What is Disk Utility?
Disk Utility, an Apple's built-in disk management tool that can be accessed with or without your Mac booting up, can partition, erase, repair, and restore internal disks and external storage devices.
Where can you find Disk Utility?
If your Mac is functioning well, you can find it in the Other folder of your Launchpad. It looks like a disk going through a stethoscope.
If you Mac failed to boot up, or the options on the toolbar are dimmed, you need to first boot into Recovery Mode to find Disk Utility on the macOS Utilities window.
What does Disk Utility look like?
Before diving into its essential functions, let's go through the items listed on its interface. The position or icons may look slightly different on your Mac running a different operating system. The picture below shows a Disk Utility interface on macOS 11 Big Sur.
Click View > See All Devices, then all detected internal or external drives and disk images will be shown on the left sidebar, beginning with the startup disk. Beneath it is the APFS container if you are running macOS 10.13 or later and two volumes - Macintosh HD for system files and Macintosh HD - Data for user data.
Take a look at the top-right of the menu. Five tools you can perform on the shown disks or volumes are listed horizontally at the right top. They allow you to add or delete volumes, check errors using First Aid, partition, erase, restore and unmount a disk or a volume.
What are the seven primary functions of Disk Utility?
This section will elaborate on the seven essential functions Disk Utility offers you and what problems they can solve.
The first tool you can see is a Volume option with add (+) and delete (-) buttons. By selecting an APFS disk from the left sidebar and click the Add Volume and Delete Volume buttons, you can create or delete an APFS volume under its container with ease.
As stated in Apple's User Guide, For Mac OS High Sierra and later, adding volumes is a faster and simpler choice than partitioning a disk. Due to the flexible space management of APFS, a container can have multiple volumes that share free space. You can also reserve size to ensure the amount of storage will always be available for the volume.
Note: You can't delete a startup volume that contains system files. Back up your disk to avoid data loss before deleting an APFS volume.
By partitioning, your physical drive will be split into multiple logical drives, which allow independent usage. After clicking on the "Partition" button, you will be brought to a window with a pie chart. Users can use the Add or Delete button beneath the pie chart to adjust the number of partitions and partition size.
You need to give the disk a name and a format and confirm by clicking "Apply".
Note: Back up data before deleting any partitions.
Common scenarios in which you need to format a disk:
- Selling your Mac
- Preparing an external drive for backups
- Reformatting a drive that is incompatible with your operating system
- Cleaning up all files to have a refreshed device
If you want to wipe your external hard disk drives securely, the Security Options, which can be seen after clicking the Erase button, allows you to select how thoroughly you want to erase the data. The Fastest mode removes only the header information, which can be quickly recovered using Mac data recovery software. You can move the slider to the Most Secure mode to ensure a complete erasure so that nobody can access your data.
One thing to be aware of is that you need to choose the format based on how you intend to use the formatted drive. Read this guide to know how to format an external hard drive on Mac step by step.
Checking and Repairing Disks Using First Aid
If your hard drive is experiencing problems and would like to make a diagnosis, First Aid is at your disposal. It's a free tool built-in Mac OS, which can check and repair directory damages. However, it's common to see reports that First Aid failed or need more operations. For example, "First Aid found corruption that needs to be repaired" is one of the most common errors you will see after running First Aid on the startup disk.
We recommend you run it more than once to ensure coherent results.
Mounting and Unmounting Disks
Disks appearing in the sidebar are already mounted, but sometimes you want to unmount a disk to avoid false information transferring. The option is often highlighted and can be found on the top right of the menu.
Creating Disk Images
Disk image copies the data and structure of a disk, which could be beneficial for copying a system to different computers, go back to a previous configuration, and backup the system. It is available through File at the top left menu bar > New Image > choose from Blank Image, Image from Floder, or Image from "disk name".
Disk Utility can be employed to restore a disk from another disk. You should back up data on the receiving end because this function will erase all the data on it.