How to Repair a Disk in macOS with Disk Utility

If a Mac drive is reporting errors, behaving strangely, or preventing macOS from starting, the built-in Disk Utility app is the first repair tool to try. Its First Aid feature checks the file system and storage structure for errors and attempts to repair problems it can fix. You can run it from a normal macOS session for most external or secondary drives, or from macOS Recovery when you need to repair the startup disk.

Before you begin, make sure you have a current backup of important files. Apple specifically recommends backing up because Disk Utility can find damage that it cannot repair. See Apple's current Disk Utility repair instructions.

Open Disk Utility

If macOS starts normally, open Applications > Utilities > Disk Utility. You can also press Command + Space, search for Disk Utility, and open the app from Spotlight.

If you are repairing the Mac's startup disk, or the Mac does not start all the way to the desktop, open Disk Utility from macOS Recovery instead. The startup method depends on the Mac:

Apple documents the Intel startup shortcuts separately in its Mac startup key combinations guide.

Repair the disk with First Aid

Once Disk Utility is open, do not simply select the first item you see and run First Aid once. Apple recommends working from the lowest volume upward, then checking the volume group, container, and finally the physical storage device.

1. Show the full device hierarchy. Choose View > Show All Devices. This reveals the physical drive, APFS containers, volume groups, and individual volumes when they are present.

2. Select the last volume on the device. On a typical APFS startup disk, this may be a data volume such as Macintosh HD - Data. Your names and number of volumes may differ.

3. Run First Aid. Click First Aid in the toolbar, then click Run or Repair Disk if that is the label shown. If Disk Utility asks for a password to unlock the disk, enter the administrator password you use to sign in to the Mac.

4. Move upward through the sidebar. After First Aid finishes, select the next item above the repaired volume and run First Aid again. Repeat this for every volume and volume group on that device.
5. Repair the container. If the disk uses APFS, select its container after the volumes have been checked, then run First Aid.

6. Finish with the physical device. Select the top-level drive itself and run First Aid one final time.

What to do after First Aid finishes

If Disk Utility reports that it repaired the errors, quit Disk Utility and restart the Mac. If you ran First Aid from Recovery, choose Apple menu > Restart.

If Disk Utility finds errors it cannot repair, do not keep rerunning First Aid indefinitely. Back up or recover any accessible data first. Apple's documented next step is to erase and reformat the disk, which removes its contents, and then restore your data or reinstall macOS as appropriate.

If the storage device does not appear in Disk Utility at all, shut down the Mac and disconnect nonessential devices before trying again. For an external drive, also check its cable, power, and connection. If an internal startup disk still does not appear, or an erase operation fails, the Mac or storage device may need service.

Does First Aid erase your files?

Running First Aid is a repair operation, not an erase command, so it is designed to check and repair the disk structure without intentionally deleting your files. However, existing file-system damage can make data inaccessible, and no repair utility can guarantee recovery. That is why a current backup should come before disk repair whenever the Mac is still usable.