Maintenance procedure · Written to ASD-STE100 Issue 9 · Formatted to ANSI Z535

Check and Repair a Mac Disk with Disk Utility First Aid

Back up before you run it, not after — and run it bottom-up: every volume, then every container, then the device itself
ApplicabilityAny Mac running a macOS that Apple currently documents, checking either the startup disk or an external disk. Checked against Apple's documentation on 2026-07-29, when the support article 'How to repair a Mac storage device with Disk Utility' carried a Published Date of 08 December 2025 and the Disk Utility User Guide identified itself as the guide for macOS Tahoe 26. Repairing the startup disk needs macOS Recovery, and the key sequence for macOS Recovery differs between a Mac with Apple silicon and an Intel-based Mac, so this page branches on that before it gives any instruction. Erasing a disk and reinstalling macOS are named here and deliberately not instructed.
Task time1 hr 57 min to 7 hr 2 min editorial estimate, not a measurement
PersonnelOne
Revisionv1 · 2026-07-29
BEFORE YOU BEGIN

Before you begin. This procedure is general reference information, not professional advice. Equipment varies by manufacturer, model, and year. Always follow the documentation supplied with your equipment — where it differs from this page, follow the manufacturer. Verify that you have the tools, the working conditions, and the ability to do this task safely. If anything is unclear, if the equipment is damaged, or if the task exceeds your experience, stop and use a qualified professional. You are responsible for your own safety and for the outcome. This site accepts no liability for any loss, damage, or injury arising from the use of this information.

Specifications marked unverified could not be traced to a manufacturer source. Do not rely on them — obtain the value from your equipment documentation.

Summary

First Aid is the disk repair tool built into every Mac. It looks for errors in the formatting and directory structure of a disk — the bookkeeping that tells macOS where your files are — and fixes what it can. Apps quitting for no reason, a file that will not open, an external drive behaving oddly: all of those can come from directory damage, and all are worth one First Aid run before you assume the worst.

Two things about it are worth knowing before you click Run, and most pages leave both out.

The first is that you back up before you run it, not after. Apple's own instruction is to have a current backup in place first, and the reason is blunt: a disk that is failing mechanically can die during the repair. First Aid asks a struggling drive to do a lot of reading and writing at once, which is exactly the workload a dying drive is worst at. Most of the time it is fine. When it is not, the backup is the only thing between you and a total loss, and you cannot make one afterwards.

The second is the order. A Mac disk is not one thing — it is a device, holding a container, holding volumes, and First Aid runs on each separately. Apple's documented order is bottom-up: start at the last volume, work up through every volume, then every container, then the device itself. People habitually select the device, run it once, and conclude the disk is fine. It is not the same check.

Written from Apple's own documentation as it stood on 29 July 2026. It stops where Apple stops: it will not tell you to erase a disk to make an error go away.

Safety

NOTICE

MAKE A BACKUP OF YOUR DATA BEFORE ANY STEP ON THIS PAGE.
A repair with Disk Utility does not correct all faults. A disk with a hardware fault can fail during a repair.

NOTICE

FIND THE TYPE OF YOUR MAC BEFORE YOU START.
Apple gives two different key sequences for macOS Recovery. The wrong sequence gives no message.

Necessary equipment

ItemNote
Mac computerThe key sequence for macOS Recovery is different for each type of Mac.
Backup diskMake a backup of your data before any repair on this page.
KeyboardUse the built-in keyboard of a laptop, or a keyboard with a cable.
Pen and paperWrite the name of each disk and the exact text of each report.

Make a backup before any repair

Estimated 35 min to 2 hr 15 min

NOTEApple gives a current backup as the first step. A disk with a hardware fault can fail during a repair. You cannot make a backup after that failure.
  1. Make a backup of your data.
    • Apple gives a current backup before any repair.
    • A repair with Disk Utility does not correct all faults.
    • A disk with a hardware fault can fail during a repair.
    30m
  2. Open one file from the backup.
    • This test shows that the backup is good.
    • A backup without a test is not a backup.
    5m

Find the type of your Mac and the disk with the fault

Estimated 2 min to 4 min

NOTEApple gives one key sequence for macOS Recovery on a Mac with Apple silicon. Apple gives a different key sequence for an Intel-based Mac.
  1. Select About This Mac in the Apple menu.
    <1m
  2. Read the label above the name of the processor.
    • A label of Chip shows a Mac with Apple silicon.
    • A label of Processor with an Intel name shows an Intel-based Mac.
    <1m
  3. Write the name of the disk with the fault on paper.
    • The default name of the startup disk is Macintosh HD.
    • An external disk connects to a port on your Mac.
    • The subsequent section is different for each of these two disks.
    1m

Open Disk Utility for an external disk

Estimated 1 min

NOTEDo this section only for a disk that is not the startup disk.
  1. If the disk with the fault is an external disk, connect it to your Mac.
    • For a fault on the startup disk, go to the section for your type of Mac.
    <1m
  2. Open Disk Utility in the Utilities folder.
    • The Utilities folder is in the Applications folder.
    • Then go to the section for First Aid.
    <1m

Start macOS Recovery on a Mac with Apple silicon

Estimated 5 min to 12 min

NOTEDo this section only for a fault on the startup disk. Do this section only for a Mac with a Chip label in About This Mac.
Maximum time to hold the power button for a forced stop
Manufacturer or standard verified
10 seconds

Source: How to start up from macOS Recovery · tier 1 · accessed 2026-07-29

NOTICE

SAVE YOUR WORK BEFORE THIS SECTION.
This section stops your Mac. A stop with the power button causes the loss of unsaved data.

  1. If your Mac has Apple silicon, save your work.
    • Do this section only for a fault on the startup disk.
    • Then close your apps.
    1m
  2. Select Shut Down in the Apple menu.
    • If your Mac does not stop, hold the power button for a maximum of 10 seconds.
    <1m
  3. Wait until the screen is black and each light is off.
    • This condition shows that your Mac is fully off.
    <1m
  4. Hold the power button.
    • On a laptop with Touch ID, the power button is the Touch ID button.
    <1m
  5. Release the power button when the screen shows "Loading startup options".
    • An Options icon on the screen has the same meaning.
    <1m
  6. Select Options.
    <1m
  7. Select Continue below the Options icon.
    <1m
  8. If your Mac asks for a volume, select your startup disk.
    • The default name of the startup disk is Macintosh HD.
    <1m
  9. If your Mac asks for a user, select your user.
    • Then type the password for that user.
    1m
  10. Select Disk Utility in the macOS Recovery window.
    • Then select Continue.
    <1m

Start macOS Recovery on an Intel-based Mac

Estimated 5 min to 15 min

NOTEDo this section only for a fault on the startup disk. Do this section only for a Mac with a Processor label in About This Mac.
Keys for macOS Recovery on an Intel-based Mac
Manufacturer or standard verified
Command and R, from the moment your Mac starts until a logo shows

Source: How to start up from macOS Recovery · tier 1 · accessed 2026-07-29

  1. If your Mac has an Intel processor, save your work.
    • Do this section only for a fault on the startup disk.
    • Then close your apps.
    1m
  2. Select Shut Down in the Apple menu.
    • If your Mac does not stop, hold the power button for a maximum of 10 seconds.
    <1m
  3. Press the power button.
    <1m
  4. Immediately hold the Command key and the R key.
    • Release the keys when an Apple logo shows on the screen.
    • A globe on the screen has the same meaning.
    • Use the built-in keyboard of a laptop for this step.
    <1m
  5. If your Mac asks for a network, select a Wi-Fi network.
    • A network cable is the alternative.
    1m
  6. If your Mac asks for a volume, select your startup disk.
    <1m
  7. If your Mac asks for a user, select your user.
    • Then type the password for that user.
    1m
  8. Select Disk Utility in the macOS Recovery window.
    • Then select Continue.
    <1m

Do First Aid from the bottom of the list

Estimated 47 min to 3 hr 3 min

NOTEApple gives this order: each volume, then each container, then the device. A repair of the device alone is not the same check.
Order that Apple gives for a First Aid repair
Manufacturer or standard verified
Each volume, then each container, then the storage device

Source: How to repair a Mac storage device with Disk Utility · tier 1 · accessed 2026-07-29

Volumes to check on a Mac startup disk
Manufacturer or standard verified
Macintosh HD and Macintosh HD - Data

Source: Repair a storage device in Disk Utility on Mac · tier 1 · accessed 2026-07-29

Time for a First Aid run on your disk
Unverified — do not rely on this value
NO PUBLISHED VALUE. THE TIME CHANGES WITH THE SIZE AND THE CONDITION OF THE DISK.

No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.

  1. Select View in the menu bar.
    <1m
  2. Select Show All Devices.
    • The sidebar then shows each device with its containers and its volumes.
    • If this command is not available, continue to the next step.
    <1m
NOTICE

STOP IF DISK UTILITY REPORTS THAT THE DISK IS ABOUT TO FAIL.
Apple states that you cannot repair this disk. Make a backup of all data that you can read. Then replace the disk.

  1. Select the last volume of the device in the sidebar.
    • The volumes are the lowest items below the device.
    • On a startup disk, the last volume is usually Macintosh HD - Data.
    • Apple gives the last volume as the start of the repair.
    <1m
NOTICE

DO NOT STOP YOUR MAC DURING FIRST AID.
DO NOT DISCONNECT THE DISK DURING FIRST AID. An interruption during a repair can damage the data on the disk.

  1. Select the First Aid button.
    • If the button is dim, go to the next item in the list.
    <1m
  2. Select Run.
    • If your Mac asks for a password, type your administrator password.
    <1m
  3. Wait until First Aid is complete.
    • The time changes with the size of the volume.
    • The time also changes with the condition of the disk.
    10m
  4. Select Done.
    <1m
  5. Do the four steps above again for each remaining volume of the device.
    • Move up the list one item at a time.
    • Do not go to a container until each volume is complete.
    15m
  6. Then do the four steps again for each container of the device.
    • A container holds the volumes below it.
    • Some disks have no container.
    10m
  7. Then do the four steps again for the device.
    • The device is the highest item in the sidebar.
    • Apple gives the device as the last item in the order.
    10m

Read the result

Estimated 21 min to 1 hr 12 min

Remaining life of your disk
Unverified — do not rely on this value
CONSULT THE DISK MANUFACTURER. APPLE PUBLISHES NO LIFE VALUE FOR A MAC DISK.

No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.

  1. Read the report from First Aid.
    • Select Show Details for more information about the repair.
    • Write the exact text of the report on paper.
    2m
  2. If the report shows no fault, stop the repair.
    • A repaired disk gives the same report.
    <1m
  3. Quit Disk Utility.
    <1m
  4. If macOS Recovery is on the screen, select the Apple menu.
    • A Mac in macOS Recovery shows a window of utilities.
    <1m
  5. Select Restart.
    • Your Mac then starts in the usual mode.
    2m
  6. If the report shows a fault that First Aid did not repair, do the First Aid steps a second time.
    • Apple gives a second attempt before any other action.
    15m
  7. If the second attempt also fails, read the professional boundary below.
    • Do not erase the disk before you read that section.
    1m

Terminology

This page uses one term for each item and holds it throughout, as ASD-STE100 requires. Equipment sellers and other guides use the names below for the same parts.

First Aid
Also called: disk utility first aid, repair disk, verify disk, mac disk repair, fix disk errors mac, run first aid on mac
Disk Utility
Also called: disk utility app, mac disk tool, disk manager mac, apple disk utility
volume
Also called: partition, drive letter, macintosh hd, macintosh hd data, data volume
container
Also called: apfs container, container disk, container disk1, the grey one in the list
storage device
Also called: disk, drive, hard drive, ssd, the physical disk, apple ssd
macOS Recovery
Also called: recovery mode, recovery mode mac, command r, mac recovery partition, internet recovery
startup disk
Also called: boot drive, system disk, the main drive, internal drive, where macos lives

When to use a professional

Stop if Disk Utility reports that the disk is about to fail. Apple states that you cannot repair this disk. Make a backup of all data that you can read. Then speak to Apple Support or an Apple Authorized Service Provider about a replacement disk.

Stop if the disk does not show in the sidebar of Disk Utility. Apple gives this condition as a possible fault in your Mac or in the disk. Disconnect each device that you do not need. Then do the steps again. If the disk still does not show, speak to Apple Support.

Stop if First Aid fails a second time. The subsequent step in Apple's documentation erases the disk and removes all data on it. This page does not give that step. Speak to Apple Support first.

Stop if the report names an overlapped extent allocation. Two or more files hold the same space on the disk. This condition usually damages one of those files. Each affected file needs an individual decision. Speak to Apple Support.

Stop if the disk makes an unusual sound. A sound from a disk is a sign of a hardware fault. A repair with Disk Utility does not correct a hardware fault. Speak to Apple Support or the disk manufacturer.

Stop if you do not have a backup. Every step on this page needs one first.

This page does not give the steps for three operations. These are an erase of a disk, a new macOS installation, and a restore from a backup.

Common questions

Do I really have to back up first? It's just a disk check.

Yes, and Apple says so too — its first instruction is to make sure you have a current backup before you begin. The reason is not paranoia about the software. First Aid is a read-and-write workload across the whole directory structure, and that is precisely what a mechanically failing drive handles worst. A drive limping along well enough to boot can stop responding partway through a repair, and at that point there is nothing left to back up. The backup is also the fallback if First Aid finds damage it cannot fix.

What's the difference between a volume, a container and a device?

Three layers of the same disk. The device is the physical hardware — what Apple lists as something like APPLE SSD. Inside it sits a container, the APFS structure that manages space. Inside the container sit the volumes, which are what you see in the Finder: on a modern startup disk, usually Macintosh HD and Macintosh HD - Data. First Aid checks each separately and finds different classes of error at each level, which is why running it once on the device is not the same as running it properly.

Why bottom-up? Why not just select the disk and run it once?

Because that is the order Apple documents, and it is the order that lets a lower-level fix happen before a higher-level check depends on it. Apple's instruction is to start by selecting the last volume on the device, run First Aid, then select the next item above it and run it again — working up through every volume, then every container, then finally the device itself. Selecting the device and running it once is the single most common way people convince themselves a disk is healthy when it has not actually been checked.

Why do I need Recovery mode for my main drive but not for an external one?

Because macOS cannot fully repair a disk it is currently running from — the files are in use. For an external disk you can open Disk Utility from the Utilities folder inside Applications and go straight to First Aid. For the startup disk, Apple's instruction is to restart into macOS Recovery first and run Disk Utility from there. Getting into Recovery is the other place Apple silicon and Intel machines diverge: power button and Options on Apple silicon, Command-R on Intel.

First Aid says 'overlapped extent allocation'. What is that?

It means two or more files have been recorded as occupying the same space on the disk, so at least one of them is very likely corrupted. Apple's guidance is that you have to go through the affected files individually — most of them will have aliases in a DamagedFiles folder at the top level of the disk. For each one, if you can replace or recreate the file, delete it; if it holds something you need, open it and check whether the contents are actually intact. This is a per-file judgement call, not something a checklist can decide for you, which is why this page routes it to the boundary.

First Aid failed. Should I just erase the disk?

Not yet, and not on the strength of one failed run. Apple's own sequence is to try the repair again first. If it fails again, Apple's next documented step is to back up what you can, erase and reformat the disk, reinstall macOS, and restore — which permanently destroys everything on the disk. This page deliberately stops before that instruction. Talk to Apple Support first: a repeated First Aid failure is also a sign of a physically failing disk, and erasing a dying disk does not fix it.

Does First Aid find everything that could be wrong with my disk?

No, and Apple says so plainly: Disk Utility 'can't detect or repair all problems that a disk may have'. It is a check of formatting and directory structure. It does not test the physical health of the drive in any depth, it does not recover deleted files, and it cannot do anything about a drive with failing hardware except tell you, sometimes, that it is about to fail. If your disk is making noise, disappearing from the desktop, or getting dramatically slower, First Aid is not the tool that will diagnose that.

The First Aid button is greyed out. What now?

Skip that item and move on to the next one in the list. Apple's instruction is explicit about this: if the button is dimmed and you cannot click it, skip that step for whichever disk, container or volume you had selected. It is not a fault and it is not something to work around. Some items in the sidebar simply do not accept a First Aid run, and the ones that do are the ones that matter.

How long does First Aid take?

There is no published figure, and anyone who gives you one is guessing. It depends on how large the volume is, how many files are on it, and — importantly — what condition the disk is in, because a drive that has to retry reads will take dramatically longer than a healthy one. A small, healthy volume can be done in a couple of minutes. A large or struggling one can run for a long time. What matters more than the duration is that you do not interrupt it: leave the Mac alone and do not disconnect the disk while it runs.

Sources

Every specification on this page is traced to one of these sources. Tier 1 is a manufacturer document, a published standard, or a government safety authority. See Standards for the full tiering rule.

  1. Tier 1How to repair a Mac storage device with Disk UtilityApple Inc. · accessed 2026-07-29 · re-verification due 2027-01-25
  2. Tier 1Repair a storage device in Disk Utility on MacApple Inc. — Disk Utility User Guide for macOS Tahoe · accessed 2026-07-29 · re-verification due 2027-01-25
  3. Tier 1How to start up from macOS RecoveryApple Inc. · accessed 2026-07-29 · re-verification due 2027-01-25
  4. Tier 1Mac computers with Apple siliconApple Inc. · accessed 2026-07-29 · re-verification due 2027-01-25

Revision history

Current version 1 · updated 2026-07-29 · next review due 2027-07-29

  1. v1 · 2026-07-29First draft. Built from Apple's own documentation, opened by direct HTTPS fetch on 2026-07-29: the support article 'How to repair a Mac storage device with Disk Utility' (Apple Published Date 08 December 2025), the Disk Utility User Guide topic 'Repair a storage device in Disk Utility on Mac', 'How to start up from macOS Recovery' and 'Mac computers with Apple silicon'. The two Apple accounts of the repair order agree — each volume, then each container, then the storage device — so there is no conflict to publish and no conflict_note on this record. That is worth recording explicitly, because the order is widely stated the other way round in circulation, and the briefing note for this record also had it reversed; both Apple documents were read specifically to settle it, and Apple's numbered steps run volumes before containers in both. The page branches on processor family before any instruction because reaching macOS Recovery, like reaching safe mode, uses a different key sequence on each. Erasing a disk and reinstalling macOS are named in the professional boundary and deliberately not instructed: both destroy data, and a repeated First Aid failure is also a symptom of a physically failing disk that an erase does not repair. The procedure was verified against Apple's documentation, not executed on a Mac, and this record says so rather than claiming a test result. The four verified specifications carry spec_key null: this record was drafted concurrently with others and the drafting session was not permitted to write data/specs.json, so the registry entries must be added when the record is merged. Each value traces to the Apple source named on it.

Corrections to this page are listed in the public corrections log. Reports that are credible and not yet verified are listed in the public errata register, and an open one renders above the step it concerns.

Comments and corrections

Found an error? A correction with a manufacturer source is applied and logged publicly. You can also write to corrections@fixchecklist.com.

Every step above carries its own report control, which tags the report with that step so a correction reaches the right place. For anything about the procedure as a whole — the order of the sections, a step that is missing, something that did not match your equipment — use this: report something about this whole procedure.

The comment system is not connected yet. Comments are stored in GitHub Discussions through Giscus, outside this site, so that a redeploy cannot destroy them.