Check a disk or volume for problems
You can use Disk Utility to check a disk for problems, then repair them using First Aid. While Disk Utility is checking your disk, your computer may become slower.
Note: Disk Utility can’t detect or repair all problems that a disk may have. Disks that can’t be repaired using Disk Utility may require service.
Choose View > Show All Devices.
Select a disk or volume in the sidebar, click the First Aid button , then click Run.
If you run First Aid on a disk, Disk Utility checks the partition maps on the disk and performs some additional checks, then checks each volume. If you run First Aid on a volume, Disk Utility verifies all the contents of only that volume.
If Disk Utility tells you the disk or volume is about to fail, back it up and replace it. You can’t repair it.
If Disk Utility reports that the disk appears to be OK, you’re done. Otherwise, you need to repair the disk.
When checking your disk for problems, you can also view the disk activity log by clicking Show Details in the First Aid window.