How to Repair a Disk in macOS

Macs are generally low-drama machines… until your disk decides to audition for a soap opera. Maybe your Mac is booting slower than a Monday morning, apps are crashing like dominoes, or Finder is giving you the spinning beach ball that says, “I need a minute (and perhaps a therapist).”

The good news: macOS ships with real disk-repair tools that can fix many common file system problems. The better news: you don’t need to be a wizardjust a careful human with a backup and a little patience.

This guide walks you through repairing disks the “Mac way,” from quick checks in Disk Utility to deeper repairs in macOS Recovery, plus safe command-line options if you want extra control. We’ll also cover what to do when repairs failbecause sometimes the best repair is a strategic retreat (and a restore).

Before You Touch Anything: What “Repair a Disk” Actually Means

When people say “my disk is broken,” they usually mean one of two things:

• File system damage (common): The disk hardware is fine, but the “table of contents” that tracks files got scrambledoften after a crash, sudden power loss, forced restart, or unplugging an external drive mid-write.
• Hardware trouble (less fun): The drive itself is failing. Software can’t truly “repair” failing hardwareat best, it buys you time to copy data off before things get worse.

Disk Utility’s First Aid focuses on file system and directory structure issues. If the drive is physically failing, First Aid might warn you or repeatedly failthink of it as your Mac saying, “This is above my pay grade.”

Step 1: Do the One Thing Everyone Skips (Until It’s Too Late)

Make a current backup

If your Mac is still usable, back up now. Repairs can go perfectly… or they can reveal corruption that forces you into erase-and-restore territory. Your future self will thank you.

• Time Machine (easy, built-in): Great for full-system restores and “oops” moments.
• Manual copy to an external drive: Fast for critical folders (Desktop, Documents, Photos library, etc.).
• Cloud sync (iCloud Drive, Dropbox, etc.): Good, but don’t assume every file is fully synceddouble-check.

Step 2: Repair a Disk Using Disk Utility (Normal Boot)

If your Mac boots normally, start here. This is the least disruptive path.

Open Disk Utility

1. Open Finder → Applications → Utilities → Disk Utility (or use Spotlight: Command + Space, type “Disk Utility”).
2. In Disk Utility, choose View → Show All Devices. This matters more than people realize.

Pick the right thing to repair (the “start from the bottom” rule)

Disks often have a hierarchy:

• Physical disk (top level)
• Container (common on APFS)
• Volumes (your actual “Macintosh HD,” “Data,” external volumes, etc.)

In general, you want to run First Aid in an order that avoids stepping on your own feet. A practical approach is to start with the last volume in the list for that disk (often a “- Data” volume), then move upward through volumes, then the container, then the physical disk.

Run First Aid

1. Select the volume you want to check.
2. Click First Aid in the toolbar.
3. Click Run (and Continue if prompted).
4. When finished, read the summary. If there’s a “Show Details” option, use itit’s where the interesting clues live.

Heads-up: If you run First Aid on your startup volume while you’re booted normally, macOS may temporarily lock the volume. Apps can become unresponsive during the check. That’s expectedtry not to panic-click everything like it’s an elevator button.

If First Aid is grayed out

If “Run” is dimmed or unavailable, it usually means the selected item can’t be checked in the current state (often because it’s in use). That’s your cue to move to macOS Recovery, where the startup disk can be repaired while it’s not actively running the operating system.

Step 3: Repair a Disk in macOS Recovery (Recommended for Startup Disks)

macOS Recovery is the repair shop where your startup disk can be inspected without macOS actively living on it at the same time. If you’re repairing the internal disk, Recovery is often the best place to do it.

Boot into macOS Recovery

Apple silicon (M-series) Macs:

1. Shut down your Mac completely.
2. Press and hold the power button until you see Loading startup options.
3. Click Options, then Continue.

Intel Macs:

1. Restart your Mac.
2. Immediately hold Command (⌘) + R until you see the Apple logo or a spinning globe.

Run First Aid the right way in Recovery

1. Select Disk Utility from the Recovery utilities window, then click Continue.
2. In Disk Utility, choose View → Show All Devices.
3. In the sidebar, expand the internal disk and identify volumes/containers.
4. Run First Aid starting with the last volume, then move upward through volumes, then the container, then the physical disk.

If First Aid reports the disk is OK or repaired, restart normally and see if your symptoms disappear. If problems persist, keep readingsome issues are more “stubborn toddler” than “minor paperwork error.”

Step 4: Check for Hardware Trouble (SMART Status and Other Clues)

If First Aid keeps failing, the disk may be physically unhealthy. One clue you can check is SMART status (where supported). In Disk Utility, select the physical disk and look for SMART status in the info panel.

Common signs the disk is failing

• SMART status shows Failing (or similar warnings).
• You see frequent I/O errors, repeated “could not be repaired,” or the drive disconnects under light use.
• Your Mac freezes when accessing certain folders or files (especially repeatedly).
• The disk disappears and reappears (external drives) even with good cables.

Reality check: If the drive is about to fail, software repair won’t “fix” it. Your priority becomes back up immediately, then replace the drive (or get service).

Step 5: When First Aid Can’t Repair the Disk

If Disk Utility says it found errors it can’t repair, you’re typically looking at one of these paths:

• Try again in Recovery (if you weren’t already).
• Run First Aid in the correct order (volumes → container → disk).
• Erase (format) the disk and restore from backup.
• Reinstall macOS (often after repairs or an erase).
• Escalate to professional recovery if the data is irreplaceable and the drive won’t cooperate.

Erase and restore (the “clean slate” fix)

If you have a solid backup and repairs won’t stick, erasing the disk and restoring is often the most reliable long-term solution. The basic flow looks like this:

1. Boot into macOS Recovery.
2. Open Disk Utility and select the correct disk/volume.
3. Use Erase (choose APFS for most modern Macs; use exFAT if you need cross-platform compatibility for external drives).
4. Quit Disk Utility and choose Reinstall macOS (or restore from Time Machine if you prefer).

Important: Erase means erase. Make sure you’re selecting the right diskyour goal is “repaired Mac,” not “accidental minimalist lifestyle.”

Step 6: Command-Line Disk Repair (For People Who Like Levers and Labels)

Disk Utility is the friendly front desk. Terminal is the workshop in the back with power tools. You can verify and repair volumes using built-in command-line utilities, which can be especially helpful when you want more visibility or Disk Utility feels stuck.

Find your disks

Open Terminal and run:

This displays disks and partitions (for example: /dev/disk0, /dev/disk1s2, etc.). Make a note of the identifier for the volume you want to check.

Verify and repair with diskutil

To verify a volume:

To repair a volume:

For the startup volume, you’ll usually want to do this from Recovery → Utilities → Terminal, because repairing the boot volume while it’s actively in use is often limited (or blocked).

Using fsck (file system consistency check)

fsck is the underlying “check and repair” tool family. The exact variant depends on the file system (APFS vs. older formats). A common general command you may see referenced is:

The -f flag forces a check, and -y automatically answers “yes” to repair prompts. This can be useful in certain Recovery/maintenance scenarios, but it’s not a magic spell. If the drive is failing or corruption is severe, fsck may not succeedand repeated repair attempts can sometimes worsen the situation on unstable hardware.

Rule of thumb: If you’re unsure, stick with Disk Utility in Recovery first. Terminal repairs are best when you know what disk you’re targeting and you’re working from a safe environment (Recovery, external boot disk, etc.).

Step 7: External Drives That Won’t Mount (But Appear in Disk Utility)

External drives love to play hide-and-seek. If the disk appears in Disk Utility but not Finder, try this sequence:

1. Check the basics: different cable, different port, avoid unpowered hubs, confirm the drive has enough power.
2. In Disk Utility, choose View → Show All Devices.
3. Select the volume and try Mount (if available), then run First Aid.
4. If it still won’t mount, try Recovery mode (especially if it’s a Time Machine or system-related disk).
5. If Disk Utility can’t repair it, consider copying data off with whatever access you can get, then erase and reformat.

If the disk contains critical data and is clicking, stalling, or repeatedly disconnecting, stop “repairing” and start “preserving.” The best move may be professional recovery.

Step 8: If Your Mac Won’t Boot at All

If your Mac won’t boot, disk corruption is one possibilitybut not the only one. Your quick triage plan:

• Boot into macOS Recovery.
• Run Disk Utility → First Aid on the startup disk (bottom-up order).
• If it can’t be repaired, consider reinstalling macOS (often preserves user data, depending on the situation).
• If the installer can’t see the disk, use Disk Utility to erase it (then restore from backup).

Use Apple Diagnostics (when hardware is suspicious)

If you suspect hardwarerandom shutdowns, repeated failures, weird artifactsrun Apple Diagnostics. It can help identify failing components so you’re not chasing file system ghosts when the issue is physical.

Quick Troubleshooting Checklist (Because We All Love a Good Checklist)

• ✅ Back up your data first.
• ✅ Disk Utility → View → Show All Devices.
• ✅ Run First Aid in the right order (volumes → container → disk).
• ✅ For startup disk issues, run First Aid from macOS Recovery.
• ✅ If repairs fail, plan for erase + restore (or reinstall macOS).
• ✅ If SMART says failing (or symptoms scream hardware), replace the drive or seek service.

Real-World “Been There” Experiences (500+ Words of What Usually Happens)

Here’s the part nobody tells you when they say “just run First Aid”: disk repair is less like flipping a switch and more like doing laundryeasy on paper, occasionally chaotic in practice, and somehow there’s always one sock missing (the sock is your corrupted file).

Experience #1: “First Aid finished… but my Mac still feels cursed.”

One of the most common outcomes is that Disk Utility reports “OK” or “repaired,” yet your Mac still behaves oddlyslow logins, Finder weirdness, apps crashing. In many cases, the disk wasn’t the whole story. The “repair” fixed directory issues, but you’re still dealing with side effects: a flaky external drive, a problematic login item, low free storage, or a macOS install that’s been upgraded over itself for years like geological layers.

What usually helps here is a clean follow-up routine: restart normally after Recovery repairs, check available storage, update macOS, andif problems persistreinstall macOS over the top (the reinstall path often preserves your data). If the system becomes stable afterward, the disk repair did its job; the OS just needed a refresh.

Experience #2: “First Aid froze, so I assumed everything was ruined.”

First Aid can look “stuck,” especially on large drives or drives with lots of small files. People often kill it too quickly because the UI doesn’t provide the world’s most soothing progress updates. In a lot of cases, waiting it out (and not running other heavy tasks) is the right move. If it truly hangs for an excessive period, running First Aid again from macOS Recovery tends to be more reliablebecause the disk isn’t juggling active system reads/writes at the same time.

Another “in the trenches” trick: run repairs in the correct order. Many failures are not “Disk Utility is useless,” but “Disk Utility is being asked to repair the parent before the child.” When you start at the last volume and move upward, you’re often giving the tool a clean runway.

Experience #3: “External drive won’t show in Finder, but Disk Utility sees it.”

This is the classic: you plug in your drive, Finder acts like it’s invisible, but Disk Utility lists itsometimes as a physical disk with an unmounted volume beneath it. The most frequent culprit is boring: cable/port/power. A surprising number of “corrupt” drives are actually “underpowered” drives, especially with bus-powered spinning disks on hubs.

What typically works: swap the cable, plug directly into the Mac, try another port, then attempt Mount and First Aid. If the volume mounts long enough to copy data, prioritize copying firstthen worry about erasing/reformatting later. If it disconnects repeatedly, stop trying to repair and focus on data recovery while you still can.

Experience #4: “Disk Utility says it can’t repair. Now what?”

When Disk Utility flat-out says it can’t repair the disk, people often try ten different apps or run increasingly spicy Terminal commands. Sometimes that works, but the most reliable solutionwhen you have a backupis still erase and restore. It’s not glamorous, but it’s effective.

The key mindset shift is this: a disk that repeatedly corrupts itself might be telling you something. If SMART warnings appear (or the drive behaves like a jumpy ghost), treat that as a hardware problem. Software can’t negotiate with failing silicon. Your best “repair” becomes getting your data off safely, replacing the drive, and moving on with your life (preferably with Time Machine running quietly in the background like a responsible adult).

Conclusion

Repairing a disk in macOS is usually straightforward: run Disk Utility First Aid, do it in the right order, and use macOS Recovery for startup disks. If repairs won’t hold, erase-and-restore is often the fastest route back to a stable Mac. And if hardware failure is involved, the priority shifts from “repair” to “rescue.”

Most importantly: keep backups current. Disk repair is way less stressful when your data isn’t trapped in a suspense thriller.