.
- Click First Aid in the toolbar.
- Read the confirmation message, then click Run.
- Wait for the process to finish.
- Click Done when the results appear.
A volume is the storage area that normally appears in Finder. For an external drive, select the volume containing the files you use.
If you are checking the startup disk, macOS may be able to inspect some parts while the system is running, but it may not be able to repair every problem on an active startup volume. If Disk Utility says the volume must be unmounted, use macOS Recovery.
4. Run First Aid on the APFS container
If the disk uses APFS:
- Select the APFS container below the physical disk.
- Click First Aid.
- Click Run.
- Wait for the check to finish and click Done.
The container is the storage pool that holds APFS volumes. Checking it can identify problems that are not limited to one volume.
5. Run First Aid on the physical disk
- Select the top-level physical disk in the sidebar. It may display the manufacturer’s name, an external-drive name, or a description such as an internal physical disk.
- Click First Aid.
- Click Run and wait for the result.
- Click Done.
The physical-disk check is different from checking a volume. It examines the device’s partition and disk structure, while a volume check focuses on the file system used to organize files.
For an external disk, make sure you select the correct device. Running actions on the wrong disk can affect access to its data.
The Recommended First Aid Order
When Disk Utility shows all devices, a practical order is:
- Run First Aid on the lowest-level volume you need to check.
- Run it on the APFS container, if one is present.
- Run it on the physical disk.
If the sidebar contains multiple volumes, check each relevant volume. On a startup disk, you may see separate system and data volumes. Follow Disk Utility’s instructions if it asks you to check related volumes together.
First Aid may automatically check related structures, but selecting each visible layer gives you a clearer picture of where a problem was found.
Run First Aid from macOS Recovery
Use macOS Recovery when:
- First Aid cannot repair the startup volume while macOS is running.
- Disk Utility says the volume must be unmounted.
- The Mac cannot start normally.
- You need to check the startup disk without booting from it.
Before beginning, save your work if possible and disconnect unnecessary external devices. Keep the Mac connected to power if you are using a portable Mac.
Warning: Do not erase or reformat a disk from macOS Recovery unless you have a backup or have deliberately chosen to delete its contents. Erasing a disk removes its data.
Start an Apple silicon Mac in Recovery
- Shut down the Mac.
- Press and hold the power button.
- Continue holding it until Loading startup options appears.
- Select Options.
- Click Continue.
- If prompted, select an administrator account and enter its password.
Start an Intel-based Mac in Recovery
- Shut down the Mac.
- Turn it on and immediately press and hold Command-R.
- Keep holding the keys until the Apple logo or another startup screen appears.
- If prompted, choose an administrator account and enter its password.
If you are unsure which type of Mac you have, you can usually check in macOS by choosing Apple menu > About This Mac before restarting.
Run First Aid in Recovery
- Select Disk Utility in the macOS Recovery window.
- Click Continue.
- Choose View > Show All Devices.
- Select the startup volume, container, and physical disk as needed.
- Click First Aid for each item.
- Click Run and wait for each operation to finish.
- Quit Disk Utility when finished.
- Choose Apple menu > Restart to start macOS normally.
If the startup volume is encrypted, Recovery may ask for a password or recovery method before it can access the disk. Use the account or recovery information associated with that Mac.
Understanding First Aid Results
Disk Utility may display different outcomes. The wording can vary by macOS version and disk type, but these results generally mean the following.
“Operation successful” or a similar success message
The check or repair completed without finding an unresolved problem. This does not prove that every file is intact or that the hardware will never fail. Continue monitoring the disk and keep regular backups.
Errors were found and repaired
First Aid detected file-system problems and corrected them. Restart the Mac if requested, then check whether the original problem has disappeared.
If errors return, the disk may have an underlying hardware or connection problem. Back up your data and investigate further rather than repeatedly relying on First Aid.
The volume appears to be OK
The selected volume passed the check. If you are still experiencing problems, check the other layers—such as the APFS container or physical disk—and test the cable, enclosure, or port for an external drive.
First Aid found corruption but cannot repair it
This means Disk Utility found a problem it could not correct. Run First Aid from macOS Recovery if you have not already done so. If the result is unchanged, back up or recover your files as soon as possible.
You may ultimately need to erase and reformat the disk. Erasing removes all data on the selected disk or volume, so do not do this until you have a verified backup or have accepted the loss of its contents.
First Aid failed
A failure can result from file-system corruption, an unmounted or inaccessible volume, a damaged partition structure, an unreliable cable or enclosure, or failing storage hardware.
Record the complete message if possible. It may identify the affected volume or provide an error code useful for further troubleshooting.
What First Aid Cannot Repair
First Aid has important limits:
- It cannot repair every physical failure in an SSD, hard drive, flash drive, or enclosure.
- It cannot replace a damaged cable, adapter, USB hub, or power supply.
- It cannot restore files that were deliberately deleted.
- It cannot guarantee recovery from a corrupted file.
- It cannot fix problems caused by insufficient free space.
- It cannot remove malware or repair damaged applications.
- It cannot undo accidental erasure or formatting.
- It cannot repair a disk that is no longer detected by the Mac.
- It cannot make a failing disk reliable for continued use.
If the disk disappears, disconnects repeatedly, makes unusual noises, or becomes extremely slow, stop treating it as a normal repair problem. Copy important data while it is available and consider professional data recovery if the files are irreplaceable.
Troubleshooting First Aid Problems
Disk Utility does not show the disk
Try these steps:
- Disconnect and reconnect the external disk.
- Try another cable, adapter, or Mac port.
- Connect the disk directly instead of through a hub.
- Confirm that the disk has power.
- Open Disk Utility and choose View > Show All Devices.
- Restart the Mac and check again.
If the disk is not detected anywhere, the problem may involve the disk, enclosure, cable, adapter, or power source rather than the file system.
The First Aid button is unavailable
Select a disk or volume in the sidebar rather than a category or empty area. Some items cannot be repaired while they are mounted or in use. Try macOS Recovery for the startup disk.
First Aid says the volume is in use
Close open files and applications, eject the disk in Finder, and reconnect it if it is external. If the volume is the startup disk, run First Aid from macOS Recovery.
First Aid keeps finding the same errors
Back up your files immediately. Repeated errors can indicate persistent file-system damage or failing hardware. Check the connection for an external disk and consider replacing the drive after securing your data.
The Mac will not start after a disk problem
Start in macOS Recovery and run First Aid on the startup volume, APFS container, and physical disk. If the Mac still cannot start, use Recovery options to reinstall macOS only after protecting your data. Reinstalling macOS is different from erasing the disk, but you should still maintain a backup whenever possible.
Frequently Asked Questions
Should I run First Aid on the volume or the whole disk?
Start with the volume that contains the problem. For a more complete check, run First Aid on the volume, its APFS container, and the physical disk. The volume contains your files, the container manages APFS storage, and the physical disk contains the overall device structure.
Can First Aid delete my files?
First Aid is intended to repair disk structures, not delete personal files. However, disk repair cannot guarantee data preservation when a disk is badly corrupted or failing. Back up important files before running it.
How often should I run First Aid?
There is no need to run First Aid on a fixed schedule when the Mac and its disks are working normally. Use it when you see symptoms such as mounting errors, unexpected disk warnings, failed copies, or a volume that will not open. Maintain regular backups instead of relying on routine repairs.
Can First Aid repair an external hard drive?
Yes, First Aid can check supported external drives and their volumes. If it fails, test the drive with a different cable, port, enclosure, or power source. A failure may be caused by the connection or hardware rather than the file system.
Should I erase a disk if First Aid fails?
Not immediately. First secure your files or create a verified backup. Erasing may be appropriate for a replaceable disk that you are willing to reformat, but it permanently removes data from the erased volume or device.
Is First Aid the same as repairing a physically damaged drive?
No. First Aid repairs certain logical file-system and directory problems. It cannot repair worn-out storage cells, a failing drive mechanism, damaged electronics, or a defective enclosure.
Final Thoughts
Disk Utility’s First Aid is the built-in way to check and repair many Mac disk problems. Back up first, enable Show All Devices, and check the relevant volume, APFS container, and physical disk. If the startup disk cannot be repaired while macOS is running, use macOS Recovery.
When First Aid repeatedly fails or the disk shows signs of hardware trouble, prioritize data recovery and replacement rather than continuing to run repairs.