macOS has a powerful built-in application called Disk Utility which is useful for performing (external and internal) disk-related tasks. Although Disk Utility appears to be mostly used by advanced Mac users, once you get the hang of it the handy tool will likely be able to save the day on numerous occasions.
Located in the Applications > Utilities folder next to other powerful tools such as Keychain Access and Console, Disk Utility can handle disk images or combine multiple hard disks into a RAID setup to act as a single disk. But most importantly is the fact that it’s the system’s built-in disk doctor, checking and repairing errors on your disk drives and volumes.
When it comes to data, organization is key, and Disk Utility can help you with that. For example, by dividing your external or startup disks into sections called partitions, you'll have each of the partitions mounted as individual volumes in Finder, giving you much more freedom in how your files are stored.
Getting Started With Disk Utility
When you launch Disk Utility it will display the available actions for that volume, which are: Add or Remove Volumes, First Aid, Partition, Erase, Restore, and Unmount. Not all of these actions will be available if you have only the startup disk mounted, however.
The utility can be used to verify and repair disks and volumes. So if you notice any performance problems with your Mac then you should follow two key steps to solving the problem. First consider using a Mac optimization app such as CleanMyMac to clean the built-in volume of any cache, junk data and unwanted files. If this doesn’t work then verify the startup disk via Disk Utility to ensure that the issue is a fault within the system and not the hardware itself.
The good news is that you don't even need to start the Mac up from another volume to do this, because Disk Utility has a neat feature called “Live Verification” that allows the software to check the drive for errors while in use by the operating system. However, if there are issues that need repairing, you will need to boot from a bootable drive and use Disk Utility to repair the disk.
How to Check the Status of a Disk Using First Aid
Disk Utility has a neat action called First Aid, which is used to check a disk volume for problems. This feature is highly useful as it will check the status of the disk and return error codes, which can then be used as the source for further research to figure out a solution to your disk-related issue.
That's if Disk Utility doesn't offer its services to repair the disk first. When you run First Aid, Disk Utility checks the partition maps on the disk and performs additional checks, then checks the volumes. If you run First Aid on a specific volume, Disk Utility verifies all the content of that volume only.
To check the disk for problems, do the following:
- Select the target disk or volume from the left sidebar.
- Click on the “First Aid” button located on the top line, and then hit “Run”.
- If Disk Utility says the disk or volume is about to fail, back up the data and replace it. Don't try to repair it, because it won't last, even if it's successful.
- If Disk Utility says the disk appears to be OK, then the process is complete.
How to Repair a Startup Disk Using Disk Utility and First Aid
Unfortunately, the possibility of having errors with the startup disk is always there, but Disk Utility can help you. If First Aid produced an error, you'll need to boot into Recovery Mode to repair the problems that Disk Utility has found. We wouldn't recommend trusting any third party app for this process.
- Restart in Recovery Mode by following our guide.
- When the Utilities window appears, select “Disk Utility” and then click “Continue”.
- Select the disk you want to repair from the sidebar.
- Click on the “First Aid” button and then “Run”.
- Possible Disk Utility errors that you may get:
- The “overlapped extent allocation” error means Disk Utility has found two or more files occupying the same space on your disk, and at least one of them is corrupted. To solve the problem, check each file in the list of affected files. Most of the files in the list have aliases in a folder called “DamagedFiles”. Delete the affected file or files, and run First Aid again.
- The “underlying task reported failure” error means you need to repair the disk or partition again. If you don't manage to do that, just back up the data and format the disk, reinstall macOS, and restore the backed-up data.
When it comes to external drives, it is also Disk Utility that you'll use to format the disk to the desired file system format available in the utility. If, for some reason, formatting the disk fails, running First Aid will provide guidance on its issue with the exit code it generates.
Using Mac Optimization Apps to Check the Status of the Startup Disk
While Mac optimization apps can't provide the advanced toolset that Disk Utility includes by default, they do have a few useful features to keep your startup disk in good shape. CleanMyMac's Maintenance section, for example, includes two key features – Repair Disk Permissions and Verify Startup Disk – which you'll need to run from time to time for the Mac to perform optimally. The repair disk permissions action is widely used among advanced Mac users because it seems to solve various file-related issues, while the second action will give you information about the health of your Mac's startup disk. Use them regularly and your system’s files should remain intact.
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