If your Mac is running slowly, showing disk-related errors, or having trouble starting, Disk Utility’s First Aid feature can check the startup disk and repair certain directory and formatting problems. For the best chance of repairing the disk, run First Aid from macOS Recovery, not while the startup volume is actively running macOS.
Back up important files first if your Mac still starts normally. First Aid is designed to repair disk structures, but it cannot recover every failing drive or restore deleted files.
Quick Answer
To repair a Mac startup disk:
- Back up your important files if possible.
- Start the Mac in macOS Recovery.
- Open Disk Utility.
- Choose View > Show All Devices.
- Run First Aid on the startup volume, its APFS container, and the physical drive, in that order.
- Restart the Mac normally.
If First Aid reports that it cannot repair the disk, back up or copy your files immediately if the Mac is accessible, then consider erasing and reinstalling macOS or replacing the drive.
What Disk Utility Can Repair
Disk Utility checks the disk’s file-system structures—the information macOS uses to locate files, folders, and free space. First Aid may repair problems such as:
- Directory errors
- Invalid file-system records
- Problems with volume structures
- Some APFS container issues
- Partition-map errors on supported disks
First Aid cannot fix every physical hardware failure. It also cannot repair severe damage, recover permanently deleted files, or guarantee that a disk with repeated errors will remain reliable.
A startup disk normally has several levels:
- Startup volume: The volume containing macOS and your user data, often named “Macintosh HD.”
- APFS container: A storage area that can hold multiple APFS volumes.
- Physical disk: The actual internal SSD or hard drive.
Running First Aid at each visible level gives Disk Utility a more complete opportunity to check the storage structure.
Before You Repair the Startup Disk
Back up your files
If macOS starts, back up important documents, photos, and other files before running repairs. Use Time Machine or another backup method. If the Mac is unstable, prioritize irreplaceable files over troubleshooting.
If the disk is making unusual noises, disappearing, or causing repeated crashes, minimize use. A failing drive can become less accessible over time.
Connect power
Connect a Mac notebook to its power adapter. A repair can take time, and losing power during storage maintenance may create additional problems.
Close apps and expect a restart
Running First Aid from Recovery requires restarting the Mac and temporarily closing all open apps. Save unsaved work first. If you erase the disk later, all data on that disk will be deleted, so do not proceed with an erase unless you have a backup or have accepted the risk of permanent data loss.
Start macOS Recovery
The startup procedure depends on whether your Mac has Apple silicon or an Intel processor.
Apple silicon Mac
- Shut down the Mac. If it is unresponsive, press and hold the power button until it turns off.
- Press and hold the power button.
- Release the button when Loading startup options appears.
- Select Options, then click Continue.
- Choose an administrator account if prompted, then enter its password.
Intel-based Mac
- Shut down the Mac.
- Turn it on and immediately press and hold Command-R.
- Release the keys when you see the Apple logo or a spinning globe.
- Select an administrator account if requested, then enter its password.
If Recovery does not load, try again while holding the keys immediately after pressing the power button. An external keyboard may not register the shortcut early enough, so use the built-in keyboard on a Mac notebook when possible.
For more detailed Recovery instructions, see How to Repair a Mac Startup Disk in macOS Recovery.
Repair the Startup Disk with First Aid
Once the macOS Recovery window appears, do not choose Reinstall macOS yet. Open Disk Utility first.
1. Open Disk Utility
- Select Disk Utility in the macOS Recovery window.
- Click Continue.
Disk Utility opens with a sidebar listing available disks and volumes.
2. Show the complete disk structure
Choose View > Show All Devices from the menu bar.
This setting displays physical disks, containers, and volumes instead of showing only mounted volumes. If you leave the default view enabled, you may not see the physical device or APFS container that also needs checking.
You can also review How to Use Show All Devices in Disk Utility on Mac for an explanation of the sidebar hierarchy.
3. Run First Aid on the startup volume
In the sidebar, select the volume that contains macOS. It is often named Macintosh HD. If you see both Macintosh HD and Macintosh HD – Data, start with the system volume, then check the data volume separately.
- Select the startup volume.
- Click First Aid in the toolbar.
- Click Run.
- Wait for the check to finish.
- Click Done when the result appears.
If First Aid finds a problem it can repair, Disk Utility may make changes automatically. Do not shut down the Mac while the operation is running.
4. Run First Aid on the APFS container
If the sidebar shows an APFS container above the startup volume:
- Select the container.
- Click First Aid.
- Click Run.
- Wait for the operation to finish.
The container manages the relationship between APFS volumes and the available storage space. Checking it can reveal problems that are not visible when you check only an individual volume.
5. Run First Aid on the physical disk
Finally, select the top-level internal physical disk. It may show a manufacturer name or a description such as APPLE SSD.
- Select the physical disk.
- Click First Aid.
- Click Run.
- Wait for Disk Utility to complete the check.
The exact labels and number of items can vary by Mac and storage configuration. If an item is dimmed or First Aid is unavailable, select the next visible level rather than forcing an action.
For general First Aid guidance, see How to Repair a Mac Disk with First Aid.
6. Restart the Mac
After First Aid finishes:
- Close Disk Utility.
- Choose Apple menu > Restart from the Recovery menu bar.
- Allow the Mac to start normally.
If the Mac starts successfully, use it briefly and check whether the original problem has improved. Create or update a backup before making further changes.
If First Aid Reports Errors
Disk Utility can produce several types of results.
“The volume appears to be OK”
This means First Aid did not find a repairable problem in the selected item. If the Mac still has startup problems, the cause may be software, insufficient storage, a damaged macOS installation, or hardware that Disk Utility did not identify.
Run First Aid on the other visible levels if you have not already done so.
First Aid repaired the disk
Restart the Mac and test it. If the same errors return, treat that as a warning. Repeated directory problems can indicate a developing hardware issue or a severely damaged file system.
Back up your data and avoid relying on the disk as your only storage location.
First Aid cannot repair the disk
Do not repeatedly run First Aid without a backup. First copy important files if the Mac can still access them. Then consider these options:
- Restart into Recovery and run First Aid once more on the relevant volume, container, and physical disk.
- If the data is backed up, erase the affected disk and reinstall macOS.
- If the disk cannot be erased, disappears, or reports hardware-related errors, arrange service or replace the storage device.
Erasing a disk permanently removes its contents. Confirm the selected device carefully before clicking Erase.
Troubleshooting
The startup disk is missing from Disk Utility
Choose View > Show All Devices and check the sidebar again. If the internal disk still does not appear, shut down the Mac and start Recovery again.
A missing internal disk may indicate a connection problem, storage failure, or another hardware issue. Do not erase a different disk simply because it is the only one visible. See How to Fix a Startup Disk Not Showing on Mac for additional steps.
First Aid is dimmed
First Aid may be unavailable for an item that is not mounted, is read-only, or cannot be checked in the current state. Select the volume, container, or physical disk above it and try again.
You can also select the item and choose File > Mount if it is unmounted. Mounting changes whether macOS can access the volume; it does not repair the disk. If the volume contains important data, avoid experimenting with mount or erase options until your files are backed up.
The Mac still shows a blinking question mark
A blinking question-mark folder means the Mac cannot find a valid startup system. First Aid may not be enough. Start in Recovery, check the internal disk, and use Startup Disk from the Recovery menu if the system volume is available.
If the startup volume is missing or macOS is damaged, you may need to reinstall macOS. Reinstalling macOS normally targets the system installation, but always read the onscreen choices carefully and maintain a backup.
The Mac is extremely slow or freezes during First Aid
Give Disk Utility time to finish, especially when checking a large hard drive. Do not interrupt the process unless the Mac is clearly unresponsive for an extended period.
If the drive repeatedly freezes, disappears, or produces hardware errors, prioritize data recovery and professional service. A failing drive may worsen when it continues operating.
First Aid completes, but problems return
Recurring errors suggest that the underlying issue has not been resolved. Update your backup, check available storage, and look for symptoms such as unexpected shutdowns, repeated kernel panics, or files that become corrupted.
If the errors continue after erasing and reinstalling macOS, the storage hardware is a likely suspect and should be evaluated.
Frequently Asked Questions
Can I repair the startup disk while macOS is running?
You can run First Aid on some volumes while macOS is running, but the startup volume is in active use. For a more complete check and repair, use Disk Utility from macOS Recovery.
Will First Aid delete my files?
First Aid is intended to repair disk structures without deleting normal files. However, disk repairs always involve risk when the file system is damaged. Back up important data first. Never confuse First Aid with Erase, which deletes the selected disk or volume.
How long does startup-disk repair take?
The time depends on the disk’s capacity, speed, health, and the type of problem. Some checks finish quickly, while a large or damaged drive may take much longer. Keep the Mac connected to power and avoid interrupting the process.
Should I run First Aid on Macintosh HD – Data?
Yes, if it appears in Disk Utility. Check the system volume and data volume separately, then check the APFS container and physical disk when those items are shown.
What if Disk Utility says the disk is about to fail?
Copy important files immediately and stop treating the disk as reliable. First Aid cannot restore a physically failing drive. Replace the disk or have the Mac serviced after securing your data.
Can First Aid fix a Mac that will not start?
It can fix some file-system problems that prevent startup, but not all startup failures. If the disk is healthy but macOS is damaged, reinstalling macOS may be necessary. If the disk is missing or failing, service may be required.
Final Thoughts
Disk Utility’s First Aid is the safest built-in starting point for many Mac startup-disk problems. Run it from macOS Recovery, use Show All Devices, and check the startup volume, APFS container, and physical disk. If errors return or the disk disappears, back up your files and treat the problem as a possible storage failure rather than repeatedly rerunning repairs.