User level: Level 2 (225 points)I have an external drive that I want to erase and re-partition. When I use Disk Utility to attempt that, I receive this error:
I don't know what this means or what I need to do to be able to erase this disk.
Here's more information. Here's what Disk Utility tells about the current partitioning on this disk:
And the current disk space:
Posted on Oct 11, 2026 8:50 PM
User level: Level 10 (123,805 points)Oct 12, 2026 2:46 AM in response to William M.
The error indicates that macOS cannot unmount the Seagate drive because it is in use by a system process (kernel, process 0). The accompanying error code, -69877, means Disk Utility could not open the device. This doesn't necessarily mean the drive is damaged.
I would try the following steps in order.
First, quit Disk Utility and, if possible, eject the drive in Finder.
Disconnect it, wait a few seconds, and reconnect it directly to your Mac mini rather than through a hub.
Restart your Mac mini, then try again before opening other applications.
In Disk Utility, select View >> Show All Devices, then select the top-level Seagate Desktop Media device rather than a volume beneath it.
Click Erase and choose GUID Partition Map as the scheme and APFS as the format if you will be using the drive exclusively with modern Macs. Name the volume backups.
In some rare situations formatting the drive as Mac OS Extended (Journaled) first is also worth considering.
Although this can be useful in some circumstances, it is not generally necessary before formatting a drive as APFS.
Since the error occurs when macOS tries to unmount the device, changing the format alone may not fix the problem.
If the error persists, Activity Monitor may help identify applications accessing the drive, such as backup software or file-management utilities.
However, because the error identifies kernel as the process preventing the unmount, Activity Monitor may not reveal the underlying cause.
At that point, Disk Arbitration is worth investigating. This macOS service manages disk mounting and unmounting.
Open Console and look for messages relating to diskarbitrationd, disk8, or Seagate Desktop Media around the time the erase fails.
These logs may provide further clues.
You can also use Terminal to check the drive's status without erasing it.
Run diskutil list to confirm the current disk identifier, then diskutil info /dev/disk8, substituting the correct identifier if it has changed.
Avoid repeatedly attempting to erase the drive, force-quitting system processes, or forcing an unmount until the cause is clearer.
Apple's Disk Utility User Guide provides additional guidance.
User level: Level 7 (22,314 points)Oct 12, 2026 12:13 AM in response to William M.
Sometimes Disk Utility fails the first erase attempt but then succeeds. If there is some process holding the drive, rebooting the Mac should clear it, better yet safe-boot (i.e. reboot holding Shift-key) which prevents many processes to launch.
Then Disk Utility > View > Show All Devices and erase the topmost external device (not any volume under it as APFS, GUID, case insensitive, with the desired name).
Originally posted at discussions.apple.com/thread/256374545