Formatting a Disk in macOS: A Step-by-Step Guide to Disk Utility

Introduction

Disk formatting is the process of preparing a storage medium (hard drive, SSD, USB flash drive) for use. It erases all existing data and creates a new file system, which determines how the operating system will store and retrieve files. In macOS, the built-in Disk Utility is used for this purpose.

With this guide, you will be able to:

• Prepare a new disk for first-time use.
• Change the file system for compatibility with other operating systems (e.g., exFAT for Windows).
• Fix disk errors related to a corrupted file system.
• Wipe a disk before selling or disposing of it.

After following the instructions, you will have a clean disk with your chosen file system, ready for data storage.

Requirements / Preparation

Before you begin, ensure that:

• You have a computer with macOS (version 12 Monterey or newer is recommended, but the instructions apply to older versions as well).
• The disk you want to format is connected to your Mac. This could be:
  • An external USB or Thunderbolt drive.
  • An internal disk (e.g., if you are replacing the primary drive). Warning: Formatting an internal disk will delete the operating system and all data!
• If the disk contains important data, back it up to another storage device or cloud service. Formatting irreversibly erases all information.
• You are logged into an account with administrator privileges (usually the account you created when setting up your Mac). Administrator rights are typically not required for external disks but may be needed for internal ones.

Step 1: Launching Disk Utility

Disk Utility comes pre-installed with macOS. There are several ways to open it:

1. Via Spotlight (fastest):
   • Press Cmd + Space to activate Spotlight.
   • Type Disk Utility and press Enter.
2. Via Launchpad:
   • Open Launchpad (the rocket icon in the Dock).
   • Go to the "Other" folder and find "Disk Utility".
3. Via Finder:
   • Open Finder.
   • In the sidebar, select "Applications" → "Utilities".
   • Double-click "Disk Utility".
4. Via Terminal (if you prefer the command line):

   open /Applications/Utilities/Disk\ Utility.app
   

After launching, you will see a window with two columns: on the left—a list of disks and volumes, on the right—information about the selected item and control buttons.

Step 2: Selecting the Target Disk

The left column in Disk Utility displays all connected storage devices. It is important to select the correct item to format:

• Disk (device) — the physical storage drive, e.g., "Apple USB External SSD" or "Macintosh HD". Its icon is usually at the top of the list, with nested volumes below it.
• Volume — a partition on the disk, e.g., "Untitled" or "Macintosh HD - Data". If you select a volume, only that partition will be formatted, leaving others untouched.

To completely format the disk (all partitions), select the top item—the disk itself. Pay attention to the name and capacity: ensure you have selected the correct storage medium, especially if multiple disks are connected.

If the disk does not appear:

• Check the connection: unplug and replug the cable, try a different port.
• Ensure the disk is powered on (indicator light, if present).
• Restart your Mac.
• Open "System Information" (About This Mac → System Report) and locate the disk under USB or Thunderbolt. If it's not listed there, the issue is with the connection or the disk itself.

Step 3: Configuring Formatting Parameters

After selecting the disk, click the "Erase" button in the top toolbar. A dialog window with settings will open:

1. Name: Enter the desired disk name. This name will appear on the desktop and in Finder. Use Latin letters and digits for maximum compatibility, but Cyrillic is also supported.
2. Format: Choose the appropriate option:
   • APFS (Apple File System): Modern system optimized for SSDs (both external and internal). Supports snapshots, encryption, and efficient space usage. Recommended for disks used exclusively on Mac with macOS 10.13 or later.
   • Mac OS Extended (Journaled): Legacy but still compatible with older macOS versions (up to High Sierra). Suitable for HDDs. An encrypted variant (Journaled, Encrypted) is also available.
   • exFAT: Cross-platform; works on both macOS and Windows without additional software. Does not support permissions but is excellent for large files (e.g., videos). Use if the disk needs to be read/written on both Mac and PC.
   • MS-DOS (FAT): Obsolete, with a 4 GB file size limit. Only for compatibility with very old systems.
3. Scheme: Defines the disk's partition map. For most cases, choose:
   • GUID Partition Map: The standard for Macs with Intel and Apple Silicon processors. Supports booting from the disk (if it's a system disk) and large drives.
   • Master Boot Record (MBR): Required only for Boot Camp Windows compatibility or very old PCs. Not recommended for modern Macs.

Important: If you are formatting an internal disk to reinstall macOS, select APFS and GUID. For an external disk that will also be used on Windows, choose exFAT and GUID.

After configuring, verify that the "Name" field shows what you want and that the correct disk is selected (its name and capacity appear in the dialog title).

Step 4: Starting the Format

Once all parameters are set, click the "Erase" button at the bottom of the window.

A warning will appear: "Are you sure you want to erase all data on the disk 'XXX'? This operation cannot be undone." If you are certain, click "Erase" again.

The formatting process will begin:

• A progress indicator will appear in the Disk Utility window.
• Execution time depends on the disk's capacity and interface speed (USB 3.0, Thunderbolt). A 1 TB disk via USB 3.0 may take several minutes.
• Do not disconnect the disk or shut down your Mac during the operation, as this could damage the disk.

After completion, the disk will automatically mount (appear on the desktop) and be ready for use.

Step 5: Verifying the Result

To ensure formatting was successful:

1. Finder: Open Finder. In the sidebar under "Locations", your disk should appear with the specified name. Double-clicking it should open an empty folder.
2. Disk Utility: In the left column, the disk should display the selected file system (e.g., APFS) and no error icons.
3. Try writing a file: Drag any file onto the disk. If copying completes without errors, the disk is functioning correctly.

If the disk does not appear on the desktop, check in Finder → Preferences → Sidebar that "External disks" is checked under "Locations".

Potential Issues

Despite the simplicity of the operation, problems may arise. Here are common issues and their solutions:

Disk Does Not Appear in Disk Utility

• Cause: Poor connection, faulty cable or port, disk not receiving power.
• Solution:
  • Reconnect the disk, try a different cable or port (if available).
  • If the disk requires external power, ensure the power adapter is connected.
  • Restart your Mac.
  • Check the disk in "System Information" (Apple menu → About This Mac → System Report → USB or Thunderbolt). If the disk is listed there but not in Disk Utility, the utility itself may be the issue—restart it.
  • If the disk is not detected at all, it may be physically faulty.

Error "The operation couldn’t be completed"

• Cause: Disk is damaged, wrong item selected (e.g., a volume instead of the disk), insufficient space for metadata backup (for APFS), permission conflict.
• Solution:
  • Ensure you selected the disk, not a volume (see Step 2).
  • Try running First Aid on the disk before formatting. Select the disk and click "First Aid". This may fix file system errors.
  • If First Aid fails, formatting may be the only option, but it will erase all data.
  • For system disks, you may need to boot into Recovery Mode (Restart → hold Cmd+R) and use Disk Utility from there.

Formatting Takes Unusually Long

• Cause: Large disk capacity (several terabytes), slow interface (USB 2.0), disk with numerous errors.
• Solution:
  • Allow the process sufficient time. A 4 TB disk via USB 3.0 may take 1–2 hours.
  • If the process seems "stuck" (progress indicator unchanged for hours), check Activity Monitor for diskmanagementd or diskutil activity. If the process is inactive, the disk may have frozen—safely eject it (via Finder) and try again.
  • Avoid formatting through USB hubs—connect directly.

Disk Does Not Mount or Appear in Finder After Formatting

• Cause: Error during file system creation, disk formatted with an unsuitable scheme, hardware failure.
• Solution:
  • In Disk Utility, select the disk and click "Mount" if the button is active.
  • If the volume still does not appear, try formatting again with a different file system (e.g., switch from APFS to exFAT).
  • Ensure the scheme is GUID Partition Map (for Mac).
  • Test the disk on another computer to rule out an issue with your specific Mac.

Accidental Formatting of an Important Disk

• Cause: Selected the wrong disk.
• Solution:
  • Immediately stop using the disk—do not write new data to it.
  • Attempt data recovery using specialized software (e.g., Disk Drill, PhotoRec, Data Rescue). Success depends on how much new data was written after formatting.
  • In the future, always verify the disk's name and capacity before clicking "Erase".

Compatibility Issues on Windows

• Cause: Selected file system is not supported by Windows (APFS, Mac OS Extended).
• Solution: Format the disk with the exFAT file system. Windows (from XP SP3) and macOS (from 10.6.5) both support exFAT. If you need APFS access on Windows, install third-party drivers (e.g., Paragon APFS for Windows), but these are paid solutions.