To check a disk for errors in macOS you can use the following tool -fsck (File system consistency check). To start fsck you need to switch to Single User Mode. It allows to modify shared user resources on this computer. Single User Mode does not run macOS, but just gives you access to Unix command line. To switch to Single User Mode: Power off your Mac; Turn it on; Immediately after the start signal, press and hold the key shortcut ⌘Cmd + S. You will see the command line soon. Type in fsck -fy to start the fsck process. Wait for fsck check to be over, and the system will report on its results.