“First Aid process has failed” means Disk Utility could not complete or confirm repair of the selected volume, APFS container, partition, or physical storage device. On macOS Tahoe 26 and other currently supported macOS versions, the safest first action is to back up as much important data as possible if the disk is still mountable. Then retry First Aid once in Apple’s required order; use macOS Recovery instead if the affected device is the startup disk.

What “First Aid process has failed” means

Apple treats this message as a repair failure rather than a standalone numeric error code. Equivalent reports can include “First Aid process failed,” “Disk Utility can’t repair this disk,” or “The volume could not be repaired.” Output such as File system check exit code is 8 can accompany the failure, but it should be treated as secondary diagnostic information rather than a separate confirmed cause.

The failure can indicate filesystem or directory errors that First Aid could not repair. It does not prove that every affected disk has physical damage. However, if Disk Utility reports that the disk is about to fail, Apple says it cannot be repaired; back it up immediately if readable and replace it or seek service.

Back up first: If the disk remains mountable and readable, copy as much important data as possible before another repair attempt. First Aid cannot detect or repair every disk problem.

If the original symptom was a Finder file copy, move, read, or write failure with code -36 rather than this Disk Utility report, use the separate guide to Finder error code -36.

Retry First Aid once in the correct order

When this applies: Use this least-invasive path after the first failure when the disk is still visible in Disk Utility. Back up first if it is mountable.

Prerequisites: Open Disk Utility and enable Show All Devices. If Disk Utility prompts you to unlock a locked volume, use the administrator password. Do not add Terminal or undocumented FileVault procedures.

  1. Run First Aid on the last volume shown for the affected device.
  2. Run First Aid on each next volume above it.
  3. Run First Aid on each APFS container.
  4. Finally, run First Aid on the physical device.

This volume-to-device sequence follows Apple’s Disk Utility repair instructions. If the attempt succeeds, Disk Utility should complete its check and report the result. If it fails again, stop repeating First Aid and move to the applicable startup-disk, missing-device, replacement, or erase path below.

Risk and rollback: This is a low-risk, non-destructive check with no rollback step. It should still follow a backup whenever the data is accessible because repair is not guaranteed.

Repair a startup disk from macOS Recovery

When this applies: Use macOS Recovery when the affected storage is the startup disk or the Mac does not finish starting. External hard drives, SSDs, USB drives, and SD cards that remain visible use the normal Disk Utility path instead.

Prerequisites: macOS Recovery must be available. Apple silicon and Intel-based Macs use different Recovery startup methods, so follow Apple’s current instructions to start up from macOS Recovery for the architecture of your Mac.

  1. Start the Mac in macOS Recovery using Apple’s instructions for either an Apple silicon or Intel-based Mac.
  2. Open Disk Utility from the Recovery utilities window.
  3. Run First Aid on the startup volume and data volume.
  4. Continue upward through the APFS containers and then the physical device if needed.
  5. After finishing, restart from the Apple menu.

Expected result: Disk Utility checks the startup storage while macOS is running from Recovery and reports whether the repair completed. If First Aid still fails, do not keep repeating it.

Risk and rollback: The confirmed First Aid path is low risk and has no repair rollback. If the startup volume is locked and Disk Utility requests an administrator password, provide only that password; no unsupported unlock commands are part of this procedure.

What to do with an external, missing, or failing disk

If an external device remains visible

For a visible external hard drive, SSD, USB drive, or SD card, back up accessible data and use the normal hierarchy: last volume, other volumes above it, APFS containers, then the physical device. Stop after one correctly ordered retry if First Aid continues to fail.

If the disk will not mount or does not appear

If a disk will not mount but still appears in Disk Utility, one correctly ordered First Aid retry remains the confirmed repair path. If it does not appear in Disk Utility, use this detection and service path instead.

  1. Shut down the Mac.
  2. Disconnect non-essential devices.
  3. Retry detection.
  4. For external storage, check its cable, connection, and power.
  5. If the device still does not appear, seek service.

Expected result: The device may become visible for assessment. If it remains missing, Apple indicates that service may be needed; do not assume it is a software-only problem.

Risk and rollback: These checks are medium risk because a missing device can indicate a hardware or service issue, although the checks themselves do not erase data. There is no rollback step.

If Disk Utility says the disk is about to fail

  1. Stop relying on the disk for important data.
  2. Back up immediately if it is still readable.
  3. Replace an external device, or seek Apple service for internal storage.

Apple’s warning and replacement guidance are documented in Apple’s Disk Utility guide. Replacement is also appropriate for physically damaged external storage. Do not try to solve an “about to fail” warning through repeated First Aid runs or by erasing the device.

Expected result: Important data is moved away from storage that can no longer be trusted. Replacement has no repair rollback; recovery depends on any backup that was successfully created.

When to erase and reformat the disk

When this applies: Consider erasing only when First Aid still fails after one correctly ordered retry, the disk is not reported as about to fail, and it remains accessible enough to back up as much data as possible. For a failing or physically damaged disk, use replacement or service instead.

Permanent data-deletion warning: Erasing or reformatting permanently deletes data on the selected storage device. Confirm that you have selected the intended device and have a usable backup before proceeding. Erase is not reversible.

Prerequisites: Back up as much accessible data as possible and accept that anything not included in the backup may be lost.

  1. Back up as much data as possible.
  2. Erase or reformat the disk in Disk Utility.
  3. If it is the startup disk, reinstall macOS.
  4. Restore the backed-up data.

Expected result: The device receives a newly formatted filesystem; a startup disk also requires macOS to be reinstalled before backed-up data is restored. This may address a filesystem problem, but it cannot repair storage that Apple reports as about to fail.

Risk and rollback: This is a high-risk, destructive path. The only rollback is restoring available data from a backup after erase and, for startup storage, after reinstalling macOS.