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Disk Utility Erase Greyed Out — Cannot Format or Partition Disk on Mac

Errordisk

Overview

Fix Disk Utility Erase button greyed out or unavailable when trying to format, repartition, or erase internal or external drives on macOS.

Key Details

  • Disk Utility may grey out the Erase button for system drives, locked drives, or unsupported configurations
  • The startup disk cannot be erased while macOS is running from it — use Recovery Mode
  • Showing All Devices in Disk Utility (View > Show All Devices) reveals the physical disk container
  • APFS containers must be erased at the physical device level, not the volume level
  • Some external drives have hardware write protection switches that prevent erasing

Common Causes

  • Attempting to erase the startup disk while booted from it (must use Recovery Mode)
  • Disk Utility showing volumes instead of physical devices — erase the container not the volume
  • External drive has a hardware write-protection switch enabled
  • Drive is mounted by another process or application preventing modification

Steps

  1. 1Show all devices: Disk Utility > View > Show All Devices — select the top-level physical disk
  2. 2For startup disk: boot into Recovery Mode (hold power button on Apple Silicon, Cmd+R on Intel)
  3. 3In Recovery Mode: open Disk Utility from the Utilities menu and erase from there
  4. 4For external drives: check for a physical write-protection switch on the enclosure
  5. 5If greyed out for external: try a different USB port or cable, or use Terminal diskutil commands

Tags

disk-utilityerasegreyed-outformatpartition

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Frequently Asked Questions

Most commonly because you need to select the physical disk (top level) instead of a volume (sub-item). Choose View > Show All Devices, then select the device at the top of the hierarchy. Also, the startup disk requires Recovery Mode to erase.