HOW TO Check a drive’s health with Disk Utility

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LAUNCH DISK UTILITY Like Activity Monitor, the Disk Utility app can be found in Applications/Utilities, but it’s easiest to open it via Spotlight (CmdSpace Bar). It opens showing you all the drives inside or attached to your Mac on the left.

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VOLUMES AND DEVICES By default, Disk Utility shows “volumes”, partitions within drives that are visible to macOS. To see which drives they’re on, choose Show All Devices from the View menu (or press Cmd-2; Cmd-1 shows volumes).

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STARTUP DRIVE You can select any drive or volume, but if it’s the one where macOS lives, Erase, Restore and Unmount are greyed out. You can run First Aid to check the drive, but repairs may need Recovery mode.

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FIRST AID When you run First Aid on any other drive, it’ll automatically repair any minor issues it finds, having asked you to confirm the action before it starts. It’ll also let you know if any problems are found that it can’t fix.

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DISK PERMISSIONS Until OS X 10.10 Yosemite, Disk Utility had an option to verify permissions. These were often responsible for glitchy behavior like settings being ignored or apps failing to run, but are no longer an issue now.

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RESTORE Select an empty drive and use Restore to duplicate the contents of a chosen drive. Try this for a drive that has unrepairable problems, then erase it; this may fix it. Again, for a startup volume, use Recovery.