I have often asked myself, if a disk or volume is corrupt. And, if so, would I be better off backing up files before or after running repair software. In other words, could the repair destroy a file that otherwise could have be copied. Therefore, I would like to separate the detection for corruption from the possible repair of corruption. Depending on the version of OS X/macOS, the Disk Utility may or may not offer this option.
The Disk Utility basically runs the command
diskutil repairdisk device, where the device is usually
disk followed by an positive integer. If you right click on a drive shown in the Disk Utility and select "Get Info", the device is the "BSD device node" shown in the popup.
Older versions of OS X/macOS allowed you to select a disk verification. This option was eliminated from the Disk Utility in the latest versions of macOS. However, you can still run disk verification by entering the command
diskutil verifydisk device in a Terminal application window. Again, you will need to replace device with the appropriate "BSD device node".
You can also apply the same to just a volume. You will need to replace
verifyvolume. Also the device will usually be
disk, an positive integer, the letter
s and finally another postive integer. For example,