Disk Utility is the built-in macOS application for managing storage devices: it erases and formats disks, creates and deletes APFS volumes, partitions drives, checks and repairs file systems and creates disk images. In macOS storage & backup, it is the standard tool for preparing internal and external drives, and it is also available in macOS Recovery, where it repairs or erases the startup disk when the system itself cannot run.
Disk Utility is a graphical front end to the storage services that the diskutil and hdiutil command-line tools also use. It covers the everyday tasks safely, while some advanced operations remain available only in Terminal.
What Disk Utility does
Disk Utility performs five groups of storage tasks: erasing, partitioning, volume management, repair and imaging. Each group maps to a toolbar button or menu command, and each acts on the device, container or volume selected in the sidebar.
| Function | What it does | Typical use |
|---|---|---|
| Erase | Creates a new file system and partition scheme | Preparing a new external drive |
| Partition | Divides a physical disk into partitions | Adding a separate HFS+ or exFAT area |
| Add or delete volume | Creates APFS volumes inside a container | Separate volume for a beta macOS |
| First Aid | Verifies and repairs file system structures | Drive that will not mount or shows errors |
| Restore | Copies one volume or image onto another | Cloning a data volume to a new drive |
| Image creation | Builds DMG or sparse bundle files | Archiving or distributing folders |
The sidebar shows only volumes by default. Choosing View, then Show All Devices reveals the physical disks and APFS containers, and many erase and partition errors come from selecting a volume when the operation requires the whole device.
Disks, containers and volumes in Disk Utility
Disk Utility displays storage as a three-level hierarchy of physical disk, APFS container and APFS volume. Understanding which level is selected is essential, because the same Erase button has very different effects at each level.
An APFS container occupies one partition and shares its free space among all volumes inside it. Volumes do not have a fixed size unless a reserve or quota is set, so adding a volume does not require resizing anything. A startup disk on current macOS contains a sealed System volume, a Data volume, plus Preboot, Recovery and VM volumes that Disk Utility hides unless the full view is active.
| Selected item | What Erase removes | Result |
|---|---|---|
| Physical disk | Everything, including partition map | New scheme, one new volume |
| APFS container | All volumes in the container | Empty container with one volume |
| APFS volume | Only that volume’s contents | Other volumes stay intact |
| HFS+ or exFAT partition | That partition’s contents | Same size, new file system |
Choosing a format and scheme
The correct format depends on which computers will read the drive and what it stores. Disk Utility offers APFS variants, Mac OS Extended (HFS+), exFAT and MS-DOS (FAT), together with a partition scheme, normally the GUID Partition Map.
| Format | Best for | Limitation |
|---|---|---|
| APFS | SSDs and modern Macs | Not readable by Windows without extra software |
| APFS (Encrypted) | Portable drives with sensitive data | Password needed on every connection |
| Mac OS Extended (Journaled) | Older Macs and some hard disks | No snapshots or space sharing |
| exFAT | Exchange between Mac and Windows | No journaling, higher corruption risk |
| MS-DOS (FAT) | Small drives for cameras or firmware tools | Maximum file size of 4 GB |
The case-sensitive APFS variant should be chosen only when a specific application requires it, because some Mac software expects a case-insensitive file system. For Time Machine destinations, current macOS formats the drive as APFS automatically, and an existing HFS+ backup disk is kept as it is.
How First Aid repairs a disk
First Aid checks the consistency of file system metadata and repairs errors it can fix safely. It runs fsck_apfs or fsck_hfs in the background, verifying object maps, allocation records, snapshots and directory structures.
On the startup disk, First Aid runs in a live verification mode and can repair only a limited set of problems while macOS is running. Running it from macOS Recovery gives it exclusive access to the volume, which is why repairs of the startup disk are usually more successful there. The recommended order is volumes first, then the container, then the physical disk.
First Aid does not recover deleted files and cannot fix failing hardware. If it reports errors it cannot repair, or if the same errors return after every repair, the correct response is to back up immediately and plan to replace the drive.
Limits and common mistakes
The most consequential mistakes in Disk Utility involve erasing the wrong item or misreading what an operation will keep. Several advanced tasks also require Terminal.
- Missing devices in the sidebar usually mean the default volume-only view is active.
- Secure erase options are not offered for SSDs, because wear leveling makes overwriting unreliable; encryption plus erase is the effective method.
- APFS cannot be converted back to HFS+ in place; the drive must be erased.
- Resizing a container in use can fail if snapshots occupy the space being freed.
- Commands such as
diskutil apfs resizeContaineranddiskutil listoffer more control than the graphical app.
On Apple silicon Macs, erasing the internal startup disk from Recovery may also require reactivation with an Apple account before macOS can be reinstalled, so the account credentials should be available before starting.
Explained without jargon
Disk Utility is the Mac’s workshop for storage drives. It can wipe a drive clean, divide it into sections, check it for damage and copy one drive onto another.
The main thing to remember is that erasing really deletes everything on the item selected. Checking that the right drive is highlighted, and that a backup exists, prevents nearly every serious accident.
A typical use case
A video editor buys a 4 TB external SSD to move projects between a Mac at home and a Windows workstation in a studio. Connected to the Mac, the drive appears with a factory format that macOS cannot write to reliably.
In Disk Utility, the editor enables Show All Devices, selects the physical drive rather than its volume and erases it as exFAT with the GUID Partition Map. Both computers can now read and write the project files.
Months later, the drive stops mounting after being unplugged without ejecting. First Aid repairs the file system in a few minutes and every project opens again. The editor then keeps a second copy of active projects on an APFS drive, because exFAT has no journaling to protect against interrupted writes.