Complete Guide to Disk Utility on macOS: Basic Usage

Introduction / Why This Is Needed

Disk Utility is a built-in macOS application that allows you to maintain disk drives: check them for errors, format them, create partitions and disk images for backups. With it, you can solve many disk-related problems, prepare a new storage device, or optimize an existing one. This guide will introduce you to its basic functions so you can confidently manage disks on your Mac.

Requirements / Preparation

Before you begin, ensure that:

• You have macOS 12 Monterey or newer installed (the interface and features may differ slightly in older versions).
• You are logged into an account with administrator privileges — some operations (e.g., formatting the system disk) require a password.
• A backup of important data has been created to an external drive or cloud storage. Formatting and other operations can lead to data loss.
• The target disk is connected (if it's an external drive) — check the cable and USB/Thunderbolt port.

Step 1: Launching Disk Utility and Getting to Know the Interface

1. Launch the utility:
   • Press Cmd+Space to open Spotlight, type Disk Utility, and press Enter.
   • Or open Finder → go to the Utilities folder (in the Go menu → Go to Folder → enter /Utilities/) and run Disk Utility.app.
2. Explore the window:
   • Left pane: shows all physical disks, their partitions, and disk images. To access all functions, select the disk itself (e.g., Apple SSD AP0256J), not its partition (e.g., Macintosh HD).
   • Center area: displays information about the selected item (capacity, used space, format).
   • Top button bar: main actions — First Aid, Erase, Partition, Create Image, Restore, and others.

Step 2: Viewing Disk Information

To understand the disk's status and parameters:

1. In the left sidebar, select the physical disk (not the partition). It is usually displayed with a disk icon and model name.
2. Click the Info button (or right-click the disk → Info).
3. In the window that opens, you will see:
   • Capacity and available space.
   • Media type (SSD, HDD, Fusion Drive).
   • SMART status — if it says "Check Required" or "Failing," the disk may be close to failure.
   • File system (APFS, Mac OS Extended, exFAT).
   • Partitions and their sizes. This data will help diagnose issues or prepare the disk for an operation.

Step 3: Checking the Disk with First Aid

The First Aid function checks and repairs file system errors on disks (except the system disk if it is active). For non-system disks:

1. Select the disk (not the partition) in the left sidebar.
2. Click First Aid in the top toolbar.
3. Confirm by clicking Run.
4. Wait for completion. The utility will show:
   • OK — no errors found.
   • Repaired — errors found and fixed.
   • Failed — serious damage; you may need to restore from a backup or format.

⚠️ Important: For the system disk (Macintosh HD), First Aid can only be run from Recovery Mode (restart your Mac while holding Cmd+R, then select Disk Utility from the menu).

Step 4: Formatting a Disk

Formatting prepares the disk for use by erasing all data and creating a new file system. Use it for new disks or when changing the OS.

1. Select the disk (not the partition) in the left sidebar.
2. Click Erase.
3. Fill in the parameters:
   • Name: a convenient disk name (e.g., Backups).
   • Scheme: GUID Partition Map (recommended for macOS and Intel-based Macs), Master Boot Record (for Windows), Apple Partition Map (obsolete).
   • Format:
     • APFS — for disks used only on macOS (optimal for SSDs).
     • Mac OS Extended (Journaled) — for compatibility with older macOS versions.
     • exFAT — for sharing data between macOS and Windows.
4. Click Erase. Wait for completion. The disk will appear in Finder with the specified name.

💡 Tip: If formatting is unavailable (the button is inactive), ensure you have selected the physical disk itself, not a partition, and that the disk is not locked (e.g., the system disk).

Step 5: Creating and Restoring Disk Images

A disk image (.dmg) is an exact copy of a disk or partition in a single file. Useful for backups or transferring data.

1. Creating an image:
   • Select the disk or partition in the left sidebar.
   • Click File → New Image → Save Image of [disk name].
   • Specify the name, location, and format:
     • Compressed (compression, slower creation) or Uncompressed (faster, larger size).
     • Encryption — optional for password protection.
   • Click Save. The process may take time depending on the data volume.
2. Restoring from an image:
   • In Finder, locate the .dmg file and open it (double-click). It will appear in Disk Utility's left sidebar.
   • Select the image in the left sidebar, then click Restore.
   • In the "Restore" section, select the target disk (physical disk) from the dropdown list.
   • Click Restore. Confirm that data on the target disk will be erased.

Verifying the Result

After each operation:

• Formatting/creating an image: the disk should appear on the Desktop and in Finder with the new name and format. Open it to confirm accessibility.
• First Aid: a message about successful completion or errors will appear in the Disk Utility window. In case of errors, repeat the check or consider formatting.
• Restore: the target disk should contain the data from the image. Open it and check for files. If the operation fails, refer to the "Possible Issues" section below.

Possible Issues

• Disk Utility does not display the disk:
  • Check the physical connection: reconnect the cable, try a different USB/Thunderbolt port.
  • If it's an external disk, ensure it is powered on (if it requires power).
  • Go to About This Mac → System Report → USB or Thunderbolt to see if the disk is recognized at the system level.
• Error during First Aid or formatting:
  • The disk may have hardware failures. Check the SMART status in the disk's Info.
  • For the system disk, try running First Aid from Recovery Mode (Cmd+R at startup).
  • If errors persist, the disk may be faulty — consider replacement.
• Buttons in Disk Utility are inactive:
  • Ensure you have selected the physical disk (with the model name), not a partition (e.g., Macintosh HD).
  • Some operations (like formatting the system disk) are blocked while the disk is in use. Boot from an external drive or into Recovery Mode.
• Restoring from an image takes too long or fails:
  • Check the .dmg file integrity (its size should match the original).
  • Ensure the target disk has enough space.
  • For large disks, use an uncompressed image for speed.

This guide covers the main scenarios for using Disk Utility. For more complex tasks (e.g., RAID management or FileVault encryption), explore specialized guides on FixPedia.