Mac Disk Utility Guide for Managing Drives
A Mac that will not start, an external drive that suddenly disappears, or a warning that your disk is almost full can make storage feel far more complicated than it needs to be. This Mac Disk Utility guide walks you through the built-in app Apple provides for checking, repairing, erasing, and organizing drives – with clear boundaries around what each tool can and cannot fix.
Disk Utility is powerful, but it is not an everyday cleanup app. Use it when you need to understand your Mac’s storage structure, prepare a new external drive, check a drive for errors, or solve a specific disk-related problem. Before changing or erasing anything, make sure important files are backed up.
Where to Find Disk Utility on Your Mac
Open Disk Utility from the Applications folder: open Finder, choose Applications, open the Utilities folder, and double-click Disk Utility. You can also press Command-Space to open Spotlight, type “Disk Utility,” and press Return.
If your Mac cannot start normally, you can open Disk Utility from macOS Recovery. On an Apple silicon Mac, shut down your Mac, then press and hold the power button until you see startup options. Select Options, then Continue. On an Intel-based Mac, restart and immediately hold Command-R. In Recovery, select Disk Utility from the utilities window.
Recovery is especially useful when you need to run repairs on your Mac’s startup disk. Your Mac cannot fully repair a disk that is actively being used to run macOS, so Recovery gives Disk Utility a safer working environment.
Understand What You See Before Making Changes
At first glance, Disk Utility’s sidebar can seem overly detailed. The key is knowing that a physical drive and the storage areas inside it are not the same thing.
Choose View > Show All Devices in the menu bar. This reveals the full hierarchy. At the top level, you may see a physical internal SSD or an external hard drive. Beneath it, you may see a container, then one or more volumes.
Most modern Macs use APFS, Apple’s file system. With APFS, several volumes can share the available space inside one container. You may see names such as Macintosh HD and Macintosh HD – Data. This is normal. The system volume holds macOS, while the Data volume holds your personal files, apps, and many settings.
This structure matters because the item you select determines what an action affects. Selecting a volume may erase only that volume. Selecting the top-level physical drive can erase everything on that drive, including all containers and volumes. Take a moment to read the selected item’s name and indentation level before choosing Erase or Partition.
Use First Aid to Check and Repair a Drive
First Aid is Disk Utility’s repair tool. It checks a disk’s file system and attempts to correct certain directory and formatting problems. It can help when a drive will not mount, files behave strangely, or your Mac reports disk errors.
For the most complete check, run First Aid from the bottom of the sidebar upward. Start with each volume, then the container, then the physical disk. Select an item, click First Aid, and choose Run. Wait for the process to finish before moving to the next item.
On an external drive, you can often do this while macOS is running. For your internal startup disk, use macOS Recovery when possible. If First Aid reports that a disk appears to be OK, that is reassuring, but it does not prove the drive has no hardware issue. Intermittent failures, slow performance, and repeated disconnections can still point to a failing cable, enclosure, or drive.
If First Aid cannot repair an external drive, copy off any accessible files immediately. You may need to erase and reformat the drive afterward. If First Aid cannot repair your Mac’s internal drive, do not keep relying on it for important work without a current backup. That is the point to consider Apple Support or a qualified repair provider.
Erase a Drive Safely
Erasing removes data. It is useful when you are preparing a new external drive, selling a Mac, repurposing a storage device, or resolving a file system problem after your files are safely backed up.
Select the item you intend to erase and click Erase. Disk Utility asks for a name, format, and sometimes a scheme. These choices should match how you plan to use the drive.
For a drive used only with current Macs, choose APFS. It is the best fit for SSDs and works well with modern versions of macOS. For a drive you need to use with both Macs and Windows PCs, choose exFAT. It supports large files and is broadly compatible, though it does not offer all the reliability features of APFS. Mac OS Extended (Journaled) is generally for older Macs or workflows that specifically require it.
When erasing a physical external drive, use GUID Partition Map as the scheme in most Mac-focused situations. If you are making a Windows-compatible drive, the right scheme may depend on the computers and devices that will use it.
Be especially cautious with an internal Mac drive. Erasing your startup disk removes macOS and your files. If you are selling or giving away your Mac, Apple’s Erase All Content and Settings feature is usually the simpler option on supported Macs. Disk Utility is most useful for deeper troubleshooting or when Recovery instructions specifically call for it.
Create a Volume or Partition
Disk Utility lets you divide storage in two different ways: volumes and partitions. They are not interchangeable.
An APFS volume shares free space with other volumes in the same APFS container. This is often the flexible choice when you want a separate area for files, a test installation, or a project without permanently assigning a fixed amount of storage. Select the APFS container, click the Add Volume button, name the volume, and choose a format. You can optionally set a size reserve or quota, but most people can leave these settings alone.
A partition divides a physical drive into separate, fixed sections. Each partition can use a different format, which is useful if one external drive needs a Mac-only APFS section and a Windows-compatible exFAT section. The trade-off is less flexibility. Space assigned to one partition is not automatically available to another.
For a simple external backup drive, avoid creating extra volumes or partitions unless you have a clear reason. A single correctly formatted drive is easier to manage and less likely to create confusion later.
Mount, Unmount, and Eject External Storage
When you connect an external drive, it usually mounts automatically and appears in Finder. If it appears in Disk Utility but not Finder, select its volume and click Mount. A volume may fail to mount because of a file system issue, a damaged cable, insufficient power, or a hardware problem.
Use Unmount when you need to temporarily disconnect a volume from macOS without unplugging the drive. Use Eject before physically disconnecting an external drive. This gives macOS time to finish pending writes and reduces the risk of damaged files.
If a drive repeatedly ejects itself, start with the simplest checks: try a different cable, a different port, and, if possible, another Mac. Portable hard drives and multiport hubs can be especially sensitive to power. Disk Utility can check the file system, but it cannot repair a worn cable or provide missing power.
Check Storage Without Erasing Anything
Disk Utility shows capacity, available space, format, and connection information, making it useful for a quick storage check. Select a volume to see its used and available space. Select a physical disk to see its total capacity and connection details.
For a clearer view of what is consuming space on your Mac, go to Apple menu > System Settings > General > Storage. This is usually the better place to identify large apps, old downloads, messages, or documents. Disk Utility tells you how storage is organized; the Storage settings help you decide what to remove.
Do not erase a volume simply because it looks unfamiliar. Modern macOS creates system-related volumes and recovery information that should remain in place. If you are unsure what an item is, stop and verify it before making a change.
When Disk Utility Is Not the Right Fix
Disk Utility is designed for drive structure and basic file system repair. It cannot recover every deleted file, remove malware, fix an app that crashes for unrelated reasons, or repair physical damage inside a failing drive.
A clicking hard drive, an SSD that is no longer detected, or a drive that disconnects during every file transfer needs more than First Aid. Prioritize your backup, minimize use of the drive, and seek help before the problem becomes worse. Repeatedly running repair tools on a failing device can consume the limited time you have to copy important files.
The best approach is deliberate rather than hurried: identify the disk, select the correct level in Disk Utility, and make sure a backup exists before changing anything. Once you understand those few habits, Disk Utility becomes less intimidating and far more useful whenever your Mac’s storage needs attention.
