Disk Utility can check and repair certain formatting and directory problems. It cannot establish that every file is intact or repair every kind of storage failure. Prepare the data and identify the device before using First Aid as a controlled check.

Apple recommends a current backup first. If important files exist only on a disk that is unstable or inaccessible, stop and decide how to preserve them before attempting changes. The absence of a backup is not a reason to move directly to Erase.

Show the complete device hierarchy

For the startup disk, Apple directs users to Disk Utility in macOS Recovery. Other disks can be checked from Disk Utility in Applications, Utilities. In either case, choose View, Show All Devices so volumes, volume groups, containers and the device are visible. Expand a volume group’s arrow if needed to reveal its volumes.

Identify the intended disk by its name, connection and capacity. Apple’s sequence starts with the last volume listed for that device, runs First Aid, and works upward through each volume and volume group. Then check each container and finally the device itself. If First Aid is dimmed for an item, skip that item as Apple instructs.

Read each result before continuing. Keep the exact message and the name of the item checked, especially if one layer passes while another reports an error. “First Aid failed” without the affected volume or container loses useful context.

Separate a check from recovery acceptance

If First Aid reports an issue it cannot repair, preserve the result and the current data situation. Apple’s broader troubleshooting may lead to erasing and restoring, but that requires a deliberate recovery plan and verified source of the needed files. It is not the next automatic click in this procedure.

If the check completes successfully, return to the original task and test it. Open representative files from the disk and confirm that the symptom has actually changed. A clean structural check alone does not prove a disconnected cable, application error or failing device has been resolved.

Keep the backup until both file access and the real workflow are accepted. Record the check date and result so a recurring problem can be compared with earlier evidence instead of repeating repairs without a history.

References: Apple: repair a Mac disk, Apple: First Aid limits.