Disk Utility

3. Click "First Aid" in the toolbar.

4. Click "Run" and wait. This will check the files and the filesystem of the disk partition you selected.

5. Click one layer up from the broken disk in the sidebar (i.e. the physical disk). For example, for "Macintosh HD", I click on "APPLE SSD SM0512F Media".

6. Click on "First Aid" again. Click "Run". This will check the disk for physical errors. It should take less time than the previous check, especially for an SSD.

7. When complete, click "Done". Your disk has been repaired.